Tag: genetics

Categories
Cottage Life

Do dogs really descend from wolves?

Curled up on the sofa, you watch your dog snoozing nearby. Is he dreaming of the bowl of biscuits he gobbled down? Or could he be picturing the great odyssey of his forbearers, who roamed in packs across the vast steppes during the last Ice Age in search for reindeer?

The story of the ancestral ties between the dog and the wolf is one of the most exciting evolutionary sagas in humanity’s history. Not only does it invite us to examine our relationship with nature, but it also brings us back to the question of who we are as humans.

Meet the grey wolf

Recent advances in genetics are starting to provide key details that can help us map out the interconnected history of our loyal pets and the proud canine predators that have been gradually repopulating our countries’ hinterlands.

The science investigating the wolf-dog kinship

The timeline of the prehistoric wolf’s domestication is arguably one of the most hotly debated topics in evolutionary science. Palaeontology brings some important elements into this debate, but it is still tricky to identify the osteo-morphological analyses (i.e., the study of bone size and bone morphology) that would allow us to differentiate between proto-dog species.

Ever since Charles Darwin’s theory of evolution, we have known that a series of phenotypic changes (i.e., observable physical characteristics) can be seen in animals undergoing a process of domestication, with retained traits often favouring the more docile members of a species. Over the millennia, domestic canines have evolved shorter snouts and smaller teeth, as well as a smaller appendicular skeleton (referring to the bones of their front and hind legs).

However, the dog’s domestic nature cannot be proven by the isolated appearance of one trait in one specimen. Instead, either a series of significant variables must be observed in one individual, or a novel trait must be observed repeatedly in a population or under a given context. The problem is that full skeletons of Palaeolithic canines are extremely difficult to come by.

The field of archaeology complements this approach by gathering information on the first interactions between humans and canines. Such data points to the existence of a special link between these two types of large predators that may have begun emerging in the Upper Palaeolithic, the period broadly spanning from 50,000 to 12,000 years ago. It has been noted, for instance, that canines were used to help make jewellery; they are also present in cave art. Again, the real significance of these clues remains unclear.

Are wolves the ancestors of dogs?

Thanks to major strides in genetics in recent years, many studies of ancient DNA can help palaeontologists and archaeologists track down mysterious origins of the “first dog”. Samples from both ancient and modern canines have been taken from every continent, enabling scientists to analyse the diversity of their gene pool. The method also has the advantage of merely relying on bone fragments, rather than whole and fully preserved skeletons.

While the majority of this research focuses on mitochondrial DNA (i.e., DNA inherited solely from the maternal line, but which is less prone to degradation), a handful of studies also look at the complete genome (i.e., chromosomes inherited from the maternal and paternal lines, but which are preserved much more poorly during fossilisation).

These results help sketch a blueprint for the overall phylogenetic history of canines. Unsurprisingly, such analyses reveal a highly complex demographic and phylogenetic history of the grey wolf down through the ages. In particular, they indicate lupine populations in the Palaeolithic (c. 3.3 million years to 11,700 years ago) were able to adapt to a changing geography caused by successive glacial events in Eurasia as well as human presence.

It is now estimated that the separation of the population into several distinct lines of modern Eurasian wolves occurred approximately 40,000 to 20,000 years ago. This would mean that the Palaeolithic wolf population may have become deeply fragmented during this period, which, incidentally, matches up with the Last Glacial Maximum (also known as the “peak” of the Ice Age).

This period is all the more interesting when we consider how it coincides with Homo sapiens’ period of migration from the East and colonisation of Western Europe, as well as a sharp increase in competition between large predators.

Even more intriguingly, several studies agree on a claim that all modern Eurasian wolves descend from a single small ancient population, which is thought to have become isolated in Beringia (north-eastern Siberia) during the Last Glacial Maximum some 20,000 years ago, notably in order to flee the major climatic instabilities that had been affecting the rest of Eurasia.

But the plot thickens when we consider the question of how domestic dogs appeared. Thanks to a study into the complete genome sequences of primitive dogs from Asia and Africa, combined with a collection of samples from nineteen diverse dog breeds from across the globe, researchers have managed to ascertain that dogs from East Asia are significantly more genetically diverse than others. This model may indicate that dogs first appeared in this region following a divergence between the grey wolf and the domestic dog some 33,000 years ago. However, a 2013 study asserts that Europe was a likelier site of domestication, and that the domestication process occurred somewhere between 32,000 and 19,000 years ago.

A third study reconciles these two theories, asserting that the wolf became domesticated independently both in East Asia and in Europe before primitive Asian dogs travelled to the west, found the human populations there and replaced the indigenous dog population, some 14,000 to 6,400 years ago.

Regardless of the chosen hypothesis, we can safely deduce that when the first settlements and the first methods related to agriculture began appearing around 11,000 years ago, the dog already had at least five distinct evolutionary lines. This tells us that human societies had caused profound changes to canine populations before the end of the Palaeolithic.

