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I am a Professor in the Department of Biological Sciences at the University of Alberta. My students and I use molecular genetics to study ecology and evolution of wildlife species.

Wednesday, 30 November 2016

The sex lives of polar bears revealed!

Recent PhD graduate Rene Malenfant recently published a paper titled "Evidence of adoption, monozygotic twinning, and low inbreeding rates in a large genetic pedigree of polar bears" in the journal Polar Biology which documents some interesting findings about reproduction in the polar bears of the Western Hudson Bay:

  • they very rarely produce monozygotic twins
  • females rarely adopt unrelated cubs - and when they do, it's probably by accident
  • there is very little close inbreeding 

The abstract is pasted below:

Multigenerational pedigrees have been developed for free-ranging populations of many species, are frequently used to describe mating systems, and are used in studies of quantitative genetics. Here, we document the development of a 4449-individual pedigree for the Western Hudson Bay subpopulation of polar bears (Ursus maritimus), created from relationships inferred from field and genetic data collected over six generations of bears sampled between 1966 and 2011. Microsatellite genotypes for 22-25 loci were obtained for 2945 individuals, and parentage analysis was performed using the program FRANz, including additional offspring-dam associations known only from capture data. Parentage assignments for a subset of 859 individuals were confirmed using an independent medium-density set of single nucleotide polymorphisms. To account for unsampled males in our population, we performed half-sib-full-sib analysis to reconstruct males using the program COLONY, resulting in a final pedigree containing 2957 assigned maternities and 1861 assigned paternities with only one observed case of inbreeding between close relatives. During genotyping, we identified two independently captured 2-year-old males with identical genotypes at all 25 loci, showing-for the first time-a case of monozygotic twinning among polar bears. In addition, we documented six new cases of cub adoption, which we attribute to cub misidentification or misdirected maternal care by a female bereaved of her young. Importantly, none of these adoptions could be attributed to reduced female vigilance caused by immobilization to facilitate scientific handling, as has previously been suggested.

Thursday, 21 July 2016

Monday, 13 June 2016

SNP array reveals evolutionary history of thinhorn sheep

PhD student Zijian Sim just published a paper in Molecular Ecology which outlines new understanding of the phylogeography of the iconic North American thinhorn sheep. Congrats to Sim!!!

The University of Alberta Press Release reads:

Kristy Condon, Communications Associate / (780) 492.5344 / kristy.condon@ualberta.ca
Edmonton, Alberta, Canada / www.science.ualberta.ca

A tale of two subspecies
DNA analysis rewrites the story of thinhorn sheep during the last ice age
(EDMONTON) - Evolutionary biologists studying the lineages of thinhorn sheep have found evidence suggesting that the species diverged hundreds of thousands of years earlier than previously thought.
During the last ice age, most of North America was covered by inhospitable glaciers, forcing plants and animals to seek refuge in ice-free regions known as refugia. In some cases, individuals from the same species were separated in different refugia where they accumulated variances between populations over time, sometimes resulting in the formation of new species.
An iconic symbol of the mountains of western North America, the ancestors of the two dominant varieties of thinhorn sheep were believed to have weathered the last ice age together in the Beringian refugium, which today spans Alaska and the northern Yukon.  After the glaciers melted some 10 thousand years ago, this theory posits, the species diverged into the white Dall’s sheep and the dark Stone’s sheep that we know today.
When scientists looked into the DNA of both subspecies, however, they found it told a different story.
“The separation is hard to date, because with glaciation, fossilization is a hard thing to achieve,” explains Sim Zijian, PhD candidate in the Department of Biological Sciences and lead author on the study. “Traditionally when you’re trying to figure out what species came first and how they split, you use fossils. But that’s not possible here because these sheep live on top of mountains, where it’s rocky. Fossils just don’t form on rock.”
Instead, scientists turned to genetics, conducting a phylogenetic study—the study of lineages—into both subspecies of sheep. Looking at samples of modern animals, they found that, based on how the lineages were split, the division between the white Dall’s sheep and the dark Stone’s sheep is deeper than would be expected if they had both survived in the Beringian refugium. The findings support the idea that there was likely a second smaller refugium located south of Beringia that sheltered one of the two thinhorn groups through the glacial advance.
“We used to think they were all in one place. Now we think they were in two places, and based on the typology of this phylogenetic study, we can show that it is this survival in different refugia that gave rise to the two different subspecies that we see today,” says Zijian.  “So that gives us the confidence to say that one subspecies, in this case the Stone’s sheep—so the dark one—probably survived in that smaller ice-free refugium.”
The findings will be reflected in an update of the subspecies distribution map, which includes a third, somewhat more nebulous group known as Fannin’s sheep, which can vary dramatically in colour from mostly light to mostly dark.
“We’ve always known that the Fannin’s sheep were there, but we didn’t really know what they were,” says Zijian. “Are they just a type of Stone’s sheep? Are they just a type of Dall’s sheep? Why are there so many colour variations in this one area?”
The answer, it turns out, is none of the above. Fannin’s sheep are a hybrid of Dall’s and Stone’s sheep—a product of the two subspecies reuniting following their separation over the last ice age.
Though this may seem like a relatively small takeaway, Zijian emphasizes the importance of maintaining an accurate picture of subspecies distribution. “In today’s management framework, the ability to define groups and what these groups are truly made of is very important,” he explains, adding that having clearly defined groups are critical when establishing conservation frameworks.
The study, “Genome-wide set of SNPs reveals evidence for two glacial refugia and admixture from postglacial recolonization in an alpine ungulate,” was recently published in Molecular Ecology. Samples for the study were provided in part by hunters and hunting outfitters. The study was supported by the Yukon Department of Environment, the BC Ministry of Forests, Lands and Natural Resource Operations, the Wild Sheep Foundation, the Wild Sheep Society, and the Habitat Conservation Trust Foundation of BC.

The University of Alberta Faculty of Science is a research and teaching powerhouse dedicated to shaping the future by pushing the boundaries of knowledge in the classroom, laboratory, and field. Through exceptional teaching, learning, and research experiences, we competitively position our students, staff, and faculty for current and future success.

For Interviews:
Sim Zijian
PhD Candidate, Department of Biological Sciences
Faculty of Science, University of Alberta
E-mail: sim.zijian@gmail.com
Phone: (780) 975-7208


Caption: Three Fannin's sheep rams in their winter range. (Photo: Sim Zijian)

Caption: Two Dall's sheep rams in their winter range. (Photo: Sim Zijian)