Does size matter when using celestial cues to navigate towards home?

A blog post highlighting the article by R. Palavalli-Nettimi and A. Narendra in Insectes Sociaux

By Ravindra Palavalli-Nettimi and Ajay Narendra

Imagine finding a location in a new city without any map. How would you navigate toward your destination?

If you were an ant, you could use celestial cues such as the position of the sun or the polarised skylight pattern (Wehner and Strasser 1985; Zeil et al. 2014) as a compass to navigate in the direction of your destination (e.g., nest). The compound eye of an ant has a few special ommatidia that are sensitive to polarised skylight (light waves oscillating in one orientation). However, the eye size and also the total number of ommatidia in the ants’ eyes decrease with their body size. Some ants have close to 4,100 ommatidia (Gigantiops destructor) in their eyes while a miniature ant has a mere 20 ommatidia (Pheidole sp.). However, it is not clear how this variation affects their ability to navigate.

 

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Size variation in ant heads.

 

In this study, we investigated how size variation affects ants’ ability to use celestial cues to navigate towards their nest.

To test this, we captured ants on their way to their nest and displaced them to a circular platform. The displacement site was at least 500-1,000 m from the ants’ nest and was surrounded by a creek. Thus, the ants had never foraged there and could not use landmark cues to navigate, but instead, they had to rely on celestial compass cues to walk towards their nest. We filmed the paths taken by the ants using a video camera and later digitized their head position frame by frame.

We found that having fewer ommatidia does not affect the ants’ ability to use celestial cues. The ants’ heading direction on the platform did not significantly differ from the fictive next direction. Since larger ants have greater strides and thus travel more distance for the same number of strides, we also analyzed their heading direction at a distance on the platform scaled to the body size of the ants.

We also found that the smaller ants were slower and had less-straight paths than the larger ants, even after controlling for differences in leg size (correlated with body size and head width) and stride length. This finding means that a reduced ability of the smaller ants to access celestial compass information results in a less straight path and reduced walking speed. However, the overall ability to initially orient towards the nest using a celestial compass is retained in miniature ants. Thus, while miniaturization in ants can affect their behavioral precision, it may not always lead to a loss of vital behavioral capability such as using celestial cues to navigate.

 

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Paths and heading directions of various ants that differed in head width and ommatidia count.

 

In conclusion, finding a destination in a new city might be a lot easier if we were ants—of any size—and could use celestial cues!

References

Wehner R, Strasser S (1985) The POL area of the honey bee’s eye: behavioural evidence. Physiol Entomol10:337–349.

Zeil J, Ribi WA, Narendra A (2014) Polarisation vision in ants, bees, and wasps. In: G Horváth (ed) Polarized light and polarization vision in animal sciences, Springer, Heidelberg, pp 41–60.

Welcome to the new Insectes Sociaux social media team

Hello social insect fans,

It is my pleasure to introduce the new social media editing duo for Insectes Sociaux, Bernadette Wittwer and Madison Sankovitz, coming to you from Australia and the United States respectively. Having worked with them over the last month to hand over the reins to the Insectes Sociaux social media accounts, I can tell you that they have lots of exciting things planned for you, including an Instagram account (@insectessociaux)!

Madison Sankoviz

I am an entomology Ph.D. student in the Purcell Lab at the University of California Riverside. My research interests are the ecological interactions and biogeography of ants. With a passion for insects and understanding the dynamics of changing ecosystems, I am interested in answering questions of what social and behavioral traits allow survival in the extremes of latitudinal and elevational gradients in Formica ants. I also explore ant-mediated soil manipulation. Passionate about teaching and communicating science to the public, I am the graduate student coordinator for our department’s outreach program. I received a B.A. in ecology and evolutionary biology from University of Colorado Boulder, where I studied the effects of Formica podzolica ant colonies on soil moisture, nitrogen, and plant communities. Not only am I constantly inspired by the research of other social insect scientists, but I admire their enthusiasm for the natural world. I look forward to highlighting future publications and investigating the stories behind them as a social media editor for Insectes Sociaux!

Bernadette Wittwer

I am an evolutionary biologist with research interests in broad evolutionary transitions. I competed undergrad and honours at the University of Queensland. My honours research examined the evolution of feeding behaviour in crocodilians, with a focus on Isisfordia duncani, a 90-million-year old crocodile from western Queensland, Australia. After honours I moved to the University of Melbourne and undertook my Ph.D. looking at the evolution of communication in bees. Bees have an extraordinary depth of behavioural diversity and it is through them that I was introduced to the wonderful complexities of insects that live in groups. My research has particularly focussed on antennal structures and how bee species have adjusted their investment in communication as they have evolved different social behaviours. Through my research I’ve been grateful to work with and meet so many enthusiastic social insect researchers and I look forward to exposing more wonderful social insect research through Insectes Sociaux’s social media channels.

The best part of this role has been working with all the contributors to the blog and our interviewees. Thank you again to all of you that have participated.

If you are interested in blogging or interviewing, do not hesitate to contact Bernie and Madison via Twitter (@InsSociaux), Facebook, or via email at bernie.inssoc@gmail.com and madisoninsectessociaux@gmail.com.

Interview with a social insect scientist: Roberto Keller

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IS: Who are you and what do you do?

RK: My name is Roberto Keller. I grew up in Mexico City where I majored in Biology, later pursuing a PhD in Entomology up north in the USA, and since the past decade I live in Lisbon, Portugal, currently working at the Nacional Museum of Natural History. I’m a comparative anatomist that specializes in ants.

IS: How did you end up researching social insects?

