Sunday, 11 January 2015

The Dog Family: Wolves, Dogs, and Dingoes

Eurasian wolf
The best known and most familiar of the species in the dog family is surely the grey wolf (Canis lupus). This is not least because it is the one that we happen to have domesticated, and which most of us see just about every day. Even the wild form is so familiar that there are a great many wildlife documentaries and web pages out there that cover the species better than I can in one blog post, and I don't want to go too much over that ground. But nonetheless, for the sake of completeness, at least some sort of overview is needed here.

The term "grey wolf" is the generally accepted one for the species as a whole. While there are other species that are referred to as wolves, this is the one that we generally mean when we say the word "wolf" without qualification. Most other terms, such as "timber wolf", "steppe wolf", and so on, refer either to groups of one or more subspecies, or are simply alternative terms for the same animal. Once being spread throughout almost the entire Northern Hemisphere (albeit to only a limited extent in Africa), it is unsurprising that there are rather a lot of subspecies.

But how many? That's a question of some debate. I have talked before about how difficult it can be, in practice, to separate one species from another; the problem is even worse when you're trying to count subspecies. One scheme, for instance, has as many as 24 subspecies in North America alone, while another, more conservative, scheme recognises just twelve worldwide. There are a great many opinions that lie somewhere in between.

The grey wolf is the largest of all living canids, at around the size of a German shepherd dog. Despite the name, they aren't always grey, although most subspecies broadly are. Some, however, are brownish, and the Arctic wolves of far northern Canada are almost pure white. Even within a subspecies, there is variation, with some individuals being a blackish charcoal even when their own relatives are a lighter grey.

They will live in pretty much any habitat imaginable, so long as there's something to eat there. In general, they tend to hunt hoofed animals larger than themselves, including deer, sheep, goats, wild boar, and even bison or musk oxen. But they certainly won't turn their nose up at smaller prey, should that be what's available, and they eat animals as small as voles on occasion. They're mostly nocturnal, but that's probably in order to stay out of the way of humans, since they're much more active during the day in places where humans aren't around.

Arctic wolf
Wolves, of course, are social creatures, even by the standards of the dog family. Wolf packs normally consist of a single mated pair, together with any of their young that have yet to leave home and strike out on their own. Since they can stay with their parents for some time, gaining both the protection of numbers and assistance in the hunt, this means that wolf packs often contain as many as twelve members, many of them adults, even if only two of them breed. Larger packs do occur, where multiple family groups join together for a while.

Wolf packs are highly territorial, but the size of that territory varies enormously depending on how much food there is to be found - it can be anything from 75 km2 (30 square miles) in dense forest to 2,500 km2 (1,000 square miles) in Arctic wasteland. They maintain these territories with a combination of scent marking, in the manner familiar to anyone who takes a dog for a walk, and howling, resorting only to violence if the intruder really doesn't take the hint. Howling is also used to gather the pack together (which is why domestic dogs sometimes howl when left alone), and while wild wolves can, of course, bark, they do so much less than domestic dogs.

Wolves breed in the spring, after which the female constructs some sort of sheltered den in which to birth and rear her litter. Once they are old enough to travel with the pack, wolf pups often receive care from more than just their mother. Even non-breeding females within the pack may lactate and give milk to the pups - who are likely to be their own siblings. As with other "wolf-like" canids, but unlike foxes, wolves also swallow and regurgitate food for pups too young to hunt.

Only one female in the pack, typically the oldest, normally breeds. Younger females do breed occasionally, so it's obviously possible, but for the most part they appear to be reproductively suppressed, and don't even come into heat. Younger males, on the other hand, are generally kept in check by the threat of violence from the alpha male. After a few years, however, adults of both sexes leave the pack, and seek out a new territory and a partner of their own. Males, which generally outnumber females, remain on their own, as "lone wolves" for much longer than females do, sometimes prowling for a year before settling down, while females are rarely alone for more than three months.

There are two subspecies of grey wolf that are different enough from their fellows that we don't normally call them wolves at all. One of these is the dingo (Canis lupus dingo). The only wild subspecies of wolf to be be found in the Southern Hemisphere, dingoes are, however, not unique to Australia, also being found in Thailand, and likely also in other parts of Southeast Asia and the neighbouring islands.

In modern Australia, dingoes' most common prey animal appears to be rabbits, supplemented by various other small animals such as rodents and lizards. Rabbits, however, are not part of the native Australian wildlife, and where they don't exist, dingoes instead seem to feed primarily on wallabies, although, like other wolves, they will eat whatever they can get, including, in this case, kangaroos, wombats, and emus.

