A cross-species test of the function of ant pilosity and sculpturing

Reading Time: 6 minutes
Buxton T. James

In the recent article “A cross-species test of the function of cuticular traits in ants (Hymenoptera: Formicidae)” published in Myrmecological News, Buxton et al. used a cross-species comparison to investigate the function of the cuticular traits ‘pilosity’ (hairiness) and ‘sculpturing’ (bumps on the cuticular surface) in ants. These traits have been linked to a range of environmental variables in other studies, but the mechanisms underlying these associations are poorly understood. Here, first author James shares pictures and answers questions.

An Interview compiled by Roberta Gibson, Patrick Krapf, and Alice Laciny

MNB: Could you tell us a bit about yourself?
JB: My name is James Buxton. I’m a PhD candidate from Melbourne, Australia.
I have wanted to be an entomologist for as long as I can remember. At an early age, armed with a ‘bug encyclopedia ‘, I was swinging nets and beating bushes until completely surrounded by jars containing my own unfortunate menagerie. The prospect of being a scientist, discovering new species in a tropical forest, sorting through drawers full of specimens, performing elaborate experiments (with, I imagined, giant microscopes, Jacob’s ladders, bubbling beakers, hunchbacked assistants, et cetera), or just thinking about theoretical problems while sitting in a comfy armchair and stroking one’s chin to a fine point; all seemed equally enthralling to my young self.
In the first year of my bachelor’s degree (2011), after jumping out of my seat in excitement during the lecture on Arthropoda, I approached the lecturer and asked her to point me to an entomologist. She kindly gave me a list and, after an awkward chat with a very friendly and patient emeritus professor, I met Heloise [MNB: Gibb] and was given the opportunity to volunteer with her and two of her students at Scotia Sanctuary. Between toilet roll burials (termite traps) and measuring soil characteristics, the time was largely spent picking things up and asking everyone questions whilst being continuously awestruck by the depth of their knowledge combined with their undying enthusiasm for the work.
After that earth-shattering experience, I knew that I had discovered my calling, and subsequently volunteered with the Gibb lab in every year of my undergraduate degree, which included arid-zone beetle identification and trait measurement, and sorting through temperate forest leaf litter. It was an industry cadetship in my third year that introduced me to myrmecology, this time assisting an honours student in the Australian Alps as well as mounting and identifying the fascinating ant species from the MacDonnell Ranges.
My honours and PhD research has been focused on exploring the functional significance of morphological traits, specifically those of potential importance to trait-based ecology. This has allowed me to combine my passion for both field and lab-based work.
‘A cross-species test of the function of cuticular traits in ants (Hymenoptera: Formicidae)’ originated as the first (major) component of my honours research but was only successful thanks to the expertise of all my gifted collaborators. Along with my supervisors, Heloise and Kylie (who provided a wealth of ant trait-ecology and animal physiology knowledge, respectively), Travis was involved in all aspects of the ‘force to puncture’ experiment, including the modification Powerlab 26T system to create our ‘force to puncture’ device, and Alan lent his vast electron microscopy wisdom to the design of the cuticle thickness comparison.
Most recently, I have been working on multispectral colour-related traits and exploring their associations with environmental variables.
On reflection, I have been incredibly fortunate to have such a long apprenticeship with such a brilliant lab group and such a brilliant scientist as my lab head, collaborator, and academic mentor.

MNB: Could you briefly outline the research you published in Myrmecol. News in layman’s terms?
JB: We used a cross-species comparison to investigate the function of the cuticular traits ‘pilosity’ (hairiness) and ‘sculpturing’ (bumps on the cuticular surface) in ants from two sites in Australia, semi-arid Scotia Sanctuary (Western NSW) and mesic La Trobe Wildlife Sanctuary (Melbourne, VIC).
These traits have been linked to a range of environmental variables in other studies, but the mechanisms underlying these associations are poorly understood.
Here, we take a step towards a greater understanding of trait-environment interactions by testing the association among these traits and a range of important physiological measurements: heat tolerance, desiccation tolerance, the ability of the body surfaces to repel water, and protection from physical forces (such as a predator’s mouthparts).
We also tested whether physiological traits differed between species that were active at day or night or between ants from semi-arid and mesic environments.

