I am really proud to congratulate Dr. Danilo Giacometti for his successful PhD Defence! The thesis entitled “Physiological and behavioural responses to temperature and humidity in fossorial amphibians” was defended today in front of his examining committee: Dr. Don Miles (External, Ohio University), Dr. Toby Mündel (External within Brock University), Dr. Diane Mack (Chair, Brock University), Dr. Miriam Richards, Dr. Kiyoko Gotanda, and myself. A very large audience was in attendance for the entire defence (!). I wanted to thank our Brasilian colleagues who were able to log in and attend as well!
As the Arctic warms at an alarming pace, we’re learning that even cold-adapted species like the thick-billed murre aren’t immune to rising temperatures. This latest study, led by Fred Tremblay from Dr. Kyle Elliot’s lab at McGill adds to the growing understanding that cliff-nesting seabirds are experiencing heat stress far despite ambient air temperatures rarely exceeding 25°C. Using custom 3D-printed murre models painted to mimic the birds’ plumage, we measured “operative temperatures” (the actual heat experienced by an animal) on Coats Island, Nunavut. These operative temperatures soared as high as 46.5°C due to solar radiation and other environmental factors. In fact, murres faced heat stress conditions on 61% of summer breeding days, which can lead to significant water loss and physiological strain.
This work highlights the impact of climate change on Arctic wildlife and illustrates the value of biophysical modelling and how important it is to consider more than air temperature measurements in macroecology/macrophysiology (see https://doi.org/10.1111/1365-2656.12818 and https://doi.org/10.1002/ece3.5721).
These models, in combination with infrared thermal imaging, offer a non-invasive and cost-effective way to measure real-world thermal conditions, paving the way for better predictions of species vulnerability. With males incubating eggs during the hottest parts of the day, this heat stress isn’t just theoretical. It could shift breeding success, survival rates, and long-term population dynamics. These type of studies demonstrate the importance of microclimates in assessing the threats facing Arctic fauna and animals around the world.
Example thermal image of biophysical models and live thick-billed murres in the breeding colony at Coats Island, Nunavut, Canada. For each model and murres where at least 1/3 of the back is visible, the back area is indicated by the white perimeter with associated mean back temperature to the right.Graphical abstract of the study
For access to the study please follow the link in the citation below.
Citation
Tremblay F, Choy ES, Fifield DA, Tattersall GJ, Vézina F, O’Connor R, Love OP, Gilchrist GH, Elliott KH. 2025. Dealing with the heat: Assessing heat stress in an Arctic seabird using 3D-printed thermal models. Comp Biochem Physiol A Mol Integr Physiol. 306: 111880. https://doi.org/10.1016/j.cbpa.2025.111880
For amphibians, water is everything. Their thin skin makes them especially vulnerable to drying out, so staying hydrated is not just about comfort—it is about survival. But how do amphibians manage their hydration state in the face of different temperatures and fluctuating humidity?
Our recent study on spotted salamanders (Ambystoma maculatum) provides some new insights into this question. We exposed salamanders to two temperatures—17°C and 22°C—within a humidity gradient (Fig 1) to understand how salamanders behaved when given the choice to move toward more or less humid conditions under contrasting thermal conditions.
Figure 1. Schematic of the humidity gradient, showing how salamanders can freely move throughout a circular environment to select from low to high humidity.
We found that salamanders consistently selected localities in the gradient that maintained a constant vapour pressure deficit (VPD), which is the key variable driving evaporative water loss (Figure 2). VPD reflects a more physiologically relevant metric for the “drying power” of air. Since they behaviourally regulate a constant VPD regardless of temperature, this provides support for a humidistat (i.e., that they regulate their water loss).
Figure 2. Summary of the selected VPD and selected RH for spotted salamanders tested at 17 and 22C.
Virtually, what this means is that salamanders prefer higher relative humidity (RH) at 22°C than at 17°C to offset the increased drying power of the air at warmer temperatures. This suggests that salamanders are not just responding to RH or temperature independently. Instead, they are tuning into the combined effects that actually influence water loss.
