Evolutionarily Stable Reproductive Strategies in Sexual Organisms. Part V—Joint Effects of Parent–offspring Conflict and Sibling Conflict in Perennial Plants

We develop a general treatment of the joint effects of parent–offspring conflict (conflict between broods) and sibling conflict (conflict within broods) in perennial plants. Parent–offspring conflict as well as sibling conflict are examined in the context of an integrated analysis of reproductive allocation, sex allocation, and the amount of resources invested in each offspring. We find that under a wide range of conditions the selected seed size is independent of reproductive effort or sex allocation. To the extent that the relationships between gamete output and resource investment are linear for both sex functions, the separate treatment of reproductive effort, sex allocation, and offspring size–number compromise in modern life-history theories is well justified, regardless of which side, parents or offspring, controls the allocation to individual seed offspring. We show that incorporation of sibling conflict results in even larger seed size, which in turn leads to even lower reproductive effort, than under pure parent–offspring conflict. If the costs of increased provisioning of selfish offspring are entirely borne by their brood mates, then offspring are selected to solicit parental care as long as they continue to benefit individually from more resources.