Interview with a social insect scientist: Raghavendra Gadagkar

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IS: Who are you and what do you do?

RG: My name is Raghavendra Gadagkar and I am currently a Professor in the Centre for Ecological Sciences at the Indian Institute of Science, Bangalore, India.

I do several things:

I research questions concerning the evolution of cooperation and conflict in animal societies, using the Indian paper wasp Ropalidia marginata for my empirical research.

I teach evolutionary biology, behavioural ecology, sociobiology and organismal biology to doctoral, masters and undergraduate students.

As President of the Indian National Science Academy (until recently) and with other similar affiliations, I contribute toward the promotion of science and good science policy in India and elsewhere.

IS: How did you end up researching social insects?

RG:  I was fond of catching and watching insects, frogs and other moving creatures as a child. In college I encountered several colonies of Ropalida marginata on the windows of the zoology department. I could not help watching them out of curiosity and have not since looked back. R. marginata also converted me from a catcher (they sting) to a watcher (their behaviour is fascinating). At first I watched them merely as a layman. Then I began to study them scientifically, but only as a week-end hobby. After my PhD in molecular biology, I converted my hobby into my full-time profession.

IS: What is your favourite social insect and why?

RG:  The tropical primitively eusocial wasp, Ropalidia marginata. I have been studying it for over 40 years and it continues to present me with new intellectual challenges and continues to give me great delight. I have not felt the need to look beyond, with the exception of occasionally studying the congeneric Ropalidia cyathiformis, but only to understand R. marginata better.

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Ropalidia marginata. Photo: arian.suresh/flickr

IS: What is the best moment/discovery in your research so far? What made it so memorable?

The discovery of behavioural caste differentiation into Sitters, Fighters and Foragers through the use of multivariate statistical analysis of quantitative behavioural data, in the early 1980’s remains, to this day the most exciting and memorable moment. Several factors have contributed to the special status of this early work. It was my first scientific discovery outside of molecular biology, it was made entirely by following my instincts rather than by following the literature and it has remained the starting point for almost everything I have done since.

IS: If teaching is part of your work, what courses do you teach? Has your work on social insects helped to shape your teaching?

RG: I teach courses in evolutionary biology, behavioural ecology, sociobiology and organismal biology to doctoral, masters and undergraduate students. During the last five years my undergraduate students regularly perform field and laboratory experiments with ants, bees and wasps.

IS: What is the last book you read? Would you recommend it? Why or why not?

RG: The most recent book I have read is “Half-Earth: Our Planet’s Fight for Life” by EO Wilson. I would strongly recommend it to any and all persons. It is remarkably well-written and passionate plea to treat the planet responsibly. Besides, it is brimming with the most recent scientific discoveries, described in Wilson’s inimitable style and laced with Wilson’s priceless wisdom.

IS: Did any one book have a major influence in shaping your career? What was the book and how did it affect you?

RG: Two books that I read as a first-year undergraduate changed my life: King Solomon’s Ring by Konrad Lorenz and The Double Helix by James Watson. Both books described great science but their real magic came from the fact that they described the process of doing science.

IS: Outside of science, what are your favourite activities, hobbies or sports?

RG: When I was doing molecular biology, watching wasps was my hobby. When watching wasps became my profession, I needed a new serious hobby, besides reading book and watching movies. My new hobby is to break the boundaries of scholarship and bring together the natural sciences, social sciences, humanities and arts, both in research and in teaching.

IS: How do you keep going when things get tough?

RG: Just keep going – there is no other way! My science itself is a hobby so that things never really get that tough.

IS: If you were to go live on an uninhabited island and could only bring three things, what would you bring? Why?

RG:  The answer to this depends on where the island is located and how long I would have to be there. Besides, today, this question has become a bit trivial – most people on the planet would say: “my smartphone is enough”. That would be my first choice with or without internet, as long as I can power it with batteries. I am not that much of a field biologist and my passion is more in watching than in catching. I suspect that I could spend endless time watching all kinds of animals, especially insects for which I need almost nothing.

IS: Who do you think has had the greatest influence on your science career?

RG:  My science teacher in sixth grade inspired me to become a scientist, my biology teacher in 8th grade inspired me to become a biologist, WD Hamilton and EO Wilson have been my role models.

IS: What advice would you give to a young person hoping to be a social insect researcher in the future?

RG: The same advice that I would give to any young researcher hoping to do any kind of science – avoid fashions and try to do something original and creative and minimize your dependence on what is hard to get (funding, equipment or whatever is hard to get). In the context of social insect research today this translates into studying behaviour in the field.

Invasive Social Wasps

Highlighting the article written by T. Takeuchi, R. Takahashi, T. Kyoshi, M. Nakamura, Y. Minoshima, J.-I. Takahashi in Insectes Sociaux

Written by Insectes Sociaux Editor-in-Chief, Michael Breed

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Vespa velutina attacking a honey bee. Photo: Danel Solabarriela/flickr

In this issue of Insectes Sociaux, Takeuchi and colleagues reveal the genetic origins of an invasive population of Vespa velutina (the yellow-legged hornet) in the western islands of Japan. This invasive wasp is a predator on the honey bee species Apis cerana in its native range and can prey on Apis mellifera outside of its normal range (Monceau et al 2013). Native to the southern part of Asia and to Indonesia, it has also been introduced into Korea and Europe. They use mitochondrial DNA sequences to generate a cladogram for populations of this wasp and are also able to draw conclusions about genetic variation in the invasive population in Japan. Genetic variation may support the phenotypic flexibility exhibited by some invasives and consequently it is an important feature to characterize in invasive populations.