Additionally, salamanders that selected higher VPDs (i.e., dryer conditions) lost more water, and body size also mattered, as larger individuals lost more water than smaller ones even after accounting for temperature. This highlights a trade-off between body size, humidity preference, and the risk of dehydration.
Temperature also played an important role in rehydration. Salamanders rehydrated faster at 22°C than at 17°C, suggesting that warmer conditions may boost water uptake—perhaps because of increased skin permeability at warmer temperatures, or from active processes that promote water uptake.
One of the most intriguing findings was the idea that salamanders might be able to sense how much water they are losing. We propose that local evaporative cooling of the skin—especially on the parts exposed to air—could serve as a sensory cue. If the dorsal skin is cooler than the ventral skin (which stays in contact with the moist substrate), that temperature difference might help the salamanders detect and respond to evaporative demand.
Overall, our study shows that rather than being passive victims of their environment, salamanders actively choose conditions that help them stay hydrated. Their behaviour is not random—it is a targeted response to complex environmental pressures.
One take home from this is that we can’t only measure relative humidity as an environmental predictor for microhabitat selection in salamanders and other ectotherms, but we need to incorporate the biophysical aspects of water loss. Hopefully this isn’t too scary!
Here’s Spotty! – All drought and no rain make salamanders insane.
Giacometti, D and Tattersall, GJ. 2025. Behavioural evidence of a humidistat: a temperature-compensating mechanism of hydroregulation in spotted salamanders. Journal of Experimental Biology, 250297 https://doi.org/10.1242/jeb.250297
Harry Kumbhani was representing the lab at the Canadian Society of Zoologists conference last week in Waterloo with his stunning poster below. And he received a little message, possibly from a journal editor encouraging he submit the manuscript, perhaps?!
Well done Harry and thank you for all your hard work on that project. Hopefully there will be good news on this soon as we finalise the manuscript.
Congratulations to Harry Kumbhani for being awarded an Ontario Graduate Scholarship for his MSc research in my lab. With coursework out of the way, conferences and summer field work beckon, so the timing could not be better!
Ectotherms from highly seasonal habitats often exhibit remarkable physiological plasticity, which allows them to balanceand adjust energy and water budgets in the face of fluctuating climatic conditions. Yet, fossorial (i.e., underground-dwelling) ectotherms are thought to experience attenuated climatic variability underground, raising the question: do fossorial ectotherms also display seasonal adjustments in key physiological functions?
In our recent publication, we investigated how seasonal acclimation (spring vs. autumn) affected energy expenditure and water loss in the spotted salamander. By measuring standard metabolic rates (SMR) and rates of evaporative water loss (EWL), we aimed to disentangle acute (i.e., exposure to test temperatures) from prolonged (i.e., seasonal acclimation) effects.
The effect of temperature over log-transformed rates of carbon dioxide (logV̇CO2) and water vapour production (logV̇H2O) in Ambystoma maculatum between the autumn and spring.
We found that increases in temperature led to increases in both SMR and EWL, demonstrating that fossorial salamanders also experience acute physiological costs when warmed. Salamanders had lower SMR in the spring, which may be beneficial in the context of overwintering emergence and breeding. In contrast, sustaining higher SMR in the autumn may allow salamanders to forage aboveground to replenish energy stores in preparation for the winter. EWL was stable between seasons, suggesting that salamanders may be more reliant on behavioural instead of physiological adjustments to manage water loss throughout the year. Together, our findings challenge the assumption that fossorial ectotherms are largely insulated from environmental fluctuations by virtue of living underground.
Giacometti, D, and Tattersall, GJ. 2025. Seasonal plasticity in the thermal sensitivity of metabolism but not water loss in a fossorial ectotherm. Oecologia. 207: 67. https://doi.org/10.1007/s00442-025-05711-6
A busy week with Honours student defences from the lab (and throughout the Department of Biological Sciences).
From our lab:
Margaret Kitney defended a brilliant thesis project on how and whether sex differences alters thermoregulatory behaviours in guppies (The effect of sex on the thermoregulatory behaviour of the Trinidadian guppy (Poecilia reticulata), having spent months watching fish swimming in shuttle boxes and months pouring over tracking algorithm detection processes. Truly a great amount of work and thought went into the thesis writing and explanations.
