STABILIZING SELECTION AND VARIANCE IN FIG WASP SEX-RATIOS

Theory predicts that the phenotypic variance observed in a trait subje ct to stabilizing selection should be negatively correlated with the t rait's impact on fitness. However, this relationship has rarely been t ested directly. The offspring sex ratios produced by pollinating fig w asp foundresses upon entrance to a fruit and oviposition alone (single foundress sex ratios) are subject to stabilizing selection because to o many males reduce the total number of dispersing females and too few males will result in unmated females or complete loss of the brood. F urthermore, we argue that the impact on fitness of, and therefore the intensity of stabilizing intensity on, single foundress sex ratios are correlated to how frequently a species produces single foundress broo ds in nature. Specifically, the intensity of stabilizing selection wil l be greater in species that encounter single foundress broods more fr equently, both because the trait is expressed more often and because f itness shows a greater sensitivity to variation (narrower fitness prof ile) when that trait is expressed. Across 16 species of Panamanian pol linating fig wasps the phenotypic variance in single foundress sex rat ios was negatively correlated with the frequency with which that speci es encounters single foundress broods in nature. In addition, a formal comparative analysis based upon a molecular phylogeny of the wasps ga ve results that were the same as when species were used as independent data points.