On the Brink of Change? Environmental Drivers of Voluntary Thermal Maximum in South American Pitvipers

Aim

We test the relationship between the voluntary thermal maximum (VT_Max; the temperature at which an individual actively retreats to a colder site) and geographical/environmental features in the distribution of South American pitvipers. Additionally, we explore the evolution of environmental temperatures and VT_Max in species' ranges.

Location

South America.

Taxon

South American pitvipers of the genera Bothrops and Bothrocophias.

Methods

We experimentally measured the VT_Max of 15 species of South American pitvipers. We explored the relationship between VT_Max and geographical/environmental features (e.g., latitude, topographic complexity and temperature) with PGLS regressions. Additionally, we explored the evolution of maximum (T_Max) and minimum (T_Min) environmental temperatures, as well as the Thermal Niche Breadth (TNB) and VT_Max, using ancestral state reconstruction and testing for phylogenetic signal.

Results

Mean VT_Max values for South American pitvipers clustered primarily within the 34°C–36°C range, exhibiting little variation among species or clades. No significant correlations were found between VT_Max and climatic or geographic variables. Furthermore, our analysis revealed that these snakes are absent from regions where maximum temperatures surpass their preferred thermal tolerances. Ancestral state reconstruction indicated divergent evolutionary pathways for thermal limits among species, independent of phylogenetic relationships.

Main Conclusions

South American pitvipers unexpectedly exhibit similar voluntary thermal maximum values across a wide range of habitats and despite distinct phylogenetic relationships. Our results indicate that there is no strong climatic niche conservatism for South American pitvipers, with a likely weak selective pressure of VT_Max.