Convergent and Divergent Effects of Natural Selection on Color Patterns in Two Fish Faunas

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Abstract
This study of Poecilia and Phalloceros shows that, at least for color patterns, there may not be a single optimum design because there is more than one way to be cryptic to predators and attractive to mates; and predation intensity changes from place to place, so the optimum color pattern parameters vary geographically. Because visual selection by predators appears to be operating according to the same rules in northern and southern South America, the response to varying predation intensities is very similar in both species. The differences are presumably related to historical differences in the genetic and social systems of guppies and Phalloceros, and differences in the background color patterns in the streams. In order to understand natural selection it is necessary to understand the mechanisms, and try to make predictions of its outcome in previously unstudied species.