# Thermal Tolerance and Preferred Temperature in the Critical Endangered Montseny Brook Newt (Calotriton arnoldi)

## TL;DR

This study examines the thermal tolerance and preferred temperature of the critically endangered Montseny Brook Newt, revealing its ability to survive extreme temperatures and its variable thermopreference.

## Contribution

The study provides the first thermal physiology data for the critically endangered Montseny Brook Newt subspecies.

## Key findings

- The CTmax of the species exceeded 31 °C, with significant differences between subspecies.
- The species tolerates low temperatures (<1 °C) well, likely due to adaptation to cold waters.
- Thermopreference ranged from 11.7 °C to 21.6 °C, showing some individuals prefer higher temperatures.

## Abstract

Thermal tolerance and preferred temperature experimental procedures were conducted on the western and eastern subspecies of critically endangered Montseny Brook newt (C. arnoldi). The results obtained showed that the CTmax of the species exceeded 31 °C, with a significant difference between the two subspecies. We found that the species tolerates low temperatures (<1 °C) well. Although the thermopreference of the species was expected to trend to cold temperatures, some individuals chose relatively high temperatures, obtaining a range of 11.7 °C to 21.6 °C.

Climate change, driven by increased human greenhouse gas emissions since the beginning of the industrial revolution up to the present day, is considered one of the major threats to biodiversity in the twenty-first century. One of the most affected groups is the ectotherms due to their direct dependence on environmental temperatures. In recent years, several studies have analysed the effects of temperature and thermal tolerance on several species of ectotherms. However, there are species whose thermal tolerances are still unknown. Such is the case of the critically endangered species, the Montseny Brook Newt (Calotriton arnoldi), endemic to the Montseny massif in Spain and whose thermal biology is unknown. Its critical situation makes it essential to know its tolerance to cooling, warming and thermopreferendum in water environments where the newt lives. Three experimental procedures were conducted from the western and eastern subspecies of C. arnoldi, considering four classes separately (males, females, juveniles and larvae). The results obtained showed that the CTmax of the species exceeded 31 °C, with a significant difference between the two subspecies. We found that the species tolerates low temperatures (<1 °C) well because the genera Calotriton is adapted to live in cold waters with temperatures below 15 °C. Although the thermopreference of the species was expected to trend to cold temperatures, some individuals chose relatively high temperatures, obtaining a range of 11.7 °C to 21.6 °C. The results presented in this study are an advance in the knowledge of the thermal physiology of this species and support the importance of the temperature of the torrent on its survival. Knowing their thermal limits and their preferred temperature range will help to propose management measures that promote the conservation of streams and riparian forest cover to mitigate temperature increases due to climate change.