RK: Back at the University in Mexico the people in our group of insect enthusiasts was choosing which taxon to specialize on. Most of my peers were drawn to shiny scarab beetles, some into colourful butterflies, but I loathed those clichés so I placed my attention into all those little brownish ants running around. Once I looked at them under the stereoscope I was surprised at how elegant and varied ants can be. I was instantly hooked. Oh, that and the fact that I never liked to mount insects with wings because getting them to look right is just a pain.

IS: What is your favourite social insect and why?

RK: Neoponera apicalis. This is an ant species that lives in the tropical forests from Mexico to South America. The workers are large, matte black, with the tip of their antennae light yellow. Workers forage alone on the shaded damp forest floor, so you only see a pair of yellow antennal tips dancing around. The first time I saw one I was so excited that I grabbed with my bare hand. Their sting feels like a painful electroshock.

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

RK: I was once reading a short paper comparing the external morphology of queens versus workers in an ant species. The whole discussion was off because the authors had wrongly assumed that the largest thoracic segment in workers was the fusion of the first and second segments when compared to queens. My first reaction was to rail against the authors for making what I consider an obvious mistake. It later hit me that not only was their error quite understandable, but that it pointed to a remarkable difference between those two castes that had been in front of me for years but I had been blind about until that moment.

That turned into a productive research project and taught me to keep a keen eye and question the obvious. I learned a lot from that short paper even with its errors, and I think that this is how science keeps moving forward— we built upon the work of others and hope that the next person who comes will be able to solve the things we were too short sighted to see.

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

RK: I teach courses in general Entomology and, once in a while, on ant morphology. I can’t think of a way in which studying social insects has influence my teaching. I often forget that ants are social, it’s bad. That is why I have collaborators: to remind me.

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

RK: I’m finishing Steven Pinker’s latest book Enlightenment Now: The Case for Reason, Science, Humanism, and Progress. It is appalling to me seeing that we live in a very modern society, and yet we have political extremes converging on pure irrationally. This is a good book to remind people how much science has benefit humankind as a whole, but I’m afraid the people who will read it already know this.

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

RK: Once I was hooked learning about ants during college I got myself a copy of Hölldobler and Wilson’s The Ants, which had been recently published. The dedication reads “For the next generation of myrmecologists.” I felt they were talking directly to me and that dispelled any doubts I still had about following a career in social insects. So at the end I am that cliché I was trying to avoid.

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

RK: I’m a portrait photographer. I’m intrigued about people, and portraiture allows me to sit down for a brief face to face conversation and try to capture that interaction through an image.

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

RK: I like to follow the advice of philosopher Paul Feyerabend:

“If you want to achieve something, if you want to write a book, paint a picture, be sure that the center of your existence is somewhere else and that it’s solidly grounded; only then will you be able to keep your cool and laugh at the attacks that are bound to come.”

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

RK: Hmm, can’t think of any objects that will make sense with the prospect of solitude other than hemlock.

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

RK: My parents. Both chemists, they created a growing environment for my siblings and me in which science was a natural part of life.

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

RK: Don’t grab large social insects with your bare hands. Unless they are termites. Termites are always safe to grab.

 

Interview with a social insect scientist: Hollis Woodard

thumb_UCR S. Hollis Woodard 2016 64 copy_1024IS: Who are you and what do you do?

HW: My name is Hollis Woodard and I’m a bumble bee biologist and an Assistant Professor in the Department of Entomology at UC Riverside. My lab group works on all sorts of things to do with bumble bees, including their nutritional biology, social organization, foraging ecology, and more.

IS: How did you end up researching social insects?

HW: I fell in love with social insects during college when I took an evolutionary biology class. We had a lecture on sociobiology and talked about insect societies and division of labor and I remember thinking it was the most interesting thing I’d ever thought about. I already had an incipient interest in social behaviour because I’d spent some time working at primate sanctuaries, and was thinking about going into primatology, but around the time I took this class I was also becoming interested in experimental biology and realized that insects would be a better way to go for taking that sort of approach in my research.

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Photo: H. Woodard

IS: What is your favourite social insect and why?

HW: Bumble bees! The group has it all: they live in some unusual places (like the Arctic), they have solitary and social stages to their life cycle, socially parasitic lineages, unique thermoregulatory capabilities, they’re dominant pollinators in a lot of systems, they buzz pollinate, and so on. I’ll never get bored working on bumble bees. Lately I’ve gotten particularly interested in queen bumble bees, which are just so special because they undergo so many changes (behavioural and physiological) across their life cycle and face so many challenges, like having to survive through the winter and start new nests on their own in the spring before their workers emerge.

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

HW: One of the highlights of my career thus far was going to Alaska for the first time, in summer 2016, to start working with arctic bumble bees. I became fascinated with them when I read Bernd Heinrich’s book Bumblebee Economics as a graduate student and had been wanting to work in that system ever since, so it was gratifying to make that a reality. There is nothing like watching giant Alpinobombus queens fly around open tundra!

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Searching for Arctic bumblebees.

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

HW: I teach an insect behaviour course for more senior undergraduates and I’m currently developing a new social insects course that I’ll teach for the first time next year, which I’m super excited about. We’re going to talk about theory in the class but I’m also going to heavily emphasize all of the insights we’ve gained through molecular work, especially in the last decade. There’s an awful lot to talk about.

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

HW: The last book I read was Bernd Heinrich’s The Thermal Warriors, which is all about how insects deal with thermoregulatory challenges. It’s a fun read; it takes a complex subject in comparative physiology and makes it very accessible. I highly recommend it, and all of the other books Heinrich has written.

