Experimental sheep at CSIRO's FD McMaster Laboratory, Armidale NSW.
A sheep in sheep's clothing
An international research team has provided an unprecedented in-depth view of the genetic history of sheep, one of the world's most important livestock species. (6:32)
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Glen Paul: G'day, and welcome to CSIROpod, I'm Glen Paul. With just over a billion globally, sheep are one of the world's most important livestock species. They’ve provided wool, meat, and milk to people for more than 11 000 years, and with selective breeding we've moulded sheep to suit a variety of environments and further our needs.
To find out just how much influence we've had on sheep diversity, an international research team has undertaken an unprecedented in-depth view of the genetic history of sheep. The study identified particular regions of the sheep genome that appears to have changed rapidly in response to selection for genes controlling traits such as coat colour, body size, reproduction, and especially the lack of horns, one of the earliest goals of selective breeding.
Lead author of the study, CSIRO's Dr James Kijas and his team, traced the relatedness between nearly 3000 sheep, and joins me on the phone. Now, James, that’s a lot of sheep, how did you go about collecting all that DNA?
Dr Kijas: It is a lot sheep. A lot of correspondence with willing researchers all over the planet, so we were able to collect blood samples, which we’d turn into DNA, from animals from Asia, from Africa, through the Middle East, the Americas, lots of different breeds from the United Kingdom, from Europe. So yeah, it was a big task, it took quite a lot of time.
Glen Paul: Hmm. And how many breeds were involved?
Dr Kijas: So there were 74 breeds included in the study, and for each breed we sampled between 30 and 40 animals for each breed, so it's a big dataset.
Glen Paul: And were there any surprises when looking back, and such as finding genes from a lost breed of sheep?
Dr Kijas: One of the first surprises that we got was when we looked at all of the breeds we found very high levels of genetic diversity. So we found much higher diversities present in modern sheep breeds than for example compared to dogs. There's much more diversity in sheep breeds than compared to for example dairy cattle, and even most breeds of beef cattle.
So sheep breeds have maintained a very high level of genetic diversity through the domestication process, and then subsequently humans sorting animals into different breeds.
Glen Paul: So how have they achieved that, because as you mentioned there with dogs that has led to medical issues from the inbreeding of domestic dogs, you see that all the time, but how come it hasn't happened with sheep?
Dr Kijas: Well one of the reasons we think, if we look into the data we can see evidence for quite high levels of movement of genes and individuals between breeds, so if you think of a dog breed, largely you could consider it as a sort of a silo, where there's not a lot of exchange between individual dog breeds.
If you look at sheep the story is different. We see evidence to there being quite a lot of exchange of animals through the development of breeds, such that if you sample breeds now they’re kind of much more overlapping genetically than for example dogs.
Glen Paul: And what about genetic variance that caused diseases; have you had any luck identifying those?
Dr Kijas: We have – not part of this work, but in other work we certainly see genetic disease in sheep populations, not at the same frequency as you say for some dogs, but for example an eye abnormality in Texel has a genetic component. We can use the same sort of approach as we used in this study to track down genes that cause disease.
Glen Paul: Right. What about the domestication and migration patterns of sheep across the globe, do they tally up with what we know about human movements throughout history?
Dr Kijas: Yeah, they do. So from archaeological evidence we know that sheep were first domesticated, or the process of domestication first started in the Middle East, so present day Turkey, in Iran. And so we were keen to look at the level of diversity in population from across the world, and sure enough what we found was that the highest levels of diversity were found in breeds from Turkey, in Iran, in the Middle East, and then we saw also very high diversity in breeds from Mediterranean Europe, and then lower diversity as you move outwards.
So breeds from northern Europe for example had slightly lower diversity, and this is consistent with this idea of a domestication centre, and then migrations of people that took domestic animals with them in the Neolithic period outwards, and we can see certainly evidence for that in the data.
Glen Paul: And in Australia then, even though we use a lot of Merino sheep, they’re still looking OK as far as genetic diversity goes?
Dr Kijas: Yeah, absolutely. That was one of the outcomes from the study, is that if you take the Merino for example, it has amongst the highest genetic diversity of any breed that we sampled on the planet.
So this is good news for producers, who of course are interested in genetic gain in their animals, and to achieve genetic gain you really need the raw material for that selection, and that raw material is the genetic diversity. So it bodes well for ongoing selection response in Australian breeds like the Merino, and Poll Dorset, and Suffolk, and so on.
So, certainly no need to worry about inbreeding or a narrow genetic base in these populations – the finding from our work is that they have very high diversity.
Glen Paul: Well that is good to hear. And how can farmers make use of this report?
Dr Kijas: Well one of the outcomes of the study for example is information about individual genetic markers all across the genome and one of the outcomes from the work will be work towards a parentage panel, so a DNA based method for cheaply and accurately determining the parentage of animals.
Glen Paul: OK. And where can people go to find out more, where can farmers read the report?
Dr Kijas: So the work is being published in the Journal PLoS Biology, and that’s a public access, you know, non-subscription required Journal, so all of the work is published in that Paper.
Glen Paul: And what if farmers need a bit of help in understanding some of the complexities of it? Can they contact yourself or others?
Dr Kijas: Yes certainly. So the work is being done by an international consortium of scientists, so CSIRO has led this particular part of it, so I can be contacted directly, or any of the members of the consortium.
Glen Paul: And those details are available on the CSIRO website?
Dr Kijas: Well the consortium has its own website, which is www.sheephapmap.org, and that details participants in the consortium, and this is only one of a number of studies that the consortium has undertaken. Another, for example, is we've created a de novo assembly of the sheep genome, so we’ve determined all of the base pairs in the base sheep genome and what order they’re in, and that’s available through the consortium.
Glen Paul: OK. Well it does sound like the farmers have got a bit of light bedtime reading there. Thank you very much for discussing it with me, James, it’s an interesting study. I do appreciate your time.
Dr Kijas: Oh, you're very welcome, Glen.
Glen Paul: Dr James Kijas. For more information find us online at www.csiro.au. You can like us on Facebook, or follow us on Twitter at CSIROnews.