Why are obese mice so easy to chase?

Dysfunctional signaling in the brain makes obese mice less active

Summary

Obesity is accompanied by a lack of motivation/desire to exercise. This has lead to the idea that lack of exercise leads to obesity. A new study challenges this by showing that both “lazy” and “active” mice gain weight on a fatty diet [1]. All mice on high fat diet become obese and then move around less than mice fed on standard chow. The researchers go on to show that the lack of motivation to exercise that accompanies obesity may well be brought about by neuronal changes in the regions of the mouse brain that respond to movement.

Introduction

The physical inactivity that accompanies obesity is frustrating for those wanting manage their own weight as well as those who want support a near and dear one who does [2,3]. A better understanding of where this seeming ‘lack of motivation’ to exercise comes from may help design better intervention strategies. Previous studies suggest that obese animals and humans may have defects in dopamine signaling in a region of the brain that controls movement behaviours with the result that they may find physical activity less rewarding [4,5]. However, does lack of exercise cause weight gain?

What did they do and find?

Mice were fed standard chow (lean) or high fat diet (obese) for 18 weeks. Mice become both obese and less active when fed a high fat diet. The researchers of this study wanted to understand if the mice became fat because they were less active. To their surprise they found that low activity and weight gain occurred hand in hand but were not cause and effect. The weight gain however was correlated to the high fat diet.

So what was causing the lower activity in obese mice? There is a bit of the brain called the striatum which is responsible for movement and is disrupted in disorders such as Parkinson’s. There are neurons in this region of the brain that are sensitive to the neurotransmitter dopamine and fire (get activated) during movement. The authors of this study reasoned that perhaps it is this region of the brain that is responsible for inactivity in obese mice.

First they looked for components of dopamine signaling, the levels of dopamine itself and the dopamine receptors which when present on neurons allows them to respond to dopamine. They found that the striatum of obese mice had Dopamine Receptors of a specific kind (D2R receptors) which showed decreased binding while the levels dopamine itself and the other receptor for dopamine was the same in lean and obese mice. This reduction in dopamine 2 Receptor binding did not correlate with weight gain but was correlated with movement loss.

So would lean mice also move less if they had lower binding D2Rs?

Indeed, in genetically modified mice that lacked D2R receptors in the striatal region – lower activity levels were observed even in lean mice. This showed that neuronal changes underlie lower activity levels in obese mice.

To probe this further the researchers measured the activity of neurons in the striatum by inserting an electrode in the brain of live obese and lean mice. These recordings showed that during movement there was less overall firing in the brain of obese mice.

In order to test if these brain regions and neurons were indeed responsible for the lower activity observed in obese mice, the researchers used a special set of mice. These mice are specially modified to express a molecule that is usually produced by active Dopamine signaling via D2R binding (Gi) coupled to an opiod receptor only in the neurons of the striata that naturally express D2R. This allows Gi to be uniquely switched on by use of a synthetic chemical (Salvinorin B). When Gi is artificially produced by the D2R expressing neurons of the striatum both lean mice and obese mice become more active.

Reducing the D2R levels artificially in the neurons of the striatum results in mice with lower activity levels however these mice were not more susceptible to weight gain. Nor are mice with low D2R binding in the beginning of the diet predisposed to weight gain.

Take homes from the study

Experiments on animal behaviour are difficult and sometimes hard to extend beyond specific cases because genetic and environmental effects play a large role in shaping observed behaviour and this study is no different. These data convincingly argue that in mice, obesity is accompanied by and not caused by lack of activity. It also gives us a perspective on how integrated an animal’s body and mind are. At the very least it makes us think that in combating obesity, a role for the mind cannot be ignored.

References

1. Basal Ganglia Dysfunction Contributes to Physical Inactivity in Obesity. Danielle M. Friend, Kavya Devarakonda, Timothy J. O’Neal, Miguel Skirzewski, Ioannis Papazoglou, Alanna R. Kaplan, Jeih-San Liow, Juen Guo, Sushil G. Rane, Marcelo Rubinstein, Veronica A. Alvarez, Kevin D. Hall, Alexxai V. Kravitz, Cell Metab. 2017 Feb 7

2. The mysterious case of the public health guideline that is (almost) entirely ignored: call for a research agenda on the causes of the extreme avoidance of physical activity in obesity. Ekkekakis P, Vazou S, Bixby WR, Georgiadis E, Obes Rev. 2016 Apr;17(4):313-29

3. Exercise does not feel the same when you are overweight: the impact of self-selected and imposed intensity on affect and exertion, P Ekkekakis and E Lind, International Journal of Obesity (2006) 30, 652–660

4. Reward mechanisms in obesity: new insights and future directions. Kenny PJ. Neuron. 2011 Feb 24;69(4):664-79.

5. Obesity and addiction: neurobiological overlaps (Is food addictive). Volkow ND, Wang GJ, Tomasi D, Baler RD. Obes Rev. 2013 Jan;14(1):2-18.

6. Do Dopaminergic Impairments Underlie Physical Inactivity in People with Obesity? Kravitz AV, O’Neal TJ, Friend DM, Front Hum Neurosci. 2016 Oct 14;10:514. eCollection 2016.

7. Increases in Physical Activity Result in Diminishing Increments in Daily Energy Expenditure in Mice. Timothy J. O’Neal,, Danielle M. Friend, Juen Guo, Kevin D. Hall, Alexxai V. Kravitz Curr Biol. 2017 Feb 6;27(3):423-430.

An Interview with Dr. Alexxai V. Kravitz

1. What is causing the change in dopamine signaling in the neurons responsive to movement in obese mice? Do you have more insights into this from your study of Parkinson’s?

This is a great question, but unfortunately one that we don’t know the answer to. Parkinson’s disease is caused by the death of neurons that make dopamine, and we looked at dopamine neurons in obese mice and learned that they were not dying. So in that way, the mechanism underlying the changes in dopamine signaling in obese mice is very different than with Parkinson’s disease. This is a good thing, as it would frankly be scary if a diet high in fat were causing the death of dopamine neurons! Instead, we observed dysfunction in a specific dopamine receptor (a protein that detects dopamine) in obese mice. We’re looking into what exactly is causing the dysfunction of this receptor, but unfortunately we do not currently know.

2. You data does show that mice become both obese and move less on high fat diet, but which bit convinces you that the “laziness” is because of the obesity? Can they not be two parallel outcomes of a high fat diet? If yes, then would a high fructose or high calorie diet lead to a similar outcome?

Let me clarify here – I don’t think the *weight* of the mice is causing the laziness, I believe dysfunction in their dopamine receptors is causing their laziness [More on this in Ref. 6]. And both this dysfunction and weight gain can be caused by the high fat diet. So in that say, yes, they can be two parallel outcomes of the high fat diet. To answer your second question, I’m not sure if other high calorie diets can cause the same dysfunction. This would be a great follow up experiment!

3. In your paper, you describe the limitations of human studies that have measured Dopamine signalling and its links to obesity. Can you tell us a bit more about what the challenges are?

To date there have been a handful of studies that have compared D2 receptor levels in people with obesity vs. normal weight, and a minority have reported dysfunction in D2Rs in people with obesity. It is not clear why some studies have reported lower levels of D2 receptors, while most have not. However, measuring dopamine receptor levels in humans is difficult. The only technique for measuring receptor levels in humans is PET scanning, a technique where a radioactive tracer is injected and the brain is scanned for the location where the tracer binds. If more tracer binds, it is assumed there are more “available” receptors in that brain area. However, this technique can be affected by many factors, including what other transmitters are bound to that receptor. If internal levels of dopamine are higher during the scan, for instance, the amount of a radio-tracer that binds to a dopamine D2 receptor will be lower. The complexity increases when we consider how many things can alter dopamine levels throughout the day, which include caffeine use, food intake, and sleep. These are some of the challenges that face clinical research. Animal studies are less likely to incur these sources of variance, and have more consistently reported decreases in D2 receptors in association with obesity.