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

HW: E.O. Wilson’s autobiography, Naturalist. I read it the first time in one sitting. Reading it inspired me to go to graduate school and pursue a career in studying social insects. It includes such an interesting treatment of the history of the division between molecular and ecological research, and the idea that that division doesn’t really exist (which Wilson talks about a lot more in Consilience) was exciting to me, given that I was thinking a lot at the time about how to use approaches from molecular biology to study social evolution. Wilson’s passion for ants also really shines through in the book and it’s clear that he appreciates them both for their own sake and because they’re a lens through which you can understand life on Earth, in the broadest sense. That influences how I think about bumble bees: I’m enamoured with them but I also think they contain the answer to every fundamental question in biology.

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

HW: To be perfectly honest I don’t have too many hobbies outside of work, but I have been learning Taekwondo and I’m really liking it. I also love to go hiking and I have three Australian cattle dogs that keep me busy.

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

HW: I experienced burnout at the end of PhD and since then I’ve tried to take it a bit easy on myself and pace myself, when I can. I’ve incorporated more fieldwork into my research program, which gets me out of the lab and office, broadens my perspective, and helps keep me more physically active. I’ve also worked hard to cultivate a buoyant mindset; academia is full of crushing blows to the ego and you have to digest and move on quickly or you’ll get overwhelmed. I also have a lot of wonderful friends in my department who are also new professors and we support each other and celebrate when good things happen.

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

HW: That’s easy, I would bring my dogs, who aren’t ‘things’ to me but I hope would be fair game. They help keep me happy. Hopefully there would also be bumble bees on this island.

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

HW: My PhD advisor, Gene Robinson, has definitely had the greatest influence on my career. When I started graduate school I had a lot of enthusiasm but I didn’t have much research experience and I hadn’t learned how to think like a scientist yet. Gene taught me to think critically, think things through, and think big. I feel so fortunate to have been given the opportunity to learn with and from him.

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

HW: My advice would be to start by picking an organism and learning it well, then the specific research questions will follow. I floundered a bit at first with my bumble bee research because I didn’t really understand them at all – I hadn’t spent time getting to know them, so to speak. Things really picked up for me after I went to Israel to work in Guy Bloch’s lab, where I took a lot of time to sit and watch them, try different things out, and hang out and talk with other bumble bee biologists. The better you know your organism, the better you’re able to formulate solid questions and effectively answer them. All of the best experiments are designed in the context of the organism, in my opinion.

Interview with a social insect scientist: Maggie Couvillon

IS: Who are you and what do you do?

MC: My name is Dr. Maggie Couvillon. I started in 2017 as an Assistant Professor of Pollinator Biology and Ecology at Virginia Tech. I consider myself a broadly trained bee biologist, with experience in stingless bees, bumble bees, and of course honey bees.

In my lab, I focus on basic and applied aspects of bee foraging. At the moment, I am developing honey bees, in particular their waggle dance communications, as bioindicators to give biologically-relevant data on the ability of landscapes to feed flower-visiting insects.  Our project will hopefully generate useful recommendations on how to improve bee nutrition by pinpointing when and where human intervention is useful.

IS: How did you end up researching social insects?

MC: I actually started out in birds. My undergrad had been from a small, liberal arts university, and I simply didn’t have the vocabulary when I graduated to describe my interests. I ended as a dissatisfied graduate student of neurobiology looking at songbird vocal learning. Then, for a class assignment in 2004, I stumbled upon a paper by Ben-Shahar and Robinson that investigated the effect of an increase in gene expression on a honey bee behavior. The data were really cool, but it was the authors’ background description of honey bee division of labor that blew my mind.

I’m really lucky. Just when I was realizing that I didn’t belong in neuro, I simultaneously fell in love with honey bee behavior and was able to find an opportunity for me to swap from the birds to the bees.

IS: What is your favourite social insect and why?

MC: The honey bee will always be my first love.

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Maggie’s favourite social insect, the honey bee.       Photo: Jill Bazeley/flickr

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

MC: During my postdoc at the University of Sussex in Brighton, I had the chance to conduct some experiments involving training honey bees to forage at feeders while we examined their waggle dance communications. At this stage, I had been decoding waggle dances for a few years to learn where and when bees are foraging in the landscape, but I hadn’t yet had the chance to do a feeder experiment.

Seeing the dances of foragers for a known location – the feeder – was just amazing. I knew of course that bees could communicate a direction and a distance, but actually seeing it in real-time was super exciting.

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

MC: I’m new faculty, so at the moment, I’m teaching a seminar course where I’m trying to train new graduate students to summarize and critique (constructively) research seminars. I hope that the students get from the course some basic tips for how to be a valuable peer-reviewer. I’m also contributing to several existing courses (Bees and Beekeeping, Insect Physiology, and Urban Greenspaces), where all my guest lectures possess a strong bee theme. Over the next year, my plan is to develop a course called The Behavioural Ecology of Pollinating Insects, where we will cover some of the major themes from a usual Behavioural Ecology course, but using flower-visiting insects as model organisms.

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

MC: I just finished Station Eleven by Emily St. John Mandel. I’ve been going through a post-apocalyptic reading binge for a few years, and Station Eleven, while fulfilling the niche of a story set in a dystopian future, takes a different focus on how civilization goes about preserving or rebuilding not just sustenance, but culture. The book is set in a near future where 99.9% of the world’s population is decimated by a pandemic called the Georgia flu. People remain in small, scattered settlements. One of the main characters, Kirsten, is a member of 20 or so actors and musicians that travel in horse-drawn wagons from settlement to settlement to perform Shakespeare, taking as a motto “Survival is insufficient”. It’s a neat idea for a book – what is important enough to you that you’d want to recreate it if it were taken away, even if that took 20 years.

