Biology subjects

Navas, C. A.

Publications and source records attributed to Navas, C. A..

3 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

Environmental Detection of the Amphibian Chytrid Fungus in Water Bodies Predicts Host Infection Along a Deforestation Gradient

Understanding pathogen dynamics during environmental life stages is vital for comprehending wildlife diseases, especially for those with a free-living phase. In amphibians affected by the chytrid fungus Batrachochytrium dendrobatidis (Bd), most studies have focused on host-pathogen interactions, with less emphasis on Bds environmental stage. We tested whether the distribution of Bd in natural aquatic environments can predict host infection patterns. We sampled four tropical amphibian species across eight rainforest landscapes with varying habitat loss, testing whether environmental and host Bd detection varied along gradients of habitat change. Using a high-capacity water filtration method coupled with digital and real-time PCR detection assays, we quantified Bd in water and amphibian samples. Our results revealed a strong positive correlation between Bd DNA concentrations in water samples and infection loads on amphibian skin samples. Forest cover and habitat split were the primary predictors of Bd distribution in both free-living and host-associated forms. We identified Bd-GPL and Bd-Asia-2/Brazil lineages across our study landscapes. Our study introduces and validates a robust protocol for detecting Bd in environmental samples, with the potential to enhance monitoring and inform management strategies. Moreover, our work contributes novel, well-replicated spatial data on Bd associations between hosts and their environments.

ecology↗

bioRxiv2021

Thermal boldness: Volunteer exploration of extreme temperatures in Drosophila melanogaster

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.

animal behavior and cognition↗