Let me ask you a very simple question:
How many species of giraffe are there?
I bet the vast majority of you would say: “Just one.”
A few might point out that next closest relative to the giraffe is the okapi, which looks like something created in gene splicing lab, and a few others might mention that most taxonomists believe the pronghorn is a close relative of the giraffe and the okapi.
But I bet that very few of you would say that there are multiple species of giraffe– unless you’ve seen this study.
Yeah. It turns out that when we examine the mtDNA and certain microsatellite markers, there are likely several species of giraffe.
But we have historically believed that there is just one species.
But this study found that there are 11 genetically distinct populations of giraffe, but six of these are fairly close to being separate species– and might very well be. (This same methodology found that there were two species of clouded leopard and two species of elephant in Africa that are quite genetically distinct from each other.)
These six populations had virtually no evidence of interbreeding. Masai giraffes, reticulated, and Rothschild’s giraffes live in roughly the same area, but they are reproductively isolated from each other.
Further, as much as 1.5 million years of evolution may be separating them.
Now, more genetic studies need to be performed on giraffes. These types of studies can be in error, but if we look at more of the genome and have more samples in the studies, we will get a better understanding of how giraffes evolved.
The evidence is pretty good that the classical classification of only a single species of giraffe might very well be in error.
This study raises some important questions for how we approach taxonomy.
Some people really like to split up related populations into species, even if we have lots of evidence of a gene flow between populations. These people are called “splitters.”
Others prefer to group related populations together within a single species, especially if there is evidence of a considerable gene flow between them. These people are called “lumpers.”
Historically, it was to a naturalist or explorer’s advantage to define something as a new species.
I have never been able to keep track of all the potential bear species that have been cataloged. Most of these fit nicely into the brown bear species, but in the nineteenth century, any number of bears could be deemed a unique species solely on the vanity and caprice of the person documenting them.
Now, we have a whole host of tools to help us see how species are related.
Traditionally, morphology was used to determine taxonomy and phylogenetic relationships, but now we are using various assays of DNA to make these judgments.
We’ve seen the validity of some potential species collapse under these analyses, the red wolf and the Eastern wolf are two that have fallen, as has the golden moon bear of Southeast Asia. A gold-colored phase of the Asiatic black bear (“moon bear”) was proposed as a new species, but it was found to be nothing more than a golden Asiatic black bear.
We’ve also seen the validity of certain species confirmed, like the kouprey of Cambodia, which was once claimed to be nothing more than a hybrid between banteng and an indicus cattle. A mitochondrial DNA study found that kouprey and Cambodian banteng had very similar mtDNA— which led to this particular speculation. But a study that included a larger sample of banteng mtDNA and as well as some nuclear DNA markers revealed that at least one kouprey cow wound up intermixing with the banteng in Cambodia during the Pleistocene. Virtually all banteng from Cambodia have kouprey mtDNA.
What’s particularly interesting is the researchers who were claiming that the kouprey was hybrid dropped the nonsense almost instantly after being shown what the nuclear DNA studies revealed. That’s how science is supposed to work. If a hypothesis is falsified, you’re supposed to accept it as being in error and not true.
For the proposed red and Eastern wolf species, researchers and people who should generally know better keep promoting both of them and also entertain denial that the genome-wide analysis that was performed on wolves and coyotes found anything uself– which was more extensive than any of these other studies that have proven very useful in determining species status.
There is more evidence that there are multiple species of giraffe in Africa than there is evidence of multiple species of wolf in North America, yet the taxonomy of giraffes has not been changed in any official capacity. And the same goes for the several species of wolf in North America. A wolf with some coyote ancestry is called a unique species of Eastern wolf, even though its mate is a pure wolf, but a Rothschild’s giraffe and a masai giraffe are the same species, even if they will not mate with each other at all.
How weird is that!
Three cheers for DNA!
Excellent logic! When it comes to dogs, I am a lumper.
Do all taxonomists belong to the same species?
