How the Lemming Got its Coat

The Ice Ages were, without doubt, the most dramatic natural climatic changes on Earth in the last few million years. The last one was particularly severe, with vast ice sheets covering much of northern Europe and northern North America. This, naturally enough, forced many species of animals in the Northern Hemisphere to move south. Even those well-suited to the cold, such as reindeer, musk oxen, and woolly mammoths, would have had to avoid the barren ice sheets, even if they were happy in the broad tundra belt to the south.

In Europe, in particular, there is only so far south you can go before hitting the coastline. This meant that many animals were forced into small areas, some of which may still have been marginal habitat for them, to avoid extinction. These areas are called "refugia", and their small size and isolation were a driver for evolutionary change. Sometimes populations were split apart for so long that they became separate species and, for example, we can date many species of northern birds to this time, even though, for them, the Mediterranean would not have been an issue. 

All the World's Deer: Small Deer of South America

Grey brocket

Deer first entered South America when that continent first connected with its northern counterpart a little over two million years ago. Finding nothing similar already there, they rapidly diversified into several distinct species, taking advantage of a wide range of different habitats. Many of the resulting species were medium to large animals, resembling their northern relatives, such as white-tailed and mule deer. But others instead took on a role closer to the muntjacs of eastern Asia. 

How many species of these small South American deer are truly distinct is a question that is not fully settled yet. In common with the scientific fashions of the time, a great many species were named in the 19th century, only to be merged in the 20th and then split apart again in the 21st (not always along the same lines, of course). As a result, many of the species we recognise today weren't considered such until recently and have not been individually studied to any great extent beyond demonstrating that they exist. On the other hand, the reason that we confused them for so long - and still aren't entirely sure how many they are - is that they are all quite similar. This is especially true of the various kinds of brocket, all of which are currently placed in the genus Mazama.

The Curiosity of Lemmings

The reason that there are so many different animal species in the world is that they all have different living requirements; it's no secret that a tiger has different needs from a hedgehog. In most land-based habitats, we can look around and see a fair variety of mammal species and it's obvious that, while they may compete in other ways (by eating each other, for example), they can all survive because they are using their chosen habitat in different ways.

But, in some cases, it's quite hard to find more than a handful of species - especially if we're going to restrict ourselves to mammals, and ignore all the birds, insects, and so on. This is often true of city centres, for example, where you may not have much aside from rats, mice, and urban foxes. But in the wild, however, we are typically talking about particularly marginal habitats, such as deserts, high mountains and other desolate wastes.

Unravelling the Bushbuck

Imbabala

Three years ago, I wrote a series of posts on the various species of bovine. This was using 'bovine' in the wider, technical, sense than it's everyday meaning, essentially including all animals more closely related to cows than to sheep or goats. This obviously includes all the really close relatives of cattle - bison, buffalo, yak, and so on - but it also includes a number of animals that are more accurately described as 'antelopes'.

Most species of these 'bovine antelopes' belong to the genus Tragelaphus, collectively known as 'spiral-horned antelopes'. Especially if we include the large cow-like elands (sometimes given their own genus, Taurotragus) these are a fairly diverse range of animals, including some adapted to open woodland or savannah, and others adapted to dry scrub, mountain slopes, dense jungle, or swampland. Perhaps because it seems to be the most adaptable of the species, the most widespread of the spiral-horned antelopes is the bushbuck (Tragelaphus scriptus).

The Hybrids are Coming

Hybrid domestic pig x wild boar

Conservation - whether it be of mammals or any other kind of animal or plant - tends to focus on the species level. These are the discrete kinds of living creature that can be most easily identified and preserved, ensuring that the mix and variety of the natural world remains as close to its original state as possible. Preservation of subspecies is often a lower priority, which makes sense if you really have to make the choice, but it, too, can be important if we want to preserve such things as genetic variation within a species.

The common understanding of a 'species' is that it consists of a group of animals that cannot interbreed with animals outside that species to create fertile offspring. This, however, is an oversimplification; lines blur, and not always in neat and tidy ways. Scientifically, there are multiple different ways of defining what a 'species' is, but the general idea is that it has to be a group of animals that can be readily identified as different from their relatives. Which tends to mean that, even if they can interbreed with other species, they generally don't, at least in the wild, and maintain a separate gene pool.

The Puzzling History of the Clymene Dolphin

The taxonomy of dolphins is, as I've mentioned on a couple of previous occasions, a complicated issue. The problem is that at least some dolphins underwent a very rapid diversification in the not-so-distant past. New species appeared so shortly after one another that, from the perspective of the present day, it's very difficult to figure out in what order it happened, or which dolphins are most closely related to which others. This particularly affects the genera Tursiops (the bottlenose dolphins) and Stenella (the spinner dolphin and its relatives), and likely has some effect on one or two others as well.

If you look back at those two posts (sorry, this won't work if you're reading this on a mobile) you'll see that I drew up a plausible relationship tree based on the research of Kate Charlton-Robb et al, who identified the existence of the Burrunan dolphin as a distinct species in 2011. One of the animals you'll notice that I mentioned was the Clymene dolphin (Stenella clymene), and that I said in one post that "the spinner, spotted, and Clymene dolphins were all assumed to be related, on the not unreasonable grounds that they look much the same as one another..." Emphasis on the past tense, because the study seemed to show that, despite their visual similarity, they weren't all that closely related after all.

