Effect of environmental factors on inter-individual differences in Engystomops pustulosus and Xenopus laevis tadpole behaviour

Abstract

Inter-individual differences in behaviour contribute to the raw material on which natural selection can act and have important ecological and evolutionary consequences for a population. Behaviour can vary at the among and within individual levels and can occur at multiple hierarchical levels. Among individual differences include how variable individuals are in their mean behaviour, their responsiveness to changes in ecological context (behavioural plasticity) and their level of behavioural predictability. Traits may also be correlated at the among and within individual levels. In this thesis, I examined how different environmental factors can cause inter and intra individual variation in activity, neophilia, exploration and predatory risk-taking behaviours. These environmental factors included 1) local adaptation to human disturbance, 2) interactions with conspecific and heterospecific competitors during early development and 3) the availability of food during early development. I looked at these effects in two anuran tadpole species, Xenopus laevis and Engystomops pustulosus.

My results showed that anthropogenic disturbance increases among individual variance in activity and predictability of neophilia behaviours and that these behavioural changes may have a genetic basis. In response to competition, tadpoles facing heterospecifics increased among individual variance in initial activity but those facing conspecifics became more predictable in activity. These specific patterns of individual level variance may minimise the costs of competition when foraging amongst different competitor species. In response to food availability, multiple hierarchical levels of individual variance were impacted in opposing ways. In activity, high feed tadpoles showed greater variation in their behavioural plasticity and predictability compared to low feed tadpoles. Low feed tadpoles also showed increased among individual variation in initial levels of exploration. Thus, the response to food availability was highly trait specific, even when both traits shared a common activity-based component.

In taking a hierarchical and multi trait approach to individual level variation, we can better understand how populations and the individuals they contain may be unconstrained or restricted in their behavioural response towards future selective challenges or early developmental conditions. This may help inform the future evolutionary trajectory of populations which face a diverse set of environmental challenges.