I am interested in understanding the evolutionary processes that generate differences in behaviour between individuals (personalities) in response to life experiences and environmental stressors. The central question of my study is "How do behavioural traits develop as a consequence of different experiences during ontogeny?" Specifically, I focus my research on the link between ecological stressors (biotic and abiotic), individual behavioural types, and metabolic rates. My main hypothesis is that behavioural variations among ontogenetic transitions can be predicted and modulated as a function of behavioural type, environmental stressor, and time. To test this hypothesis I will investigate: i) the role of several environmental stressors in modulating the relationship between physiology and behaviour (within individuals); ii) the susceptibility of environmentally-induced behavioural changes among different moments of the lifetime (within individual); and iii) the heritability of life experience through generations (between individuals). The eastern mosquitofish (Gambusia holbrooki) is the principal model species that I am using to conduct behavioural, metabolic, and life-history measurements, using a combination of field and laboratory studies. Positive empirical evidence could be essential in predicting animals' responses to human-induced environmental changes and diffusion of non-native species.