4. Are the changes in the striatum reversible, by forced exercise for example or are there natural molecules that could restore Gi signaling?

There are no known ways to reverse these changes, but there is also very little research on this. There is a small amount of evidence in rats that forced exercise increases D2 receptor levels, but this is very preliminary and has not been replicated, nor studied in humans. This idea of how to alter D2 receptor levels is an extremely important concept for future research!

5. Are there common themes about obesity and lower activity levels that have emerged from animal studies and how would you extend them, if at al, to humans? For instance, you say mice and rats are different, then would you expect people to be more similar to mice than rats? Why?

It is very difficult to extend results from mice to humans, so I will be cautious on this one. However, there are some concepts from animal work that are relevant to humans. Many researchers have noted that animals voluntarily over-eat high fat diets, and that this leads to weight gain and obesity. While the specific macronutrient (fat vs. carbs vs. protein) content of human diets is the subject of a lot of debate when it comes to human obesity, it is fair to say that diets that induce over-eating will lead to obesity. Typically, foods that induce over-eating are highly palatable, such as junk foods that pack large numbers of calories into small volumes. While people are all different from one another, understanding the foods that a specific person overeats will inform what is likely to cause that person to gain weight.

As another concept that I believe is relevant to human s, in our study we reported that physical inactivity did not correlate with weight gain in mice. That is, we examined inactive mice that lacked D2 receptors, and found that they gained weight at the same rate as normal active mice. We also examined the natural variation of activity levels of normal mice and did not note any relationship here either. This seems to counter the conventional wisdom that inactivity should cause weight gain. However, this conventional wisdom is based largely on correlations between obesity and inactivity, rather than causal tests of this hypothesis. We all know that correlation does not imply causation, but it is very easy to get caught in this trap. In fact, in causal tests, the contribution of exercise alone (without changes in diet) to weight loss in humans is fairly small, generally resulting in 3-5 pounds of weight loss over the first year. This is consistent with our conclusions in mice. Studies in mice can help us understand at a mechanistic level why changes in activity (both increases and decreases) don’t translate into large changes in body weight [More on this in Ref.7].

6. In their natural habitats animals such as mice and rat consume high fat diets. Do you think your results would hold in wild rodents instead of lab reared ones, especially if they were allowed to interact freely with each other and the environment?

Wow, what a great question! We use lab mice, which have been bred in captivity for many decades. This is somewhat similar to studying domesticated dogs vs. wild dogs. And in many ways, our laboratory mice are quite different from wild mice. However, I believe that even wild mice would become inactive on a high fat diet. The association between obesity and inactivity has been seen in many species including humans adults, children, non-human primates, domesticated cats and dogs, rats, and mice. When an association occurs across so many species of animals, I think it is likely that it would extend to wild mice as well as laboratory mice. This would be a great student project to find some wild mice and test!

Frigate birds keep their eyes wide open during flight – most of the time!

Sleep patterns of flying birds

Snap-Shot of the study

Birds fly enormous distances during migratory flight. It seemed reasonable therefore to think that birds sleep while flying, especially since birds can go to sleep -one brain-half at a time.

But then, how can they function and be attentive to the demands of flying, foraging, avoiding predators, finding their route, often over water, over such long periods of time? Imagine the frigate birds with the wind on their wings as they begin their flight across the ocean, flying continuously and majestically for upto 2 months! In an elegant and well written piece of research, the authors find that frigate birds sleep very little during their long flight (1). By recording brain activity in flying birds, the authors show for the first time that these birds take short and light naps but mostly forgo sleep during migratory flight.

Background to this study

A single late night is enough to send most adult humans into a downward spiral the next day, fruit-flies that don’t sleep have their lives cut short (2-4). Birds however have been shown i) to go on long flights without resting (5) ii) to sleep uni-hemispherically – single eye open – keeping one part of the brain alert to the requirements of the environment while the other part rests (6). iii) are able to function more or less normally even when deprived of sleep (7)

So what happens during flight? Given the high energy/metabolic demands of flying the need for rest and sleep must be high, on the other hand the need for attention is also high during flight, can birds afford to sleep on the wing? One way to find out is to record the patterns of brain activity in migratory birds during flight and look for patterns of sleep and wakefulness.

What did they do?

In this study (1), sleep patterns of 15 female great frigate birds flying over the Pacific Ocean and after returning to their nest on Genovesa Island (Galápagos) were recorded using implanted devices that measured brain activity (EEG – electroencephalogram), movement of the head as well as acceleration. No behavioural differences were observed in the birds with implants during and after removal of the devices. Using these devices, the researchers measured movement of the bird, acceleration, deceleration, flapping of the wings and brain activity near the primary visual area and also collected data on weather conditions. Measuring movement of the head allowed them to separate patterns formed by head movement from actual changes in brain activity.

What did they find?

The overall EEG patterns were similar in the birds on land and during flight, allowing the researchers to look at duration and intensity of sleep. They describe three sleep-awake states roughly – wakefulness, rare episodes of REM sleep (like in humans, this is deep sleep characterized by rapid eye movement) and slow wave sleep – this is the most frequent type of sleep described in birds which can be bi-hemispherical or uni-hemispherical or assymetric (6).

During the day, the birds showed patterns of wakefulness (fast head movements together with high amplitude signals in the EEG), even at night during flapping of wings wakefulness patterns were observed. These were interspersed with slow waves which the authors identify as slow wave sleep. Rarely, between bouts of slow wave sleep, short bursts of deep sleep or REM sleep patterns characterized by dropping of the head, and twitching were also observed. Interestingly, birds ascended in altitude during slow wave sleep and descended during wakefulness. All types of slow wave sleep, including unihemsipherical, asymmetrical (when one hemisphere was more active than the other)  and bihemispherical slow wave sleep were observed during flight. There was an increase in asymmetric sleep in flight than on land but this was not correlated with any one type of movement.

Overall, frigate birds seemed to sleep very little during flight – in shorter bursts and less soundly –  a homeostatic balance was restored when these birds landed. Further, preliminary evidence from this study suggests that these bursts of sleep are enough to sustain the birds during flight.

Why is this interesting?

The very fact that these birds are able to accomplish Himalayan tasks such as follow migration routes, feed themselves, with such low levels of sleep suggests that, at least for frigate birds, sleep may be dispensable during flight. Are they postponing this need? What sort of adaptations allow them to postpone sleep or perform sleeplessly? This study is a step towards understanding adaptations to lack of sleep and perhaps a way to understand the very nature of sleep itself.

1. Evidence that birds sleep in mid-flight. Rattenborg NC, Voirin B, Cruz SM, Tisdale R, Dell’Omo G, Lipp HP, Wikelski M, Vyssotski AL. Nat Commun. 2016 Aug 3;7:12468. doi: 10.1038/ncomms12468. PMID: 27485308

2.Reduced sleep in Drosophila Shaker mutants. Nature. 2005 Apr 28;434(7037):1087-92  Cirelli C, Bushey D, Hill S, Huber R, Kreber R, Ganetzky B, Tononi G.

3. Genetics of sleep and sleep disorders. Cell. 2011 Jul 22;146(2):194-207. doi: 10.1016/j.cell.2011.07.004. Sehgal A, Mignot E.

