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Examining Evidence for Phenotypic and Genetic Convergence in the Guppy (Poecilia reticulata)

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Convergent evolution of a trait can occur at interspecific or intraspecific levels. Traits that are convergent within species are predicted to have a similar genetic basis due to recently shared ancestry. However, it is unclear how likely it is to find similar genetics during cases of rapid evolution or evolution on historic timescales. My dissertation examines evidence for phenotypic and genetic convergence in guppies, which are found in recently-introduced and historically-existing sites that differ in predation regime. I use ornamental tail coloration as it varies highly among developmental stages within an individual, males and females, individuals within a site, and between sites.

In Chapter one, I demonstrate that color develops in a consistent order among males from different predation regimes and I propose that early maturing males are the ideal stage for future experiments. In Chapter two, I determine that black melanin-related genes are likely candidates for genetic differences among fish varying in the presence of ornamental coloration. In Chapter three, I find evidence that phenotypic color pattern differences during rapid evolution follow a mixture of unique and similar trajectories based on current selective environment experienced. The color gene differences exhibit partial molecular convergence, indicating that guppies maintain variation within and between sites. In Chapter four, I discover phenotypic color pattern similarity among independently derived drainages and predator communities with substantial genetic divergence. I find a lack of molecular convergence in the identity of differentially expressed color genes among geographic locations. Taken together, these results suggest that the scale at which convergence is examined is very important. Sites may exhibit an overall signal for convergence, but may also follow slightly different trajectories upon closer examination. Convergent evolution of a trait should not be considered as being entirely present or not present, but rather a mixture of contingent and similar evolutionary processes acting at the level considered.

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