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

MC: I’d say the combination of Niko Tinbergen’s “The Study of Instinct” and his 1963 paper “On aims and methods of Ethology” were both pretty influential to me, partly because they came at just the right time when I was leaving neurobiology for honey bee behavioral ecology. I was entranced by the idea that there are four different ways to study the same behavior (i.e., how does it work, how did it develop, what is it for, and how did it evolve). My early training heavily focused on the physiological aspects of behavior (or the “how does it work”), which felt unsatisfying to me. And so it was really exciting to learn that there are other approaches.

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

MC: I enjoy reading, swimming, cycling, cooking (and therefore eating), and traveling. The best times are the experiences that bring it all together. We have a 10 month old baby, so the cycling holidays that my husband and I enjoy are on hold, but we can’t wait until he’s old enough that he can join us cycling between beautiful places with delicious food.

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

MC: I mostly feel extremely grateful that I’m able to have the career that I do. There are times that I feel overwhelmed, that I’m not doing enough, and that I’m not nearly smart enough to pull off this career, but with a little one at home that I want to spend time with after work and on weekends, there is simply a limit to how much work I can do and how much worrying I can handle. So life and career keep each other in check, whether I like it or not!

Probably one recent challenging time was when we moved to Switzerland for 2 years and I found out just how abysmal I am at learning new languages. And without German AND French AND English, I was virtually unemployable in Bern. I had months of struggling with “who am I” if I am not a bee researcher. Eventually I found ways to stay active in science as an advisor to EFSA (European Food Safety Authority) on bee health across EU-member states. I also worked on analyzing human health data, looking at the non-compliance in HIV treatment in sub-Saharan Africa. Both of these felt like jobs, not careers, which was tough at first, but it allowed me to enjoy other things for a few years. And then, in 2016, I thought I’d try myself on the job market for one final season, and lo, I got my present position.

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

MC: Well of course top pick would be my family, especially as my husband has a Swiss army knife! But otherwise, I’d say my kindle to keep my brain active, some bubble wrap because it has been shown that keeping one’s hands busy reduces stress and the perception of wait time, and some sunscreen because I burn and freckle easily.

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

MC: I’d say it was my advisor Professor Francis Ratnieks. When I started in his lab, fresh from leaving a bird neurobiology program, I had no experience with honey bee research in any incarnation – from experimental design, to field work, to analysis, and writing. Francis is a very clear thinker and an exceptional scientist, able to turn small observations of “something interesting” into research projects. He also is good at bringing together a great team of people to work in his lab. This team always provided me with equal parts scientific inspiration, hilarity, and some excellent pranks.

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

MC: It’s just as important to know what you don’t find interesting as it is to know what you do. And be open to different opportunities in different places.

Digging in the deep: how does carbon dioxide affect communal nest building in ants?

A blog post highlighting the article by D. Römer, F. Halboth, M. Bollazzi and F. Roces in Insectes Sociaux

By Daniela Römer

Watch a nature documentary of the South American tropics and it’s almost a given you will see some columns of leaf-cutting ants, busily carrying leaves back to their nest. Aside from their photogenic foraging behaviour these ants are also known for having developed the ability of farming, a feat only humans and some termite species have achieved. Perhaps less well known to the public, but equally as impressive, are their underground nests. The ants use the freshly cut plant material as a substrate to grow a symbiotic fungus, which is very voluminous and therefore needs a lot of space. Adding to the space demands of their nests are the high number of ‘citizens’ a single leaf-cutting ant colony can have, sometimes reaching millions (Moreira et al. 2004a, b). When scientists want to make casts of the nests to discover the intricate network of their nest chambers and connecting tunnels, they need tons and tons of cement to fill the complete structure (Forti et al. 2017). And yet, the tiny single workers measure less than a centimetre and weigh only 5-25 mg. How do these little, autonomous units coordinate their digging effort with thousands of other small units so that these huge functional nest structures are created?

The answer to this question is a process known as ‘self-organization’. The tiny workers with their very limited view of the nest structure react to very simply cues of their immediate environment and so decide where and when to excavate (Deneubourg and Franks 1995).

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Worker of Acromyrmex lundii leaving a digging arena.       Photo: James Waters

Having encountered an underground environment to their liking, the workers dig with their mandibles into the earth and, as if it would be a piece of vegetation to harvest, ‘cut’ out little bits of soil, which they then discard outside of the nest. Digging is a strenuous process and a colony spends considerable energy excavating their nest. What the ants gain from such a herculean effort is a structure that offers the colony, and in the case of leaf-cutting ants, their symbiotic fungus (on whose survival colony success depends) an environment suitable for both.

Underground, the three main environmental factors are temperature, humidity and carbon dioxide. The latter is quite frequently mentioned in the media in connection with global warming, where even seemingly small increases in CO2 levels can lead to dramatic environmental changes. Subterranean ants are confronted with CO2 concentrations vastly exceeding atmospheric levels (currently ~0.04%), even very close to the soil surface. These levels increase even more with depth so that 5-6 meters underground ants encounter an environment with 6-7% CO2 (Kleineidam and Roces 2000; Bollazzi et al. 2012). At these high levels, the growth of the farmed fungus seems to be compromised (Kleineidam and Roces 2000), so that leaf-cutting ants should try to control carbon dioxide levels to ensure the best possible fungus harvest. A recent study showed that when given the choice, the leaf-cutting ant Acromyrmex lundii indeed avoids such high CO2 levels for fungus farming and, surprisingly, also atmospheric levels (Römer et al. 2017). Instead, it chose levels associated with soil strata close to the surface.

