Phenotypic variation in male guppies from natural inland populations: an additional test of Haskins' sexual selection/predation hypothesis

Abstract

In Venezuela, guppies,Poecilia reticulata, are found in a diversity of aquatic ecosystems fringing the western slope of the eastern Andes. These inland drainages are associated with large between-site variation in both physical and biotic environments. Numbers of potential guppy predators vary greatly between low diversity piedmont streams and high diversity llanos swamps. We analyze geographic variation in several phenotypic traits associated with conspicuousness of male guppies as an independent test of Haskins' (Haskins et al. 1961) hypothesis of natural balance between sexual selection (driving male conspicuousness) and predation (driving crypsis). Four sites were compared: a diverse llanos swamp (high predation), two Andean piedmont streams (intermediate and low predation), and a spring pool located south of Venezuela's Paria Peninsula (no aquatic predators). Because tropical wet and dry seasons are associated with varying degrees of environmental change at these sites, within-site seasonal samples provided an additional test of the role of selective predation on Male phenotypes. Phenotypic traits associated with both size and coloration supported the sexual selection/predation hypothesis. male guppies from the spring were generally more colorful than male guppies from inland drainages. Males from the diverse swamp site were smaller and less colorful than guppies from other sites. Males from the swamp population were smallest and least colorful during the early dry season, when diurnal aquatic piscivores were more diverse and abundant. Dominant spot pigments at each site were generally those that provided greatest contrast with the predominant environmental background color, lending further evidence that coloration patterns in male guppies enhance conspicuousness.