UC Riverside

Multiple, potentially interacting features of the environment and the phenotype shape the way organisms evolve through adaptation. Ecomorphology aims to understand such intricate relationships between and within environmental and phenotypic variables. In this dissertation I made an integrative analysis of the combined effects of current velocity and predation on the evolution of body shape and life history of fishes.

In the first chapter I made an interspecific analysis of body shape in Gambusia females. As predicted, they showed larger caudal areas in high-predation sites. In contrast, flow was not related to shape but an interaction between flow and predation was detected. Pregnancy reduced the magnitude of phenotypic divergence between females from contrasting predation and flow regimes. These results indicate that adaptation to predation, and to a lesser extent flow, is key to body shape evolution in the genus Gambusia.

In the second chapter I analyzed the macroevolutionary pattern of life history in female Gambusia and its relationship with predation, flow, and latitude. Gambusia females showed a large range of variation in reproductive allocation, number of embryos, and size of embryos whereas they varied little in their mode of maternal provisioning. Contrary to predictions, life history was not related with predation, flow, or latitude. This may indicate that life history traits are more labile than shape traits, and that other factors could be responsible for the variation observed.

In the third chapter I explored more in deep the relationship between flow regime, shape, and life history. I compared populations of Trinidarian guppies from sites with contrasting hydrologies but similar predation regime. Females from sites prone to floods had larger caudal peduncles, which could be useful to escape during a flood. Male shape was not related to flow regime. High-flood sites had females with more babies and higher reproductive allocation, and males maturing at larger sizes. This pattern of life history matches the predicted effect of an in increase in resource abundance under density dependence. In guppies, flood-prone sites may be environments with increased food abundance for the survivors, allowing them to grow larger and invest more in reproduction.