We therefore asked ourselves whether the ants also use the carbon dioxide concentration underground as a cue when they excavate their nests and examined this question by performing different experiments. In the first, we tested whether the ants’ digging activity and soil pellet transport was affected with increasing CO2 concentrations (from atmospheric values to 11%). In the second experiment, we evaluated what CO2 concentration workers prefer for nest digging, using a binary setup, offering atmospheric, shallow soil (1%) and deep soil (4%) CO2 concentrations.

digging arenas

Digging arenas at end of  experiment 1. CO2 levels L to R: atmospheric, 4%, 11%.           Photo: Daniela Römer

Acromyrmex lundii is a species whose nest is usually characterized by having only superficial nest chambers. This is apparently not due to the inability of the ants to excavate under higher CO2 concentrations, as digging activity was comparable whether the ants excavated under atmospheric CO2 concentrations or levels of deeper nesting leaf-cutting ants. Only at 11%, a level so high that it was never measured around any leaf-cutting ant nest (Nielsen et al. 2003), the ants reduced their digging activity. Therefore, a negative effect of CO2 on digging activity does not seem to be the reason why this ant species only excavates superficial chambers. Soil pellet transport away from the digging site, on the other hand, increased when CO2 concentration underground increased. We do not know whether this was because ants were physically unable to excavate and therefore switched to soil carrying (masked at most CO2 levels by replacement workers) or whether ants ‘aimed’ to increase ventilation at the site by creating more open space. When creating a situation where workers could choose where they wanted to dig, they preferred superficial-soil CO2 levels and avoided levels of deeper soil strata. These choices help to explain the ants’ nesting biology.

One might therefore ask ‘Then why do other leaf-cutting ants excavate deep nests if the high CO2 concentrations there hinder the growth of their food source?’ The answer to this question might be a competition between the different environmental factors in the soil. Leaf-cutting ants should trade-off their microclimatic preferences to ensure the excavation of a suitable nest, but that is an experiment for another day

References

Bollazzi M, Forti LC, Roces F (2012) Ventilation of the giant nests of Atta leaf-cutting ants: Does underground circulating air enter the fungus chambers? Insectes Soc 59:487–498. doi: 10.1007/s00040-012-0243-9

Deneubourg JL, Franks NR (1995) Collective control without explicit coding: The case of communal nest excavation. J Insect Behav 8:417–432. doi: 10.1007/BF01995316

Forti LC, Protti de Andrade AP, Camargo R da S, et al (2017) Discovering the giant nest architecture of grass-cutting ants, Atta capiguara (Hymenoptera , Formicidae). Insects 8:39. doi: 10.20944/preprints201702.0027.v1

Kleineidam C, Roces F (2000) Carbon dioxide concentrations and nest ventilation in nests of the leaf-cutting ant Atta vollenweideri. Insectes Soc 47:241–248. doi: 10.1007/PL00001710

Moreira AA, Forti LC, Andrade APP, et al (2004a) Nest architecture of Atta laevigata (F . Smith , 1858) (Hymenoptera : Formicidae). Stud Neotrop Fauna Environ 39:109–116.

Moreira A, Forti L, Boaretto M, et al (2004b) External and internal structure of Atta bisphaerica Forel (Hymenoptera: Formicidae) nests. J Appl Entomol 128:204–211. doi: 10.1111/j.1439-0418.2004.00839.x

Nielsen MG, Christian K, Birkmose D (2003) Carbon dioxide concentrations in the nests of the mud-dwelling mangrove ant Polyrhachis sokolova Forel (Hymenoptera: Formicidae). Aust J Entomol 42:357–362. doi: 10.1046/j.1440-6055.2003.00372.x

Römer D, Bollazzi M, Roces F (2017) Carbon dioxide sensing in an obligate insect-fungus symbiosis: CO2 preferences of leaf-cutting ants to rear their mutualistic fungus. PLoS One 12:e0174597. doi: 10.1371/journal.pone.0174597

Biting down on colony membership in the Eastern subterranean termite

A blog post highlighting the article by V. Simkovic, G. J. Thompson, J. N. McNeil in Insectes Sociaux

By Vicki Simkovic

If you want to discover the secrets of life as a subterranean termite, you (literally) have to dig beneath the surface. Hidden from view, termite colony members (namely workers) are busy excavating and connecting networks of foraging tunnels to various food and nest sites. Each termite worker is small, delicate and soft-bodied, yet is formidable and impressive as part of its larger colony. A colony containing thousands to millions of termites – made up of workers, soldiers and reproductives – can build hundreds of intersecting tunnels within an hour and in urban centers a single colony can stretch across several city blocks. How they determine who belongs to which colony, however, is not as clear as you might expect.

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Eastern subterranean termite (Reticulitermes flavipes) workers.   Photo: V. Simkovic

One integral aspect of social living is maintaining well-defined colony boundaries through the defense of nest territory, keeping colony members safe in the colony and defending the colony from intruders. Among termites, both workers and soldiers participate in defensive behaviors, which can be both active (i.e. biting, lunging, stinging) and passive (social avoidance or blocking tunnel entrances) (Šobotník et al., 2010; Prestwich 1984). However, in some cases, colonies may take on a more diffuse form with no obvious inter-colony aggression or nestmate recognition. Why some colonies are well defined (‘closed’) while others are diffuse (‘open’) is not well understood.

