Male survival patterns do not depend on male allocation to sexual competition in large herbivores

Abstract

Understanding causes of between-sex differences in survival patterns is a long-standing challenge in evolutionary biology. Interspecific differences in male allocation to sexual competition have been suggested to shape species-specific patterns of male adult survival and actuarial senescence, and thereby the extent of between-sex differences in these parameters. Sexual competition is complex and involves both competition for gaining mating (i.e., precopulatory competition) and competition for fertilization opportunities (i.e., postcopulatory competition). However, to date, studies seeking for a relationship between allocation to precopulatory competition and male absolute adult survival have led to contrasting results and the influence of postcopulatory competition on these parameters has never been yet investigated. To fill the gap, we performed a comparative study in large herbivores using median lifespan (i.e., age at which only half of the initial cohort is still alive) and actuarial intensity of senescence (i.e., number of years elapsed between the median lifespan and the age where only one-tenth of the initial cohort is still alive). As expected, we found a lower adult survival and a stronger actuarial intensity of senescence in males than in females. Conversely, we did not find any evidence that variation in male allocation to pre- and/or postcopulatory traits explain between-species differences of both absolute and relative adult survival and intensity of actuarial senescence. These results challenge the idea that allocation to specific traits associated with sexual competition is responsible for between-sex differences in survival and senescence patterns generally reported in mammals. Key wor ds: actuarial senescence, aging, sexual selection, sexual size dimorphism, testes mass, ungulates, weapon size. [Behav Ecol]