Collaborative Research: The Evolutionary Interplay Between Life-Histories, Morphology, Performance, and Behavior in Trinidad Guppies

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Evolution by natural selection, or the principle of adaptation, was Charles Darwin's proposed mechanism for evolution. Darwin viewed an adaptation as any feature of an organism that arose as consequence of natural selection and enhanced the survival and reproductive potential of the individual. Yet, understanding and empirically documenting the relationship between a particular trait that appears to be adaptive and the factors that selected for the evolution of the trait remains a challenging and controversial task. In the time since Darwin, the main lessons learned from empirical studies of natural selection are that adaptations rarely occur in isolation, but rather are constrained by the function of other interacting traits, and are a ultimately a compromise between integrated aspects of the organism. Accordingly, the study of adaptation requires an understanding of how different traits constrain each other and how they are integrated to produce locally adapted phenotypes. There is only limited empirical evidence for how such constraints are manifested in real organisms. The proposed work will examine how selection acts on the integration of reproductive strategies, body shape, swimming performance, and behavior in natural populations of the guppy, Poecilia reticulata. The guppy is a model organism for the proposed work because it is one of the few organisms where adaptation has been documented. This previous work shows rapid adaptive changes in the reproductive traits of guppies in response to predatory fish. The work proposed here will first document the correlations among reproductive traits, body morphology, habitat use, foraging behavior, and stream type with field observations on female and male guppies from populations that are subject to different selection pressures. It will focus on the combined influences of stream current and predation. Because the reproductive traits of guppies are already known from these sites, the morphological and behavioral results obtained will provide the first data on whether body morphology, foraging behavior, habitat use, and reproductive strategies predictably covary with each other, or whether they vary independently in response to different selection pressures. Guppies will then be reared in the lab under different environments to test the degree to which these trait differences between populations represent fixed genetic differences or phenotypic plasticity. Finally, the proposed work will examine for the first time the consequences of pregnancy on body morphology and locomotion in an aquatic species by measuring how body profile and swimming performance change over the course of the reproductive cycle. Steady and escape swimming performance of gravid females from high and low predation localities will test the consequences of different reproductive allotments on locomotion and how adaptive changes in offspring number may compromise locomotion. By studying how reproductive strategies, morphology, locomotor performance, and behavior interact with each other and collectively respond to different selection pressures, the proposed work will provide a better understanding of the trade-offs faced by live-bearing fish adapting to their local environments.