4. http://www.curiouscascade.com/blogpost/clocking/

5. Frigate birds track atmospheric conditions over months-long transoceanic flights. Science. 2016 Jul 1;353(6294):74-8. doi: 10.1126/science.aaf4374. Weimerskirch H, Bishop C, Jeanniard-du-Dot T, Prudor A, Sachs G.

6. Half-awake to the risk of predation Nature 397, 397-398 (4 February 1999) | doi:10.1038/17037 Niels C. Rattenborg, Steven L. Lima & Charles J. Amlaner

7. Adaptive sleep loss in polygynous pectoral sandpipers. Science. 2012 Sep 28;337(6102):1654-8. Epub 2012 Aug 9 Lesku JA, Rattenborg NC, Valcu M, Vyssotski AL, Kuhn S, Kuemmeth F, Heidrich W, Kempenaers B.

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An interview with Alexei Vyssotski

Q. Can you tell us a little more on how you determined that the birds were sleeping? How did you identify the pattern corresponding to sleep when you got all your recordings?

Sleep was identified by visual inspection of 4-sec episodes of raw EEG records. Slow-wave sleep is characterized by large amplitude low-frequency oscillations in EEG. These episodes are easily-detectable. Visual scoring was used because automated methods of sleep staging can’t separate properly large-amplitude EEG events from movement artifacts in all cases. Locomotor artifacts can have similar amplitude to slow-waves during in sleep.

Q. Do you think these birds sleep a lot during an annual cycle? Do migratory birds tend to sleep longer than non-migratory birds on average – there must surely be some compensatory mechanisms?

We have found that frigatebirds sleep on average 9.3 hours per day when on land and only 0.69 hours per day when flying. We did measurements only during breeding period. While the frigatebirds live in equatorial area with relatively small weather seasonal changes, one can suppose that the duration of sleep is linked stronger with the pattern of animal activity than with the time of the year per se. It is known that migratory species can stay on the wing for a long time. Extrapolating our findings to these species one can suppose that they should sleep in the flight smaller amount of time than on land, and might compensate migratory sleep loss on land later like our frigatebirds did. However, the compensatory increase in sleep duration and intensity upon landing after the trip is relatively small comparatively to missed amount of sleep on the wing. One can speak only about partial compensation of sleep loss. The birds have, probably evolutionary formed, an ability to stay without sleep significant amount of time without physiological dysfunctions. Unlike most mammals, the birds do not have so called sleep-deprivation syndrome. If a rat will be forced to stay without a sleep for significant time, it will die, but a homing pigeon can stay month-long awake and still behave properly. Migratory birds definitely reduce amount of sleep during migration, but whether they sleep longer than non-migratory birds in other situations is difficult to say.

Q. Do you think that migratory birds produce neurochemicals that resist the urge to sleep or have special brain structures?

The neurochemistry of avian sleep is investigated in much less extent than mammalian sleep. To the best of my knowledge, no special anatomical structures that are responsible for sleepless in birds have been discovered. It is assumed that the avian sleep control brain system is similar to mammalian. However, additional studies are needed to check how strong this similarity is indeed and what are the differences.

Q. Does the slow sleep wave recordings refer to the activity of only certain regions of the brain?

No. It is assumed that like in mammals, the vigilance states in birds are controlled by deep brain structures that modulate activity of superficial brain regions in a synchronous manner. However, contrary to most of mammals that have only bi-hemispheric sleep, the birds have so- called unilateral sleep, when one hemisphere is sleeping and another is awake. Thus, the avian brain hemispheres are more independent from each other than mammalian. One should note that the phenomenon of “local sleep” has been also discovered in birds. This means that if a particular region of the brain has been used intensively in a wake state, the slow waves of increased amplitude will be observed during the following sleep in this brain area.

Q. Did you have independent recordings of some of the parameters using a high speed camera to set the baseline for each bird?

Do you mean Ca2+ brain cells imaging? No, we did not do this, but of course, if would be nice to monitor how activity of different cells ensembles changes in sleep in birds. The recently developed head-attached microscopes can help to film brain in freely behaving animals.

Q. It is astonishing that you got so much information that you could put together, did you expect that when you captured the 15 birds? What were the unexpected challenges in the study?

That is true, this time we collected more information than in our previous studies. We alreadyhad experience with EEG and GPS logging. This time we compensated luck of GPS precision by the acceleration data to reveal the flight mode of the animal. 3-D acceleration data practically doubled the dataflow, but this was not a problem to log in 1 GB onboard flash memory. We did not predict the particular way of the data analysis in advance, but observing three-modal distribution of sway acceleration leaded us to separate analysis of EEG in three different flight modes (straight flight, circling to the left and to the right). The real challenge was to master the surgery and handling in an animal-friendly way to have the birds back with the equipment. Indeed, the rate of return 14 from 15 birds exceeded our expectations. To be honest, I expected larger losses and was very happy when returns exceeded 50%.

Q. Have you been to the Galapagos? What is it like to do research in that setting? Do you think that nearly 180 years after Darwin’s voyage, the biodiversity of Galapagos still holds new discoveries?

Yes, I have a real luck to spend a week at the Darvin station in Santa Cruz and then a week on Genovesa island working in the bird colony. My colleagues Bryson Voirin and Ryan Tisdale spent two weeks more waiting for birds return. This is the best place for animal study that I have ever seen. Wild birds behave almost like tame animals there and do not run away from humans. Thus, it is easy to handle them. This is, of course, one of the features that attracts biologists. The biodiversity of these islands is definitely not studied completely and will attract scientists for a long time.

Game of Theories: A Policy of Bribery and Punishment

Theoretical study suggests that encouraging complaints from citizens may be the most effective way of reducing incidents of bribery

 

Article

Data analysis is critical for the formation of any robust policy. But reliable data in economics is not always available, since unlike in the natural sciences, controlled experiments at the population level are not possible.  Moreover, present data may not have sufficient predictive power, since population behavior changes over time. Economists use theoretical models to account for variables and parameters to predict end-results in such situations. These models can serve as prototype systems on which to test the possible consequences of a new policy.

In this particular study, the authors use evolutionary game theory to approach bribery, a prevalent problem in may societies.

What is Game Theory?

Economics, broadly defined, is the science of human behavior. And much like in the natural sciences, economists look for “bottom-up” explanations of phenomena, where simple underlying rules give rise to complex behavior. The rules generally take the form of mathematical equations, the solutions to which are expected to capture (and predict) the essential features of social dynamics.

A central theory which has proved useful is game theory. A more accurate name for it is “multi-person decision theory” – because that’s exactly what it is. It deals with situations where multiple players engage with each other, each armed with a repertoire of possible strategies, and the outcome (or “payoff”, as it is called) for each player depends on the strategy adopted by all the players.  The aim of each player is to choose the strategy that maximizes her payoff. As you can see, the theory potentially covers a very broad range of human interactions, and thus the widespread application of game theory in economics is hardly surprising.

But how do we adopt and revise our strategies over time? A set of perfectly rational beings with complete information would quickly reach a unique equilibrium situation (provided such a situation is allowed by the dynamics of the game). But in the real world, people are neither perfect computing machines, nor do they have perfect information. So the strategies we use, and the way we update them with further experience, depends a lot on the context.

What game does this article study?

