Proximate and ultimate controls on life-history variation: the evolution of litter size in white-footed mice ( Peromyscus leucopus).

Abstract

A theoretical analysis of optimal parental investment in offspring was initiated under the assumption that optimal brood size represents a maximization of differences between age-specific costs and benefits of reproduction, both of which should be measured in constant currency of inclusive fitness. Reproductive value weighted by offspring survival and devalued by degree of genetic relatedness defines a new currecy, replacement value, which is more appropriate for evaluating costs and benefits of parent-offspring conflict over parental investment in current as opposed to future young. Total parent-offspring conflict intensifies with increases in current brood size. For species with severe reproductive constraints, eg post-partum estrus in white-footed mice, such conflict may force parents to curtail investment in current offspring at or near parturition of subsequent litters, even if that means reducing survival of current young.-from Author