One Gazelle or Two?

Mountain gazelle (probably)

According to the International Union for the Conservation of Nature, there are sixteen living species of gazelle. However, as I've mentioned before, counting species isn't always as simple as we might like to think, because the lines between them often blur. Are those two, similar-looking, animals separate species, or just two subspecies of the same thing? And how would we know?

You might suppose that the answer is something along the lines of 'do they cross-breed to produce fertile offspring or not?' Horses and donkeys are different species, you might think, because, while they can interbreed, the result is a sterile mule. Similarly, tigers and lions can also cross-breed, but the results are usually infertile. (Actually, fertile mules and "ligers" do exist, but they seem to be rare). If they don't cross-breed at all, of course, the answer is even simpler. So, take the two gazelles you're wondering about, mate them, and see what happens. Right?

Well, not really. For one thing, that's much easier said than done, especially if one of the possible species is endangered. It's hard enough getting pandas to mate with other pandas to be sure that mere lack of mating proves anything at all. Not only that, but there are, believe it or not, a number of cases where animals that are clearly different species can, indeed, interbreed to produce fertile offspring. Polar bears and grizzly bears, for instance, to give one example becoming more common of late.

Weasels in Burrows: the 'True' Badgers

European badger

The word 'badger' has been applied to a number of species of stocky, moderately sized, members of the weasel family, that are not necessarily all closely related to one another. That's not due to any sort of carelessness with the names, because, for a long time, it was thought that they were closely related.

It's hardly an unreasonable conclusion, because they do look strikingly similar to one another, even to the extent of having similar coat markings. Modern genetic analysis, however, has shown that they are rather more different from one another than appears at first glance. Indeed, one group of 'badgers' - the stink badgers - turned out not to belong to the weasel family at all, but, instead, to the skunk family.

The stink badgers are obviously beyond the scope of this series on mustelids, but the various other species are not. The remaining badgers, however, still do not constitute a single group within the weasel family, as was once thought. That's because they don't have a single ancestor from which all other badgers - and crucially, nothing but badgers - are descended. All badgers are related, because everything is related, if only you go back far enough, but they're often more closely related to other animals than they are to each other.

Wolf or Jackal?

This one really is a golden jackal

A species, you may have been told, is a group of animals that can breed with each other, but cannot breed with other species to produce fertile offspring. So wolves and domestic dogs are the same species, because they can interbreed, while horses and donkeys are not, because mules are infertile. There are a lot of problems with this idea, because it turns out that nature isn't really all that neat and tidy. For example, polar bears are quite clearly not the same thing as grizzly bears, but the two can produce fertile offspring - something that is happening increasingly as the polar ice caps melt and the natural habitat of the polar bears shrinks.

Its also not at all obvious how you're supposed to apply this definition to animals that don't reproduce sexually (though that's obviously not a problem with mammals). And what about those cases where two species have separated so recently in the evolutionary past that some individuals can crossbreed, but others can't? The classic example here are the herring gulls and lesser black-backed gulls, where the Siberian populations of these two species can interbreed, but the British ones can't. It really does get messy very quickly.

Even if it wasn't for all this, if we really did use the fertile interbreeding definition, how useful would it be? Well, we would have to accept that polar bears are really just odd-looking brown bears, for a start. But more than that, what about other species? Are we really going to try and cross-breed every plausible combination to see what happens? It can be hard enough to get some animals to breed in captivity at the best of times, making the whole idea completely impractical.

Inevitably, this means you sometimes have to end up applying some common sense, and describing something as a separate species largely because it's useful to do so. So polar bears, for example, are considered a species, because they are different in so many ways from brown bears. At the opposite end of the scale, there are many species that don't generally interbreed, but are so closely related that they look almost exactly the same, making it really hard to tell where one species starts and another ends. A lot of these are mice of various kinds, but it's also true of dogs.

The wolf (Canis lupus) is a very widespread species. Before humans drove it off from many parts of its range, it was found throughout Europe, and in most parts of Asia and North America. Human intervention brought them to Australia, in the form of dingos, and the domestic dog is also considered a subspecies of wolf. They once used to inhabit the southern coast of the Mediterranean, but now wild wolves are completely absent from Africa. Or are they?

The closest living relative of the wolf is the golden jackal (Canis aureus). Golden jackals are found in the Balkans, and across Arabia and southern Asia, but they are also found across northern and eastern Africa as far south as Nigeria. It would seem, therefore, that the golden jackal is more suited to these hot climates than its more northerly cousin, the wolf.