To find out more, we studied Canadian populations of the Eastern subterranean termite (Reticulitermes flavipes), as they provide an interesting case study in nestmate recognition and territorial defense. Colonies of R. flavipes are found in isolated pockets in Ontario, having been introduced to the province on at least three separate occasions (Scaduto et al. 2012). Populations show a mixture of open versus closed societies, they may vary in their propensity for inter-colony aggression or resource defensiveness, and their differing backgrounds provide a potential source of genetically variable recognition cues (Scaduto et al. 2012). In the City of Toronto, termite colonies show low levels of genetic diversity, low inter-colony aggression (Grace 1996), and are more typical of invasive ‘open societies’. In contrast, termites in the Pelee region form discrete colonies that are genetically well differentiated from each other (Raffoul et al. 2011). The Pelee termites live independently of any human habitation, are potentially native to the area (Kirby 1965) and are effectively ‘closed’ societies.

Finding out about the cryptic world beneath our feet is not always easy. As termite behaviour occurs underground, we need to collect a sub-sample of live individuals and study their interactions in artificial lab-designed arenas or assays to evaluate their behaviour. However, designing an assay that truly reflects field conditions can be challenging. One method common method in termite and ant aggression studies is using a Petri dish lined with moist filter paper. Although convenient and easy to replicate, this artificial situation may not reflect ecological context, particularly for termite species, which are soft-bodied and desiccate quickly in open air. In previous studies using Petri dishes, R. flavipes showed no evidence of aggression towards non-nestmates (either intra or interspecific) and possibly a lack of nestmate recognition (Polizzi and Forschler 1998; 1999; Bulmer and Traniello 2002a, b; Fisher and Gold 2003; Perdereau et al. 2011).

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Petri dish trials.   Photo: V. Simkovic

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Resource Foraging Design: experimental set-up used to examine the distribution and survivorship of workers as they tunnel and forage through a shared resource. Side containers consisted of moistened inert sand, joined by eight small glass tubes to the central chamber that contained moist sand, 60g of water-soaked maple and oak shavings, two corrugated cardboard rolls and small wooden blocks. Two longer glass tubes also directly joined the compartments. Photo: V. Simkovic

We paired Ontario populations (Toronto and Pelee colonies) of R. flavipes of varying geographic distance in both short-term (5-minute) Petri dish and longer-term (2- and 7- day) shared-resource assays, in order to test for evidence of aggression or nestmate recognition. The resource-design assay was meant to be more reflective of field conditions and introduce the soil interface, simulating two colonies meeting and foraging at a central food resource. In Petri dish trials, we found no evidence of aggression or nestmate recognition. However, in shared-resource assays we observed very little inter-colony mixing and high mortality in non-nestmate pairings, indicating that R. flavipes can sort and potentially compete on the basis of nest origin, and that this recognition is influenced by ecological context. In our study, the soil interface was essential as aggressive encounters occurred while the termites were foraging for new resources. This behavior would not be evident from Petri-dish style assays, which lack the soil interface and may explain why prior studies of nestmate recognition have had mixed results. These results therefore highlight the importance of designing an assay that accurately reflects the ecological context of a species.

 

References

Šobotník J, Jirošová A, Hanus R (2010) Chemical warfare in termites. J Insect Physiol 56:1012–1021

Preswitch GD (1984) Defense mechanisms of termites. Ann Rev Entomol 29:201–232

Scaduto DA, Garner SR, Leach EL, Thompson GJ (2012) Genetic evidence for multiple invasions of the Eastern subterranean termite into Canada. Environ Entomol 41:1680–1686

Grace JK (1996) Absence of overt agonistic behavior in a northern population of Reticulitermes flavipes (Isoptera, Rhinotermitidae). Sociobiology 28:103–110

Raffoul M, Hecnar SJ, Prezioso S, Hecnar DR, Thompson GJ (2011) Trap response and genetic structure of Eastern subterranean termites (Isoptera, Rhinotermitidae) in Point Pelee National Park, Ontario, Canada. Can Entomol 143:263–271

Kirby CS (1965) The distribution of termites in Ontario after 25 years. Can Entomol 97:310–314

Bulmer MS, Traniello JFA (2002a) Foraging range expansion and colony genetic organization in the subterranean termite Reticulitermes flavipes (Isoptera: Rhinotermitidae). Environ Entomol 31:293–298

Bulmer MS, Traniello JFA (2002b) Lack of aggression and spatial association of colony members in Reticulitermes flavipes. J Ins Behav 15:121–126

Fisher ML, Gold RE (2003) Intercolony aggression in Reticulitermes flavipes (Isoptera: Rhinotermitidae). Sociobiology 42:651–661

Perdereau E, Dedeine F, Christides JP, Dupont S, Bagnères AG (2011) Competition between invasive and indigenous species: an insular case study of subterranean termites. Biol Invasions 13:1457–1470

Untangling the opposing effects of ants on plants: lessons from the field

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Ants harvesting.   Photo: A. Fargi-Brener and M. Tadey

A blog post highlighing the Insectes Sociaux Best Paper Award Winner for 2017

Alejandro Farji-Brener and Mariana Tadey received the prize for their paper “Consequences of leaf-cutting ants on plant fitness: integrating negative effects of herbivory and positive effects from soil improvement”. This paper appeared in the February 2017 issue of the journal and can be found here.

