The melting of the Arctic Ocean may result in a loss of marine mammal biodiversity, reports a new study published in the journal Nature and conducted jointly by the National Oceanic and Atmospheric Association (NOAA), the University of Alaska, and the University of Massachusetts. The study is the first to project what might happen if species pushed into new habitats because of ice loss hybridize with one another, resulting in such crossbreeds as “narlugas” and “grolar bears”.
Scientists expect that if greenhouse gas emissions continue at current rates, the Arctic Ocean could be completely free of permanent sea ice by the end of the century. The sea ice acts as a barrier which separates many marine mammal populations; with the loss of the ice, populations which have been isolated from each other for millennia could potentially interbreed. This could result in the disappearance of unique, adaptive characteristics.
Examples of hybridization have already been documented. In the 1980s, the skull of a narwhal/beluga washed up on a beach in Greenland; in 2006, a hunter shot a polar/brown bear hybrid; and just last year a bowhead/right whale was observed in the Bering Sea. Andrew Whitely, a conservation geneticist at the University of Massachusetts Amherst, explains that while hybridization has the potential to offer certain advantages, it can also result in the lack of adaptive traits or the addition of maladaptive ones. The arctic is a hostile environment, and survival often hinges on the presence of specific characteristics. Muddling of the gene pool via hybridization could result in the dilution of important genes. For instance, the mating of brown bears with polar bears produces offspring with mottled coats which are far less effective camouflage in either environment. And a hornless male narwhal/beluga living in a narwhal pod would not be able to compete for mates.
 Photo by Rhett A. Butler |
Additionally, through hybridization more numerous species could potentially overwhelm those whose numbers are low. For example, the critically endangered North Pacific right whale which numbers only around 200 is at major risk of getting its genome swallowed up by the much more numerous bowhead whale.
According to the study, at least 22 species are at risk of hybridizing in 34 combinations, and includes whales, bears, and seals. Many are endangered. The authors of the study advise that if stringent monitoring of all at-risk populations is not implemented soon, many discrete populations will disappear through hybridization.
Specifically, the researchers call for the modeling combination of sea-ice loss, oceanography, and landscape genomics to predict when and where hybridization is most likely to occur. National organizations should also work with tribal organizations to monitor high-risk populations.
“By melting the seasonal ice cap, we’re speeding up evolution.” lead author and NOAA scientist Brendan Kelly told OnEarth.org, “People often talk about species adapting to climate change, but the kind of adaptation that’s necessary is a change toward genes that fit the new climatic environment better than the old genes. Individuals don’t adapt genetically. Populations do. That requires generations, which requires time. Bears, seals, whales — these are long-lived animals. They need decades and centuries to adapt. But we’re talking about losing the Arctic summer sea ice in a matter of a few decades. So the time for adaptive response may not be there.”
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