Despite their enchanting appearance and popularity, beluga whales remain a mystery to many. The harsh and secluded Arctic environment they inhabit poses significant challenges for research. However, scientists have recently made strides in understanding these creatures by analyzing DNA samples from a specific population in Alaska. Unexpectedly, the findings suggest that the belugas’ reproductive strategies may be key to their survival, offering insights into how they avoid inbreeding within their isolated groups.
Studying beluga whales is no easy feat due to their elusive nature and habitat under the Arctic ice. Through DNA analysis, researchers have gained valuable insights into the mating behavior of a beluga group in Bristol Bay, Alaska. The discovery that both male and female belugas engage with multiple partners over their lifespan may play a crucial role in maintaining genetic diversity in this small population.
“We still know very little about beluga whales, despite their immense popularity,” said Dr. Greg O’Corry-Crowe of Florida Atlantic University, the study’s lead author, as reported in Frontiers in Marine Science. “The primary reason for this is the difficulty of studying a species that lives beneath the waves in the cold and often frozen north. But this is the challenge that makes discovery, when it happens, more exciting.”
Secrets of Beluga Mating
Over an extensive 13-year period, a team comprising scientists from Florida Atlantic University, the Alaska Department of Fish and Game, and Alaska Native subsistence hunters collected tissue samples from 623 whales. Without much existing data on wild belugas’ mating habits, researchers applied evolutionary theory alongside biological facts about the species to form hypotheses, such as the larger size of males compared to females and the females’ limited reproductive rate.
“We predicted that beluga whales had a polygynous mating system where a few of the most competitive and possibly largest males secure most of the matings within a season or even across a few seasons, and that they provide little or no parental care,” O’Corry-Crowe explained.
Nevertheless, given that belugas form large social groups that frequently change, the researchers also considered that females might mate with multiple males over different breeding seasons.
Complex Mating Dynamics
The study’s findings revealed that both male and female belugas reproduce with different partners over time. Calves commonly had siblings from only one shared parent, indicating varied mate selection. Although all belugas had a limited number of offspring, some males were slightly more successful in reproduction.
“Beluga males were indeed polygynous, but, surprisingly, only moderately so,” noted O’Corry-Crowe. “The three-dimensional aquatic environment likely limits a male’s ability to successfully court or corral multiple females. However, a long life may also be key. Belugas can live 90 years, possibly more. Male beluga whales may, therefore, play a long game of securing a few matings each year over a very long reproductive life!”
He added, “The female story is just as fascinating. The genetic profiling revealed that female belugas regularly switch mates across breeding seasons, also over a long reproductive life. This could be a bet-hedging strategy to limit the risk of mating with low-quality males.”
Genetic Diversity and Resilience
Unexpectedly, the research uncovered high genetic diversity and low inbreeding levels in the small population of approximately 2,000 individuals. Comparison with other populations and historical samples from Bristol Bay shows that their genetic diversity is comparable to that of larger populations and has remained stable.
“A leading concern for small populations is that they tend to lose genetic diversity faster than large populations and the risks of inbreeding are higher,” explained O’Corry-Crowe. “We expected to find low diversity and high inbreeding, but we found something quite different. The mating system may explain this surprising finding. Frequent mate switching limits the number of highly related offspring in the population. This in turn reduces the risk of highly related individuals mating and producing highly inbred offspring. It also minimizes the risk of diversity loss. We cannot afford to be complacent, but we can be optimistic that beluga whale mating strategies provide evidence of nature’s resilience.”
The researchers caution that other populations may display different behaviors. The relatively low sexual dimorphism in Bristol Bay could suggest that competition is less of a factor in mating there compared to other regions.
“To me, the differences in sexual dimorphism among populations of beluga whales could indicate that mating systems also vary, and this is something we are currently working on,” said O’Corry-Crowe. “We also can’t determine if females mate with multiple males within a season using genetics, as a female only produces one calf from one lucky male. But we are working on this, using drones at other locations to determine if we can observe mating behaviors in the wild. More on that soon…”
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Original Story at www.frontiersin.org