By Stephen Beech
Beluga whales indulge in wife swapping to enhance their long term survival chances, reveals new research.
Ground-breaking DNA analysis shows both males and females of the species that live in the cold Arctic and sub-Arctic waters of the Northern Hemisphere have many different mates.
Belugas are harder to study than most whales as they spend so much time under the Arctic ice.
But now DNA analysis has given scientists a precious glimpse into the social life of a beluga population living in Bristol Bay, Alaska.
They found that both males and females mate with many different partners over the years.
The “mate switching” results in many half-siblings and few full-siblings and may reduce the risk of inbreeding and help maintain genetic diversity despite the population’s small size, according to the researchers.
Study lead author Dr. Greg O’Corry-Crowe, of Florida Atlantic University, said: “We still know very little about beluga whales, despite their immense popularity.
“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.”
Over 13 years, a team – including scientists from Florida Atlantic University and the Alaska Department of Fish and Game, as well as Alaska Native subsistence hunters from Bristol Bay – collected small tissue samples from 623 whales.
With little existing information about wild belugas’ mating habits to go on, researchers used evolutionary theory and facts about the species’ biology to make predictions they could test against the real-life data.
For example, males are significantly larger than females, and females can only have one calf every few years.
Dr. O’Corry-Crowe said: “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.”
But he said belugas live in large social groupings which split up and reform over time, which could increase females’ access to different potential mates.
So the researchers also predicted that females might mate with many different males across breeding seasons.
When they looked at the results, they found that both male and female belugas had calves with different mates over the years.
If calves had siblings, they usually only shared one parent.
All belugas had a small number of calves, but there was more variation in males’ reproductive success: some males fathered slightly more calves.
Dr. O’Corry-Crowe said: “Beluga males were indeed polygynous, but, surprisingly, only moderately so.
“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.
“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.
“It’s a striking reminder that female choice can be just as influential in shaping reproductive success as the often-highlighted battles of male-male competition.
“Such strategies highlight the subtle, yet powerful ways in which females exert control over the next generation, shaping the evolutionary trajectory of the species.”
The findings, published in the journal Frontiers in Marine Science, also revealed unexpectedly high genetic diversity and low levels of inbreeding, despite a small population of just 2,000 individuals.
Comparing the results to other populations and historical samples from Bristol Bay indicates that the belugas’ genetic diversity is roughly equivalent to larger populations and has remained stable over time.
Dr. O’Corry-Crowe said: “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.
“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 minimises 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 research team say other populations could behave differently.
The difference in appearance between males and females – known as “sexual dimorphism” – is comparatively low in Bristol Bay, which the researchers say may indicate that mating depends less on competition between the males than it does elsewhere.
Dr. O’Corry-Crowe said “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.”
He added: “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.”