The study employs different players and their corresponding strategies; an honest officer, a bribe-taking officer, an honest citizen, a bribe-paying citizen who doesn’t report on the crime, and a bribe-paying citizen who reports on the crime. The advantage to reporting, of course, is that you have a chance of getting your bribe refunded. These players (citizens and officers) interact at random and such interactions can potentially involve a corrupt transaction (depending on the strategies of the interacting players) leading to payment of a bribe. Like Kaushik Basu, the authors focus on the problem of harassment bribes. These are bribes paid by citizens to corrupt officers for getting access to a service they are legally entitled to (such as acquiring a passport or getting a driver’s license)

The authors also consider two different ways in which the citizens and officers may update their strategies over time. First is the Replicator model, where an officer or citizen randomly chooses a fellow officer or citizen, and tends to imitate their strategy if they have been more successful. In the second scenario, called the Alternative Strategy Exploration model, they first make their moves and receive their payoffs, then consider whether the possible alternatives may have given them a higher payoff, and if so, update their strategies accordingly. In both the cases, it is found that the population finally reaches a fixed frequency distribution of the various strategies.

What is the question?

The authors consider two major punishment models:

1. Symmetric punishment, where both bribe taker and bribe giver are punished

2. Asymmetric punishment, where only the bribe taker is punished.

In fact, a major motivating point for the study was the claim by economist Kaushik Basu that bribe-giving, as opposed to bribe-taking, should be legalized for harassment bribes, as this would increase the frequency of complaints and help bring down bribery.

The authors numerically simulate the evolution of strategies under both kind of punishment models to find out which might be better in curbing bribery incidents. They further analyze conditions under which a decrease in incidents of harassment bribery might be possible.

What do they find?

Contrary to the claims by Basu, they find that the effect of asymmetric punishment depends on the update strategies used by the players, and cannot be considered a universal solution. Lowering the cost of complaint, however, seems to work under both the asymmetric and symmetric punishment models. However, the extent of bribery reduction depends on other parameters as well.

What are the conclusions?

Bribery is a very complex and dynamic issue. While there can be no single way to get rid of it, the authors suggest that bringing down the cost of complaint to negligible might be important in an overall reduction in incidents of bribery, irrespective of the punishment model. On the other hand, what happens under more complicated updated strategies is still an open question. As the authors say in their article, “It would perhaps be more pragmatic to look at a combination of technological fixes and public policies targeting the myriad underlying causes of bribery in order to effect reduction in bribery and ease the toll it takes on public finances.”

It is interesting to note that even in relatively idealized economic models, a simple and universal solution may prove to be elusive. This should make us more skeptical of quick fixes suggested by policy leaders that seem to make intuitive sense, and look for solutions that are customized to individual scenarios.

References

Bribe and Punishment: An Evolutionary Game-Theoretic Analysis of Bribery,Prateek Verma, Supratim Sengupta, PLoS One. 2015 Jul 23;10(7):e0133441.

An interview with Dr. Supratim Sengupta

Q. Basu (2011) had submitted a report to the Government to inform on policy for bribery punishment. Why did you choose to study this report using game theory and which facets of this report have your study addressed in more depth?

When this report came out, a literature search revealed that there was practically no quantitative analysis of the issues raised and claims made in the report. The principle claim was that incidents of harassment bribery could be substantially reduced if only the bribe-taker but not the bribe-giver was penalized for the crime. It was also evident to us that the problem was ideally suited to be analyzed using evolutionary game theory since it presented a very well-defined scenario of social conflict with mutually exclusive interests of the principle parties (bribe-giver and bribe-taker) involved. Our main objective was to quantitatively examine in great detail the principle claim of Basu’s report (mentioned above) and understand how reduction in incidents of bribery depend on factors like the amount of bribe demanded, the cost of complaining about a bribery incident, the penalty to a bribe-taker if caught. We also examined how the manner in which individuals updates their strategies in response to a bribery incident affect the prevalence of bribery in the population. None of these aspects had been examined in such detail using the framework of evolutionary game theory and our work (carried out with my PhD student Prateek Verma) is the first to do so.

Q. Your models indicate that low cost of complaint may eradicate bribery. In countries with low bribery, are there platforms which make registering complaints easier?

Yes, most western European countries and places like USA, Canada etc., have efficient grievance redressal systems and harassment bribes are practically non-existent for basic services provided by the government. Even in India, a website called ipaidabribe.com started by an NGO in Bangalore has made it easy to report incidents of bribery and bring grievances to the notice of public officials. Such steps have led to positive outcomes which suggest that reducing the cost of reporting bribery incidents and establishing an efficient grievance redressal system by using technology can be quite helpful. If there is one policy proposal that we could advocate to reduce incidents of bribery, it would be this.

Q. Countries with low corruption indices seem to have a higher national income and lower inequality. But these factors do not seem to be explicitly incorporated in your model. Would you like to comment on that?

Bribery is a multi-faceted social problem and has many underlying causes including (but not restricted to) high levels of income inequality, as you have pointed out. However it is quite difficult to quantify the impact of such income inequality on the problem of harassment bribes. We took into consideration the most relevant factors that directly affect harassment bribery and that could be incorporated into a tractable mathematical model that would enable us to obtain insights into the problem and identify steps that can be taken to reduce such incidents of bribery.

Q. Why did you choose the two strategies: Replicator dynamics and alternative strategies dynamics for the study? What other scenarios might have been considered?

We wanted to highlight the difference in outcome when individuals choose two completely different methods to update their strategies over the course of time. We found that in the alternative strategy exploration case, the reduction in incidents of bribery was far less pronounced even when we followed Kaushik Basu’s proposal. However, these two methods are not the only ways individuals can choose to update their strategies and hence the outcome would indeed depend on the method followed. For instance, different individuals in the population could choose different methods to update their strategies and that would affect the outcome.

Q. Since collecting bribery data is difficult due to the secretive nature of the phenomenon, how do we check if some bribery-related policy has worked?

Collecting bribery data may not be as difficult as it seems. The government can ask citizens to fill out a simple questionnaire given by the service provider to report incidents of bribery. For example, the regional passport office can ask citizens applying for a passport to submit their feedback online by filling out an online questionnaire at the end of the process. Statistics based on such documents can be a very useful indicator of the prevailing levels of bribery in different services. It would also provide clues on how to allocate resources to reduce incidents of bribery in different services provided by the government.

Q. Do you expect your study or other related studies to have an impact on government policy?

It is difficult to predict whether any study of this kind will impact public policy. This is a topic of great public interest and Kaushik Basu’s original proposal certainly garnered a lot of attention. But that was in no small measure due to the important position he held at that time (Chief Economic Advisor to the PM) as well as his influence as a well-known economist. However, many (but not all) of the responses to that article in the press at that time were simplistic, knee-jerk reactions. Moreover, they were not grounded on objective analysis. We hope our work along with those of others have contributed towards a critical analysis and will at least rekindle the debate and stimulate new proposals on how to reduce harassment bribery. Despite the controversial nature of the proposal, we believe there are concrete and simple steps that can be taken that may have an impact. As I mentioned in my previous response, using web-based technology to streamline access to services, gather critical feedback and reduce the cost of complaining can definitely have a positive impact. However, we also acknowledge that technological fixes alone cannot and will not get rid of such a complex social problem that is definitely affected by income-inequality, the efficiency of the public justice system etc.

Q. In general, how much do you think game theory models accurately capture real world dynamics?

Evolutionary game theory is employed when the effectiveness of a strategy depends on the presence of other competing strategies in the population. It relies on specifying the net gain or loss (referred to as “payoffs”) to each strategy when it interacts with different strategies. It is very useful in analyzing how the number of individuals employing different strategies change over time and the conditions under which a specific strategy can out-compete all other strategies and take over the population. Unlike conventional game theory used by economists, which is involved only in finding equilibrium solutions (the so-called Nash equilibrium), evolutionary game theory allows us to see how the population gradually progresses towards an equilibrium state by tracking the change in number of individuals employing different strategies over time. The usefulness of evolutionary game theory in accurately capturing real world scenarios depends on the question being asked. There have been some criticisms (valid in my opinion) of using game theory to understand how cooperative behavior can spread or be sustained among groups of individuals. Experiments have revealed that people have an intrinsic tendency to cooperate more than game theoretic analysis predicts, despite cooperation being costly. In such scenarios, it is necessary to be cautious in drawing conclusions based on game theory. However, in the current scenario, such concerns do not apply since the primary interests of the principle players are at cross-purposes. We therefore feel that evolutionary game theory is well suited to accurately address the bribery problem. Nevertheless, some words of caution are in order. Our models employ quantities like the prosecution rate and penalty when prosecuted to understand the effects of punishment and its deterrence on bribery. In reality, these depend on the efficiency and integrity of the public grievance redressal systems and justice systems. These can vary a lot not just across countries but also across jurisdictions within the same country. These factors need to be given serious consideration before framing any public policy dealing with bribery.

