Evolution of individual behavioural plasticity and behavioural syndromes

Abstract

The study of behavioural variation and covariation has become very popular in the last decade. And yet the evolutionary tools used to understand how selection and genetic and environmental variation shape individual difference in behaviours remain underused. In this thesis I seek to advance the study of animal personality using the tools of multivariate selection analysis, phenotypic plasticity and quantitative genetics. Here I studied multiple behavioural traits in two water strider (Heteroptera:Gerridae) species, Tenagogerris euphrosyne and Gerris gracilicornis, and examined individual variation in behaviour and behavioural plasticity over time and across situations. I also estimated multivariate linear and nonlinear sexual selection on behavioural traits and on individual behavioural plasticity. Under scramble competition, water strider males differed in their sexual behaviours and their plasticity across social contexts (Chapter 2). The level of age-related behavioural plasticity also varied according to the type of behaviours and rearing environments (Chapter 3). Individual variation in behavioural plasticity over time or across situations significantly affected individual fitness (Chapter 2 and 3). However, with the exception of same-sex behaviour of males, there was little genetic variation in behavioural plasticity across development conditions (Chapter 4). I then tested the hypotheses that correlated behaviours (i.e. behavioural syndrome) evolve via correlational selection when certain behavioural combinations enjoy greater fitness than others. I found that current patterns of correlational selection were not likely to drive or maintain the observed correlations underpinning the behavioural syndrome (Chapter 5- 7). While much can be learned about behavioural syndromes and variation in behaviours by resolving the basis of behavioural plasticity, a more complete understanding of how behavioural variation and covariation arise might be provided by focusing on physiological and genetic mechanisms as well as contemporary patterns of multivariate selection.