Biology subjects

Giacometti, D.

Publications and source records attributed to Giacometti, D..

6 recordsLinked to original sources

bioRxiv2026

When cold-bloods heat up: meta-analytical evidence that climatic variability mediates behavioural fever in amphibians and reptiles

Fever is a widespread and adaptive defence response that enhances immune performance through an increase in body temperature above normal values. In ectotherms, fever is expressed behaviourally through the selection of warmer microhabitats following infection, yet its magnitude and determinants vary widely across species and environments. Here, we performed a phylogenetically informed meta-analysis of behavioural fever in amphibians and reptiles to test whether its expression was shaped by climatic thermal variability, pathogen identity, and taxonomy. Specifically, we tested the hypotheses that (i) species from thermally variable environments would exhibit stronger behavioural fever than species from thermally stable environments, consistent with the climate variability hypothesis, and that (ii) reptiles would exhibit stronger fever responses than amphibians due to lower hydrothermal constraints. Across 47 studies encompassing 103 effect sizes, we found that behavioural fever is widespread but highly context-dependent. We found that evidence for behavioural fever was strongest in species from more thermally variable habitats, regardless of body size and phylogeny, suggesting that access to thermally heterogeneous landscapes and enhanced behavioural plasticity amplify the capacity to sustain febrile responses. Contrary to our hypothesis, amphibians exhibited stronger fever responses than reptiles, possibly reflecting differences in baseline thermoregulatory demands and environmental opportunity, or as a consequence of methodological artefacts. The expression of behavioural fever also varied with pathogen identity, with bacterial infections eliciting larger body temperature increases than fungal or viral challenges, although pathogen representation was uneven across studies. Together, our results support the idea that the capacity to express behavioural fever depends on access to thermally heterogeneous landscapes, and may vary according to pathogen biology. Ultimately, our study emphasises that temperature is not a background condition for host-pathogen interactions, but an active and environmentally contingent component of ectotherm immune defence in amphibians and reptiles.

physiology↗

bioRxiv2025

Operative temperatures of Eastern Garter Snakes (Thamnophis sirtalis sirtalis) reveal a Goldilocks effect for habitat use

Garter snakes (Thamnophis spp.) are the most widespread reptiles in North America, although evidence suggests that thermal preference has not diverged much among populations or Thamnophis species. To shed light on how thermal decisions influence local habitat use by the eastern garter snake (Thamnophis sirtalis sirtalis), we measured the thermal profiles of three habitats differing in canopy cover: open peat, mixed shrub, and closed forest. We installed biophysical models to record operative temperatures at a fine scale and assess habitat thermal quality. We also used coverboards to survey habitat usage. While the open canopy offered the highest thermal quality, we recorded the greatest number of snakes in the mixed shrub which had a lower thermal quality. Since environmental temperatures regularly exceeded the upper thermal limit of T. s. sirtalis in the open canopy, snakes might favour the use of habitats that minimise the odds of overheating. Therefore, open habitats potentially restrict snakes activity window and may not be thermally attractive. Our data show that T. s. sirtalis use habitats that vary in thermal quality, but warmer habitats are not necessarily better. Rather, snakes preferentially seek areas that offer a mix of open and closed canopies to suit their thermoregulatory needs.

ecology↗

bioRxiv2025

Sub-zero temperatures during early spring migration in blue-spotted salamanders (Ambystoma laterale)

Amphibians that reproduce in early spring at northern latitudes may encounter environmental ice while migrating to their breeding sites. Due to the nucleation properties of ice, contact with environmental ice may induce rapid freezing of body tissues, which can cause irreversible damage to cells and lead to death. Although some species of salamanders are known to move over ice during early spring migration, freeze-intolerant species are expected to avoid physical contact with ice crystals to minimise the risk of freezing. Here, we documented the thermal biology of the freeze-intolerant blue-spotted salamander (Ambystoma laterale Hallowell, 1856) migrating at sub-zero temperatures in Algonquin Provincial Park, Ontario, Canada. During our surveys, we found sheltered, inactive, and migrating individuals; some in direct contact with ice. Our field measurements of skin temperature using high resolution thermal imaging suggest that A. laterale can sustain activity in a supercooled state (i.e., chilled below the freezing point of body fluids but not frozen). By migrating in a supercooled state, these salamanders may overcome the risk of freezing while simultaneously prolonging their breeding season and potentially avoiding predators.

