Hybrid zone dynamics are influenced by genotype-specific variation in life-history traits: experimental evidence from hybridizing Gambusia species

Abstract

Results from two experiments are presented that contrast differences in life-history traits and population dynamics between two species of live bearing fishes (Gambusia affinis and G. holbrooki) that hybridize across portions of the SE USA. Affinis populations consistently exhibited smaller population size, lower carrying capacity, lower recruitment, and larger over-winter mortality than did holbrooki or mixed populations. Evidence for density-dependent reductions in fecundity and concomitant increases in juvenile mortality rates were observed in all populations, but were most pronounced for affinis populations. Genotype-specific differences in life-history traits appear to confer differential advantage to offspring of parental holbrooki origin and F1 progeny of holbrooki maternal parentage given the resource availability and the age structure and densities experienced during these experiments. -from Author