Author: gtattersall

Misconceptions and Set-Points

/ gtattersall

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:

https://doi.org/10.1111/1365-2656.12818

https://doi.org/10.1002/ece3.5721

Latest “buzz” about nesting choices poses a sunny conundrum for bees

/ gtattersall

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

See Dr. Miriam Richards lab page for more details about bees and her bee research!

Unlocking the Motivations of Repetitive Behaviours in Reptiles

/ gtattersall

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

Shrinking Shorebirds & How Climate is Reshaping Them

/ gtattersall

Shorebirds across Australia are experiencing notable changes in size and shape, offering a vivid example of climate change’s impact on wildlife. In a recent publication in Ecology Letters (McQueen et al), using comprehensive 46-year study involving over 200,000 observations across 25 species we show widespread declines in body size (“shrinking”) and concurrent increases in bill length (“shape-shifting”). These shifts appear to align with thermal adaptation, where smaller bodies and elongated bills would help dissipate heat more effectively in warmer environments. However, we also found that smaller species exhibited the most pronounced changes, while long-distance migratory species showed weaker trends, possibly due to physical constraints needed for efficient flight over vast distances.

Interestingly, while bill lengths have generally increased over time, they shortened following exposure to recent hot summers, hinting at complex evolutionary trade-offs between short-term vs. long-term climatic fluctuations.  We suggest these changes may reflect not only adaptations for thermoregulation but also responses to nutritional stress or other environmental pressures. These findings emphasize the dual role of climate change as both a selective force and a stressor. As global temperatures continue to rise, understanding these morphological changes is crucial for predicting their effects on species survival and the ecosystems they inhabit.

Field sites and climate information for northern and southern Australian shorebird populations. A and B show locations where shorebirds have been sampled by members of the VWSG and AWSG (black circles) and nearby Australian Bureau of Meteorology weather stations with summer temperature data from 1970-2021 (blue triangles); colour scale shows average summer daily maximum temperatures (December-February). 

To read more about the study, it in open access below. 

Citation

A. McQueen, M. Klaassen, G. J. Tattersall, S. Ryding, Victorian Wader Study Group, Australasian Wader Studies Group, R. Atkinson, R. Jessop, C. J. Hassell, M. Christie, A. Fröhlich, M. R. E. Symonds. 2024. Shorebirds are shrinking and shape-shifting: declining dody size and lengthening bills in the past half-century. Ecology Letters. 27:e14513. https://doi.org/10.1111/ele.14513

When Salamanders Surface: Understanding the Secrets Behind Spotted Salamander Overwintering Emergence

/ gtattersall

Amphibians have long fascinated researchers due to their unique life cycles and environmental sensitivities, but many aspects about the biology of fossorial (i.e., burrowing) species remain shrouded in mystery. Fossorial amphibians like the Spotted Salamander (Ambystoma maculatum) spend most of their lives underground, emerging to the surface only briefly to breed or forage. In our latest paper, we address some of the intrinsic and extrinsic factors that may trigger emergence from overwintering by evaluating the interplay between temperature, gravity, and innate migratory cues over salamander behaviour.

Our study focussed on the role of soil temperature inversion—a seasonal shift where surface soils warm faster than deeper layers—in signalling salamanders to leave their winter refuges and begin their overland journey to breeding ponds. Using a vertical thermal gradient in the lab, we examined how salamanders responded to temperature cues at different depths and whether their activity levels changed with temperature shifts that mimicked soil temperature inversion. Our findings suggested that salamanders are not only tolerant of a wide thermal range but are also displaying a circannual phenomenon known as “migration restlessness”. Migration restlessness is characterised by a surge in movement often seen in animals preparing to migrate. Coupled with negative geotaxis, a tendency to move upward against gravity, this restless behaviour may explain why salamanders begin their spring migration at just the right moment, maximising their chances of reproductive success while avoiding the dangers of emerging too early and potentially freezing.

Representation of soil temperature inversion in the forest surrounding Bat Lake, Algonquin Provincial Park, ON, Canada, from where the spotted salamanders were collected.

A. Schematic of the vertical thermal gradient used to assess the effects of thermal inversion and gravity on salamander behaviour. Thermal image of the active (B) and overwintering (C) thermal gradients used in the study. The thermal gradient was always kept at a 45º angle relative to the horizontal axis, imitating underground burrows. 

Sped-up time-lapse of a male Ambystoma maculatum tested within the active thermal gradient. Frames were taken every 30 s, for a total of 18 h of experiment (20 frames/sec).