Written by Alejandro Farji-Brener and Mariana Tadey

At the same time that I [Alejandro] was working on the ecology of the leaf-cutting ant, Acromyrmex lobicornis, in the north-western part of the Patagonian steppe (Argentina), Mariana was investigating the indirect effects of livestock on pollination in the Patagonian Monte Desert, 400km away from my study site. Mariana told me about the great abundance of leaf-cutting ants in her study area and soon we started our first ecological investigations there. It was interesting because in the Patagonian steppe, leaf-cutting ants were restricted to roadsides and in the Monte Desert, they were everywhere!

Looking at the ants, it was very impressive to see them harvesting a lot of plant species and dumping huge amounts of organic waste on the soil surface. We knew about the literature describing the potential negative effects of leaf-cutting ants as plant-damaging herbivores and the literature describing their positive effect on vegetation as soil improvers via dumping their nutrient-rich organic waste. Given these opposing effects of ants in an ecosystem, we wondered what their net effect was on the nearby plants.

Acromyrmex nest mound (above) and its waste piles (below)

Acromyrmex nest mound (above, pictured with measuring tape) and its waste piles (below). Photo: Farji-Brener and Tadey

Up to this point, several studies demonstrated the trade-off between herbivory and nutrient intake under greenhouse conditions. However, there were few studies investigating what happens in nature were plants are subjected to both situations, the loss of green tissue by ant defoliation and the enhanced plant growth caused by the ant-generated organic waste piles. Given that in this water poor habitat, both the loss of photosynthetic tissue and nutrient availability are key factors for the health and survival of plants, we thought that the net consequence on plant fitness should depend on the relative importance of these opposite ecological effects. Hence, we started our research about the fitness of native plants growing on, or near, ant organic waste piles (our nutrient hot spots) and on bare soil.

In our study site, plant species were differentially subject to defoliation by leafcutter ants, but there was no clear pattern of growth compensation for defoliation due to plant growth on organic waste. We proposed that this lack of compensation was caused by the water limitations imposed by the aridity of this environment, which restricted nutrient uptake for the plants. Overall, our work suggests that the interpretation of nice outcomes from controlled experiments may be unsupported by work under field conditions, highlighting the importance of the ecological context in scientific studies. Studies like ours allow us to include the particularities of ecosystems into theoretical frameworks so we can improve our understanding of how ecosystems work. Our study also shows how collaboration among scientists can lead to a big change our understanding of how organisms interact in nature.

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Ants carrying leaves. Photo: Farji-Brener and Tadey.

Teleporting ants: how foragers cope with unusual navigational tasks

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Melophorus bagoti.   Photo: Patrick Schultheiss

A blog post highlighting the article by C. A. Freas & K. Cheng in Insectes Sociaux

By Cody A Freas and Ken Cheng

Imagine that you travel from your house to your favourite restaurant by walking 10 blocks due west and then need to return home. Under normal circumstances you would simply walk back 10 blocks due east. Ant foragers travelling from home to find food, can easily return to the nest in this situation through a process called path integration. During path integration, ants count their steps to estimate distance and use the sky to keep track of their current direction, combining these two measurements to travel back home. Now let’s imagine a less conventional trip. After travelling 10 blocks to the west, you leave the restaurant and are suddenly transported 10 blocks south of home. The first time this occurs you may have some difficulty, yet if this happens every time you make this trip, you would most likely become rather talented at managing this new homeward route. Humans and other animals can deal with unusual navigational problems such as teleportation by using familiar visual cues like landmarks in their environment (Warren et al. 2017).

Ants can also learn to adjust their homeward trip when the outgoing and incoming journeys do not match, by shifting the direction of their path integration system. Ant foragers will keep track of their direction and distance on both the outbound and inbound portions of their foraging trips. On succeeding trips, an ant can learn to shift its homeward direction based on experience during previous trips, which is called calibration. Earlier work involving these shifts in ants has focused on Cataglyphis fortis, a north African species living in environments with no landmarks where these foragers are able to partially shift their homeward heading after being displaced every time they collect food from a feeder (Collett et al. 1999; Wehner et al. 2002). Yet these foragers are unable to fully shift their homeward direction to the correct nest direction even after many trips, instead taking a compromise direction. In the current study, we explored this navigational process in the Australian desert ant Melophorus bagoti, a species living in areas with many landmarks (buildings, trees and bushes) which could help guide these ants after being moved off their normal route. Each time a forager reached a feeder and picked up some food, we moved them to another location 45º, 90º, 135º, or 180º away from the nest-feeder path and then allowed them to return home. Before releasing each forager, we tested their homeward heading in a uniform arena designed to block the surrounding landmarks and only allow ants to rely on path integration to navigate. The purpose of this test was to see how quickly and the degree to which their path integration system changed or calibrated in response to having different outgoing and incoming trip directions.

We found that foragers learn to acclimate to teleportation quickly. After being teleported on three consecutive trips, these foragers began to choose a compromise direction between their original position and their teleported position. Furthermore, we found that these foragers continued to improve over the first ten trips ultimately reaching a plateau. The directional difference (45º, 90º, 135º, or 180º) of the outbound and inbound trips appears to affect the degree to which ants can shift to the inbound path. When the difference is small (at 45º), ants are able to shift completely to the homeward direction and many return directly home. Yet as the difference between routes increases, ants shift less, choosing compromise directions at 90º and 135º locations. When we transported the foragers 180º from the feeder route, the ants did not shift their homeward path at all. These ants will travel in the wrong direction every time they are moved 180º off outbound route even after 25 trips.

