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

Abstract

Alternative mating strategies are common in nature and are generally thought to increase the intensity of sexual selection. However, cuckoldry can theoretically decrease the opportunity for sexual selection, particularly in highly polygamous species. We address here the influence of sneaking (fertilization thievery) on the opportunity for sexual selection in the sand goby Pomatoschistus minutus, a marine fish species in which males build and defend nests. Our microsatellite-based analysis of the mating system in a natural sand goby population shows high rates of sneaking and multiple mating by males. Sneaker males had fertilized eggs in Ϸ50% of the assayed nests, and multiple sneakers sometimes fertilized eggs from a single female. 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 opportunity for sexual selection, an outcome that contrasts with the usual effects of cuckoldry in socially monogamous animals. These results highlight a more complex and interesting relationship between cuckoldry rates and the intensity of sexual selection than previously assumed in much of the literature on animal mating systems.microsatellites ͉ mating systems ͉ paternity ͉ polygyny

Mito-nuclear discordance in the degree of population differentiation in a marine goby

“…The Pmin20 locus was excluded from the analysis because, after genotyping more than 90 individuals, the number of alleles almost matched the number of fish genotyped. The studies of Jones et al (2001) and Pampoulie et al (2004) also observed microsatellite markers with a very high number of alleles. By organizing a better sampling strategy and using straightforward N e -estimation methods incorporating migration (Wang and Whitlock, 2003), better estimates of the N e might confirm the expected high N e for P. minutus.…”

Little Effect of Extrapair Paternity on the Opportunity for Sexual Selection in Savannah Sparrows (Passerculus Sandwichenisis)

“…Extrapair components of fitness may increase or decrease the standardized variance in male reproductive success (I s ), depending on how within-pair and extrapair fertilization success covary (Webster et. al 1995;Jones et al 2001). If the covariance is minimal or negative, EPP may have little effect on the opportunity for sexual selection.…”

“…Alternatively, if many extrapair young are sired by floaters not included in the sample (Kempenaers et al 2001), the study will fail to reveal a negative covariance between within-pair and extrapair success among true breeders since, by definition, floaters sire no within-pair offspring. I s will thus be overestimated while variation in apparent success (I s,app ) will be underestimated, making EPP seem much more influential than it truly is in generating variance in reproductive success among males (Jones et al 2001).…”

“…While it is relatively easy to assess a male's success at siring young on his own territory, it is often difficult to tally the number of young he produces outside the pairbond either because the geographic scale of reproductive interactions exceeds the boundaries of the study site or because of methodological limitations associated with the molecular techniques used to include or exclude potential sires (Webster and Westneat 1998;Ligon 1999). This sampling bias is problematic because it can potentially inflate I s in two ways, one statistical (Møller and Ninni 1998) and the other biological (Webster et al 1995;Jones et al 2001). First, when excluded young remain unallocated to extrapair sires, the mean reproductive success of males (T ) is artificially decreased, leading to an increase in the standardized variance:…”

The polyandry revolution

“…This is followed up by a contribution in which Shuster et al [14] develop a quantitative framework to measure the impact that polyandry has on the variance in reproductive success, and thus on the opportunity of sexual selection in a population. The approach proposed helps contextualize recent empirical demonstrations of the strong impact that polyandry can have on different episodes of sexual selection [15,16]. Another fundamental consequence of polyandry is that the operation of pre-and post-copulatory episodes of selection favours the evolution of alternative mating tactics.…”