For a link to an interview with the first author ECR, Danilo Giacometti, please see the following link.

For a link to the paper, please see the citation below.

Citation

Giacometti D., Moldowan P. D., Tattersall G. J.; Ups and downs of fossorial life: migration restlessness and geotaxis may explain overwintering emergence in the Spotted Salamander. J Exp Biol 2024; jeb.249319. doi: https://doi.org/10.1242/jeb.249319

Blog Author: Danilo Giacometti

Shape-Shifting in the Face of Climate Change: The Long and the Short of How Australian Birds Are Adapting

/ gtattersall

As global temperatures rise, animals are facing mounting pressure to adapt, and Australian birds are no exception. Our recent research (from Sara Ryding’s PhD research) has examined over 5,000 museum specimens, representing 78 bird species across Australia, revealing clear changes in their body and appendage sizes. These changes are aligned with two well-known ecological principles: Bergmann’s rule, which predicts smaller body sizes in warmer climates in endotherms, and Allen’s rule, which argues that animals (namely endotherms) will develop larger appendages to regulate body heat. Consistent with these theories, our study found that birds are experiencing a long-term decrease in body size, particularly in absolute wing length, while their appendages, such as bills and tarsi (leg bones), are getting larger relative to their bodies. This phenomenon, often referred to as “shape-shifting,” is a widespread response to the increasing temperatures driven by climate change.

Interestingly, our research also highlights a more complex picture when it comes to short-term responses. While long-term trends show a clear increase in appendage size to aid thermoregulation, birds displayed smaller appendages in the years following hotter temperatures. This suggests that while birds are gradually adapting to rising temperatures over time, short-term weather events may create different selection pressures that affect growth and development. Factors like food availability and reproductive challenges could contribute to these opposing trends. This study underscores the intricate balance between long-term evolutionary changes and the immediate pressures exerted by fluctuating environmental conditions, offering critical insights into how birds—and potentially other animals—might continue to respond to our rapidly changing world.

For a link to the study, please see the citation below.

Citation

Ryding, McQueen, A, Klaassen, M, Tattersall, GJ, and Symonds, MRE. 2024. Long- and short-term responses to climate change in body and appendage size of diverse Australian birds. Global Change Biology, 30:e17517. https://doi.org/10.1111/gcb.17517

Twists of fate and the hidden story of salamander abnormalities

/ gtattersall

A new paper has been accepted in the Canadian Journal of Zoology, resulting from Gloria Gao’s (Njal Rollinson’s lab at University of Toronto) hard work and based (in part) on the long-term study of the spotted salamanders at Bat Lake, Algonquin Park along with other field sites in Algonquin Park.

This study investigates the prevalence and fitness consequences of morphological abnormalities in Spotted Salamanders (Ambystoma maculatum) within an uncontaminated ecosystem in Algonquin Provincial Park, Canada. Over a 12-year period, the study found that abnormality rates ranged from 4.3% to 5.8% annually, aligning with baseline frequencies observed in other minimally impacted amphibian populations. Interestingly, despite expectations that abnormalities might reduce fitness, salamanders with abnormalities in this study displayed slightly higher body condition and significantly earlier arrival times at breeding sites—traits typically associated with high fitness. These results suggest a potential survivorship bias, where only individuals with favourable genetic or environmental factors survive to be observed, masking the true impact of abnormalities.

The study also highlights the importance of understanding abnormality rates in uncontaminated environments, as these can provide valuable baselines for comparison with more impacted habitats. It appears that Caudata (salamanders and newts) generally have a higher prevalence of abnormalities compared to Anura (frogs and toads), although the reasons for this remain speculative. The findings from this study underscore the complex relationship between abnormalities and fitness and emphasize the need for further research to explore how environmental factors influence these dynamics in amphibian populations.

Examples of abnormalities observed among Spotted Salamanders at Bat Lake, Algonquin Provincial Park: A. polydactyly (additional phalanges) resulting from partial duplication of the hand on the right forelimb; B. partial syndactyly (fused digits) and abnormal arrangement of the right forelimb phalanges; C. polymelia (limb duplication) of the right forelimb; D. micromelia (proportionately small or short limb) of the left hindlimb demonstrating early stage regeneration following probable amputation; E. tail bifurcation.

Citation

Gao, GHY, Moldowan, PD, LeGros, DL, Sahar, M, Tattersall, GJ, and Rollinson, N. 2024. Frequency of adult amphibian abnormalities and consequences for traits related to fitness in an uncontaminated environment. Canadian Journal of Zoology, doi.org/10.1139/cjz-2024-0063.