The underlying cause of the differences we find in M. bagoti when compared to C. fortis remain unknown, but it is possible that the presence of landmark cues plays a large role. M. bagoti inhabits a cluttered habitat with many landmark cues to guide them when they are moved off the outbound route, while C. fortis lives in a barren desert and must search to find the nest after being moved. The presence of landmarks during training in our study may help M. bagoti foragers find the correct homeward direction easily, resulting in larger shifts just as recognisable landmarks would help a teleported human return home from a similar trip. To further explore this question, we hope to replicate this experiment on a third desert ant species endemic to southern Spain (Cataglyphis velox) which is closely related to C. fortis yet lives in cluttered environments similar to M. bagoti.

References

Collett M, Collett TS, Wehner R (1999) Calibration of vector navigation in desert ants. Curr Biol 9:1031–1034

Warren WH, Rothman DB, Schnapp BH, Ericson JD (2017) Wormholes in virtual space: From cognitive maps to cognitive graphs. Cognition, 166:152-163.

Wehner R, Gallizzi K, Frei C, Vesely M (2002) Calibration processes in desert ant navigation: vector courses and systematic search. J Comp Physiol A 188:683–693.

What’s in a face?

Highlighting the article written by R. Branconi,  D. Baracchi , S. Turillazzi and R. Cervo (2018) in Insectes Sociaux

Written by Insectes Sociaux Editor-in-Chief, Michael Breed (michael.breed@colorado.edu)

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Polistes dominula Photo: Jean-Raphaël Guillaumin/flickr

 

Social recognition in animals often relies on multiple cues representing disparate sensory modalities.  Humans can individually identify others using several types of cue, including voice, appearance, gait, odor, and mannerism. This redundancy makes social recognition particularly robust to changes in surrounding conditions. Even in full darkness human individual recognition is accomplished by voice and odor. The use of overlapping information sets in recognition suggests that identification of others is a key adaptive trait in human social biology.

In eusocial insects, social recognition is equally important and often relies on chemical cues carried on the external surfaces of colony members.  A very large body of literature supports the use of chemical cues in social recognition in a wide variety of bees, ants, wasps and termites (Breed 2014).  Odors work well in the dark environments of nest interiors and can be blended among workers to yield colony-level identity badges.

The finding, slightly over a decade ago, that a species of paper wasp, Polistes dominula (=dominulus), uses visual signals for social recognition was surprising and, indeed, revolutionary (Tibbets 2006). Other wasps, such as Liostenogaster, are now known to also use variation in facial markings as social signals. The social use of visual signals is probably facilitated by the openness of Polistes nests, allowing vision to function as a cue when wasps are on the nest surface. The variability in cuticular marking patterns is an important component of this system, and significantly, the degree of variability differs among populations of P. dominula.

In this issue Branconi et al (2018) test the function of facial pattern variation in an Italian population of P. dominula. Branconi and colleagues found no evidence for social discrimination based on facial markings. Their extensive experiments were performed in two behavioral contexts, competition during foraging and nest defense.  They carefully controlled for odor and movement cues, but did not manipulate potential visual signals by modifying markings on the animals’ faces.  In this respect, the experiments differ from those of Tibbets (2006 and a series of more recent studies), leaving a gap that should be filled in future work. The findings of Branconi et al (2018) follow on a similar set of tests in a Spanish population by Green and Fields (2011) which also yielded negative results.

The Italian and Spanish populations have far less phenotypic variation in facial markings than the North American population, an interesting factor in the evolutionary dynamic. A very salient question is whether in the North American population release, from the evolutionary pressures of parasites or predators that are present in the wasp’s native habitat, has relaxed canalization of facial patterns. High levels of signal stereotypy are perfect for species recognition, which is valuable in exclusion of intruders to a nest. On the other hand, highly variable signals are foundational for individual recognition (Breed and Bekoff 1981).

As a general feature, social wasps may have evolved to use visual signals in species identification. Stereotypical, at the species level, cuticular color patterns are prominent in many wasps. Perhaps aposematic signals were co-opted in evolution for recognition purposes.  Perhaps it went the other way, with initial selection pressure for interspecific variation in coloration for identification purposes, and then enhancement of these signals through selection for increased aposematic value.  Explorations of the evolutionary pathways leading first to cuticular coloration patterns and then to intraspecific variation in pattern will yield fascinating results.

This study should stimulate reflection on the value of negative results, and of the importance of expressing negative results as contributing to a larger view of a problem, rather than invalidating a specific set of previous studies. There is no basis in Branconi et al’s (2018) results and interpretation to question the veracity of the findings from the North American population, and Branconi et al (2018) have in a quite laudable way steered clear of questioning the earlier findings. This study should open the door to truly matched studies between North American and European populations of P. dominula, as well as to deeper considerations of the evolutionary dynamics that have caused wasp populations to differ so dramatically in phenotypic variation of visual signals.

References

Branconi R, Baracchi D, Turillazzi S, Cervo R (2018) Testing the signal value of clypeal black patterning in an Italian population of the paper wasp Polistes dominula. Insectes Sociaux https://doi.org/10.1007/s00040-017-0598-z

Breed MD (2014)  Kin and nestmate recognition: the influence of W.D. Hamilton on 50 years of research.  Anim Behav 92:271–279

Breed MD, Bekoff M (1981) Individual recognition and social relationships. J Theoret Biol 88:589-593

Green JP, Field J (2011) Interpopulation variation in status signalling in the paper wasp Polistes dominulus. Anim Behav 81(1):205–209. https://doi.org/10.1016/j.anbehav.2010.10.002

Tibbetts EA (2006) Badges of status in workers and gyne Polistes dominulus wasps. Ann Zool Fenn 43:575–582

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Michael Breed, Department of Ecology and Evolutionary Biology, The University of Colorado, Boulder, Boulder CO 80309-0334 USA