Q. What do you think is the role of theory in economics, in general terms? I come from a background in theoretical physics (says Jabali) and now work in biology. And I and others like me sometimes wonder about whether we are making the right kind of assumptions in our models, or whether the phenomena we are describing are really reducible to a mathematical description, given the current state of knowledge. Does a theoretical study in economics contain the same kind of concerns? Or is the picture there very different?

You raise a very pertinent point here that I will not be able to satisfactorily address. I am not an economist by training. Like you, I am a theoretical physicist interested in analyzing complex social and biological systems using quantitative tools inspired by Physics and Mathematics. I am therefore not qualified to comment about the real-world relevance and drawbacks of theoretical models in Economics in general. However, the concerns you raise are surely relevant to studies of this kind and any honest scientist/economist needs to ponder about them. These concerns certainly informed our formulation of the problem and we tried to make the model as realistic as possible. But we also admit that some simplification was inevitable and we could not incorporate every single factor (like income-inequality for example) that may play a role in the prevalence of harassment bribes. Sometimes, even the factors incorporated, like prosecution rate, penalty for taking bribes etc. may not reveal the true complexity of the real world problem where such quantities depend on the efficiency and integrity of the police and justice systems. In some cases, the simplifications (like our assumption of a mixed population) can be addressed by studying the effects of a structured population of citizens and officers, as we are currently doing in an ongoing work (with Prateek Verma and Anjan Nandi) which is being written up. It is therefore important to acknowledge the potential consequences of the underlying assumptions and the associated simplifications while proposing new public policy based on such studies. It is also important for us (the community of social and natural scientists) to continue to strive to develop more realistic models by improving on existing ones whenever possible. Finally, I believe it is necessary for policy makers to pay attention to such studies and start a dialogue with social scientists to critically examine the consequences of such studies on public policy.

A whole new whale

A whole new whale- genetic analysis supports the existence of a new whale species

Snap-shot

In the mysterious dark waters of the deep seas, imaginative explorers have chased mythical creatures – from mermaids to kraken, creating an endless list of adventures. Even in the 21st century, we know very little about the creatures that inhabit these worlds. Now, a shy whale species comes into molecular spotlight as scientists use genetic tools to reveal its existence and decipher its relationship with better known cousins (1).

Background

Public Domain, https://commons.wikimedia.org

The beaked whales are a mysterious and diverse family – characterized by teeth and a prominent beak. Very little is known about this family of whales because they live in remote oceanic habitats, dive deep and seem to be sparse (1, 2). The existence of a black beaked whale is long rumored among Japanese fishermen and was first described as a possible new species by Japanese researchers in 2013 (3). A type of beaked whale known as ‘Baird’s beaked whale’ are seen the north pacific (ranging from Japan to Mexico), these whales are slate-gray in colour. Rare sightings of smaller black whales have also been reported around these regions (only around Japan). Although the black whales are distinguished by their skin tone and smaller size, these criteria alone were not sufficient to to classify them as a new species. One explanation for example could be that the black whales were just the young juveniles of the slate-gray Baird’s beaked whale. A recently published study (1) uses mitochondrial DNA sequencing to show that the black beaked whales are genetically distinct from other beaked whales and are only distantly related to the slate-gray whales with overlapping geographical niches.

What did they do?

The team has analyzed the DNA sequence of a total 178 samples of Baird’s beaked whales. These samples were painstakingly collected  from the rare live animals captured across the entire north pacific range including  two  museum samples. Unsurprisingly, majority of these samples (170) belonged to the slate-gray forms and only 8 belonged to the suspected black whales. They compared the genetic sequence (haplotype https://en.wikipedia.org/wiki/Haplotype) of particular stretches about 450 base pairs (nucleotide lengths) of mitochondrial DNA of these whales. If indeed the 8 black samples belonged to a new species, then their DNA sequence is expected to be quite similar to each other and differ considerably from the slate-gray ones.

What did they find?

Genetic analysis showed that a particular stretch of  mitochondrial DNA from the black and slate-gray whale samples had only 6-7 differences within their own group but differed from each other in 16 positions. This compares with the difference of 12 nucleotides positions that the slate-gray whales have  with a different beaked whale species Arnoux’s beaked whale, a completely  different species found in southern hemisphere (a benchmark for genetic disparity the authors have used to validate the genetic differences-). This analysis in combination with the known physical characteristics of size and colour, positions the rare black whale as a new species. The presence of 6 nucleotide differences in the mitochondrial DNA of the 8 black whales suggests that there may be high diversity within the species as well.

Why is this important?

This work highlights how little we still know about the fascinating world around us. It uses relatively inexpensive, and widely available molecular methods (sequencing short stretches of mitochondrial DNA) to support the claim of a new species of whale in the North Pacific Ocean. This raises new questions about how this species lives and thrives in the remote oceans and how it is affected by human activity.

References

References

1.Morin, Phillip A., C. Scott Baker, Reid S. Brewer, Alexander M. Burdin, Merel L. Dalebout, James P. Dines, Ivan Fedutin, et al. 2016. “Genetic Structure of the Beaked Whale Genus Berardius in the North Pacific, with Genetic Evidence for a New Species.” Marine Mammal Science, July. doi:10.1111/mms.12345.

2. (http://www.beakedwhaleresource.com/aboutbeakedwhales.htm)

3. Kitamura, Shino, Takashi Matsuishi, Tadasu K. Yamada, Yuko Tajima, Hajime Ishikawa, Shinsuke Tanabe, Hajime Nakagawa, Yoshikazu Uni, and Syuiti Abe. 2012. “Two Genetically Distinct Stocks in Baird’s Beaked Whale (Cetacea: Ziphiidae).” Marine Mammal Science, September, doi:10.1111/j.1748-7692.2012.00607.x.

An interview with Dr. Phillip Morin

Q. You have performed analysis on 5 blacks and 8 gray beaked whales, how would you increase sampling? Would you deploy a dedicated team/ facility or co-ordinate more with the fishermen in the area to collect more samples? Does the constraints of sampling limit the interpretation of your finding?

Actually, we have sampled 5 of the new black form, included DNA sequences from the 3 that were previously analyzed in Japan, for a total of 8 of the black form. We included 170 of the gray form in our study, ranging from Japan to Mexico across the North Pacific. We would certainly like to have more samples of the black form, and hope that researchers who have data on additional beached whales that they think may be the black form will contact us, and that researchers, fishermen and others who see live beaked whales can help us to find where they spend their time when they are alive. At the moment we do not have funding to commit to this type of study, but if we are able to get a better idea of where to look for them, that could help us develop a more specific (and less expensive) study. Although the sample size is fairly small, the fact that samples are from both Japan and the Bering Sea strengthens the result, and the fact that we have sampled across the known range of Baird’s beaked whales (the gray ones) also strengthens our interpretation of 2 separate species in the North Pacific.