The role of social insects, such as this hornet, as biologically invasive species is well known, principally because of the prominence of invasive ants through the last 100 years in ecological studies and their creation of important issues in public health and agriculture. The numerous exemplars of high-impact invasive ants include the red imported fire ant, Solenopsis invicta, the pharaoh ant, Monomorium pharaonis and the Argentine ant, Linepithema humile. The Formosan termite, Coptotermes formosanus, is a major pest in many habitats.   The western honeybee, Apis mellifera, is invasive throughout the Americas, first as an introduction by European colonialists on the east coast of North America in the 1600s, and then by the introduction of a more aggressive form in the 1950s in Brazil.

In some cases invasive social insects, such as the fire ant and the Argentine ant, are perceived to have essentially overrun an entire ecosystem. These species cause massive shifts in the terrestrial invertebrate fauna, impact the reproductive success of ground nesting birds, and have ripple effects on other trophic levels. However, many social insect invasions occur quietly and go largely unnoticed because the ecological impacts of the invasion are subtle and there are no apparent public health or agricultural implications of the invasion. Whether the impacts are large or small, understanding the processes of biological invasions is a key question in evolution, ecology and behavior.

What makes some social insects such effective invasive species? Ecological flexibility, high reproductive rates, and ability to disperse within the landscape all must be important factors. But many populations of invasive species, social insect or otherwise, survive very narrow genetic bottlenecks. Introductions of species to new areas often involve the transport (typically by humans) of a very small number of individuals or colonies. This may translate into invasive populations with low genetic diversity.

Takeuchi et al (2017) sequenced three mitochondrial genes, COI, Cytb, and 16S rRNA, from samples of V. velutina collected across its natural range, plus invasive populations in Japan and Korea. Their results show that this species is likely monophyletic, but that there are two relatively distinct geographical clades, one in Indonesia and Malaysia, the other more broadly distributed in continental Asia. The invasive Korean population nests within the populations from China, and the invasive Japanese population probably derives from the geographically nearby Korean population.

Significantly, Takeuchi et al (2017) found no genetic variation in these genes in the Japanese population. While their finding is unusually low, even for an invasive that has gone through a genetic bottleneck, it is by no means out of the ordinary to observe invasive social insect populations that derive from a few individuals or a few colonies. In the case of V. velutina, Takeuchi et al. (2017) argue that fertilized queens could easily be carried along in goods transported by humans and that, in a practical approach to regulation of invasions, vigilance for fertilized queens might be useful. It would be very interesting to compare the social flexibility and ecological adaptability of the Japanese population of V. velutina with Chinese populations to see if these features have been affected by the bottleneck.

These findings raise the very interesting question of how invasive social insects are able to retain ecological and social flexibility, keys to being successful invasive species, through periods of small population size. Mechanisms for carrying characteristics that are key to invasiveness through a bottleneck could include having multiple queens in colonies mating more than once, plasticity in phenotypic expression, or rapid evolution of genetic diversity via mutation. Each of these strategies could be effective, and future work building on approaches like those of Takeuchi et al (2017) should help to explain the properties that make some social insects such effective invasive species.

 

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Vespa velutina, the yellow-legged hornet. Photo: Danel Solabarriela/flickr

References

Monceau K, Arca M, Leprêtre L, Mougel F, Bonnard O, Silvain J-F, et al. (2013) Native Prey and Invasive Predator Patterns of Foraging Activity: The Case of the Yellow-Legged Hornet Predation at European Honeybee Hives. PLoS ONE 8(6): e66492. https://doi.org/10.1371/journal.pone.0066492

Takeuchi T, Takahashi R, Kyoshi T, Nakamura M, Minoshima Y, Takahashi J-I. (2017) The origin and genetic diversity of the yellow-legged hornet, Vespa velutina introduced in Japan. Insect Soc DOI: 10.1007/s00040-017-0545-z

 

Unexpected stop signaling in a foraging honey bee colony

A blog post highlighting the article by  P. M. Kietzman, P. K. Visscher, J. K. Lalor in Insectes Sociaux

By Parry Macdonald Kietzman

The remarkable system of communication used by honey bees to coordinate their daily activities is well known, though most people are primarily aware of the waggle dance. This positive feedback signal is one that communicates the distance and direction of some item of interest, most commonly a food source, to a worker bee’s nestmates. Perhaps less well-known is the stop signal, an acoustic negative feedback signal that can be used as a counter to the waggle dance, inhibiting recruitment and decreasing foraging (reviewed in Kietzman and Visscher 2015).

One use of the stop signal occurs when foragers encounter danger, such as an attack from other bees or a predator, at a food source (Nieh 2010). Nieh (2010) simulated such attacks at a feeding station by pinching foragers’ legs with forceps. Back at the hive, these foragers were then much more likely to use the stop signal on other bees advertising that same location with the waggle dance than they were on dancers advertising other food sources.

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Parry observing the honey bee dance floor in her two-frame observation hive.

Our experiment was originally intended as a pilot study with the goal of practicing a method similar to Nieh’s (2010) technique of pinching bees’ hind femurs during their visits to a feeding station so that we could then use that technique in a later study. We established a colony of bees in a two-frame observation hive (1/4 or 1/5 a regular-sized hive with observation windows on the sides) on the premises of the University of California, Riverside’s Agricultural Operations. We trained the bees to visit a feeding station baited with sugar water 100m away from the hive, and an observer there gently caught visiting foragers in a small net and marked them on the thorax with one of two colors of paint pen depending on which treatment they received.

