Post-reproductive lifespan, grandmother effect, mother effect, reproductive conflict, inclusive fitness, kin selection

Contrary to life history theory suggesting individuals should reproduce until death, females of a small number of mammal species are known to live for a significant period after they cease reproduction. It is thought that this trait is facilitated by either female-biased dispersal or bisexual philopatry, leading to increased local relatedness throughout a female’s lifetime, allowing greater inclusive fitness to be gained through kin selection. Currently, 3 non-exclusive hypotheses attempt to explain how females might gain this fitness: females halt reproduction to maximise investment in existing offspring (mother effects), females halt reproduction to aid in raising grandoffspring (grandmother effects) and females halt reproduction to minimise intergenerational reproductive competition with sexually mature daughters (reproductive conflict). Despite having similar relatedness and dispersal patterns to species possessing a post-reproductive lifespan, female long-finned pilot whales (Globicephala melas) do not halt reproduction significantly prior to death. This study investigates whether a lack of post-reproductive lifespan in long-finned pilot whales results from minimal benefits incurred from mother and grandmother presence or from a lack of costs incurred from mother-daughter co-reproduction. Using microsatellite data to conduct parentage analysis on a dataset collected at a legal drive fishery in the Faroe Islands between 1986-1988, I show that the size and pregnancy status of individuals is not influenced by mother effects or grandmother effects. Results show that individuals under 20 were more likely to have philopatric offspring assigned if their mother was present, indicating mothers may assist inexperienced daughters in raising offspring. No evidence of reproductive conflict between consecutive generations was found, indicating females are able to reproduce into old age whilst simultaneously aiding their daughters in reproduction. This highlights the importance of reproductive conflict in the evolution of a post-reproductive lifespan and demonstrates mother and grandmother effects alone do not predispose the decoupling of reproductive and somatic senescence