Q. What do we know about the behaviour of the black whale – are they solitary or social? Are they hunter carnivores or live on krill? Usually food is abundant in the shallow sea near the coast and in deeper sea basins the food becomes scarce, do we know something about their dietary habit that allows them to survive? Is the restriction of their abundance in particular geographical locations is because of a known nutrient gradient around your sampling sites?

There are 22 known species of beaked whales, and to my knowledge all of them live primarily in deep waters and feed on squid and/or fish at depth, and are naturally not abundant, probably due to this dietary specialization, high energy needed to obtain sufficient food, and patchiness of food sources. All are also typically found in smaller groups, though Baird’s beaked whale is known to travel in larger groups of 30 or 40 at times. Although we don’t know anything about the behavior or habits of the new species, we can infer that, like other beaked whales, it feeds at depth on squid or deep/bottom fish, and probably travels in small groups (a few individuals).

Q. Mitochondrial DNA versus genomic DNA for phenotyping – what are the challenges of using complete genomic sequences – What would the advantages of doing complete genome sequencing be?

Genome sequencing remains relatively expensive and requires quite a lot of high-quality DNA. For the purposes of determining whether there are 2 species, short sequences of mitochondrial DNA are actually very diagnostic (and therefore adequate), very inexpensive, and can be generated even from bone specimens in museums. We will very likely do some additional sequencing from the nuclear genome to get a more precise estimate of the amount and timing of divergence among the 3 species in the genus Berardius, but full genome sequencing is unlikely to contribute much in the absence of more information on the biology, life history, behavior, etc. of the species, so that is were we are better off putting our research time and effort.

Q. When do you call something a new species ?Can you tell us a little bit more about how haplotypes are used to infer distance and diversity? What other lines of evidence would further strengthen the black beaked whale as new species?

That’s a difficult question, as evolution is a continuous process, and taxonomy (the process of describing species and higher taxa) is an artificial hierarchy imposed on evolution to help us understand and describe biodiversity. We are using a species concept that infers species when genetic evidence indicates that they are evolving along independent evolutionary trajectories, e.g., they do not significantly interbreed and have not for long enough that they have evolved different ecosystem niches and functions (e.g., different food sources or feeding behaviors, habitat use, mating systems, acoustics, etc.). The mtDNA data strongly suggests that this is the case, as there are only very small differences between haplotypes of individuals within each form (≤5), and much larger differences between haplotypes of the two forms (16-26). The fact that the 2 adult specimens of the black form from which we have measurements are only about 2/3 the size of adult Baird’s beaked whales (far outside the normal size range for adult Baird’s whales), and that they have darker skin and several other recognizable (to experts) physical differences also indicates that they are different species, not just variation within a species.

Q. Do you see yourself as a sort of molecular explorer? How would you go about naming the new black whale?

This study has very much been like molecular exploration! We’ve used genetics to help us identify specimens that were previously identified as Baird’s beaked whales, and then been able to follow up with additional studies on those specimens. We use genetics that way frequently for marine mammals because it is so difficult to study them in their natural habitats. Official naming of the new species is done by publishing a complete description of the species (as complete as the specimens will allow), including some skull morphology if possible, and identification of a type specimen (the “holotype”) that will mostly likely be a skull in the Smithsonian Museum that was collected in 1948, but previously thought to be from a small Baird’s beaked whale. There is a team of researchers from Japan that are currently working on that publication and will most likely propose a scientific name. They were the first to indicate that this might be a new species in 2013 based on the 3 specimens from Japan, so that is why they have taken the lead in describing and naming it.

Q. What are the implications of your findings for whaling and conservation?

Baird’s beaked whales and several other toothed whales and dolphins are still commercially hunted in Japan, so it will be important for the whaling industry and scientists there to monitor the hunts to make sure that the new species, which appears to be much more rare than Baird’s beaked whales, is not taken. There are also other potential human impacts that could endanger this species, including seismic exploration, navy sonar, increasing ocean noise from other sources, pollution, entanglement in fishing gear, competition with humans for food, and climate change. Now that we know it’s there, we can work to learn more about it and, hopefully, how to protect it from these potential impacts

Scouting for the forager ant

– Identifying the basis of labour division in carpenter ants

 

Short summary

What determines the way animals behave? Is this almost unalterably in their genes or in their environment or a complex interaction between what is within and without? A recent study explores the division of roles within the worker caste of the carpenter ant and shows for the first time that these roles can be reversed using mind-altering drugs (1).

 

“Minor”carpenter ants are the foragers

Anyone who has observed the incessant activity of a beehive or a column of ants between their nest and a food source can appreciate how wonderfully co-ordinated and orderly it all looks. This coordination is brought about by a fascinating division of labour – well separated roles of who must do what for the colony. How do insects develop these identities? This becomes especially intriguing in insect colonies in which all inhabitants are children of the same parents and hence genetically related to each other. In carpenter ants, which are the subject of this study, there are two castes within the female workers – minor and major. The minors are smaller do most of the foraging whereas the majors rarely forage. This was established by setting up an arena for foraging around an ant nest and measuring to which caste they belonged and how many individuals came out to forage. While foraging activity for both minor and majors increased with age of the ants, the minors still performed most of the foraging. Additionally, the lead foragers – called scouts were also mostly minors and older scouts were much better/faster foragers than young ones -even when they were foraging in unfamiliar arenas. Hence, the foraging activity was established as a minor worker specific behaviour in these ants.

 

What makes “minor” ants better at foraging?

So what determines the foraging behaviour of minors? Genetic differences were undermined by the relatedness of minors and majors (they are sisters (2)) – suggesting that the differences is unlikely to be due to differences in genes. Also, multiple studies suggest that such behaviours are likely to be controlled by epigenetic mechanisms. Epigenetic modifications are modifications of the genetic material, without changes to the genetic material/ DNA itself (check out a beautiful introduction to the world of epigentics from MinuteEarth in the video below). These modifications which are chemical groups added on proteins that bind DNA, determine the context in which genes are expressed i.e form a basis for the conversion of genotype to phenotype. In this study they focused on the presence of a chemical group (an acetyl group) on histones. Previous studies have suggested that these marks may determine caste specific behaviour in other eusocial insects.

Consistent with this idea, a drastic increase in foraging activity of both majors and minors was brought about by feeding them drugs that inhibit the enzymes that remove the acetyl marks from the histone – or histone deacetylase inhibitors (Valproic acid – used to treat mood disorders in humans and Trichostatin A).  However, the minors continued to forage more and performed almost all the scouting.

Molecules and mechanisms of caste-identity

The authors then determined the molecular mechanisms of how the acetyl marks were placed on the histones in the first place what genes were responsive to these changes. When they inhibited the enzyme responsible for this behaviour (the histone acetyl transferase domain of the Creb binding protein (CBP)) they saw a drastic decrease in scouting. This established the scouts as a distinct behavioural caste within the minors and suggested that acetylation of histones by CBP is the molecular mechanisms that generate this behaviour.

They then looked at what makes major and minor workers different from the perspective of gene expression and came up with a different idea. What if there was a basal behaviour – “to forage” in ants and this was actively suppressed by all these molecular mechanisms? This suggested that injecting drugs at an early stage may prevent this suppression of behaviour. Voilà! in ants injected with drugs (Trichostatin A) the majors started to forage actively! In this case, it seems like timing was everything (look above for what happens when the treatment is started later!). Surprisingly, even when tested as a whole colony (with minors), the majors upon treatment participated more often in foraging. To dissect this further, the authors directly inhibited a single enzyme HDAC1 (Histone deacetylase 1 also called Rpd3) and found the same increase in foraging activity in the majors. This suggests a central role for HDAC1 in repressing foraging behaviour in majors.