Using a coin toss to help randomize the treatments, approximately half the visiting foragers were “attacked” with a pinch to the hind femur and the other half were not. I watched the marked bees’ waggle dances back at the hive and recorded them using an HD video camera. A detailed analysis of the video recordings revealed that bees that had not been pinched at the feeder performed significantly more and longer waggle dances than the bees that had been pinched. Additionally, the pinched bees produced significantly more stop signals upon their return to the hive than the unpinched bees.

These results were very much in line with what we expected based on Nieh’s (2010) findings, however, we also made the surprising observation that most of the stop signals we recorded—about 70%–were performed by unmarked bees that had probably never visited the feeding station at all.

Though we don’t have a definitive answer for why so many unmarked bees used the stop signal on dancers advertising the feeding station, there are a few possible explanations. One is that the unmarked bees may have been foraging at another location and were not promptly unloaded upon their return to the hive because the unloader bees were overwhelmed by the influx of food coming from the feeding station. Stop signaling has often been found to increase when the bees have access to a feeding station (reviewed in Kietzman and Visscher 2015), and most of this stop signaling is produced by tremble dancers. Foragers perform the tremble dance when they are not unloaded quickly (Seeley 1992), so if there were insufficient unloader bees available due to the large amount of food coming from the feeding station then this could account for the stop signaling performed by unmarked bees.

A second explanation is that the stop signalers could have been unloader bees rather than foragers, and that these bees were using the stop signal in an attempt to decrease what had become an unmanageable number of foragers exploiting the feeding station. This use of the stop signal, while plausible, has not yet been measured and would likely be an interesting and productive area of study.

Finally, a rich, unlimited source of food such as a feeding station can readily be compared to hive robbing rather than typical foraging on flowers. Johnson and Nieh (2010) modeled a robbing event and showed that the stop signal could successfully be used to quickly shut it down, which would be beneficial if the robbed hive were very strong and an excessive number of robbing foragers were being killed. It is possible that the pinched bees from our experiment were emitting alarm pheromone (signaling a threat to the other bees), and that other bees in the colony interpreted this as evidence that they had been present during a robbing situation. If this were the case, the stop signaling we observed could have been an attempt to shut down what was perceived as an unfavorable robbing event.

Clearly, we have yet to decipher all the meanings of what is a versatile and effective communication signal.

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Photo: Rachael Bonoan/flickr

 

References

Johnson, BR and Nieh, JC. 2010. Modeling the adaptive role of negative signaling in honey bee intraspecific competition. Journal of Insect Behavior 23: 459-471.

Kietzman, PM and Visscher, PK. 2015. The anti-waggle dance: use of the stop signal as negative feedback. Frontiers in Ecology and Evolution 3: 54-58.

Nieh, JC. 2010. A negative feedback signal that is triggered by peril curbs honey bee recruitment. Current Biology 20: 310-315.

Seeley, TD. 1992. The tremble dance of the honey bee: messages and meanings. Behavioral Ecology and Sociobiology 31: 375-383.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 1: observing waggle dances and stop signals.

The smell of a brand new house

A blog post highlighting the article by M.F. Torres and A. Sanchez in Insectes Sociaux

By María Fernanda Torres

Perhaps one of the most astonishing features of ants is their ability to establish mutualistic associations with plants, myrmecophyte plants in particular. About 110 ant species nest exclusively inside hollow structures in leaves, stems or roots the host plant produces (Chomicki and Renner 2015). The mutualism is beneficial for the ants because the host plant provides the colony with housing and food. This food can be obtained directly from the plant or honeydew secreted from the ant-tended hemipterans living on the plant. For the plant, hosting an ant colony is comparable to having its own defense army for a lower cost than producing extensive chemical defenses.

For both members of a mutualism, identifying and locating (or attracting) the right partner is a crucial step in the establishment of the mutualism. Fertile founding queens (alates) emerge from the colony and, after the nuptial flight, they start their quest for a host for her new colony. Finding a place as fast as possible contributes to the survival of the both queens and host plants. For the ant queen, flying towards the wrong plant species or finding a colony already occupying a host translates into wasted energy and increased competition.

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Alate P. mordax queens running away from the researchers after a branch was cut open. Photo: M.F. Torres

So, how do plants advertise available spaces to the founding queens, especially when host plants are dispersed over large areas? What signals are queens recognising? Communication between plants and ants is mostly mediated by volatile chemical compounds (Heil and McKey 2003; Edwards et al. 2006). In our study, we wanted to test if the plant chemical signals that attract ant queens vary depending on the plant’s developmental stage and if queens respond to such variation. Every new generation of founding queens must be capable of distinguishing the most suitable available host from a pool of hundreds of other plants across large distances. It is a question of survival for both ants and hosts, requiring that the mechanisms of recognition and attraction are precise and informative to be successful.

To help us understand ant-plant communication, we studied Pseudomyrmex mordax queens to test their preferences between young and mature leaves or seedling and adult Triplaris americana plants. Pseudomyrmex is a genus of ants restricted to the Neotropics. Some species of the aggressive Pseudomyrmex nest inside myrmecophyte plants like Acacia, Cordia, Tachigali, and Triplaris, (Ward 1991, 1999) and tend coccids (Hemiptera) to obtain sugar. To survive, P. mordax must form a mutualism with T. americana and it is such a good guardian that has made Triplaris earn the name of “vara santa” (or holy rod) as the colony members will painfully sting however comes into the plant’s proximity.

