How cuckoldry can decrease the opportunity for sexual selection: Data and theory from a genetic parentage analysis of the sand goby, Pomatoschistus minutus

Alternative mating strategies are common in nature and are generally though t to increase the intensity of sexual selection. However, cuckoldry can the oretically decrease the opportunity for sexual selection, particularly in h ighly polygamous species. We address here the influence of sneaking (fertil ization thievery) on the opportunity for sexual selection in the sand goby Pomatoschistus minutes, a marine fish species in which males build and defe nd nests. Our microsatellite-based analysis of the mating system in a natur al sand goby population shows high rates of sneaking and multiple mating by males. Sneaker males had fertilized eggs in approximate to 50% of the assa yed nests, and multiple sneakers sometimes fertilized eggs from a single fe male. Successful males had received eggs from 2 to 6 females per nest (mean = 3.4). We developed a simple mathematical model showing that sneaking in this polygynous sand goby population almost certainly decreases the opportu nity for sexual selection, an outcome that contrasts with the usual effects of cuckoldry in socially monogamous animals. These results highlight a mor e complex and interesting relationship between cuckoldry rates and the inte nsity of sexual selection than previously assumed in much of the literature on animal mating systems.