Research: Ecological Genetics of Color and Size Polymorphism in Guppies

Guppies show extreme variation in the color patterns of males. The picture above shows three females from a natural population in Trinidad (middle panel), and six males from the same population (left and right panels). Each male is essentially unique in his color pattern, and this variation is almost entirely genetically based. The genetic variation in color pattern is so extreme it is likely to be actively maintained by some form of balancing selection (Hughes et al 2005).

Frequency dependent selection operating either through mating success or differential survival is a potential mechanism for the maintenance of variation. We are currently conducting experiments to investigate the effects of male color pattern on mating success and survival. Female guppies may be attracted to the uniqueness of individual males. In this situation, the reproductive success of a male with a particular pattern would be inversely proportional to the frequency of the pattern. Alternately, predators may form search images for common phenotypes in the population. Males with a rare or novel color pattern might therefore have a survival advantage. We have obtained evidence for frequency dependent mate choice in laboratory studies (Hughes et al. 1999), and for frequency dependent survival in natural populations (Olendorf et al., ms. in preparation), so it is possible that selection maintains variation by acting on both survival and reproduction. We are currently evaluating molecular paternity data from manipulative field experiments in order to determine of rare phenotypes have a reproductive advantage in nature.  

Created 08/01/01
Updated 08/01/01