Wolf      Golden     Coyote    Ethiopian
          Jackal                 Wolf
  |          |         |           |
  |          |         |           |
  |          |         |           |         Other
  ------------         -------------        Jackals
       |                     |                 ^
       |                     |                 |
       -----------------------                 |          Dhole
                 |                             |            |
                 |                             |            |
                 -------------------------------            |
                                |                           |
                                |                           |
                                -----------------------------
                                              |
                                              |

Like the wolves, golden jackals are a varied bunch, with several different subspecies recognised. Indeed, one subspecies, found in Egypt, is quite hard to tell apart from a wolf - were it not for the fact that, officially, there are no wolves in Egypt. There had been some dispute in the past as to the exact status of these Egyptian animals, but, more recently, some very wolf-like jackals were also spotted much further south, in Ethiopia. Were they really jackals, as the textbooks said they had to be, or were they something else?

You can't just capture them, breed them with wolves, and see what happens. Not least because we know that wolves can breed with coyotes without any difficulty, and they're certainly a different species, so fertile offspring produced in captivity wouldn't prove anything either way. To see what they really are, we need to look at their genetics. If two groups of animals regularly crossbreed in the wild, their genetics should be very similar, and we have as good a reason as any we can come up with to say that they're really the same species.

So that's what the researchers did. They collected samples of the animals' dung, sequenced their DNA, and compared it with samples taken from jackals in Egypt, with wolves and golden jackals from a range of locations, and, for good measure, from seven other species of the dog family. (Including foxes - when you're doing this sort of test, you need to include something that's sort-of-similar yet manifestly not the same, just to make sure it's working properly).

Of course, they didn't analyse the entire genome, since modern technology isn't up to making that at all routine. Instead, they looked at a particular gene, cytochrome b, which is used as a standard in these sorts of studies. It's presumably not perfect, but with everyone using the same gene, at least it is possible to compare results with those from other workers, and this particular gene has done a good job so far at figuring which mammals are related to which other mammals.

The results showed, firstly, that these Ethiopian jackals were almost identical, genetically, to the ones seen in Egypt. This alone is significant, since it means that this subspecies is found much further south than previously thought. But it also showed that these animals were more closely related to wolves than to other golden jackals. Indeed, in some respects, they were more similar to wolves from places like Canada and Sweden than they were to wolves from the Himalayas.

So, whatever these animals are, they can't possibly be golden jackals. It appears that they diverged from the main group of wolves after the Himalayan wolves did, which means they have to be wolves, too. All the textbooks say there are no wild wolves in Africa, but we now know that there are - at least in Egypt and Ethiopia, where they have been living alongside golden jackals, and looking so similar that few people could tell them apart.

This is exactly the sort of problem that occurs when you have very similar looking species living side by side. Indeed, this sort of finding crops up quite often with mice, with nobody much noticing (or caring, frankly). But even then, is this animal actually a subspecies of wolf, or something else entirely? Just a few years ago, it was argued that Himalayan wolves were themselves a separate species. If that's right, then the Ethiopian animals might well be a species of their own, too - one we didn't previously know about. It's debatable either way, since they do seem to be much closer to northern wolves genetically than we'd expect a new species to be, yet different enough that a blood test will tell them apart.

Does it matter, though? Do we care whether this is a species or a subspecies? Well, funnily, enough, yes it does make quite a difference. Wolves are not an endangered species (and neither are golden jackals), so if these animals are a special sort of wolf, they will get relatively little protection from the various international conventions about such things. But if they're a species, then there's pretty good reason to suppose they might be endangered - there certainly aren't very many of them, and the local farmers do have a habit of killing them to protect their livestock. That's not a problem (from a species conservation perspective) if they're also found elsewhere in the world, but if this is the only place the species is found, then they can get protection under international law.

Considering that we can't come up with a good definition of what a species is, it makes a heck of a lot of difference whether a group of animals is one or not.

[Picture from Wikimedia Commons]

Telling fossil species apart - a brontothere's nose

Brontotherium skull - or should that be Brontotherium prousti?

When we think of specific kinds of living animals, we tend to think of individual species, at least where those animals are fairly familiar to us. But prehistoric animals are almost always referred to just by their genus name. A proper species name has two parts to it (such as Homo sapiens), but the genus name is just the first part of that, and that's how we think of most prehistoric creatures. Consider the dinosaurs, such as Triceratops, Velociraptor, and Diplodocus, or mammals such as Smilodon, the sabre-toothed cat. Probably the only exception - and arguably one of only two creatures whose common name is the same as its scientific name - is Tyrannosaurus rex. (The other one is Boa constrictor, if you're wondering).

A genus is a group of closely related species. There are many genera that only contain one species, but most have a number of different species at any given point in time, and even more when you look over the whole of their evolutionary history. It's as if we thought of the living genus Canis as a single entity, ignoring the fact that it includes wolves, coyotes, and jackals, never mind extinct species such as the dire wolf.

There's a reason for this, of course, which is that it's really tricky to tell actual species apart from their fossils. Taking the traditional definition of a species as something that doesn't cross-breed with other species to produce fertile hybrids (and the modern definition is a bit more complicated than that), how on Earth would you know, if you're only looking at a fossil? Instead, the definition more commonly used for fossil animals is that a species is a group of specimens so similar that there's no way to consistently tell them apart, even when you have a complete skeleton. But most fossils aren't complete, or are at least damaged by several million years of being squished under tons of rock, which makes it very difficult to spot the tell-tale differences between the equivalents of coyotes and jackals.