Ecophysiology of neotropical amphibians and reptiles: lessons learned from Colombia.

Ecophysiology and herpetology share a close historical relationship, but earlier work at the interface of these disciplines was carried out in temperate regions. Tropical regions like the Neotropics exhibit the highest species richness for amphibians and reptiles, but the pace for ecophysiological research on tropical herpetofauna has been slower relative to temperate counterparts. We are a group of early-career, Latin American researchers interested in the physiological diversity exhibited by neotropical herpetofauna. As such, we have engaged in the organization of the Symposium on the Ecophysiology of Neotropical Amphibians and Reptiles (ECOPHYSHERP) to integrate the scientific community interested on these topics. ECOPHYSHERP has been held three times already within the Colombian Congress of Herpetology, and collectively it has hosted >60 contributions from researchers at 26 institutions and eight countries. Participation has been diverse in terms of gender, age, and career stage, but most participants have been young undergraduate biology students. This generation of early-career researchers is producing excellent research in a broad range of topics, but difficulties to convert this research into scientific publications may exist. Identifying and contributing in order to solve such problems are priorities for this organizing committee, and also our endeavours towards ECOPHYSHERP 4.0 in Santa Marta in 2025.

Thermal boldness: Volunteer exploration of extreme temperatures in fruit flies.

A dominant perception is that small and motile ectothermic animals must use behavior to avoid exposure to critical or sub-critical temperatures impairing physiological performance. Concomitantly, volunteer exploration of extreme environments by some individuals may promote physiological adjustments and enhance ecological opportunity. Here we introduce to the literature a Thermal Decision System (TDS) which is fully modular, thermally stable, versatile, and adaptable to study navigation through thermal landscapes in insects and other small motile animals. We used a specific setting of the TDS to investigate volunteer navigation through critical cold and hot temperatures in Drosophila melanogaster. We demonstrate that a thermally bold behavior (volunteer crossings through a Critical Temperature Zone, CTZ) characterized a fraction of flies in a sample, and that such a fraction was higher in an outbred population relative to isofemale lines. As set, the TDS generated a thermal gradient within the cold and hot CTZs, and the exploration of this gradient by flies did not relate simply with a tendency to be thermally bold. Mild fasting affected thermal exploration and boldness in complex manners, but thermal boldness was evident in both fasted and fed flies. Also, thermal boldness was not associated with individual critical temperatures. Finally, some flies showed consistent thermal boldness, as flies that performed an extreme thermal cross were more likely to perform a second cross compared with untested flies. We hypothesize that a simple "avoidance principle" is not the only behavioral drive for D. melanogaster facing extreme temperatures over space, and that this pattern may characterize other small motile ectothermic animals with analogous natural history. The physiological correlates, genetic architecture, and interspecific variation of thermal boldness deserve further consideration.

Fungal infections lead to shifts in thermal tolerance and voluntary exposure to extreme temperatures in both prey and predator insects.

Pathogens can modify many aspects of host behavior or physiology with cascading impacts across trophic levels in terrestrial food webs. These changes include thermal tolerance of hosts, however the effects of fungal infections on thermal tolerances and behavioral responses to extreme temperatures (ET) across trophic levels have rarely been studied. We examined how a fungal pathogen, Beauveria bassiana, affects upper and lower thermal tolerance, and behavior of an herbivorous insect, Acyrthosiphon pisum, and its predator beetle, Hippodamia convergens. We compared changes in thermal tolerance limits (CTMin and CTMax), thermal boldness (voluntary exposure to ET), energetic cost (ATP) posed by each response (thermal tolerance and boldness) between healthy insects and insects infected with two fungal loads. Fungal infection reduced CTMax of both aphids and beetles, as well as CTMin of beetles. Fungal infection modified the tendency, or boldness, of aphids and predator beetles to cross either warm or cold ET zones (ETZ). ATP levels increased with pathogen infection in both insect species, and the highest ATP levels were found in individuals that crossed cold ETZ. Fungal infection narrowed the thermal tolerance range and inhibited thermal boldness behaviors to cross ET. As environmental temperatures rise, response to thermal stress will be asymmetric among members of a food web at different trophic levels, which may have implications for predator-prey interactions, food web structures, and species distributions.

Thermal adaptation revisited: How conserved are thermal traits of reptiles and amphibians?

Ectothermic animals, such as amphibians and reptiles, are particularly sensitive to rapidly warming global temperatures. One response in these organisms may be to evolve aspects of their thermal physiology. If this response is adaptive and can occur on the appropriate time scale, it may facilitate population or species persistence in the changed environments. However, thermal physiological traits have classically been thought to evolve too slowly to keep pace with environmental change in longer-lived vertebrates. Even as empirical work of the mid-20th century offers mixed support for conservatism in thermal physiological traits, the generalization of low evolutionary potential in thermal traits is commonly invoked. Here, we revisit this hypothesis to better understand the mechanisms guiding the timing and patterns of physiological evolution. Characterizing the potential interactions among evolution, plasticity, behavior, and ontogenetic shifts in thermal physiology is critical for accurate prediction of how organisms will respond to our rapidly warming world. Recent work provides evidence that thermal physiological traits are not as evolutionarily rigid as once believed, with many examples of divergence in several aspects of thermal physiology at multiple phylogenetic scales. However, slow rates of evolution are often still observed, particularly at the warm end of the thermal performance curve. Furthermore, the context-specificity of many responses makes broad generalizations about the potential evolvability of traits tenuous. We outline potential factors and considerations that require closer scrutiny to understand and predict reptile and amphibian evolutionary responses to climate change, particularly regarding the underlying genetic architecture facilitating or limiting thermal evolution.

Interactive effects of experimental heating rates, ontogeny and body mass on the upper thermal limits of anuran larvae.

Biological and methodological factors influence the upper thermal limits (UTL) of ectothermic animals, but most factors have been studied independently. Few studies have integrated variables, so our understanding about sources of UTL variation remains fragmentary. Thereby, we investigated synergic effects of experimental protocols (heating rates, ΔTs) and biological factors (ontogeny and body mass) on the UTL on the larvae of two anuran species (Physalaemus nattereri and Boana pardalis), specifically their Critical Thermal Maximum (CTmax). The species displayed slightly different responses to ΔTs: In B. pardalis tadpoles both average and variance of CTmax increased at a fastest ΔT, the same response happened in P. nattereri tadpoles at slow and moderate ΔTs. Also, the CTmax of P. nattereri declined at the end of metamorphosis independently of ΔT, but tadpoles at all developmental stages still displayed higher heat tolerance at the slow ΔT. Finally, we detected small, synergic effects of body mass and ΔTs on the CTmax of both species. In small B. pardalis tadpoles and premetamorphic P. nattereri tadpoles, body mass had a positive effect on CTmax, but only at slow and moderate ΔTs, probably indicating physiological responses. A similar trend was observed in large B. pardalis tadpoles at the fast ΔT, but this result is likely to be influenced by thermal inertia. Our findings contribute to integrate the understanding of factors influencing UTL in small ectothermic animals. This understanding is critical to discuss the physiological component of vulnerability to climate change that is related to acute temperatures.