Topic 17: Brown bears, Polar bears, and Hybridization through time Flashcards
Which bear species are likely to hybridize and produce fertile offspring?
Any Ursinae bears that come into CONTACT, any bears that have the same number of chromosomes 2N=74
TRUE OR FALSE: Polar bear Brown bear hybrids are fertile and can backcross to parents and other hybrids in captivity
TRUE
What was the contribution of Li et al. Nature 2010?
De novo assembly of mammalian genome using only short read technology of panda bears, found adaptation to bamboo diet is dependent on gut microbiome NOT genetic composition
What are 5 adaptations of the polar bear that make it different from the brown bear?
Diet (lipids/ fats because too costly to digest muscle)
Locomotion (swimming)
Cold tolerance (small ears, small tail, large feet and pads)
Morphology (reduced claws, white coat colour)
Geographic location (overlap in few spaces, except for north side of NWT)
What three different types of genes undergo rapid selection?
Genes involved in:
Lipid metabolism
Cardiovascular system
Hair pigment
Are polar bear and brown bear populations structured?
YES there are four main clusters of bears in canada
Why is the proposed mitochondrial tree different than the nuclear tree?
The mitochondrial genome was passed from brown bears into polar bears and therefore results in different trees, mt gene says they differentiated later than the nuclear
Do hybrids occur in the wild?
Yes but they are rare because the bears have to come into contact with each other
Sachs hybrid analysis of a bear that was killed showed it was a polar bear and brown bear hybrid
What is the future of hybrids?
They are usually raised as a polar bear by their mother, and they show maternal care, phenotypically the hybrids resemble brown bears more and more with increasing introgression
Suggestion that mating is always directional (female polar bear and male brown bear)
How common is contemporary hybridization?
Using available genomic toold and samples a study was designed to look for evidence of hybrid ancestry in polar and brown bears, use markers than can detect backcrosses, confirm hybrid ancestry of known hybrids
Results: no additional hybrids detected among 371 polar bear and 440 brown bears from certain area
What are the 5 main takeaways from this lecture?
Polar bears and brown bears have a complex evolutionary history (mtDNA and nuDNA phylogenies differ and likely periods of introgression ongoing during speciation)
They have genetically determined adaptive traits
Can produce fertile offspring in the wild and in captivity
Hybrids in the wild are rae and may occur due to mate preferences in restricted geographic regions
Hybridization is not likely a threat to persistence of polar bears