Learning from ants

Behaviours are baffling and possibly emerge from complex interactions between genes, how these genes get expressed and what triggers them. Such triggers can come from what we eat, what we smell, how we interact with our environment and one another. Animal behaviour – especially in the context of colonies or societies, is likely to involve intricate rules for function and order. Unraveling these rules is an exciting area of ongoing research. In a surprising but retrospectively sensible turn of events, the authors of this study have found that the division of labour among worker ants lies in the mind, is set up very early and can be reversed.

Acknowledgement

Thank you!  Riley J Graham for helping out with this post

More about the cool process of epigenetic inheritance from the wonderful Minute Earth

youtu.be/AvB0q3mg4sQ

An interview with Riley J. Graham

 

Q. You note in your study, that a carpenter ant colony in nature, maintains a 2:1 ratio of minors to major worker ant. What do you think are the mechanisms for maintaining that ratio? Is it likely to be the same mechanism (HDAC and HAT dependent) as you describe?

It’s difficult to say how this could occur, and there is likely a degree of variation in caste ratio in wild colonies. One of our ongoing questions is whether caste fate can be influenced during development by epigenetic drugs. To address this, we are developing methods to deliver controlled treatment doses to during larval development to determine if this influences caste fate. Such a result would strongly suggest that HDAC and HAT activity is important for regulating the generation of caste specific morphological traits, which could account for how this ratio is maintained in our experimental colonies.

Q. Will the drug reversed majors show increased foraging even when there is an abundance of resources? 

Yes, in fact this is precisely what we saw. All of our colonies were fed ad libitum, for 10 days after injection, and majors treated with HDACi foraged significantly more than controls. However, because minor workers can feed their major sisters after foraging, a mixed caste setting may keep majors full of food even when they never forage. To control for this type of between-caste effect we did a different test in which we separated major and minor workers and withheld sugar water. This ensured all of our test subjects had a similar motivation to exit the nest in search of sugar, and prevented intrinsic behaviors of one caste from biasing behavior of the other.

Q. Have you or others seen such role reversals/ caste reversals in a natural setting? For example – colonies that are stressed for food.

Camponotus floridanus and its relatives in the subfamily Formicinae are interesting because of their discrete morphological caste systems, (e.g. minor, major) but all eusocial insect species rely on some form of caste-based division of labor to survive. Brian Herb and colleagues reported differences in genome-wide patterns of DNA methylation between nurse and forager honeybees. These two groups are behavioral subcastes that arise as younger nurse workers age and progressively become active foragers later in life. Experimental reversion of foragers back to nurses caused a coordinated reversal of DNA methylation to reflect this behavioral change, suggesting epigenetic regulation of behavior is a common trait among social insects, and that behavioral castes are sensitive to environmental changes.

Q. What major contribution do you think will come out of studying eusocial insects like ants or honeybees when compared to solitary insects like fruit flies? 

Fruit flies do not exhibit the vast range of behaviors seen in social insects. Over evolutionary time, some eusocial insect species have acquired sophisticated division of labor strategies, enabling colonies to undertake complex collective tasks including nest architecture, cooperative brood care, and even horticulture, as in the leaf-cutter ants Atta and Acromyrmex. Given that single queens can give rise to millions of individuals in thier lifetime, epigenetic regulation, rather than genetic differences between individuals are expected to have an important role in the expression of caste specific traits. We have not found allelic predictors of caste identity in C. floridanus, suggesting that the exceptional phenotypic differences between major and minor workers are likely attributable to epigenetic mechanisms. Eusocial insects are therefore excellent models for the study of how epigenetic changes can contribute to morphological and behavioral variation.

Q. Earlier studies, for example those by Sokolwaski et. al. have shown single locus polymorphisms controlling foraging behaviour in fruit flies. In the light of this evidence, one might think that epigenetic control of foraging behaviour in ants could be an adaptation to their social lives. What do you think?

I believe you are referring to Marla Sokolowski’s work showing that mutations in the gene foraging (for) can lead to differences in foraging behavior in flies. Such polymorphisms might cause variation in foraging behavior in flies, but in ants, this SNP would contribute to increased foraging in all castes, perhaps even the queen. Given that queen foraging would typically be highly damaging to a colony’s survival, this SNP would be evolutionarily suppressed in queens, but could become positively selected for in minor workers. This variation in the fitness landscape between castes is one reason to think that epigenetic regulators could be important when different castes need to express different genetic profiles from a common genome. Molecular heterochrony allows different genes to be expressed at different times in an animal’s life, and while a very young queen might benefit from a SNP causing increased foraging, a mature queen would not. The genome’s ability to activate or suppress genes depending on caste and age is an important aspect of social insect biology that likely relies on epigenetic mechanisms.

Q. Carpenter ant workers in the study are genetically related, which led you to investigate the possible epigenetic mechanisms determining the cast specific behaviours. Would you expect genetic bases for caste identity in species where genetic relatedness among the workers is not as high as the carpenter ants?

A number of studies describing genetic aspects of caste fate also suggest that the interaction of each genotype with the environment influences caste fate. In this light, it seems that genetic variation primarily alters an organism’s likelihood of becoming a particular caste, rather than rigidly determining caste fate. Allelic predictors of caste identity were not found in our ant species, suggesting behavioral and morphological phenotypes in social insects are likely the product of a gene by environment interaction that is facilitated by the epigenome.

Q. Insect colonies are fascinating systems to study genetic links to behaviour. Your study added valuable insights in mechanisms of determination of a caste specific behaviour. How easy (or hard) would it be to study more complex behaviours in other social animals (not necessarily insects)? 

Our work is among the first to look for indications that social insect behavior can be altered by the epigenome without any change in DNA sequence. Ants are a fascinating middle ground between the moderate behavioral variability seen in solitary insects, and the overwhelming complexity of higher order social behaviors, such as the relationships between kin grooming and reproductive hierarchies in primates. As scientists begin to consider more complex social features, they must also consider the vast array of behaviors that can be performed by each individual. In the case of kin grooming, researchers might be compelled to annotate a complex and fluid social network of kin grooming interactions, which may require a model that considers the behavior of each animal, as well as the behaviors of their social partners. This can get complicated quickly. This is not an insurmountable goal, but it is certainly harder to conceptualize and design experiments around. However, any molecular variation in the population that robustly contributes to behavior can hypothetically be measured, so it is not impossible to study organisms with greater behavioral complexity.

Two wings that beat like one

Wing-wing and wing-haltere coordination in insect flight

 

Snap-shot

Even at incredibly high wing beat frequencies, small insects maintain precise control of relative wing movement. A recent study explores how this control is achieved (1).

Background for this work

Flight and mechanism of flight have captured human imagination since time immemorial. Ancient insects had four wings, two of these wings morphed into accessory flight organs, responsible for stability during flight, called halteres (2,3). In dipterans, a class of insects (4), it was the second pair or the hind wings that got modified into halteres.

People have noted for a long time that the two wings (on either side) move precisely in phase, while halteres and wings move anti-phase during flight, (i.e. pair of wings moves antiphase with the pair of halteres). How do insects manage this precise control?

There are at least two ways in which this can be achieved, neuronal connections which would instruct the flight muscles or a mechanical coupling of the wings/halteres themselves. The really fast movement of the wings and halteres in small insects ( about 100Hz or higher, which can be visualized using high speed videography) precludes neurons. If it were neuronal, it would be pretty close to the fastest connectivity known to us.

What did they do and find?

