This blog post is provided by Elsa Youngsteadt and tells the #StoryBehindthePaper for the paper “Can behavior and physiology mitigate effects of warming on ectotherms? A test in urban ants”, which was recently published in Journal of Animal Ecology. In their paper they explore how ants might react to climate change, and whether they can adapt their behaviour to new conditions.
Spring flowers are bursting earlier, growing zones are marching ever poleward, and bumble bees are shrinking away from their southern range limits. Climate change is well underway and some of its biological effects have been established for decades. But other effects are more subtle. For example, physiologists predict that, as temperatures increase, some animals’ metabolisms will also ramp up. They’ll need more food to get by, they’ll live faster, and die younger; some will go extinct. But are animals really getting hotter as the climate warms up?
Ectotherms are animals that don’t maintain a constant body temperature, instead letting it fluctuate along with the environment. But they do exert some control, for example by moving between sun and shade or retreating underground at certain times of the day or year. Given this ability to thermoregulate, ectotherms might also buffer their own exposure to climate change by subtly shifting their activity to cooler microclimates within their habitat. Although some modeling studies have suggested that this ability would save many insects from heat-induced extinction, it’s not clear that they really have the behavioral flexibility to pull it off. This is one of the main questions my team and I had heading into the spring of 2020.
Of course, the spring of 2020 didn’t go as planned. We had meant to ask this question in the warm tropics, where ectotherms are closer to their maximum heat tolerance and may take more urgent measures to stave off heat stress. But instead of spending the spring in the tropics, we spent it in lockdown, trying to stay sane and figure out some justifiable use of our time. Once we began to creep back into public, we decided to pilot our tropical methods at home in Raleigh, NC. That pilot project never made it out of the temperate zone, but it did get bigger. Ultimately, we found that our own local ants—although not obviously heat stressed—are surely warming up.
To detect behavioral thermoregulation, it’s not enough to just measure an ectotherm’s body temperature. You need to know its preferred body temperature, and what range of temperatures are available in its habitat—in the thermal mosaic created by shade, sun, darker surfaces, lighter surfaces, and little breezes. With those pieces of information, you can see how challenging the thermal environment actually is. (If the animal moved carelessly through the habitat, would it ever encounter intolerable conditions, or only pleasant ones?) And even if no part of the environment is truly pleasant, you can see whether the animal is making the best of it, spending time in the microclimates that bring it closest to its preferred temperatures, even if it’s still way off.
We chose ants as our focal ectotherms because they’re common models for thermal biology research, and because they’re generally important participants in their ecosystems, acting as predators, herbivores, seed dispersers, and so on. To look at a climatic challenge to ant thermoregulation, we worked on an urban warming gradient. All our sites were forested, but the ones located along urban greenways averaged about one degree Celsius warmer in the summer than the non-urban forest sites.
We worked with several ant species that were common across most of the study sites, and collected four kinds of data. First, we measured thermal preference—the range of temperatures where each species chose to settle on a gradient from a heat block to an ice bath. (Because the university was still closed, I did this assay in my home office using an apparatus my husband helped build during lockdown. The frozen bowl of our ice cream maker helped keep the cold end cold.) We also measured each species’ maximum heat tolerance. (Sarah Ferriter, an undergrad researcher, took ants to her apartment for this assay.) And finally, research associate Sara Prado measured available and occupied temperatures along transects at each site in the field. For these last two, Sara used operative temperature models of three focal ant species; these were dead, posed ants mounted on thermocouple probes. You can think of them a little bit like a species-specific heat index thermometer: they incorporate effects of air temperature, surface temperature, solar radiation and wind, as well as the size, shape, and color of the ant species. It doesn’t necessarily tell you the body temperature of live ants, but it tells you how comfortable the thermal environment is. If the operative temperature model is hotter than the live ant prefers, then the live ant shouldn’t just hang out in that spot until her own body reaches that unpleasant temperature; she should move along and find some shade.
