Mating system transitions drive life span evolution in Pristionchus nematodes

Interactions between the sexes influence evolution at many scales, but not all animal species conform to the familiar male-female (dioecious) mating system; such taxa are powerful tools for studying the evolutionary importance of sexual selection and conflict on all manner of life-history traits, including longevity. We tested for an effect of mating system on adult life span in Pristionchus nematodes, where self-fertile hermaphrodites have replaced females multiple times independently throughout the genus (androdioecy). By measuring adult life span for 11 species (6 dioecious, 5 androdioecious), we found that life span is considerably shorter in hermaphrodites relative to closely related females. This effect is not a cost of reproduction; brood size did not reliably trade off with life span in self-fertilizing hermaphrodites or in mated females. Furthermore, we found that sexual dimorphism in life span varied among dioecious species, with females generally outliving males. Finally, we documented intraspecific variation for life span and cuticular disease (blistering) prevalence in Pristionchus pacificus, a model system for evolutionary-developmental biology. This work demonstrates that mating system transitions and life span evolution are linked in Pristionchus nematodes and provides a foundation for future comparative and mechanistic studies of aging in this genus.