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P. mordax worker patrolling T. americana flowers. Photo: M.F. Torres

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Location of Guamo, Tolima-Colombia, where we performed the experiments.

For the experiments, we collected young and mature leaves from both seedling and adult T. americana trees from a population in Colombia. We also collected alate P. mordax queens from the branches of nearby T. americana trees that were not used for the experiment (as we were subject of the ants’ aggressiveness). In an experiment conducted in the field, we placed the leaves of the young and mature T. americana on opposite sides of a two-sided olfactometer and recorded the time each queen spent on each side. We also performed the experiment leaving one of the sides empty as a control. We then compared the differences between the time on each side across all the queens used in the experiment to establish whether the young ant queens had a significant preference for a particular leaf age or plant age.

We found that while queens do not show a preference for young and mature leaves from the same plant, they do prefer leaves from T. americana seedlings over adults. Queens also spent more time in the arm of the olfactometer containing T. americana leaves when the other arm was left empty. Our findings show that P. mordax queens are attracted by volatile chemical compounds produced by T. americana and discriminate signals produced by its seedlings from other signals. The ability to distinguish between plant development stages, along with the use of chemical cues to find a mutualist plant partner increases the chances of a queen’s survival. For the seedling, the ant queen and her future colony provide early protection against herbivores and competition by pruning competing plants, enhancing seedling survivorship. Knowing the age of plant that the queens prefer is only one part of the story. Comparing the relative abundance of the chemical volatiles from each type of leaf will provide more information about how the plant uses odors to signal the queen to her new home.

References

Chomicki G, Renner SS (2015) Phylogenetics and molecular clocks reveal the repeated evolution of ant‐plants after the late Miocene in Africa and the early Miocene in Australasia and the Neotropics. New Phytol 207(2):411-424

Edwards DP, Hassall M, Sutherland WJ, Yu DW (2006) Assembling a mutualism: ant symbionts locate their host plants by detecting volatile chemicals. Insect Soc 53:172–176

Heil M, McKey D (2003) Protective ant-plant interactions as model systems in ecological and evolutionary research. Annu Rev Ecol Evol S 34:425–553

Ward PS (1991) Phylogenetic analysis of Pseudomyrmecine ants associated with domatia-bearing plants. In: Huxley CR, Cutler DF (eds) Ant-plant interactions. Oxford University Press, Oxford, pp 335–352

Ward PS (1999) Systematics, biogeography and host plant associations of the Pseudomyrmex viduus group (Hymenoptera: Formicidae), Triplaris– and Tachigali-inhabiting ants. Zool J Linn Soc 126:451–540

 

Interview with a social insect scientist: Madeleine Beekman

Madeleine in the field

Madeleine in the field.

IS: Who are you and what do you do?

MB: My name is Madeleine Beekman and I study how insect colonies are organised and the ways by which they deal with conflict within their societies. I have done quite a bit of work on foraging behaviour in mass recruiting ants and honey bees as well as nest-site selection in different species of Apis. Currently I continue to work on the amazing Cape honey bee, a subspecies of honey bee in which the workers are capable of cloning themselves. Workers can now produce females instead of males, which completely changes the relatedness within the colony. This change in relatedness in turn leads to very interesting conflicts not usually seen in other honey bees. More recent is my adventure into honey bee virus land. Here the aim is to unravel how honey bee RNA viruses become more virulent and what role exactly the ectoparasite Varroa destructor plays.

IS: How did you end up researching social insects?

MB: While doing my MSc at the University of Amsterdam, people were trying to commercialise the use of bumble bees in glasshouse pollination, particularly of tomato crops. Tomatoes are a funny crop; the plants continuesly produce flowers which can pollinate themselves, but the pollen needs to be actively loosened. When grown outside, the wind does the trick, but not in glasshouses. For a long time every tomato plant had to be touched daily with a vibrating stick to ensure pollination. Enter honey bees….they are much more efficient and cheaper. But honey bees are also picky, so as soon as there are nice plants in flower outside, honey bees ignore the tomato crop (remember they have a very useful communication dance, so only a few workers need to find something better and soon the whole colony knows about it). Obviously glasshouse growers could have screened their glasshouse, but there are other disadvantages to honey bees. Their colonies are large, they poo a lot and they can sting. The bumblebee Bombus terrestris started to look like an interesting alternative. The problem was that bumble bees are annual insects, and tomatoes are grown almost year round. What they needed was a PhD student who was going to figure out how to prevent bumble bee queens from going into diapause, how best to survive artificial diapause, and how to obtain good quality colonies year round. That PhD student was me. I was already obsessed with insects and mites, was an amateur beekeeper and loved the challenge.

IS: What is your favourite social insect and why?

MB: That is a tough question….I think I will settle for the blue-banded bee Amegilla cingulate. It is simply gorgeous and the males have this funny habit of forming social roosts (to be honest the blue-banded bee is not the only one in which the males hang out together at night, but they are the blue-est…).

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Roosting blue-banded bee. Photo: James Niland/flickr

IS: What is the best moment/discovery in your research so far? What made it so memorable?

MB: I think the most memorable occasion was when I got to work one morning and my then Honours student Alex Jordan said to me: ‘I think I found something really cool’ (or words to that effect; it has been a while). Alex had spent a field season in South Africa working on the Cape honey bee and was analysing his data. When I excitedly asked what that might be, he replied by saying he wasn’t going to tell me until he was certain. Turned out he found that workers of the Cape honey bee parasitise queen cells of other honey bee colonies on a massive scale, a discovery that changed the direction of the research on the lab on this weird bee. Because these workers produce clones, they reincarnate themselves in genetical terms.

