Life-History Evolution in Guppies (Poecilia reticulata: Poeciliidae). V. Genetic Basis of Parallelism in Life Histories

Abstract

We document a genetic basis for convergent life-history evolution in guppies from high- and low-predation sites on the north slope of the Northern Range Mountains of Trinidad. In previous work, we showed that guppies from high-predation sites on the south slope attained maturity at an earlier age and smaller size; produced more, smaller offspring per litter; and had higher reproductive efforts than their counterparts from low-predation localities. The south slope has predators derived from a mainland South American fauna. These predators are absent from the north slope drainages and are replaced by species derived from a marine fauna. Nevertheless, the same contrast between high- and low-predation sites appears to exist. In a companion article we demonstrate differences in the life-history phenotypes of guppies from high- versus low-predation localities on the north slope. The patterns are similar to those on the south slope for almost all dependent variables. A study of life-history phenotypes is based on wild-caught individuals, so any observed differences in life histories can be attributed to environmental effects. The virtue of such an investigation is that it is possible to efficiently survey a large number of populations from a wide geographical area. In the current study, we evaluate the life-history genotypes of guppies from two high- and two low-predation localities. We reared guppies for two generations in a common environment, then compared the life histories of individuals reared on controlled levels of food availability. This methodology allows us to evaluate more components of the life history than is possible in a study of life-history phenotypes, including age at maturity and reproductive effort, and to conclude that these differences have a genetic basis; however, it is limited in the number of populations that can be evaluated. A combination of the geographical breadth of the first study and the greater depth of this study provides a more complete picture of interpopulation variation in guppy life-history patterns.