Beluga whales are one of the most difficult marine mammals to study. They spend much of their lives in the Arctic Ocean and under sea ice, making it difficult to observe them directly. Now, long-term DNA research has provided valuable insight into how beluga whale populations in Alaska’s Bristol Bay form family ties and maintain genetic health.
The findings suggest that male and female beluga whales breed with multiple partners throughout their lives. Researchers believe this behavior may help this relatively small, isolated population avoid inbreeding and maintain genetic diversity.
“Despite their huge popularity, we still know very little about beluga whales,” said lead author of the study, Dr. Greg Okoley-Crow of Florida Atlantic University. Frontiers of marine science. “The main reason for this is that it is difficult to study northern species that live under frigid waves and often freeze. But this is what makes discoveries even more exciting challenges when they happen.”
Using DNA to study elusive Arctic whales
Researchers collected small tissue samples from 623 belugas over 13 years. The project involved scientists from Florida Atlantic University, the Alaska Department of Fish and Game, and Alaska Native subsistence hunters from Bristol Bay.
Little was known about the mating patterns of wild beluga whales, so the researchers based their predictions on evolutionary theory and what scientists already knew about the species. For example, male beluga whales are significantly larger than females, and females typically only give birth to one calf every few years.
“We predicted that beluga whales have a polygamous mating system, with the most competitive and perhaps the largest few males securing most mating within a season or over several seasons, and that they provide little or no parental care,” Okolie-Crow said.
At the same time, beluga whales live in large social groups that periodically separate and come together. The researchers reasoned that this social structure gives females access to a variety of potential mates over time. As a result, the researchers predicted that females could potentially reproduce with multiple males over different breeding seasons.
DNA reveals unexpected hybridization patterns
Genetic analysis yielded surprising results. It turns out that both males and females have had offspring with different partners over the years. If a calf has siblings, they usually share only one parent, not both.
All whales left relatively few offspring, but there was greater variation among males. Some males produced more calves than others, but the differences were not as extreme as the researchers expected.
“Male beluga whales were indeed polygynous, but surprisingly only to a moderate degree,” Okolie-Crow said. “The three-dimensional aquatic environment is likely to limit the ability of males to court and corral multiple females. However, longevity may also be key. Beluga whales may live for 90 years, and possibly even longer. Male beluga whales may therefore play the long game of securing several matings each year during their very long reproductive lives.”
“The female story is equally fascinating. Genetic profiling reveals that female beluga whales change mates regularly across breeding seasons and over their long reproductive lifespan. This may be a gamble-hedging strategy to limit the risk of mating with lower-quality males.”
High genetic diversity in small populations
One of the most unexpected discoveries concerned the genetic health of the population.
Despite having a population of only about 2,000 individuals, the Bristol Bay beluga whale showed high levels of genetic diversity and relatively little evidence of inbreeding. The researchers compared their results to both historical samples and other beluga populations and found that the genetic diversity in Bristol Bay was comparable to that of much larger populations. It is also stable over time.
“The main concern with small populations is that they tend to lose genetic diversity faster than larger populations, and there is a higher risk of inbreeding,” Okolie-Crow explained. “We expected low diversity and high inbreeding, but we found something quite different. Mating systems may explain this surprising finding. Frequent mate switching limits the number of highly related offspring in a population. This causes high inbreeding. It reduces the risk of closely related individuals mating with each other and producing highly inbred offspring.Although we cannot afford to be complacent, we are optimistic that beluga whale mating strategies provide evidence of natural resilience. ”
Other questions about beluga behavior
Researchers warn that other beluga populations may not behave in the same way.
Bristol Bay beluga whales have relatively small differences in body size between males and females compared to other populations. This may indicate that competition levels between males are low and that different mating systems may exist elsewhere.
“To me, the differences in sexual dimorphism between beluga whale populations could indicate that their mating systems are also different, and this is something we are currently working on,” Okolie-Crow said. “We also cannot use genetics to determine whether a female will mate with multiple males within a season, as she only gives birth to one calf from one lucky male. However, we are working on this by using drones elsewhere to determine whether we can observe mating behavior in the wild. We’ll have more information on that soon…”
This study provides the clearest view yet of the hidden social lives of beluga whales. It also suggests that flexible mating behavior may help arctic animals maintain strong genetic diversity, even though they live in relatively small and isolated populations.
