Intralocus sexual conflict, adaptive sex allocation, and the heritability of fitness

Evolutionary potential and constraints in an aposematic species: genetic correlations between warning coloration and fitness components in wood tiger moths

Variability in warning signals is common but remains puzzling since deviations from the most common form should result in a higher number of predator attacks. One explanation may lie in constraints due to genetic correlations between warning color and other traits under selection. To explore the relationship between variation in warning color and different life-history traits, we used an extensive data set comprising 64,741 individuals from a Finnish and an Estonian population of the wood tiger moths, Arctia plantaginis, that have been maintained in captivity over 25 generations. This species exhibits variable warning coloration in larval and adult stages. Measuring these traits alongside several fitness components allowed us to set color variation into context and obtain a better understanding of selection and constraints. Complete pedigree information enabled us to estimate genetic variances and covariances, which revealed several complex interplays between fitness components: Selection for faster development led to a significantly reduced fecundity. Fecundity was also constrained by negative correlations between direct genetic and maternal effects. However, we found no evidence that genetic associations with life-history traits constrain the efficiency of warning colors.

Is there indirect selection on female extra-pair reproduction through cross-sex genetic correlations with male reproductive fitness?

One key hypothesis explaining the evolution and persistence of polyandry, and resulting female extra‐pair reproduction in socially monogamous systems, is that female propensity for extra‐pair reproduction is positively genetically correlated with male reproductive fitness and consequently experiences positive cross‐sex indirect selection. However, key genetic correlations have rarely been estimated, especially in free‐living populations experiencing natural (co)variation in reproductive strategies and fitness. We used long‐term life‐history and pedigree data from song sparrows (Melospiza melodia) to estimate the cross‐sex genetic correlation between female propensity for extra‐pair reproduction and adult male lifetime reproductive success, and thereby test a key hypothesis regarding mating system evolution. There was substantial additive genetic variance in both traits, providing substantial potential for indirect selection on female reproductive strategy. However, the cross‐sex genetic correlation was estimated to be close to zero. Such small correlations might arise because male reproductive success achieved through extra‐pair paternity was strongly positively genetically correlated with success achieved through within‐pair paternity, implying that the same successful males commonly sire offspring produced by polyandrous and monogamous females. Cross‐sex indirect selection may consequently have limited capacity to drive evolution of female extra‐pair reproduction, or hence underlying polyandry, in systems where multiple routes to paternity success exist.

Field estimates of parentage reveal sexually antagonistic selection on body size in a population of Anolis lizards

Sexual dimorphism evolves when selection favors different phenotypic optima between the sexes. Such sexually antagonistic selection creates intralocus sexual conflict when traits are genetically correlated between the sexes and have sex‐specific optima. Brown anoles are highly sexually dimorphic: Males are on average 30% longer than females and 150% heavier in our study population. Viability selection on body size is known to be sexually antagonistic, and directional selection favors large male size whereas stabilizing selection constrains females to remain small. We build on previous studies of viability selection by measuring sexually antagonistic selection using reproductive components of fitness over three generations in a natural population of brown anoles. We estimated the number of offspring produced by an individual that survived to sexual maturity (termed RS^V), a measure of individual fitness that includes aspects of both individual reproductive success and offspring survival. We found directional selection on male body size, consistent with previous studies of viability selection. However, selection on female body size varied among years, and included periods of positive directional selection, quadratic stabilizing selection, and no selection. Selection acts differently in the sexes based on both survival and reproduction and sexual conflict appears to be a persistent force in this species.