IS: If teaching is part of your work, what courses do you teach? Has your work on social insects helped to shape your teaching?

MB: I teach in a first year unit called Life and Evolution, and in two third year units: Animal Behaviour and Evolution and Biodiversity. In my teaching I am foremost an evolutionary biologist. I do give examples of my own work where relevant, and obviously social insects are ideal if you want to impress first year students, but I am careful in pushing it too far.

IS: What is the last book you read? Would you recommend it? Why or why not?

MB: ‘A little life’ by Hanua Yanagihara. One of the most beautiful books I have read, so I most certainly recommened. Science-wise, the last book I read was Frans de Waal’s latest book: ‘Are we smart enough to know how smart animals are?’, also highly recommended as it makes us think about what exactly intelligence is. I look forward to reading Peter Godrey-Smith’s latest book ‘Other minds: the octopus and the evolution of intelligent life’ (see a pattern here?) and Menno Schilthuizen’s upcoming ‘Darwin comes to town: how the urban jungle drives evolution’ (so many books, so little time….).

IS: Did any one book have a major influence in shaping your career? What was the book and how did it affect you?

MB: Boring anwer I fear, but that must be Richard Dawkin’s ‘The selfish gene’ and ‘The extended phenotype’. Not very original, I know, but they are extremely influential books.

IS: Outside of science, what are your favourite activities, hobbies or sports?

MB: I would love to spend more time reading books, both science and fiction. But I also love exercising and horse riding. My main form of exercise is RPM, where you get on a stationary bike and go nowhere but end up completely exhausted after 45 minutes because there is a trainer shouting instructions such as ‘go faster’, ‘put more gears on’ or (my favourite) ‘suck it up’. I also spend (too little) time on a yoga mat.

IS: How do you keep going when things get tough?

MB: I exercise or get on a horse.

IS: If you were to go live on an uninhabited island and could only bring three things, what would you bring? Why?

MB: Sunscreen, because I would only go to a tropical island. This is cheating I suspect, but a huge bookchest full of books. And my husband, as I’ll get lonely after a while (and we can swap books if he also takes a book chest….).

IS: Who do you think has had the greatest influence on your science career?

MB: Different people at different stages in my career, but I can easily single out two. Foremost my PhD supervisor Maus Sabelis, who sadly died too young. He taught me to believe in myself. And ever since I moved to Australia Ben Oldroyd, life partner and close colleague. Without his support I wouldn’t be where I am now.

IS: What advice would you give to a young person hoping to be a social insect researcher in the future?

MB: I think these days young researchers need to be much more strategic than I have been. Obviously doing good science is essential, but you also need to make sure people know who you are and what you do. So make sure you give brilliant talks at national and international conferences. Make yourself visible, even as a postdoc. If opportunities arise, people need to know you exist; if you hide in the lab or your office, people may not think of you even if you are be the best person. I realise this is not specific to social insect research….

Your baby doesn’t look so well …or the effects of developmental stressors on larvae in a young termite colony

A blog post highlighting the article by T. Chouvenc, M. Basille and N.-Y. Su in Insectes Sociaux

By Thomas Chouvenc

One of the reasons for the success of social insects is that their nest provides a homeostatic fortress for the colony, protecting it from external environmental changes and external threat. This is particularly true in large, mature colonies of ants, termites and bees, where a large worker cohort can provide optimal care for the developing brood and the modification of the nest structure itself provides a safe “home”.

However, like any other organisms, social insects may still be susceptible to developmental stress. Embryos first develop in the womb (or egg), and after birth continue to develop until it reaches maturity (adulthood). During this development phase, an individual is subjected to environmental and epigenetic stressors throughout its growth phase. Fluctuating asymmetry has historically been used as an indirect measure of exposure to developmental stress, and the relationship is that, the more stressful the conditions are for a developing organism, the more it will display asymmetrical traits at the end its development.

In the Asian subterranean termite, Coptotermes gestroi, soldiers sampled from mature colonies display highly symmetrical traits, suggesting that conditions for a developing termite in a large and healthy colony are optimal, and very little stress is imposed on the developing brood (Chouvenc et al. 2014). This is because there is an army of workers taking care of them in the most dedicated nursing behavior. However, in newly started colonies, the king and queen are alone to take care of their initial brood, and for many months, all the young termites hatching and developing in this stressful environment are subjected to limited resources and less than optimal parental care. As a result, the first few termites produced in a new colony are highly deformed and display highly asymmetrical traits. However, as the colony grows and additional workers are produced, the brood receives additional care and the individuals produced are progressively looking more symmetrical. I sent a few termite samples from my incipient colonies to a colleague for identification, without telling him the origin of the samples. His response was: “Tom, your samples are all messed up! You didn’t do a good job conserving the samples.” The fact was I preserved them in the same way that I preserved my other samples but the source of the deformed samples was from a young colony.

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A: C. gestroi soldier from an incipient colony, B: Soldier from a mature colony.

In Chouvenc et al. 2017, we showed that the quality of termites produced in a colony improves over time and that, as the colony grows, termite eggs and larvae develop in better conditions, resulting in “better looking” termites. We were able to identify two independent origins of the stress imposed on very young termite colonies. First, the quality of brood care was found to be critical in producing highly symmetric individuals, and that the more workers present in a colony, the more symmetrical the newly produced termites looked. Second, in the first year of development, the termite colony produces “cheap” soldiers, as their development is accelerated.

