Age-dependent inbreeding risk and offspring fitness costs in female black grouse

<p>Dispersal is an important mechanism used toavoid inbreeding. However, dispersal may onlybe effective for part of an individual’s lifespansince, post-dispersal individuals that breed overmultiple reproductive events may risk matingwith kin of the philopatric sex as they age. Wetested this hypothesis in black grouse Tetraotetrix, and show that yearling females nevermated with close relatives whereas older femalesdid. However, matings were not with direct kinsuggesting that short-distance dispersal to sitescontaining kin and subsequent overlap of reproductivelifespans between males and femaleswere causing this pattern. Chick mass was lowerwhen kinship was high, suggesting importantfitness costs associated with inbred matings.This study shows that increased inbreeding riskmight be a widespread yet rarely consideredcost of ageing.</p>