Surprising similarity of sneaking rates and genetic mating patterns in twopopulations of sand goby experiencing disparate sexual selection regimes

Molecular markers have proved extremely useful in resolving mating patterns within individual populations of a number of species, but little is known about how genetic mating systems might vary geographically within a species . Here we use microsatellite markers to compare patterns of sneaked fertili zation and mating success in two populations of sand goby (Pomatoschistus m inutus) that differ dramatically with respect to nest-site density and the documented nature and intensity of sexual selection. At the Tvarminne site in the Baltic Sea, the microsatellite genotypes of 17 nest-tending males an d mean samples of more than 50 progeny per nest indicated that approximatel y 35% of the nests contained eggs that had been fertilized by sneaker males . Successful nest holders mated with an average of 3.0 females, and the dis tribution of mate numbers for these males did not differ significantly from the Poisson expectation. These genetically deduced mating-system parameter s in the Tvarminne population are remarkably similar to those in sand gobie s at a distant site adjoining the North Sea. Thus, pronounced differences i n the ecological setting and sexual selection regimes in these two populati ons have not translated into evident differences in cuckoldry rates or othe r monitored patterns of male mating success. In this case, the ecological s etting appears not to be predictive of alternative male mating strategies, a finding of relevance to sexual selection theory.