Females allocate differentially to offspring size and number in response to male effects on female and offspring fitness

Female investment in offspring size and number has been observed to vary with the phenotype of their mate across diverse taxa. Recent theory motivated by these intriguing empirical patterns predicted both positive (differential allocation) and negative (reproductive compensation) effects of mating with a preferred male on female investment. These predictions, however, focused on total reproductive effort and did not distinguish between a response in offspring size and clutch size. Here, we model how specific paternal effects on fitness affect maternal allocation to offspring size and number. The specific mechanism by which males affect the fitness of females or their offspring determines whether and how females allocated differentially. Offspring size is predicted to increase when males benefit offspring survival, but decrease when males increase offspring growth rate. Clutch size is predicted to increase when males contribute to female resources (e.g. with a nuptial gift) and when males increase offspring growth rate. The predicted direction and magnitude of female responses vary with female age, but only when per-offspring paternal benefits decline with clutch size. We conclude that considering specific paternal effects on fitness in the context of maternal life-history trade-offs can help explain mixed empirical patterns of differential allocation and reproductive compensation.