Effects of elevated temperatures and prolonged thermal stress on physiology and behaviour of the American bullfrog (Lithobates catesbeianus): correlations between stress physiology and animal personality

Author(s)

Diego Pereira Nogueira da Silva

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2022-10-06

Examining board members

Fernando Ribeiro Gomes; Hilton Ferreira Japyassú; Patricia Izar Mauro

• Advisor: Fernando Ribeiro Gomes

Abstract

Anthropogenic environmental change, particularly, climate change, is one of the most important factors associated with the great biodiversity crisis observed in the past few decades. It is known that rises in average global temperature are associated with stress responses at the hormonal and behavioural levels in several species in the wild, and that ectotherms are especially vulnerable to these changes. Recently, the study of animal personality (consistent interindividual differences in behaviour) e its importance to understand how animals cope with stressors, and the implications of this behavioural consistency for conservation has gained a lot of attention. In this work, I investigated the existence of personality differences and how they interact with stress physiology in the American bullfrog (Lithobates catesbeianus) when animals are exposed to elevated temperatures for long periods of time. For each animal, I measured exploration and boldness multiple times before and after exposure to high temperatures, and I also measured plasma concentrations of corticosterone (CORT) and testosterone (T) throughout the experiment. Elevated temperatures were shown to be a potent stressor for the bullfrogs. Animals exposed to thermal stress had higher levels of CORT and lower levels of T throughout the entire experiment (∼7 weeks). Furthermore, individuals were consistent both in measures of boldness as well as exploration, indicating the existence of personality traits. However, there was no evidence for a boldness-exploration behavioural syndrome. Personality differences were responsive to increases in temperature, with long-term (across contexts) consistency being lowered for exploratory variables and increased for boldness. Finally, animals with higher plasma concentration of CORT and lower concentration of T explored their environment faster and were more risk-averse (shy), and shy individuals also had a larger loss of body condition throughout the experiment. These results might indicate that shyer animals are more vulnerable to climate change in this species, with possible negative impacts arising from elevated temperatures in reproduction and survival in a natural setting. This was the first time that differences in personality were correlated with possible underlying proximate mechanisms in a species of amphibian, which are notably understudied in personality literature. Given that amphibians are currently the most vulnerable vertebrate group in the context of climate change, studies investigating interactions between personality differences and environmental change are likely to be very promising in aiding programmes for management and conservation of endangered species. (AU)

• FAPESP's process: 18/12773-8 - Behavioural analysis of the American bullfrog (Lithobates catesbeianus): personality, behavioural syndromes and the effect of chronic exposure to thermal stress on behaviour
• Grantee: Diego Pereira Nogueira da Silva
• Support Opportunities: Scholarships in Brazil - Master