MNB: What is the take-home message of your work?
JB: Hairy ants tended to have a higher tolerance to heat and lose less water. Sculpturing was strongly linked to cuticle thickness and hardness (the force to puncture the cuticle) as well as a lower water loss rate. However, it was negatively associated with heat tolerance, possibly because many highly sculptured ants were nocturnal in this study, though there several other possible mechanisms, including a trade-off between benefits associated with biomechanical properties (e.g. harder/denser cuticles) and the ability to tolerate high temperatures.
Our results provide support for the continued use of these easily measured traits in future work.  However, empirical investigations of trait function across a broader range of ecosystems are critical to ensure that the ecological importance of trait-environment relationships and their inter-relatedness as components of an ‘ecological strategy’ are better understood. 

MNB: What was your motivation for this study?
JB: Recording the occurrence of species traits of known functional importance and linking them with environmental variables has been touted as a way to understand the structure of species-assemblages in a mechanistic way, allowing patterns in assemblage structure to be predicted on a global scale. This trait-based approach to ecology promises greater generality in our understanding of how species assemblages are structured, and has already yielded some fascinating links between traits and environmental variables in several taxa.  Ants have been employed as study species in trait-based ecology research only relatively recently, but there have already been several large-scale studies and the development of a global database (The Global Ants Database).
The value of the trait-based approach, however, depends on linking traits with ecological functions, but there have been few tests of proposed functions for many commonly used and easily measured traits, leaving some of the most fascinating findings from large-scale comparisons difficult to interpret.
This requires a lot of work and is just one small step towards more informed trait-based studies.   

MNB: What was the biggest obstacle you had to overcome in this project?
JB: There was so little similar work (a few more functional morphology studies would have been nice), limited time, and so many aspects to consider. Once my supervisors narrowed down my many unrealistic ideas for the project, the major issue was how best to measure pilosity and sculpturing-related traits. There were many different alternatives, and we needed the best approach possible that was also easy and quick enough to be incorporated into studies including many traits. To achieve this, I compared as many traits associated with pilosity and sculpturing as possible (detailed in Table 2 of the paper), selected based on utility in the literature and potential biophysical qualities.

MNB: Do you have any tips for others who are interested in doing related research?
JB: Thinking about different scales is very important for this kind of study; make observations in the lab, under the microscope, and, most importantly, of the animals in the field. Take the time to make informed speculations.
Reading widely, without prejudice, is also very important as functional ecomorphology incorporates a wide range of disciplines, and interpretations of findings can be severely limited by an overly narrow focus or sticking to traditional approaches. Taxonomic literature and some of the old tomes are treasure troves of description and speculation (some wilder than others).
Most of what I have considered to be my most original ideas/observations often turn out, to my chagrin, to have been made by Wheeler in the 1910s, if not by an earlier naturalist in the 18th or 19th centuries, often in a cheeky throwaway sentence. This knowledge also allows you to be the annoying person at conferences who points this out in other researchers’ work. Of course, I try to avoid the temptation (great power, great responsibility, et cetera).
Finally, it is always handy to have some electron micrographs or at least some high-quality macro images on your phone, ready at all times, to convince laypeople (and occasionally other ecologists) to believe in hairy ants. A nicely varied selection of mesosomas under a SEM, some looking like photographs of densely vegetated moonscapes, are very effective at persuading even the most skeptical audience.

MNB: Where do you see the future for this particular field of ant research?
JB: There is still so much to discover! Reading through any trait database will yield a huge range of traits that need to be explored more thoroughly.
For example, pubescent hairs in ants represent a widely variable trait, with some species almost completely covered with tiny hairs and others almost completely bald, something we didn’t have the opportunity to consider in detail in this study.
Could it be protection from solar radiation (via physical and reflectance properties)?
Physical protection from coarse dirt particles that may damage the cuticle or the wax layer (the latter may influence water loss)?
Thermoregulation?
None of these reasons, or a combination?  I, for one, would love to find out.
We hope to inspire others to incorporate mechanistic trait work into their research agendas, and eventually develop a solid cohesive foundation for trait-based ecology. This will take many years, and there are many challenges, especially determining the non-independence of trait responses and their contribution to a whole-of-organism ecological strategy, but if this improves the ability of the trait-based approach to ecology to produce accurate predictive models of assemblage responses to global change, as well as more accurately test the potential of this approach as a means to provide general rules for ecology, the herculean effort will definitely be worthwhile.
MNB: Thank you for this interview!

In the updated version, the link to the contribution was added.

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