The beluga whales in Alaska switch partners several times over their lifetimes, which helps maintain their genetic viability and ensures the long-term survival of this small isolated population.
Researchers from the Harbor Branch Oceanographic Institute of Florida Atlantic University (United States), in collaboration with the Alaska Department of Fish and Game and the North Slope Borough Department of Wildlife Management in Alaska, have discovered how wild beluga whales mate and how these reproductive strategies influence genetic diversity and inbreeding.
The study, whose findings were published on Wednesday in the Frontiers in Marine Science journal, revealed that a small beluga population (Delphinapterus leucas) survives in the long term through a surprising strategy, mating with multiple partners over several years.
The combination of long-term genetics, careful observation, and meticulous analysis is beginning to reveal some of the most intimate insights about one of the Arctic’s most elusive whales, animals extremely difficult to observe and study as they disappear beneath the ice.
Over 13 years, the researchers collected genetic samples from 623 beluga whales in Bristol Bay, while observing their social groups and ages.
This population, composed of about 2,000 whales, is largely isolated, with little or no interbreeding with other populations, which offers a unique opportunity to study them as a distinct group, the researchers noted.
Because belugas can live more than a hundred years, the researchers focused on short-term mating strategies (those that occur within a single reproductive season or over several years), rather than lifetime mating, to determine whether the Bristol Bay belugas were polygynous (when a male mates with several females), polyandrous (when a female mates with several males), or possibly polygynandrous (when males and females have multiple partners).
They concluded that this whale population is polygynandrous and that the constant partner exchanges result in many half-siblings and few full siblings, reducing the risk of inbreeding and helping to maintain genetic diversity, despite the small size and isolation of this population.
The researchers did not find differences between older and younger adults in terms of the number of offspring in the population, nor for males or females.
However, they found that older mothers had more surviving offspring than younger mothers, suggesting that experience, physical condition and partner choice influence reproductive success.
Most adults, both males and females, had only a few offspring at a time, which also reflects the low reproductive rate of females and the fact that males produce only a small number of offspring per year, the researchers concluded.
Understanding this dynamic could be crucial for conservation, since when only a few males produce most of the offspring, the effective population size declines, and this loss of genetic diversity increases the risk of inbreeding and reduces the population’s ability to adapt to changes.
However, frequent partner exchanges, combined with low reproductive skew and the absence of mating with close relatives, may be effective strategies for maintaining the genetic health of relatively small populations.