Natalie Bakker defended an awesome thesis project on bearded dragon cognition (Quantity Discrimination and Detour Task Performance of Bearded Dragons (Pogona vitticeps)), expanding our knowledge of how reptiles think and assess food resources. Months of challenges associated with our “lazy lizards”, but the project came together brilliantly in the end.
For decades, the concept of a thermoregulatory “set-point” has been a cornerstone of physiological research, yet its definition and application remain surprisingly inconsistent across disciplines. Our recent study, spear-headed by the inimitable Dr. Duncan Mitchell, soon to be published in Biological Reviews, revisits and clarifies this fundamental concept by bridging perspectives from control theory and thermal biology. We explore how the set-point framework has been misinterpreted, and we argue for a more precise definition rooted in negative feedback principles. By revisiting foundational work and integrating recent empirical data, we demonstrate that set-points should not be conflated with operating body temperatures. Instead, they represent the thresholds at which thermo-effectors—such as sweating, shivering, or behavioural thermoregulation—are activated.
By incorporating an historical perspective, and combining control theory research with research into behavioural thermoregulation in lizards, our work highlights that, while lizards select body temperatures within a narrow range under stable conditions, their ability to do so is governed by multiple overlapping control mechanisms rather than a singular, static reference point.
This nuanced understanding has broad implications for comparative physiology and ecological research, especially in the face of climate change. The mischaracterization of set-points has led to confusion in both homeothermic and ectothermic species, potentially skewing interpretations of thermal adaptation and stress responses. By refining the definition of set-points within a rigorous control-theory framework, our study provides a clearer foundation for future research on thermal biology. We emphasize the importance of distinguishing between physiological thresholds and behavioral outcomes, urging researchers to adopt a systems-based approach to thermoregulation. Ultimately, our work seeks to reframe the discussion, ensuring that the next generation of studies can build on a more precise and unified conceptual framework.
This review is part of a series of “Misconceptions in thermal biology” papers, mainly from the Brain Function Research Group in South Africa, but the list of co-authors includes experts in thermal physiology and ecophysiology. Stay tuned for more papers in the future, and I encourage anyone new to thermoregulation and thermal biology research to read some of these.
Citation
Mitchell, D, Fuller, A, Snelling, EP, Tattersall, GJ, Hetem, RS, and Maloney, SK. 2025. Revisiting concepts of thermal physiology: understanding negative feedback and set-point in mammals, birds, and lizards.Biological Reviews. https://doi.org/10.1111/brv.70002
For other misconceptions in thermoregulation papers see:
Nest site selection is a critical decision for many animals, but for small carpenter bees (Ceratina calcarata), it’s a gamble with possibly far-reaching consequences. In our recent study, deHaan et al. explored the delicate balance between benefits and risks when mother bees choose to nest in sunny or shaded environments. The research uncovers an intriguing trade-off: while sunny nests boost maternal fitness by reducing the chances of complete brood failure, they come at the cost of smaller, thermally- stressed offspring. Thanks Mum!
Sunny nests, which are warmer, offer distinct advantages to mother bees. These nests enable earlier foraging activity and faster brood development, reducing the window of vulnerability to predators and parasites. To test this in an field experiment, however, we (i.e., Jessie deHaan) had to find nests early in the spring and relocate some nests to the shade and some to the sun to allow for these effects to be tested across the summer. Sunny nests reached maximum temperatures that were up to 3.8 °C higher than the maximum temperatures reached in the shade; further, the sunny nests would have been warmer for ~14-15 hours per day during the study period. In short, sunny nests are obviously warmer than shady nests, but also undergo wider diurnal changes in temperature.