Proofs are not yet available, but will update when they are.

Salamanders show inherent seasonal differences in thermal preference

/ gtattersall

Very pleased to have my PhD student, Danilo Giacometti’s paper accepted recently in Royal Open Science. This represents the culmination of over a year’s work carefully measuring temperature selection. He has a much better blog post here on the subject by Danilo Giacometti, but I’ll post the abstract and citation below.

Abstract

Temperature seasonality plays a pivotal role in shaping the thermal biology of ectotherms. However, we still have a limited understanding of how amphibians maintain thermal balance in the face of varying temperatures, especially in fossorial species. Due to thermal buffering underground, theory predicts relaxed selection pressure over thermoregulation in fossorial ectotherms. As a result, fossorial ectotherms typically show low thermoregulatory precision and low evidence of thermotactic behaviours in laboratory thermal gradients. Here, we evaluated how temperature selection (Tsel) and associated behaviours differed between seasons in the Spotted Salamander (Ambystoma maculatum). By comparing thermoregulatory parameters between the activity and overwintering seasons, we show that A. maculatum engages in active behavioural thermoregulation despite being fossorial. In both seasons, Tsel was consistently offset higher than prevailing thermal conditions. Thermoregulation differed between seasons (see table below), with salamanders having higher Tsel and showing greater evidence of thermophilic behaviours in the active compared to the overwintering season. Our study highlights that the combination of behavioural and thermal biology measurements is a necessary step to better understand the mechanisms that underlie body temperature control in amphibians. Ultimately, we provide a broader understanding of thermoregulation in the context of behavioural responses to seasonality in fossorial ectotherms.

Citation

Giacometti, D and Tattersall, GJ. 2024. Seasonal variation of behavioural thermoregulation in a fossorial salamander (Ambystoma maculatum). Royal Open Science, https://doi.org/10.1098/rsos.240537

Just how big is that bill?

/ gtattersall

Dr. Sara Ryding’s next thesis chapter just came out in the Journal of Avian Biology. Sara (co-supervised) just finished her PhD with Matt Symonds, Deakin University. Congratulations Sara!

Here is a summary of the study:

Unidimensional measurements for estimating bill size, like length and width, are commonly used in ecology and evolution, but can be criticised due to issues with repeatability and accuracy. Furthermore, formula-based estimates of bill surface area tend to assume uniform bill shapes across species, which is rarely the case. 3D surface scanning can potentially help overcome some such issues by collecting detailed external morphology and direct measurements of surface area, rather than composite estimates of size. Here, we evaluate the use of 3D surface scanners on avian museum specimens to test the repeatability of 3D-based measurements and compare these to traditional formula-based methods of estimating bill size from unidimensional measurements. Using 28 Australian bird species, we investigate inter-observer repeatability of surface area measurements from 3D surface scans. We then compare 3D-based size estimates to formula-based size estimates to infer the accuracy and precision of formula-based measurements of bill surface area. We find that morphometric measurements from 3D surface scans are highly repeatable between observers, without the need for extensive training, demonstrating an advantage over unidimensional measuring methods, like callipers. When comparing 3D-based measurements to formula-based estimates of bill surface area, most formulae for estimating size consistently underestimate surface area, and with considerable variation between species. Where 3D scanning is not possible, we find that a commonly used cone formula for estimating bill size is most precise across diverse bill shapes, therefore supporting its use in interspecific contexts. However, we find that incorporating an additional unidimensional measure of bill curvature into formulae improves the accuracy of the calculated area. Our results reveal the high potential for 3D surface scanners in avian morphometric research, especially for studies necessitating large sample sizes collected by multiple observers, and gives suggestions for formula-based approaches to estimate bill size.

Citation

Sara Ryding, Glenn J. Tattersall, Marcel Klaassen, David J. Wilkinson, Matthew R. E. Symonds 2024. Measuring avian bill size: comparing and evaluating 3D surface scanning with traditional size estimates in Australian birds. Journal of Avian Biology, 2024 e03248. https://doi.org/10.1111/jav.03248

Animal Behaviour Society Presentation

/ gtattersall

Melanie Denommé (PhD student in the lab) is attending the Animal Behaviour Society meeting today, presenting on her PhD research, entitled “Enclosure style preferences are influenced by experience in bearded dragons (Pogona vitticeps)“.

She shows some intriguing results about how early life exposure to different housing conditions alters subsequent preference tests for how bearded dragons interact with enrichments!