These cheap soldiers are a way for the colony to quickly produce a few soldiers to defend the young colony and reach the optimal soldier ratio for the colony (Chouvenc et al. 2015). However, accelerated development imposes a heavy stress on developing soldiers, which display strong asymmetrical traits as a result. Later in the life of the colony, soldiers are then produced through a different developmental pathway, with additional time and resources invested in them, resulting in larger, better looking, and more functional soldiers.

Therefore, a newly established termite colony is extremely limited in its caring capacity, time and resources, and the initial investment in the first brood is very poor, resulting in termites exhibiting morphological evidence of their stress. When the colony grows, the care toward the brood improves and more time and resources are allocated to the new brood, providing stable developing conditions resulting in “good looking” termites.

One could say that the appearance of a termite may not say much about the quality of an individual, however these asymmetric individuals produced early in the life the colony have a short life span, confirming the cost of developmental stress on their individual physiology and metabolism. Workers and soldiers produced from the first initial egg batch laid by the queen usually die within the first year of the life of the colony (Chouvenc and Su 2014). In contrast, termites that developed in a mature colony in optimal conditions can live up to four years. Therefore, the initial parental and alloparental care toward the developing brood can directly be a measure of the initial investment in larvae, and the longevity and functionality of the resulting individual, a measure of the return on investment.

References

Chouvenc T and Su NY. 2014. Colony age-dependent pathway in caste development of Coptotermes formosanus Shiraki. Insectes Sociaux, 61: 171-182.

Chouvenc T, Basille M. Li H-F and Su N-Y. 2014. Developmental instability in incipient colonies of social insects. PloS one, 9: p.e113949.

Chouvenc T, Basille M and Su N-Y. 2015. The production of soldiers and the maintenance of caste proportions delay the growth of termite incipient colonies. Insectes Sociaux, 62: 23-29.

Chouvenc T, Basille M and Su N-Y. 2017. Role of accelerated developmental pathway and limited nurturing capacity on soldier developmental instability in subterranean termite incipient colonies. Insectes Sociaux. In press.

Calling nestmates to the rescue

A blog post highlighting the article by K. Miler & K. Kuszewska in Insectes Sociaux

Written by  Krzysztof Miler

Pit-building antlion larvae are predatory neuropterans which co-occur with some sand-dwelling ants, their main prey. The ants evolved rescue behaviours as means of avoiding antlion predation: when an ant stumbles into the pit and is captured by an antlion larva, its nearby nestmates may act to free it. No one knows how exactly that happens.

ant lions

An example of the “antlion zone” with several antlion larvae pits (conical traps). When an ant stumbles inside one of these pits, its near-by nestmates may come to rescue. Photo: K. Miler [Błędowska Desert, Poland].

In 2002, Czechowski and his co-authors [1] observed that some species of ants rescue their nestmates from the pits of antlion larvae. Since their discovery, several papers about this phenomenon have been published. However, no one knows how exactly rescue behaviour is elicited. The main hypothesis states that when an ant stumbles into the pit of the larva and gets captured, it sends some kind of signal (“call for help”) which summons its nearby nestmates to the site of capture and triggers their rescue behaviour, but the form of this signal remains unknown.

I recently published a paper saying that soon-to-die ants stop calling for help and thus elicit lower levels of rescue than longer-lived individuals [2]. Prof. Martin Collinson tweeted shortly after my publication: “Moribund ants do not call for help. They’re probably too knackered to use their little ant smartphones.” But the call for help likely doesn’t come from a tiny smartphone.

If rescue is indeed elicited by a call for assistance, then in my study species, Formica cinerea ants, the “call for help” signal is most likely chemical, originating from one of glands releasing volatile substances. Together with my colleague, Karolina Kuszewska, we performed two experiments to test whether mandibular gland excretions elicit rescue behaviour. We focused on mandibular glands because they were obvious candidates due to their other communication functions in ants.

In the first experiment, we impaired communication of some ants via their mandibular glands and checked whether they were rescued less frequently than other ants with unchanged mandibular communication skills. In the second experiment, we dissected some ants and checked whether the content of their mandibular glands applied onto dummy-ants made of pieces of toothpicks would elicit rescue from nearby (real ant) nestmates.

Apparently, mandibular glands have nothing to do with the elicitation of rescue behaviour in F. cinerea. Blocking the release of excretions of mandibular glands has no effect on rescue frequency, and applying the content of these glands onto dummies elicited no rescue towards them. Our study is the first one to look into the mechanism of the “call for help” signal. We plan to perform another set of experiments looking into gaster-tip glands, aiming at finding out whether the mechanism of rescue behaviour in ants is as we currently assume it is. We expect that we won’t find a tiny Bluetooth device either.

An ant captured by an antlion larva summons its nestmate to the site. The rescuing ant grabs the victim by its leg and pulls, holding on even when the antlion larva starts to bury deeper in the sand to prevent losing its victim as a result of this rescue action. Unfortunately for the victim, the rescuing ant is not successful. Video: K. Miler [Jagiellonian University, Poland].

 

References

[1] Czechowski et al. 2002, Ann Zool 52:423-431.

[2] Miler 2016, PLoS ONE 11:e0151925.

Find out more in Hollis et al. 2015.