In our experiment, we found that 59% of sunny nests successfully produced offspring, compared to only 32% of shaded nests. However, these sunnier sites posed challenges for developing juveniles, who faced higher temperatures that necessitated energy-intensive thermoprotective measures. Juveniles from sunny nests were smaller and had elevated heat tolerance thresholds (CTmax), suggesting they diverted resources from growth to survival. Since mothers provision each brood cell with a fixed amount of pollen after laying their egg, the size the young bees reach must reflect the trade-off between temperature-dependent energy expenditure and development. This trade-off also highlights how maternal decisions prioritize their own fitness, sometimes at the expense of their offspring’s long-term prospects.
Close-up image of Ceratina calcarata (photo by Jessie deHaan).
This research sheds light on the intricate dynamics of environmental stress, maternal investment, and juvenile development in ectotherms like bees. With climate change amplifying temperature extremes, understanding these relationships could be crucial for predicting the future of pollinator populations.
This paper was the result of Jessie deHaan’s MSc research in Dr. Miriam Richards lab (co-supervised in part in my lab), but conducted during the lockdown period during the COVID-19 travel and research restrictions. At the time, faculty and student researchers were not permitted to come to campus, or initiate new research projects in the field (even though government scientists were allowed to carry on their research). For an MSc student in the middle of their research project, 2020 presented challenges to which Jessie rapidly adapted by running their experiments in their own backyard and in the basement of their house, using a modified PCR machine as the bee incubator! Hats off to ingenuity in the face of adversity.
Citation
deHaan, JL, Maretski, J, Skandalis, A, Tattersall, GJ, and Richards, MH. 2025. Costs and benefits of maternal nest choice: trade-offs between brood survival and thermal stress. Ecology. https://doi.org/10.1002/ecy.4525
Our latest study (https://doi.org/10.1016/j.applanim.2024.106484) sheds light on a perplexing behaviour seen in captive reptiles, namely their interactions with barriers (IWB), a form of repetitive behaviour akin to pacing in mammals. As part of her PhD research, Melanie Denommé investigated the motivations behind IWB in bearded dragons (Pogona vitticeps; Figure 1) over a three year period, and formally tested whether it stems from a “desire” to escape their enclosures.
Figure 1. Photo of a bearded dragon interacting with a barrier (called glass surfing sometimes if the lizard moves back and forth across the transparent barrier, although reptiles may do this on non-transparent barriers as well).
Our findings revealed a strong preference for performing IWB near the front barrier of their environment (Figure 2), the only known escape route; even when half of it was obscured; they also direct more of their behaviour toward the transparent part of the front barrier. Interestingly, IWB was 15 times more likely to occur around the time when lizards defecated, supporting an argument that these behaviours may be driven by escape-related motivations, at least with respect the need to find suitable defecation areas. However, no clear link was found between IWB and anticipation of feeding, suggesting species-specific differences in how repetitive behaviours are triggered. Despite these results, lizards would still exhibit IWB with non-transparent barriers (Figure 2), suggesting that escape is not the exclusive explanation for these repetitive behaviours.
Figure 2. Results from multiple rounds of home cage observations of barrier wall interaction (minutes per day). Bearded dragons interacted more with the front barrier (that is, the barrier from which escape could occur), although still exhibited IWB (interacting with barriers) along the other 3 walls of the enclosure.
Seasonal and sex-related patterns offered further nuance. Contrary to expectations, female lizards performed IWB more during spring, while males showed consistent levels year-round. This might reflect frustrated breeding-season motivations, as females in the wild often roam widely in search of mates, a behaviour restricted in captivity. These findings emphasize the complex interplay between natural instincts and captive conditions, highlighting the importance of tailoring environments to better meet the needs of individual animals. By understanding these behaviours and using an evidence-based approach, we can deepen insights into the diverse causes of repetitive behaviours across species and thereby improve captive reptile welfare.
Note that the actual levels of IWB seen were low throughout the study, with numerous animals never performing the behaviour. There appear to be individual differences in the expression of IWB.
Citation
Denommé, M and Tattersall, GJ. 2025. Investigating the motivations of repetitive barrier interactions in Pogona vitticeps. Applied Animal Behaviour Science, 283: 106484. https://doi.org/10.1016/j.applanim.2024.106484
Tattersall Lab (TEMP) 