climate-change

Why leave the water if you are a fish?

/ gtattersall

Despite being a major event in early tetrapod evolution, many living fish species occasionally leave water, but the reasons are not always obvious. Some do it to feed, some to escape predation, and some to cope with poor water quality, although rarely for long periods of time. Another intriguing possibility is that fish may use land to help regulate their body temperature.

The mangrove rivulus (Kryptolebias marmoratus) is a particularly good species to explore this question. This small tropical fish is famous for its ability to survive on land for weeks at a time, provided the humidity levels are high. When water gets warm, mangrove rivulus will often emerge onto land, where evaporative cooling can rapidly lower body temperature, as we showed previously (https://doi.org/10.1098/rsbl.2015.0689). But leaving the water also comes at a cost: gas exchange becomes much more difficult, leading to temporary oxygen limitation and CO₂ buildup.

The mangrove rivulus fish (Kryptolebias marmoratus), is typically found in areas with Red Mangrove trees, like Florida, Mexico and Brazil. (Photo from Dr. Andy Turko)

In many ectotherms, low oxygen levels are known to shift thermal preferences toward cooler temperatures. That led us to ask a simple question: when rivulus go onto land, do they actively seek cooler temperatures than they would in water? 

To test this, we (former Honours students Katlyn Dundas and Philip Bartel) gave fish access to choice of temperatures along a thermal gradient under three conditions: water only, land only, or a combination of both. What we found was striking. Rivulus only selected cooler temperatures when they were on land. When confined to water, their preferred temperatures remained higher, even when the same thermal options were available.

This suggests that their terrestrial emergence is not simply a passive escape from warm water to benefit from evaporative cooling. Instead, fish on land appear to actively choose cooler environments, which is a response consistent with anapyrexia, the deliberate reduction in the regulation of body temperatures (analogous but quite different from fever). In this case, leaving the water may help offset the physiological challenges of breathing air through gills that are adapted for water.

Together, these results add a new piece to the puzzle of why some fishes venture onto land. For mangrove rivulus, emerging from water may provide more than just temporary cooling. It may fundamentally change how they regulate temperature when oxygen becomes limiting.

The study is now available at the Journal of Experimental Biology website, citation below.

Citation

Dundas, KE, Bartel, PB, Turko, AJ, and Tattersall, GJ. 2026. Terrestrial emergence reflects lower thermal preferences in the mangrove rivulus (Kryptolebias marmoratus). Journal of Experimental Biology, 229 (4): jeb251829. https://doi.org/10.1242/jeb.251829

Many thanks to Brock University Library open access fund for supporting publication in the Journal of Experimental Biology!

Smooth scatter plot of mangrove rivulus space use within the thermal gradient chamber and depicting the three conditions tested.

Handle with care: when measuring temperature changes the temperature

/ gtattersall

Measuring body temperature should seem straightforward, but in ectotherms, the act of measuring can be part of the problem. For especially small amphibians in particular, common approaches like cloacal thermometry require restraint and direct contact, raising the possibility that handling itself alters body temperature before it is even recorded. In this study, we asked a simple but important question: does brief, gentle handling measurably change the body temperature of salamanders?

Using infrared thermography, we examined how short periods of handling affected skin temperature in two closely related mole salamanders, the blue-spotted salamander (Ambystoma laterale) and the spotted salamander (A. maculatum). We also combined field measurements with controlled laboratory experiments to tease apart the effects of physical contact, heat transfer, and behaviour.


The answer was clear. Even short handling periods caused salamanders to warm rapidly. In the field, handled animals were consistently warmer than unhandled controls, with the head warming more than the rest of the body. Not surprisingly, smaller salamanders showed larger temperature changes, suggesting body size plays an important role in how quickly heat is gained.

Change in skin temperature of yellow spotted salamanders either handled or placed on a warm plate (set to the same temperature as human handler).



In the lab, salamanders placed on a warm surface (set to hand temperature) also warmed up, but not as much as animals that were actually handled. This tells us that handling is not simply about contact with something warm. While we don’t know precisely why yet, the most likely explanation is that salamanders manifest a stronger cardiovascular response to human handling and the heat that they pick up is transferred more quickly throughout the body.

Temperature changes matter from a behavioural perspective. Warmer salamanders were more likely to become active, regardless of whether that warmth came from handling or from contact with a warm surface. That means handling can influence not only the temperature we measure, but also the behaviour we observe.
Taken together, these results highlight a subtle but important issue: brief handling can rapidly alter body temperature, sometimes at rates comparable to experimental heat stress studies. For researchers, this has implications for data accuracy in thermal biology. More broadly, it is a reminder that even well-intentioned, gentle handling can have unintended physiological effects, especially for small ectotherms.

Some caveats: this study is not to be interpreted as alarmist. Warming up from being in contact with warm temperatures is a pretty obvious expectation. These results would only have possible impacts for studies concerned with accurate temperature measurements or those that perform very brief behavioural observations during or immediately after handling (which is probably very rare) that are temperature dependent. And as one of the reviewers of the manuscript rightly pointed out, we measured surface temperatures, which will differ and lag with core temperature measurements.

We do note that there is a related study appearing in the same issue of the Journal of Thermal Biology highlighting similar cautions as this one, and that particular study actually measures core temperature of really tiny frogs!

Citation

Giacometti, D, Montes, LF, Denommé, M, Andrade, DV, and Tattersall, GJ. Handle with care: the thermal consequences of short-term handling in mole salamanders. Journal of Thermal Biology, 136: 104390. https://doi.org/10.1016/j.jtherbio.2026.104390

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