The Consequences of Polyandry for Sibship Structures, Distributions of Relationships and Relatedness, and Potential for Inbreeding in a Wild Population

AbstractThe evolutionary benefits of simultaneous polyandry (female multiple mating within a single reproductive event) remain elusive. One potential benefit could arise if polyandry alters sibship structures and consequent relationships and relatedness among females’ descendants, thereby intrinsically reducing future inbreeding risk (the indirect inbreeding avoidance hypothesis). However such effects have not been quantified in naturally complex mating systems that also encompass iteroparity, overlapping generations, sequential polyandry, and polygyny. We used long-term social and genetic pedigree data from song sparrows (Melospiza melodia) to quantify cross-generational consequences of simultaneous polyandry for offspring sibship structures and distributions of relationships and relatedness among possible mates. Simultaneous polyandry decreased full sibships and increased half-sibships, on average, but such effects varied among females and were smaller than would occur in the absence of sequential polya...