Clutch size evolution under sexual conflict enhances the stability of mating systems

Models of optimal clutch size often implicitly assume a situation with unip arental care. However, the evolutionary conflict between males and females over the division of parental care will have a major influence on the evolu tion of clutch size. Since clutch size is a female trait, a male has little possibility of directly influencing it. However, the optimal clutch size f rom a female's perspective will depend on the amount of paternal care her m ate is expected to provide. The sexual conflict over parental care well in its turn be affected by clutch size, since a larger clutch makes male care more valuable. Hence, there will be joint evolution of mating system and cl utch size. In this paper, we demonstrate that this joint evolution will ten d to stabilize the mating system. In a situation with conventional sex role s, this joint evolution might result in either increased clutch size and bi parental care or reduced clutch size and uniparental female care. Under som e circumstances the initial conditions might determine which will be the ou tcome. These results demonstrate that it may be difficult to deduce whether biparental care evolved because of few opportunities for breeding males in creasing their fitness by attracting additional mates or because of the imp ortance of their care for offspring fitness by studying prevailing mating s ystems using, for example, male removals or manipulation of males' opportun ities for fielding additional mates. In general terms, we demonstrate that models of life-history evolution have to consider the social contest in whi ch they evolve.