Supplementary file 2_Mating systems, parentage, and reproductive success of beluga whales in Bristol Bay, Alaska.docx

An aquatic mode of life and sociality influences mating strategies in cetaceans. In high latitude species, like the beluga whale, extreme seasonality likely imposes additional constraints on parental care, competition, and mate choice. Genetic profiling of 623 biopsy-sampled beluga whales in Bristol Bay, Alaska revealed that both sexes were polygamous, calves associated predominantly with their mothers, variation in reproductive success was slightly greater in fathers, and there was low short-term positive reproductive skew in both sexes. Males were moderately polygynous within and across breeding seasons and females were polyandrous across breeding seasons, (within breeding seasons was undetermined), indicating a polygynandrous mating system. In addition, although the effective population size (Ne) was much lower than census population size (Nc), high levels of genetic diversity and low levels of inbreeding were found within and across generations. Despite larger body size and polygyny, short-term male reproductive success was limited, possibly due to challenges of guarding multiple females and female mating strategies. A long reproductive life, however, may lessen the selective pressure for intense intrasexual competition and strong polygyny within seasons. Polygynandry across breeding seasons leads to long, loose-chain pedigrees that can lower inbreeding and maintain diversity, even in populations with small Ne.