Polygynandry Strategy in Isolated Beluga Population Maintains Genetic Diversity

A comprehensive 13-year study of the isolated beluga whale population in Bristol Bay, Alaska, has revealed a highly flexible mating system—polygynandry—a finding critical for the conservation efforts of this Arctic species. This specific population, estimated at approximately 2,000 individuals, is geographically separated from other beluga groups, a condition that theoretically raises the risk of inbreeding depression due to reduced genetic diversity.

The research, published in the journal Frontiers in Marine Science, analyzed genetic samples from 623 beluga whales to accurately map their reproductive patterns. The findings significantly challenge the long-held assumption that beluga whales, given the larger body size of males, adhered to a polygynous system dominated by a few alpha males. The identified polygynandrous system indicates that both males and females actively engage in mating relationships with multiple partners over a period spanning several years, rather than being restricted to a single breeding season.

This moderate distribution of reproductive success ensures that genes are widely dispersed throughout the population, acting as a natural buffer against the genetic diversity erosion that threatens small, isolated groups. Researchers, including Greg O'Corry-Crowe of Florida Atlantic University (FAU), noted that the resulting family structure is characterized more by half-sibling relationships than full siblings from the same parents. This 'partner swapping' strategy, involving both sexes, effectively mitigates the inbreeding risk inherent in populations where the effective population size (Ne) is significantly smaller than the census size (Nc).

The long lifespan of beluga whales, estimated to reach up to a century, provides essential context for this long-term reproductive strategy, described as a 'long game' approach to reproduction. With such an extensive lifespan, males do not need to force intense intraspecific competition within a single season; instead, they spread their reproductive efforts across decades. For females, this strategy of multiple partnering serves as a reproductive risk management mechanism, allowing them to avoid exclusive commitment to low-quality or closely related males.

Professor O'Corry-Crowe, the study's senior author, emphasized that this discovery represents a paradigm shift in understanding beluga mating behavior. The intensive 13-year research was a collaboration between scientists from Florida Atlantic University's Harbor Branch Oceanographic Institute, the Alaska Department of Fish and Game, and the North Slope Borough Department of Wildlife Management. Genetic data was gathered by working with local beluga hunters to collect biopsy samples from the 623 individuals in Bristol Bay waters during a roughly two-week period each year.

The implications of these findings are substantial for the conservation of beluga whales, a species generally dependent on sea ice and facing challenges from climate change, including rising sea surface temperatures that may affect distribution. By demonstrating that this flexible mating behavior actively enhances the population's genetic viability, the research offers an optimistic insight into the species' adaptive capacity. Well-maintained genetic diversity through polygynandry may improve the population's resilience against future, shifting environmental pressures.