As well as this, far from becoming compartmentalised, co-evolution among canines has never ceased. To this day, the wolf continues to hybridise with other canines, such as the dog and the coyote (Canis latrans). It has also interbred with the latter.

In conclusion, although question marks still hover over the geographic origin of the domestic dog and the circumstances and timeline of its domestication, developments in the study of ancient DNA now allow us to disentangle the links that bind the canines of past and present.

So, in response to the question “Do dogs descend from wolves?”, we can indeed say they do, but genetics now give us the tools to clarify which ones. Modern dogs, irrespective of their variety, all stem from a now-extinct line of prehistoric wolves that are only very distantly linked to modern wolves.

Translated from the French by Enda Boorman for Fast ForWord.The Conversation

Elodie-Laure Jimenez, Chercheure en archéologie préhistorique et paléoécologie, University of Aberdeen

This article is republished from The Conversation under a Creative Commons license. Read the original article.

 

The wolf cull isn’t killing caribou

A voice from the wilderness

Get The Great Outdoors, our biweekly brief on all things nature

Sign up here

Categories
Cottage Life

New bear research: She ain’t grizzly, she just looks that way

Photo by BGSmith/Shutterstock

Black bears are black, and grizzly bears are brown, right? Turns out, it’s not so simple. Some black bears are, in fact, brown—and perhaps increasingly so. A new study published in Current Biology sheds light on the cause. 

“Sometimes called cinnamon bears, black bears can appear in a variety of shades: a chocolate, a blond, a brown,” says Emily Puckett, an assistant professor of biological sciences at the University of Memphis. 

Puckett wanted to know whether black bears are appearing brown due to interbreeding between grizzlies and black bears. “Because they come out similarly coloured we had a reasonable hypothesis that it was an interspecies movement of alleles [or genes].” But the answer to that, they discovered, is no. “It’s a unique mutation and it’s unique to black bears,” she says. 

One of the most fun aspects to the work, and what gave them a hint as to the actual mechanism for the change in bear colour, according to Puckett, was looking back at a study that was done in the1980s that drew on the diligent work of natural historians and wildlife communities. “I was astounded at this paper. They surveyed managers across the US and Canada, and came up with a series of maps of the percentage of black animals on the landscape across the geography.” That study looked at about 40,000 bears, and there was an older paper from the ‘70s that tracked the colour of female bears and their cubs. From those frequencies, which were remarkably consistent, Puckett and her team could guess that the mechanism probably arose from a dominant mutation. 

Wild profile: meet the black bear

To find that out Emily Puckett and her team used tissue samples from bears that were hunted, killed by vehicles, or animals captured for other research studies or management purposes. They did genetic analysis and hair colour analysis on samples from hundreds of black bears (Ursus americanus) and a small number of grizzly bears (Ursus arctos). In the end, they concluded that the “cinnamon morph” is caused by a mutation in the TYRP1 gene. Puckett effuses about being able to build on the work of past citizen scientists and wildlife biologists. “These natural histories from wildlife communities were spot on,” she says, “then I get to come in with the latest technology and create 200 bear genomes.” 

Puckett was amazed to discover that her allele frequency data (what the genetic analysis shows) “matches up very very closely to the data measuring phenotype frequency” (or what the animals actually look like). “Which actually makes sense,” she says, “because it’s a dominant mutation.” 

Not only did they discover the gene mutation that causes the colour morph, they also found out when, historically, the mutation took place. “We used a very fancy population genomics coalescent model that estimates when in time the mutation arose on the chromosome,” she says. “And we ran that for the specific point mutation that we identified that caused the brown colour and estimated that it was 9,360 years—or 1,440 generations—old.” 

So, where could you expect to see a so-called cinnamon bear? In the US, in the Southwest, the Sierras, and California is where the researchers saw the brown version of the gene showing up in the highest frequency, decreasing as you move north up into the Rocky mountains. “The Rockies are of course this massive barrier even for a large, strong animal like a bear to move through,” says Puckett. “So once you get east of the Rockies, or north of the Rockies, into the Yukon, you see that gene showing up, but in lower frequencies.” 

Puckett explains that genes spread as one animal moves from its natal area to a second area and breeds, moving alleles, or genes, from population one to two. “This is such a fun part of the paper—it’s basically the same piece of DNA being copied over and replicated—from bear parent to kid—found in the southwest, found in Alaska, found around the Great Lakes, Manitoba, Ontario, and then in Connecticut—that’s as far east as we’ve found it.”

