Juneau, AK - Three local scientists merged their studies to provide a look at how the changing arctic environment can affect species through hybridization. Their work led to a commentary article published last month in Nature, an international science journal.
The lead author on the article, titled "The Arctic Melting Pot," was Brendan Kelly, who was working at the National Oceanic and Atmospheric Administration's National Marine Mammal Laboratory. The other authors are David Tallmon of the University of Alaska Southeast's biology and marine biology faculty and Andrew Whiteley of the Department of Environmental Conservation at the University of Massachusetts, Amherst. Whiteley worked with Tallmon on post-graduate studies at UAS when they began efforts in this study. The research leading to the article took a couple years to complete.
Their article examines how climate changes can be influential for species to cross-breed, creating hybrids for offspring. Such hybrids have been evident in arctic bears, whales, porpoises, seals and other mammals. They found that large losses of sea ice removed continent-sized barriers against interbreeding. The article describes how this can sometimes create new species, but is most often harmful to the populations for the existing ones.
"Our research should serve as a cautionary note. We don't know how Arctic ice loss will affect species, but the evidence suggests hybridization may be an additional threat to Arctic lineages that scientists and policymakers should consider. Up to this point, no one seems to have considered this threat," Tallmon said in an e-mail.
The article states hybridization can result from several factors, both natural and human-caused, that affect environments over time. Tallmon said habitat change is the most important factor in hybridization.
"What we did was look at all of this and see if it reflects the environmental change," said Kelly. "Hybridization is particularly inclined during environmental changes."
Kelly, who just left Juneau to become the deputy director of the Division of Arctic Sciences at the National Science Foundation, said the danger is that declining species that interbreed can die out. He gave an example of how polar bears in Alaska are in low density and can be inclined to mate with grizzlies as sea ice loss can encourage them to spend more time on the coast.
"Hybridization is a threat for those species that are reduced in number and come into contact with closely related, more common species. Essentially, the more numerous species can absorb a less common one by breeding with it until the less common one is gone," Tallmon said. "There are more subtle things that can happen along the way, but the outcome is that diversity is lost because an evolutionary lineage that has evolved independently over time along a given trajectory is absorbed by another lineage."
Besides losing species diversity, he said hybrids can result in decreased genetic fitness, which can be less obvious. This is because a hybrid is not naturally adapted to both of its parents' environments.
The authors found social and ecological behaviors can be affected as well.
However, they state that hybridization is not always a bad thing, as it can lead to new species or evolutionary novelties, thus increasing diversity.
Kelly said it's more common when species of different population sizes interbreed for the lower population to die out.
"If their density becomes low, their probability to hybridization can increase," he said.
Kelly and Tallmon said a number of species in Alaska show evidence of interbreeding, such as polar and grizzly bears or spotted and ribbon seals. Kelly said that crosses of Dall's porpoises and harbor porpoises in British Columbia are the only kind he's found around Southeast.
Tallmon said they looked through extensive scientific literature and museum collections for hybridization examples while studying the genetic compositions of Artcic mammals to see if hybrids were possible.
"We found 28 examples where hybridization might occur if formerly disjunct lineages are brought into contact by sea ice loss," he said.
Kelly said tissue samples that confirm hybrid DNA can be rare.
Kelly said views on hybridization can often come from how much one values species diversity. He said this can be an important issue for subsistence hunters.
The authors recommend researchers combine models of sea ice loss, oceanography and landscape sciences to help predict where hybridization is more likely to occur and monitor at-risk species' genetics. They conclude that national and tribal governments should work together to do such monitoring and hybrid prevention.
"One thing we wanted to do was get people to think about this. What we were trying to do is raise awareness in this article, and we should make some decisions," Kelly said.
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