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 (VTMax; 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 VTMax in species' ranges.

[Location] South America.

[Taxon] South American pitvipers of the genera Bothrops and Bothrocophias.

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

[Results] Mean VTMax 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 VTMax 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 VTMax.

This study benefited from grants from the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP; 2023/14087-2, 2015/20215-7, 2018/14091-1, and 2020/12658-4); the H2020 MSCA (897901) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brazil (CAPES)—Finance Code 001. MM thanks Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for a fellowship and a grant (309772/2021-4).

Peer reviewed