The last piece of the puzzle was what adaptive advantage did it serve to have brown fur instead of black? The researchers tested two proposals. First, could being a lighter colour give an advantage for thermoregulation, since the trait arose in a hotter, drier environment? Second, could it have allowed the American black bears to ride on the coattails, or reputations, of grizzlies where their ranges overlapped, allowing them to better compete? They tested the different factors and didn’t get support for either hypothesis. “So we don’t know why it happens,” says Puckett. But they now wonder whether some type of selective advantage, such as, perhaps light coloured fur might be hard to spot in different environments. “In forest habitats, they might blend in more if they are black. In more edge habitat, where the forest cover is more open, maybe those are places where brown allele might be more favoured.” 

In the meantime, we can say that for some bears at least, cinnamon is the new black.

Wild profile: meet the grizzly bear

 

A voice from the wilderness

Get The Great Outdoors, our biweekly brief on all things nature

Sign up here

Categories
Cottage Life

Your genetics influence how resilient you are to cold temperatures, says new research

Photo by Dudarev Mikhail/Shutterstock

Some people just aren’t bothered by the cold, no matter how low the temperature dips. And the reason for this may be in a person’s genes. Our new research shows that a common genetic variant in the skeletal muscle gene, ACTN3, makes people more resilient to cold temperatures.

Around one in five people lack a muscle protein called alpha-actinin-3 due to a single genetic change in the ACTN3 gene. The absence of alpha-actinin-3 became more common as some modern humans migrated out of Africa and into the colder climates of Europe and Asia. The reasons for this increase have remained unknown until now.

Our recent study, conducted alongside researchers from Lithuania, Sweden, and Australia, suggests that if you’re alpha-actinin-3 deficient, then your body can maintain a higher core temperature and you shiver less when exposed to cold, compared with those who have alpha-actinin-3.

Take the plunge: the benefits of ice baths and cold-water swimming

We looked at 42 men aged 18 to 40 years from Kaunas in southern Lithuania and exposed them to cold water (14℃) for a maximum of 120 minutes, or until their core body temperature reached 35.5℃. We broke their exposure up into 20-minute periods in the cold with ten-minute breaks at room temperature. We then separated participants into two groups based on their ACTN3 genotype (whether or not they had the alpha-actinin-3 protein).

While only 30% of participants with the alpha-actinin-3 protein reached the full 120 minutes of cold exposure, 69% of those that were alpha-actinin-3 deficient completed the full cold-water exposure time. We also assessed the amount of shivering during cold exposure periods, which told us that those without alpha-actinin-3 shiver less than those who have alpha-actinin-3.

Our study suggests that genetic changes caused by the loss of alpha-actinin-3 in our skeletal muscle affect how well we can tolerate cold temperatures, with those that are alpha-actinin-3 deficient better able to maintain their body temperature and conserve their energy by shivering less during cold exposure. However, future research will need to investigate whether similar results would be seen in women.

ACTN3’s role

Skeletal muscles are made up of two types of muscle fibres: fast and slow. Alpha-actinin-3 is predominantly found in fast muscle fibres. These fibres are responsible for the rapid and forceful contractions used during sprinting, but typically fatigue quickly and are prone to injury. Slow muscle fibres on the other hand generate less force but are resistant to fatigue. These are primarily the muscle you’d use during endurance events, like marathon running.

Our previous work has shown that ACTN3 variants play an important role in our muscle’s ability to generate strength. We showed that the loss of alpha-actinin-3 is detrimental to sprint performance in athletes and the general population, but may benefit muscle endurance.

This is because the loss of alpha-actinin-3 causes the muscle to behave more like a slower muscle fibre. This means that alpha-actinin-3 deficient muscles are weaker but recover more quickly from fatigue. But while this is detrimental to sprint performance, it may be beneficial during more endurance events. This improvement in endurance muscle capacity could also influence our response to cold.

A beginner’s guide to cold-water surfing in Canada

While alpha-actinin-3 deficiency does not cause muscle disease, it does influence how our muscle functions. Our study shows that ACTN3 is more than just the “gene for speed”, but that its loss improves our muscle’s ability to generate heat and reduces the need to shiver when exposed to cold. This improvement in muscle function would conserve energy and ultimately increase survival in cold temperatures, which we think is a key reason why we see an increase in alpha-actinin-3 deficient people today, as this would have helped modern humans better tolerate cooler climates as they migrated out of Africa.

The goal of our research is to improve our understanding of how our genetics influence how our muscle works. This will allow us to develop better treatments for those who suffer from muscle diseases, like Duchenne muscular dystrophy, as well as more common conditions, such as obesity and type 2 diabetes. A better understanding of how variants in alpha-actinin-3 influences these conditions will give us better ways to treat and prevent these conditions in the future.The Conversation

This article—by Victoria Wyckelsma, Postdoctoral Research Fellow, Muscle Physiology, Karolinska Institutet and Peter John Houweling, Senior Research Officer, Neuromuscular Research, Murdoch Children’s Research Institute—is republished from The Conversation under a Creative Commons license. Read the original article.

A voice from the wilderness

Get The Great Outdoors, our biweekly brief on all things nature

Sign up here