Shared ancestry, sexual size dimorphism, and reproductive strategies jointly explain sex differences in adult lifespan in insects

Sex differences in lifespan provide a valuable framework for understanding lifespan evolution more broadly. Although such differences are widespread across animals, research on their evolutionary drivers remains strongly biased toward vertebrates. Comparative studies have substantially advanced knowledge of the extent and determinants of sex differences in lifespan in vertebrates, yet comparable research in invertebrates remains scarce and taxonomically limited, despite the wealth of available species-level data. Here, we present a broad-scale comparative analysis of sex differences in adult lifespan (SDL) in insects, using literature-derived data on 395 species spanning 17 orders. Across this dataset, female adults outlived males in 65% of species, and their median lifespan was 9% longer than that of males. Mean adult lifespan was consistently female-biased across taxonomic and functional groups, although the magnitude of this bias varied considerably. Phylogeny explained a relatively modest 28% of the variation in SDL, with qualitatively contrasting patterns of SDL occurring within most orders, and even among congeneric species. SDL was positively, albeit weakly, associated with sexual size dimorphism. Lifespan differences between sexes were generally more female-biased in functional groups in which extended lifespan is expected to more strongly enhance female reproductive success, either because of time-consuming resource acquisition for egg production (e.g., predators), or prolonged search for suitable oviposition substrates (e.g., parasitoids). Overall, our findings indicate that shared ancestry, sexual size dimorphism, and sex-specific reproductive strategies each contribute to variation in sex differences in adult lifespan, without any single factor clearly predominating.