Every polar bear alive today share a unwashed maternal antecedent , and it is n’t even a bear from the same species . Their mitochondrial DNA reveal a 100,000 year storey of interbreeding and hybridisation … and the story is far from over .
Mitochondrial DNA is passed along exclusively from mother to their young . Because this DNA never mixes with familial stuff from the Church Father , it remains jolly much completely unchanged over the generations . By studying the mitochondrial DNA of the exist members of a given species , it ’s possible to work rearward and figure out when their most recent common maternal ancestor – in other words , the individual that supply that same art object of mitochondrial DNA to all her descendants – must have lived . ( For a more complete overview of what mitochondrial DNA is and why it ’s important , check outthis earlier post . )
https://gizmodo.com/why-humans-are-all-much-more-related-than-you-think-5791530
Researchers have now been able to do that with polar bear , and the results are surprising . The distaff ancestor of all frigid bear is n’t a polar bear at all , but instead a browned bear , a species that includes Grizzlies and Kodiaks . This ascendant lived 20,000 to 50,000 years ago during one of the last major Ice Ages . It in all likelihood was located on the glacier in good order around what is now Ireland and Britain .
The differences between the two bear metal money is n’t minuscule – they ’re dissimilar sizes , their pelt and tooth have dissimilar structures , their skin and coating colors are n’t anything alike , and that ’s not even getting into their behavior . Polar bears are rude swimmers that live in the glaciers and tundra of the Arctic , while brown bears inhabit out in the wad , forests , and river valley of North America and Europe .
So what happened all those thousands of years ago ? To find out , we spoke with Penn State life scientist Beth Shapiro and University of Dublin geneticist Daniel Bradley , the two authors of the study . Shapiro explained to us just how they picture out what , when , and where the maternal ancestor of all arctic bears must have been :
We liken the DNA sequence isolated from the dissimilar pearl . We ramp up evolutionary Tree that draw how each of the individuals is related to every other someone . These trees showed that all living icy bear have a common maternal ancestor that live only 20,000 to 50,000 years ago , when that ancestor diverged from a brown bear . This was surprising , because diametrical bear existed prior to 50,000 eld ago : there area fogey that are 100,000 years one-time , and they are morphologically and behaviorally quite different from each other . The only direction to excuse what we observed with the mitochondrial DNA is that , sometime after the two bear species split from each other , mating between the two already - unlike species happen . That mating leave in the mitochondrial genome from the Irish browned bear being capture by pivotal bear . It then diffuse throughout the entire opposite bear population , leaving the dispersion we see today . We could tell this happened in Ireland because we have it off where , in space , each bone amount from that we have desoxyribonucleic acid succession information .
The finicky Irish brown bear population with which these frigid bears hybridize all those age ago most belike died out about 9,000 year ago . Daniel Bradley expatiate on how they determined the enate ancestor ’s Irish origin :
The closest sequence we found to innovative gelid bear are those we uncovered from Irish bears . We estimate that these were brown bear because stable isotope analysis indicates they had a planetary dieting , unlike polar bear which are strongly conform to a maritime ecology .
They explain that it ’s not clear whether this interbreeding actually bestowed an evolutionary advantage . Bradley suggests this may have been an adaptive response to climate change , but it might well have just have been happenstance , the by-product of the Ice Age forcing the bear ’ instinctive habitats to temporarily overlap . We do now have it away that crossbreeding among big mammals is surprisingly coarse – we see a lot of productive interbreeding with various specie associate to the cow , there ’s evidence of hybridization among the mammoth species , andeven ancient humans probably crossbred with Neanderthals .
https://gizmodo.com/sex-with-neanderthals-gave-humans-the-strength-we-neede-5812639
While this particular period of hybridizing happened tens of G of geezerhood ago , polar bears and browned bear have been interbreeding for far , far longer than that , plump back as much as 500,000 year . It appears that whenever climate variety changed their home ground enough to fetch the species into contact , they started match without hesitancy . During this special period , the Ice Age would have translate Ireland pretty much uninhabitable due to glaciation , which forced the native brownish bears to survive out on the ice ledge . That bring them into contact with pivotal bear , and the rest is mitochondrial chronicle .
So what does this mean for the time to come of these species , particularly since we ’re now run short through a period of climatic hullabaloo that isbringing the two species back into contact ? Shapiro explained to us that the bear will in all probability again sprain to hybridization to survive , but that is n’t necessarily a good thing in the retentive run , particularly for the more vulnerable polar bears :
https://gizmodo.com/grizzly-bear-vs-polar-bear-who-will-win-5697839
Clearly , they are crossbreed today , as their cooking stove commence to overlap and they bechance to bump into each other . But , as long as polar bear habitat remains , polar bears will be able to mate with opposite bear , and will carry on to expand in their very specific home ground . If the polar bear habitat disappear , so will the polar bear . If the only manner they can hold out is to interbreed with brown bear , then all the genetic adaption that are specific to the glacial bear risk being lost .
What both researchers stressed to us is the often forget grandness of interbreeding and interbreed in our biological history . frigid bear and brown bears , it seems , are in particular dynamic species and well - suited to crossbreeding in rules of order to pull through times of pronounce thawing and cooling . The only Leslie Townes Hope , perhaps , is that things do n’t get so extreme that one species breeds the other out of being .
Read the original paper atCurrent Biology .
BearBiologyEvolutionirelandPolar bearScienceZoology
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