If ants are actually good thermoregulators, then we should find them disproportionately often at places and times where the operative temperatures most closely matched their preferred temperatures. This was the case for four of our five focal species. (The fifth had such a broad range of preferred temperatures that we could hardly ask the question.) But if ants were capable of saving themselves from climate warming by shifting their activity patterns, they should also occupy cooler parts of the transect at sites that were too hot, and hotter parts of the transect at sites that were too cool. This did not happen. Cool-loving ants, for example seemed to use fixed behaviors (like being more active at night) to avoid the hottest conditions across the board—even at sites where the temperature was more comfortable during the day.
None of the ants got dangerously hot or cold during our study. But they did get warmer than they preferred to be, and they didn’t shift their behavior to compensate. That means urban ants are hotter than non-urban ants, and as climate change progresses, future ants will probably be hotter than past ants. If this pattern holds, their metabolisms will increase, and they’ll live faster-paced lives. Because ants are social animals, the bottom line for the superorganism—as opposed to just its individual workers—is still unknown. That’s something we’d like to know next. Only this time, I hope it doesn’t take a pandemic to send us back out to our local field sites to find out.
Author bio
Elsa Youngsteadt is an assistant professor in the Department of Applied Ecology at North Carolina State University.
Lab website: http://youngsteadtlab.org/
Read the paper
Read the full paper here: Youngsteadt, E., Prado, S. G., Keleher, K. J., & Kirchner, M. (2022). Can behaviour and physiology mitigate effects of warming on ectotherms? A test in urban ants. Journal of Animal Ecology, 00, 1– 12. https://doi.org/10.1111/1365-2656.13860
The morning session of the symposium will serve the additional purpose of celebrating the career and accomplishments of Louis Lefebvre, Professor in Biology at McGill University, Montréal, Canada. Speakers include Louis Lefebvre, Laure Cauchard (United Kingdom), Alexander Kotrschal (Sweden), Daniel Sol (Spain), and myself (Canada). Those who know the work of Dr Lefebvre will remember his contribution to the study of social learning, whose work with Luc-Alain Giraldeau demonstrated plasticity in the use of social information: pigeons who could scrounge from a knowledgeable individuals did not socially learn from this demonstrator, while those who were prevented from scrounging did (
Another very important facet of Louis’ research consists in his innovative work on behavioural innovations. Before the turn of the millennium, most comparative cognition research quantified species’ cognitive abilities in standardized laboratory tests. As a trained psychologist engaged in behavioural ecology research, Louis was well-positioned to bring in a complimentary approach, which focused on behaviours expressed spontaneously by animals in their natural environments. But how can we identify behavioural plasticity in the wild that is brought about by cognitive processes such as learning and generalization? Louis had the idea of compiling published observations of birds engaged in unusual behaviours that were clearly not species-typical, and represented invented or modified behaviours allowing the innovator access to an unexpected food source. The comparative study of animal innovation was thus born in the basement of the Redpath library at McGill, where Louis and his students surveyed ornithological journals from all around the world. This work blossomed into >2000 innovation records from hundreds of avian species, and later a similar database on primates collated by Simon Reader and Kevin Laland, as well as exciting findings by Louis and collaborators on the links between innovation rate and: evolutionary diversification rates, the probability of colonization and invasion, the frequency of tool-use, social learning and the size of the whole brain as well as specific brain regions (
Louis also taught thousands of undergrads and supervised many theses, among whom I figure as a PhD graduate from his lab at McGill. Today, and on July 24th, I would like to celebrate his accomplishments and the impact his work had on the development of several research avenues combining natural history, evolutionary biology, animal cognition and neurosciences, as well its profound influence on the development of my own research career, which I look forward to discuss in my presentation in Chicago.
Join us on July 24th at the joint meeting of the International Ethological Congress & Animal Behavior Society: exciting presentations, stimulating discussions, and celebrations throughout the day on the menu. Why not also take the opportunity to read a good book while on the plane or train, and visit some of the world-famous art galleries of Chicago? I think Louis would say that if you enjoy these activities, you should always make time for them, even in the midst of a busy research life.
Animal Ecology in Focus 