Life History of Brachyraphis rhabdophora (Pisces: Poeciliidae)

Abstract

We describe the life-history pattern of Brachyraphis rhabdophora from several Costa Rican locations. This species is nonsuperfetating, meaning that it carries only one brood of developing young at a time. They are also lecithotrophic (ovoviviparous), meaning that there is no evidence of maternal provisioning of the young after the eggs have been fertilized. These female life-history traits are typical of other species in the tribe Gambusiini, as illustrated with a multivariate analysis. We also found considerable variation among populations for offspring size, fecundity, reproductive allocation, and fat content of the females. The size distribution of mature males was bimodal in two of four samples, significantly skewed in a third, and normal in a fourth. Because there is believed to be little growth after maturity, bimodality suggests genetic polymorphism for age and size at maturation, as described for other species of Poeciliidae. Avirtue of comparative studies is that they allow one to perceive patterns that are not attainable in any other fashion. This is true because compiling data from a large number of species reveals a range of variation not found within any one species. It is then possible to generate testable hypotheses for the evolution of these patterns and develop the appropriate