Life history variation in recently established populations of western mosquitofish (Gambusia affinis)

We report life history characteristics for 4 recently established populatio ns of western mosquitofish (Gambusia affinis). Mosquitofish from thermally stable habitats, Bonham and Garrett, were characterized by maturity at larg e sizes, high fat reserves, and large embryos. In contrast, females from a thermally unstable habitat, Wabuska, matured at small sizes and had low fat reserves and small embryos. Females from Parker, a site with no appreciabl e thermal input, matured at intermediate sizes and had low fat reserves as well as large embryos. These populations shared a common ancestor in 1937: therefore, these results suggest either phenotypic plasticity or rapid evol ution.