Date of Award


Level of Access Assigned by Author

Open-Access Dissertation

Degree Name

Doctor of Philosophy (PhD)


Biological Sciences


Michael T. Kinnsion

Second Committee Member

William Glanz

Third Committee Member

Andrew Hendry


In this dissertation I quantify spatial and temporal variation in the pattern and strength of natural selection in wild populations of Trinidadian guppies (Poecilia reticulata), and assess the demographic costs of ongoing contemporary evolution in the form of selection against migrants. First, I describe the results often mark-recapture experiments to test hypotheses concerning the role of natural selection in geographic patterns of trait variation. Previous work has reported that guppies inhabiting high- and low-predation sites differ in both body shape and color. These patterns of phenotypic variation have been theorized to reflect differences in the balance between functional trade-offs among various aspects of performance. For example, natural selection is hypothesized to disfavor bright male color (owing to predation) and sexual selection is hypothesized to favor bright color (owing to female choice). My results support some of the predictions generated from considering these functional trade-offs. However, for many color and shape traits, my results do not support the prediction that viability selection is weaker in low-predation experiments. Instead, some of the most intense bouts of selection occurred in low-predation experiments. My results illustrate considerable spatiotemporal variation in selection among experiments. It seems more complex selective interactions, possibly including the indirect effects of predators on variation in mating behavior, as well as other environmental factors, might be required to more fully explain patterns of color and shape variation in this system. Second, I quantify the demographic costs of ongoing contemporary evolution. Fine-scale genetic diversity and contemporary evolution can theoretically influence ecological dynamics in the wild. Such eco-evolutionary effects may be particularly relevant to the persistence of species facing acute or chronic environmental change. One way that ongoing evolution may influence the dynamics of threatened populations is through the role that selection plays in mediating the "rescue effect", the ability of migrants to contribute to the recovery of populations facing local disturbance and decline. I combined field experiments with natural catastrophic events to show that ongoing evolution is a major determinant of migrant contributions to population recovery in Trinidadian guppies.