Breeding cycles in natural populations of Xiphophorus nigrensis, X. multilineatus, and X. pygmaeus

" Poeciliid fishes are well studied in relation to demography and life-history evolution (Stearns, 1978; Constantz, 1979; Reznick and Miles, 1989); one of the critical variables in these studies is the breeding cycle. Therefore, it is surprising that, for most of the species in this family, breeding cycles in nature have not been documented. A series of studies on the alternative mating strategies in Xiphophorus nigrensis have shown that body size is correlated with mating strategy (Ryan and Causey, 1989), that variation in body size is due to a genetic polymorphism at the pituitary (P) locus (Kallman, 1984, 1989), and that the fitnesses of the two mating types are equal (Ryan et al., 1992). It was important to determine whether breeding was continuous or discrete in order to design an appropriate model to test the hypothesis of equal fitnesses of two mating strategies in this species. In the present study, we determine female breeding cycles in three species- Xiphophorus nigrensis, X. multilineatus, and X. pygmaeus- and discuss the relationships between brood size, female size, and time of year "