physiology↗

bioRxiv2025

Regional heterothermy in Megasoma gyas is not related to active heat dissipation by the horns

Animals rely on physiological and behavioral processes to maintain thermal balance. Some animals, however, bear structures that help dissipate excess heat when body temperatures rise. Although widespread in animals, animal weapons--exaggerated morphological structures with multiple characteristics that can make them good at dissipating heat--have rarely been studied in the context of thermoregulation. Here, we investigated whether the horns of the Rhinoceros Beetle (Megasoma gyas) acted as a thermal window. We heated live and dead beetles to 30{o}C and allowed them to cool to 20{o}C while measuring surface temperature changes in four body regions: the cephalic and thoracic horns, the scutellum, and the abdomen. If horns actively dissipated heat, they would show the lowest cooling rate among body regions. Contrary to this expectation, we found that the cephalic horn had the highest cooling rate, followed by the abdomen, thoracic horn, and scutellum, respectively. This suggests that the horns are not used for active heat dissipation in M. gyas. The low cooling rate of the scutellum can be explained by the presence of large flight muscles in the thorax, which play a role in heat generation, but could also aid in heat dissipation by pumping hemolymph across tagmata or through the low-insulated cuticle to prevent thoracic overheating. We also demonstrate that beetles show regional heterothermy even in the absence of exercise or stress. As such, we propose that regional heterothermy may result from both active (control of hemolymph flow) and passive (heat dissipation through poorly insulated structures) processes within individuals.

animal behavior and cognition↗

bioRxiv2025

Behavioural evidence of a humidistat: a temperature-compensating mechanism of hydroregulation

The ability to control hydration state essential for terrestrial species, especially amphibians, which are highly susceptible to dehydration. Here, we examined how temperature (17{degrees}C vs. 22{degrees}C) influenced behavioral hydroregulation in spotted salamanders (Ambystoma maculatum) using a laboratory humidity gradient. Salamanders defended a constant vapour pressure deficit (VPD) between temperatures by targeting higher RH at 22{degrees}C than at 17{degrees}C, possibly to compensate for increased evaporative demand at warmer temperatures. Individuals selecting higher VPDs experienced greater evaporative water loss (EWL), with larger salamanders losing more water than smaller ones after accounting for temperature. Together, these results highlight a trade-off among body size, humidity preference, and desiccation tolerance. Salamanders also rehydrated faster at 22{degrees}C than 17{degrees}C, highlighting temperature-dependent water uptake rates. Our finding that salamanders regulated a constant driving force of evaporation between temperatures suggests the ability to detect rates of EWL. Local cooling of the skin arising from evaporation is a plausible mechanism: if moist-skinned ectotherms allow for a specific, fixed decline in skin relative to core temperature, they can effectively detect the drive for evaporation. Ultimately, our study underscores the complexity of amphibian hydroregulation and emphasises the role of behaviour in maintaining hydration state.

animal behavior and cognition↗

bioRxiv2024

Seasonal variation of behavioural thermoregulation in the Spotted Salamander (Ambystoma maculatum)

Mounting evidence suggests that 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 when tested in laboratory thermal gradients. In this study, we evaluated how temperature selection (Tsel) and behavioural thermoregulation differed between seasons in the fossorial Spotted Salamander (Ambystoma maculatum). By comparing thermoregulatory parameters between the activity and overwintering seasons, we provide evidence that A. maculatum engages in active behavioural thermoregulation despite its fossorial habit. In both seasons, we found Tsel to be consistently offset higher than prevailing thermal conditions. Thermoregulation differed between seasons, with salamanders having higher Tsel and showing greater evidence of thermophilic behaviours in the active season 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, our study provides a broader understanding of thermoregulation in amphibians, particularly in the context of behavioural responses to seasonality in fossorial species. Summary statementBy comparing thermoregulatory parameters between seasons, we demonstrate that the Spotted Salamander engages in active behavioural thermoregulation despite being fossorial.

animal behavior and cognition↗