But, seriously, how many waves of migration from Asia have we had in North America? In Africa, first it was elephants, then giraffes. What next? Do we have multiple closely related species of anything in North America? I’m thinking more than one invasion of Africa (from Asia?), but only one pleistocene invasion of North America? (We know there are multiple everything in Asia.) Any thoughts?
Leopard frogs have proven to have lots of cryptic species:
http://www.nytimes.com/2012/03/14/nyregion/new-leopard-frog-species-is-discovered-in-nyc.html (this is the most unusual one).
If you’re going to find them, it’s better to look at small animals that don’t travel far. There’s a lot more room for genetic drift with those sorts of animals than things like wolves.
Thank you. Sorry I asked this question. Should have done some research first.
politics at work. there’s a political advantage to insisting that the red wolf and Eastern wolf are real subspecies of wolf. It’s easier to preserve a “wolf” than it is to argue preserving a coyote with some wolf blood. As for giraffes, if they are seperate species, then the Rothchilds is “done” — wikapedia states The Rothschild Giraffe (Giraffa camelopardalis rothschildi)[1] is one of the most endangered giraffe subspecies with only a few hundred members in the wild — probably not enough animals to maintain genetic health if “no crossings with other giraffe species” is established. (Wikapedia –While giraffes in general are classified as Least Concern, the Rothschild Giraffe is at particular risk of hybridisation).
How different really are the giraffes? MTDNA may show different lineages that may not have “mixed” because of geographic isolation, but are there other significant DNA differences? Clearly they DO interbreed when humans put them together — and apparently have fertile offspring. So it might be more of a “ring species” than it is clearly distinct species.
The red wolf has almost no wolf in it, so I don’t see the point in going nuts conserving it.
As for giraffes, it’s more than mtDNA. Nuclear DNA markers show they do have have lot of variance.
I think the new thinking on giraffes is that young giraffes imprint upon their mother’s pattern and want to mate only with other giraffes with those patterns.
All of these “subspecies” are different because they live in different habitats and require different coat patterns as camouflage.
And there is a selection pressure for uniformity in giraffe spots within a population. There were some researchers who spray painted giraffes with numbers in order to tell them apart, and one by one these giraffes became lion food.
That alone would put a major selection pressure on giraffe populations that would select for giraffes to be very conservative about which patterns they mate with.
In captivity, they all mate.
I don’t think the Rothschild’s giraffe is capable of being saved. I thought so even when it was just a subspecies.
Nuclear DNA markers show they do have have lot of variance.–ok. as for selection for uniformity within a population, aparently this isn’t the case with the hybrid Rothschilds — or do the only ones that survive have the pattern of their mother? It’s possible that the number disrupted the pattern enough that the giraffes became “lion food” – I seem to remember something about putting a mark on gulls resulting in that animal being harassed by the others. Pretty much anything the size of a giraffe is only going to survive in a “wild animal park” / preserve environment. It’s too much meat on the hoof for those who live in the area to avoid being poached and it’s too much competition with the cattle and other livestock for the pastoralists and farmers to allow to run free. The same applies to elephants. The only survival method is setting aside (fenced or otherwise) preserves or in somehow managing to reduce the human population. They aren’t going to manage completely free roaming as they might have done 10,000 years ago or so. Climate change and hunting eliminated whatever subspecies that once roamed in Egypt — so the issue is — how much human intervention is going to be used to preserve the giraffe as a whole and if it is better to allow some mixing or to struggle to preserve “pure” very small populations. This is one of the underlying issues between splitters and lumpers. An animal is more likely to survive within “lumpers” but unique characteristics are more likely to be preserved with splitters.
But if you lump, some of those characteristics that get lost at first will show up as traits in some of the future generations. So maybe some the genes aren’t lost in a lumping unless the population is too small and other factors come into play.
Be grateful you aren’t in botany . . . where polyploidy and apomictic reproduction, along with hybridization, cause further havoc in species identification. For entertainment, have a read on the sub-genus Rubus. Wikipedia: “The genus Rubus is a very complex one, particularly the blackberry/dewberry subgenus (Rubus), with polyploidy, hybridization, and facultative apomixis apparently all frequently occurring, making species classification of the great variation in the subgenus one of the grand challenges of systematic botany.