Forced Queen Associations

Highlighting the article written by M. Motro, U. Motro and D. Cohen in Insectes Sociaux

Written by Insectes Sociaux Editor-in-Chief, Michael Breed

Investigations of colony founding by groups start with the question: What happens if an animal that could survive perfectly well on its own is confined with others of the same species? Queens of the harvester ant species Messor semirufus typically found nests on their own, but occasional observations have been made of small groups of queens founding nests together. Many species of ant solitary queens initiate colonies, but in some species groups of queens come together and co-establish a nest. In this issue of Insectes Sociaux, Motro et al. (2017) investigate the outcomes of keeping M. semirufus queens in small groups. This study fits with a growing literature on how social cooperation might emerge when solitary animals are placed in groups by looking at success of group colony foundation in a species which normally does not express this behavior.

When animals have no option but to occupy the same space, the first obvious outcome is battle and possibly cannibalism. Second, the animals could ignore one another, perhaps only interacting if competing for a limited resource. Third, they could start working together to modify their environment, making it more suitable for habitation, and possibly they could collaborate in provisioning and caring for young.

This third outcome is highly significant to our understanding of the evolution of eusociality. If cooperation and division of labor emerges in a forced grouping, then many of the tools needed for successful eusocial living are already at hand. In some species of ant multiple queens come together to found nests. These groups work cooperatively and ultimately either transition to monogynous colonies via queen or worker culling of queens or become fully functional polygynous colonies. In these cases, whether the outcome is monogyny or polygyny, groups have survival advantages over single foundresses.

Motro et al (2017) found that pairs of M. semirufus queens performed less well than solitary queens at nest construction and that mortality was higher in pairs. Aggressive interactions, rather than cooperative behaviors emerged when ants were paired, suggesting that in this species queens attempt to usurp other queens’ nests, rather than joining for the benefits of mutual assistance. Crowding and difficult environmental conditions, exemplified by hard soil, favored co-founding in this species. Motro et al (2017) suggest that such forced associations could lead to selection for mutual tolerance, which is a critical first step in the emergence of cooperation.

Messor is a particularly interesting target for these experiments because similar studies have been conducted in another seed harvesting ant, Pogonomyrmex. The two genera are relatively phylogenetically distinct within the Myrmicinae (Ward et al. 2015) but have similar nesting and trophic biologies. Pogonomyrmex californicus queens found colonies singly at some locations (haplometrosis) and in groups at other locations (pleometrosis) (Overson et al 2014). The behavior of M. semirufus more closely resembles the haplometrotic populations of P. californicus.

Particularly notable about this study is that the data were collected a full quarter-century ago. This shows that careful studies with thorough documentation can retain their value. The value of this study perhaps even increased over time, as the theoretical framework about emergent cooperation developed and data were published on forced associations in other species of ant.

Studies of emergent cooperative behavior in groups of animals will continue to play a key role in improving our understanding of the evolution of social behavior. While this study of harvester ants found no advantage in living in groups, it reminds us that a key gateway to group living is social tolerance, and that even if ecological circumstances force animals into close proximity, there are other barriers to establishing a cooperative relationship. The evolution of the breakdown of those walls should play a key role in studies of social evolution.

References

Motro M, Motro U, Cohen D (2017) Forced associations by young queens of the harvester ant Messor semirufus during colony founding. Insect Soc. DOI 10.1007/s00040-017-0551-1

Overson R, Gadau J, Clark RM, Pratt SC, Fewell JH (2014) Behavioral transitions with the evolution of cooperative nest founding by harvester ant queens. Behav Ecol Sociobiol 68:21–30

Ward PS, Brady SG, Fisher BL, Schultz TR (2015) The evolution of myrmicine ants: phylogeny and biogeography of a hyperdiverse ant clade (Hymenoptera: Formicidae). Syst Entomol 40:61–81. DOI: 10.1111/syen.12090

 

 

 

Interview with a social insect scientist: Katja Hogendoorn

IS: Who are you and what do you do?

KH: Katja Hogendoorn, bee researcher at the school of Agriculture, Food and Wine of the University of Adelaide. At the moment, I lead a project that investigates revegetation strategies for crop pollinators.

IS: How did you end up researching social insects?

KH: I love solving puzzles and have always been fascinated by animal behaviour. As a lonely four year old, I spent many days observing the effects of manipulations of ant foraging trails. In Utrecht, where I studied, the choice in ethology was between primates and social insects. Insects seemed relatively easy study objects and the evolution of the worker caste was one of the more intriguing puzzles.

IS: What is your favourite social insect and why?

KH: There isn’t one, but there is a family: the Xylocopidae. The variation in social behaviour within this family is phenomenal- everything from solitary to primitively eusocial and there is even a species with an allometric worker caste. Together with the Halictidae, the Xylocopidae offer the best opportunities for studying the evolution of sociality.

The great carpenter bee (Xylocopa aruana) which is found in Australia. Photo: Alan Wynn/flickr

IS: What is the best moment/discovery in your research so far? What made it so memorable?

KH: I’m not one to look back – my best is still to come. I thrive on new insights, which do not necessarily get published. So I’m happiest when, through thinking, I can make sense of something that I earlier didn’t understand. The best moments were when I finally understood the factors that shape mating strategies, the drivers in the evolution of buzz pollinated plants and the morphology of Australian flowers. At the moment I am grappling with the evolution of diet width and male sleeping clusters in bees.

IS: If teaching is part of your work, what courses do you teach? Has your work on social insects helped to shape your teaching?

KH: I supervise postgrads, but I don’t teach.

IS: What is the last book you read? Would you recommend it? Why or why not?

KH: The ‘Noise of Time’, by Julian Barnes, whom I consider one of the best living authors. He writes beautiful prose and combines humour with sensitivity.

