Question

EVOLUTION CLASS

How does natural selection interact with sexual selection and affect traits such as color brightness in a guppy male population?

Answer 1

The guppy (Poecilia reticulata), a polyandrous livebearing fish, is a model organism in the study of sexual selection. This species exhibits sexual dimorphism, such as male body coloration (orange, black, or iridescence color spots). Although there is evidence of a preference for colorful males in female mate choice, a wide variation in male color patterns is found even in a population. Recently, there has been an increase in studies examining the postcopulatory processes involved in sperm competition and cryptic female choice in this species. If male traits that favor sperm competition and/or cryptic female choice correspond with traits preferred in female mate choice, then postcopulatory processes will reinforce the selection to colorful males. In contrast, if males with traits preferred by females are not favored by sperm competition and/or cryptic female choice, then postcopulatory processes will weaken the selection to colorful males. In this paper, I review studies of the relationships between male guppy coloration and female mate choice, sperm competition, and cryptic female choice, and discuss the possible factors that maintain the variation in male coloration.