MULTIPLE MATING IN XIPHOPHORUS BIRCHMANNI, A LIVE-BEARING SWORDTAIL FISH

Abstract

Male and female mating behaviors have been extensively studied in Xiphophorus birchmanni; however the genetic mating system has not been characterized in this species. X. birchmanni is a live-bearing fish, so females can be easily collected with their young. Gravid females were collected from two populations of sheepshead swordtail, X. birchmanni in the state of Hidalgo, Mexico. To determine if female phenotype is related to number of mates, we examined female body size, number of offspring, and number of mates. We used four polymorphic microsatellite markers to genotype 40 wild caught X. birchmanni females and their offspring. COLONY was then used to assign parentage and estimate the rate of multiple mating (Wang 2004). From our analysis, we can conclude that X. birchmanni females mate multiply at rates between one and eight male sires per brood. There was also a positive correlation between the number of mates and size of the females, as well as the number of offspring per brood and size of the females. Interestingly, X. birchmanni females have a higher average rate of multiple mating compared to other species in this genus. These results suggest that sexual selection may be acting very differently in X. birchmanni compared to congeneric species. In particular, the high rate of multiple mating by females may open the door for post-copulatory sexual selection to play a significant role in determining reproductive success.