IS: Did any one book have a major influence in shaping your career? What was the book and how did it affect you?

KH: Two books: ‘Onder proffessoren’ by Willem Frederik Hermans, and ‘Brazzaville Beach’ by William Boyd. Though neither are very good books, both satirise the pettiness, jealousy and power games that occur in the academic world, which I loathe. The books improved my ability to place that kind of behaviour and therefore allowed me to better savour the wonderful sides of working in academia.

IS: Outside of science, what are your favourite activities, hobbies or sports?

KH: Reading a very wide range of books, growing and cooking food.

IS: How do you keep going when things get tough?

KH: Prioritise and relativise. Not everything is important – some things are allowed to fall by the wayside. Then knuckle down and get at least the most important things done one at a time.

IS: If you were to go live on an uninhabited island and could only bring three things, what would you bring? Why?

KH: A large box of matches, a knife and a boat. I’d need to eat, make tools and leave the island.

IS: Who do you think has had the greatest influence on your science career?

KH: Three people: My dad. I couldn’t compete with his knowledge of art and languages, so I turned towards science instead. My PhD supervisor Hayo Velthuis. He was very encouraging during my first forays in honey bee kin recognition and encouraged me to publish my results. He also introduced me to the IUSSI. Attending IUSSI conferences has been a major influence in the early stages of my career. My partner, Remko Leijs. Exploring life’s puzzles together remains great fun.

IS: What advice would you give to a young person hoping to be a social insect researcher in the future?

KH: Try to design intelligent, elegant experiments that can give answers to interesting questions. Publish early in your career.

 

Sex between species: what happens when invasive honey bees meet the locals?

 

A blog post highlighting the article by R. Gloag, K. Tan, Y. Wang, W. Song, W. Luo, G. Buchman, M. Beekman, B. P. Oldroyd in Insectes Sociaux

Written by Ros Gloag

Some social insects have proved to be adept invaders. Assisted by the international trade of the modern world, these species have spread far beyond the ocean and mountain barriers that once determined their distributions. In some cases, these range expansions have brought previously isolated sister species back into contact. What happens when such species try to mate?

We were interested in this question of interspecific mating in the case of two honey bees: the Western honey bee Apis mellifera and the Eastern honey (or hive) bee, Apis cerana. These species diverged from a common ancestor at least 6 million years ago, with A. mellifera native to Europe and Africa and A. cerana native to Asia and India. Western honey bees have of course since been transported, in association with agriculture, to every human-inhabited continent on earth. Eastern honey bees meanwhile, have been quietly expanding their range too in recent decades, invading both Papua New Guinea and Australia. Thus what were allopatric (or separate) ranges for millions of years have suddenly become partially sympatric.

A cerana

A swarm of Apis cerana hangs from a branch in its invasive range of Northern Australia, where the species has recently come into contact with A. mellifera. The newly-mated queen will be concealed at the centre of the swarm: but who did she mate with?

The possible outcomes of A. mellifera and A. cerana mating are varied. It may produce high-fitness hybrids, low-fitness hybrids or no viable offspring at all. In the case of honey bees, there is also a more unusual possibility; interspecific mating might cause queens to produce some female diploid offspring asexually via a process called thelytokous parthenogenesis. Thelytoky is not uncommon in Hymenoptera, though the mechanisms controlling it vary between species. In honey bees, it appears to have some genetic basis, but its unclear whether environmental factors – such as interspecific mating – also play a role in determining its incidence. Honey bee queens mate with twenty or more males during a short period early in their lives and store the sperm, so it is unlikely that naturally-mated queens will have mated exclusively with the wrong species. As such, any peculiar effects of interspecific mating could be easily obscured in populations where the two species co-occur.

We decided to perform an experiment to reveal the effects of interspecific mating on the offspring of A. mellifera and A. cerana. We performed reciprocal crosses via artificial insemination (inseminating queens of each species with the sperm of the other species) in China. Artificial insemination is a fairly standard beekeeping procedure for A. mellifera, but a much trickier business for the relatively diminutive A. cerana. Enough inseminated queens survived the procedure though to confirm that theytoky is not a consistent outcome of these matings. We detected only the odd few thelytokous eggs, from both queens and laying workers. Rather, our results confirmed that interspecific mating has fitness costs for both species: cross-inseminated A. mellifera queens produced only males or inviable hybrid females, while cross-inseminated A. cerana queens produced either males only or no eggs at all. Interestingly, A. cerana workers sometimes rebelled against their “wrongly-mated” queen and took control of reproduction themselves by laying unfertilized male-destined eggs.

Of course, understanding what happens if species mate is different to knowing whether they do mate. A previous study confirmed that A. mellifera will sometimes mate naturally with A. cerana males, but whether the reciprocal pairing ever occurs is unknown. We checked the sperm-storage organs of 17 A. cerana queens collected from Australia’s invasive population and failed to detect A. mellifera semen, despite the fact that we have observed A. mellifera males hanging about in areas where Australian A. cerana queens mate. Possibly A. cerana queens simply cannot survive interspecific matings with their larger sister species, which would be a particularly brutal and conclusive form of reproductive interference because its effects could not be diluted by multiple mating.

Wherever interspecific mating does occur between Western and Eastern honey bees, we can expect that natural selection will eventually intervene. After all, there are other honey bee species in the world that naturally coexist without incident, generally by having species-specific mating times and locations. A. mellifera and A. cerana are recent bedfellows, but given that interspecific mating in their case appears to have no redeeming features, selection should act to favour those queens and drones that succeed in keeping sex strictly within the species.