In this work, Deora et al., have examined these phenomena in soldier flies,  dipteran insects with easily tractable (relatively large and white -aiding contrast) halteres. They asked, how are the wings able to beat in unison and how are the halteres maintained so precisely in the opposite phase to wings? The first clues came from serendipitous observations. Dead flies were able to maintain the in-phase and anti-phase relationship of their wing -wing and wing- haltere movements. Suggesting that this connectivity was not a result of neuronal instructions and possibly resulted from mechanical linkages.

The researchers then examined which part of the exoskeleton was maintaining this connectivity by surgically removing different parts of the thoracic exoskeleton. They were able to identify a region on the thorax necessary for the near perfect co-ordination of the wings, when they removed this region, the flies were unable to maintain coordinated wing movements. Interestingly they were able to stick the piece of exoskeleton back again and restore coordinated wing beating. They also identified the region responsible for maintaining mechanical coupling between each wing and it’s haltere (on the same side).

The researchers then tested the nature and limits of this coupling. The decrease in length of wings results in increased frequency of wing beats, how long can the halteres keep up? It seems like the halteres keep up till about the time when the wing is 60% of its original length and then quite suddenly, the coupling between the haltere and wings break down.

Another unknown, which Deora et al., are trying to work out is how this mechanical coupling is switched on during flight and otherwise switched off. This question is posed by behaviours in flies for which only one wing is used. The authors suggest a gearbox and clutch mechanism and attempt to find this clutch that allows the connection of the wings during flight. As yet, the nature, position and exact mechanism of the clutch is not known.

Conclusions from this study

This work shows for the first time that the wing-wing in-phase motion is due to mechanical connections across the sides- left-right axis. The wing-haltere anti-phase relationship is maintained by mechanical connections along the body axis. But how does this mechanical connection maintain a precise phase-angle? This is still not known and remains an active area of investigation.

An interview with Dr. Sanjay Sane

Q. In your work you address the biomechanics of wing-wing coordination and wing-haltere coordination, during flight. What about insects lacking halteres altogether (like dragonflies and damselflies) and insects in which the forewings are modified into halteres?

Excellent question. Insects outside of the Order Diptera lack halteres. The only exception to this is the Order Strepsiptera, in which the forewings have been modified into halteres. In both these cases, halteres are thought to serve the function of gyroscopic sensors which are essential in informing the nervous system about the changes in body orientation during flight. They may also be sensors that provide feedback about timing which is very important for wing motion control. In larger and slower insects such as Dragonflies and damselflies, aerial control is thought to be exquisitely visually driven. Not surprisingly, almost all dragonflies and damselflies operate only under conditions of bright lights. One may ask then: what about insects that are nocturnal but lack halteres (such as moths and antlions), or else insects such as bees which typically operate under bright lights but with very high wing beat frequencies? We have experiments to show that for such insects the antennae serve a role that is similar to halteres. It is not clear presently whether the precise mechanism underlying their sensory function is the same as halteres (i.e. gyroscopic, or timing-related), and that is a major subject of investigation in my lab.

Q. Your work shows a precise control of relative wing angle and haltere angle? Why does this angle matter? Is it just to keep the halteres out of the wing’s path?

Again, an excellent question! It is not clear at all whether the precise control of wing/haltere relative angle matters or is just a results of the physics of coupled oscillators (which wings and halteres seem to be). In some flies, the phase difference is not 180 degrees, so there appears to be nothing sacrosanct about that value. Yet, in a majority of the flies, the phase difference is 180 degrees despite great variation in thoracic morphology – so that cannot be coincidental. What dies matter, as we have shown in the paper, is that whatever the characteristic phase difference is for the given insect, it stay true because the timing information is a crucial feature of the feedback that the haltere provides. Our current hypothesis is that the actual phase difference is just a consequence of the physics of the coupled oscillators that causes their motion to fall into fixed in-phase or out-of-phase modes.

Q. What inspired you to think about mechanical connectivity?

When we observed the maintenance of wing/wing and wing / haltere phase difference in dead flies, it was immediately evident that the nervous system was not involved. The only other possibility was mechanical connectivity – which was fantastic because it answered many other questions that we had about speed and precision.

Q. Tell us more about the clutch? If it is internal , how would you probe it?

Two ways to probe it. One is careful experiments in which we can manipulate individual components of the wing hinge. Not easy, but if we find the right kind of flies in plentiful supply, it may be possible. The second and more direct way is to use X-ray micro-tomography – except this is very difficult and you need to know where to look. Our old-fashioned experiments may help there.

Q. Did you think of using other insects with different wing sizes, instead of manipulating the same insect and making its wings shorter?

Whatever insects we use, we will need internal controls because various aspects of the thorax do not scale isometrically. Manipulating the same insect is a far better option under the circumstances because internal control is then guaranteed.

Q. How does your work impact the way we think about insect flight?

In a major way, I think. For one, it clearly demarcates which aspects of wing and haltere coordination are active vs. passive. This has not been clear at all in previous studies on this topic. The second is that it generates clear and predictive and minimal hypotheses to explain a diverse set of observations (such as bee wing warm-up etc.) in a vast number of insects. It also throws light on how insect flight coped with miniaturization of the body form, which is an important evolutionary question because it appears to underlie the spectacular evolutionary success of insects as a group.

Q. Can you reduce insects to mechanical machines? If yes, does this affect the way you view the world as well as investigate a question?

This is a philosophical question and my answer is going to be speculative. Also, it is a question that applies not only to insects, but to animals in general. I do not think animals can be reduced to mechanical machines, although the way we conduct our science is such that we cannot help but assume some reductionist scenario like that. Our approach is at least as old as and derived from Rene Descartes, who in his brilliant treatise “A discourse on method” argued that all animals are machines (except for humans, of course, because they “possess a soul” unlike the brutes). His ideas were influenced by Newton’s recent discovery of laws of mechanics, and William Harvey’s discovery of heart being merely a mechanical pump, etc. It must have been tempting to think that everything can be explained by laws of mechanics. In later years, this approach has included the function of nervous system which is also essentially driven by the physics of cable theory and electrical conduction and gained currency through Sherrington’s discovery of reflexes and the idea of “a chain of reflexes”. So, add electrical circuits to the mix – but keep the basic idea of a mechanical machine. Where this approach fails however, is that it is unable to explain how animals, including insects, generate new and “spontaneous” activity. If they did not generate spontaneous activity, one imagines a universe in which all animals were essentially fancier versions of wind-up toys – but we know from experience that they are not. How can humans or circus elephants learn to ride bicycles or mice their pin-wheels? How do insects learn to deal with scenarios such as electric shocks which they may have never encountered in their evolutionary history? Surely, the brain is capable of generating novelty activity that ensures that it does not produce simple, copy-book, discrete set of responses to challenges posed by a continuum world.

Q. Humans have historically been interested in all things that fly, with the vested interest of putting ourselves in the sky. Do you have a similar motivation for studying insect flight?

Not particularly. One has to choose one’s battles, and mine has been to understand the nature which is far more sophisticated and fascinating than anything I will be able to build, or have the expertise for. That said, I am in full admiration of anyone who tries to use these concepts for building things that fly. We collaborate with such engineers, and help them as much as we can, and sit back and watch with admiration when they achieve incredible feats of engineering. It makes us appreciate the intricacies of nature even more!

References

1.“Biomechanical basis of wing and haltere coordination in flies.” Tanvi Deora et al., Proc Natl Acad Sci U S A. 2015

2. “The Gyroscopic Mechanism of the Halteres of Diptera”, J. W. S. Pringle, Philosophical Transactions B., 1948

3. “The evolution of insect wings and their sensory apparatus.” Dickinson MH et al., Brain Behav Evol. 1997

4. Classification of Insects from the Royal Entomological Society

5. “The aerodynamics of insect flight.” Sanjay Sane, J Exp Biol. 2003