That such large prey aren't a part of their regular diet is likely due to the fact that, while they certainly hunt in packs where they can, in modern times their population density is low, and they are often found alone or in mated pairs - limiting the size of what they can take down. Dingoes breed at much the same time of year as other wolves, which, in their case, means that the pups are born in winter, rather than in summer. It doubtless helps that the Australian winter bears no resemblance to that of Canada or Siberia, leaving no great evolutionary pressure to adjust to the reversed seasons.

But then, dingoes haven't exactly been around a long time. They appear to have originated somewhere around Thailand, and to have once been widespread across that part of the world. Exactly when this happened is unclear, although the oldest Australian remains date from around 3,000 BC, so that's a reasonable bet. This is, however, much later than the first arrival of humans on the continent, which would help explain why there are no dingoes in Tasmania.

The most likely explanation for their existence in Australia is that they were brought across on boats by some later group of maritime travellers, presumably as at least semi-domesticated animals, and subsequently returned wholly to the wild. This has led to a debate as to whether they are really a subspecies distinct from domestic dogs. It can be hard to tell, not least because many modern dingoes are likely hybrids with actual dogs. Recent analysis of the historical remains of pure dingoes, however, does show that they can be reliably distinguished from domestic dogs, and likely justifies their subspecific status.

Which brings us to the origin of the other subspecies that we don't normally call "wolves": the domestic dog (Canis lupus familiaris). Dogs used to be recognised as a species in their own right, not least because, back in the nineteenth century, it wasn't entirely clear that they were wolves - as opposed to, say, a wolf/jackal hybrid, or perhaps descendants of something that's now extinct in the wild. We now know that they definitively are wolves, and modern schemes of scientific naming therefore don't allow them to be described as a full species, although the old term "Canis familiaris" is still used in many contexts.

Exactly which subspecies of wolf the dog might be descended from, and where domestication originally occurred, is still a matter for debate. Origins in Southeast Asia, the Middle East, and Europe have all been proposed, and all are supported by at least some of the genetic evidence. The issue may well be complicated by dogs having back-crossed with wolves at various times during the past, and by the fact that the ancestral subspecies is probably one that's now long extinct.

The oldest undisputed fossil dogs date from at least 12,000 BC, in Europe and the Levant. This, it should be noted, is before the dawn of agriculture, suggesting that the first dogs were domesticated as hunting animals. It's entirely possible that domestication occurred more than once, and, in this light, it's interesting to note that some much older fossils, from well over 30,000 years ago in Belgium and the Altai Mountains of central Asia, do resemble dogs, both physically and genetically, more than they do living wolves. The best guess seems to be that these were early attempts at domesticating wolves, separate from those that led to the modern dog, and which left no descendants in the long term.

Definitely not a wild animal
The changes that took place in ancestral wolves to turn them into dogs are equally fuzzy, not least because there are so many different breeds of dog today, many of them bred for highly specialised purposes. In general, there seems to be a trend towards "neoteny", the retention of juvenile features in the adult. Much of this is behavioural, and likely linked to an extended period during which puppies can acclimatise themselves to the presence of humans, treating them as members of the pack, rather than rejecting them as a wild wolf would do. As part of this, dogs apparently co-evolved with humans to be better able to understand and communicate with them.

It is, however, also physical, which explains the short snouts, large eyes, and so on of many dogs compared with adult wolves. At its extreme, this leads to breeds like the Pekinese, which has a skull that is essentially that of a foetus. Recent studies, however, have shown that the changes in body and skull shape are more complicated than this, and that simply describing the dog as an overgrown wolf puppy is grossly over-simplifying things.

These changes sound like they should have taken a remarkably long period of time, but that's not necessarily the case. In 1957, in a now-famous ongoing experiment, geneticist Dmiti Belyaev began to breed silver-coloured red foxes for tameness. Within just six generations, a small number of the foxes were wagging their tails, whining for attention, licking their handlers, and otherwise acting just like dogs. By the end of the century, forty years later, a full three-quarters of all the foxes acted in this way, essentially fully domesticated.

Interestingly, even though the experimenters only bred for the ability of the foxes to tolerate human presence, unintended physical changes began to appear, too. Many of the tame foxes developed spotted coats, floppy ears, and curled tails, along with the shorter snouts that would be predicted by the theory of increasing neoteny. Presumably, these are in some way linked to the delayed onset of adult behaviour, and to the lower levels of adrenaline and other stress hormones that the domesticated foxes possess.

That this could happen in just forty years implies that the domestication of the wild grey wolf into the early domestic dog may not have been so difficult a process as one might think, even without the benefit of a controlled environment.

[Photos by " 4028mdk09", "tsaiproject", Sam Fraser-Smith, and "Томасина", from Wikimedia Commons]

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