DNA analysis reveals there are four distinct giraffe species, not one

https://www.researchgate.net/blog/post/dna-analysis-reveals-there-are-four-distinct-giraffe-species-not-one-as-previously-thought

by Jerry2 • 10 years ago

109 37 10 years ago

researchgate.net

dforrestwilson1• 10 years ago

So is Pluto a planet or not then?

kristofferR2• 10 years ago

Since this wasn't known before, am I right to assume that a lot of giraffes in zoos are hybrids of the different species?

sandworm1012• 10 years ago

They were believed to be sub-species and so I doubt zoos mixed and matched.

The real outcome seems to be that the species is now 1/4 its previous size. Where there was once one endangered species, now stand four very endangered species.

Similar and more dramatic story with mantas: http://news.nationalgeographic.com/news/2008/07/080731-new-r...

kristofferR2• 10 years ago

There's a philosophical question in the fact that something just became more treasured because of DNA testing results, but I'm not even going to attempt answering that.

ksenzee• 10 years ago

The real outcome seems to be that the species is now 1/4 its previous size.

I had a sudden panicky vision of miniature quarter-size giraffes caused by improper zoo breeding before I figured out what you meant.

guessmyname2• 10 years ago

Off topic — How do I click the links at the bottom of this website?

EDIT: To clarify, as some people thought this was a stupid question... Every time I scroll down to click one of the links the website scrolls my browser back up and loads a new article below the one I was reading. I don't want to read more articles, I want to click the links at the bottom of the website!!! I was not asking if the links work, they probably do, I am asking how do I "click them" if the website keeps moving the webview back up when I scroll to the bottom?

wodenokoto2• 10 years ago

they work for me

guessmyname2• 10 years ago

How? Every time I scroll down to click one of the links the website scrolls my browser back up and loads a new article below the one I was reading. I don't want to read more articles, I want to click the links at the bottom of the website!!!

I was not asking if the links work, they probably do, I am asking how do I "click them" if the website keeps moving the webview back up when I scroll to the bottom?

clort• 10 years ago

noscript solves it for this site at least, since the script which does it appears to live on rgstatic.net

dschiptsov2• 10 years ago

The classic operational definition of different species, as far as I remember, is that cross-breading between species is not possible.

achr2• 10 years ago

It's a very blurred line.

micahbright• 10 years ago

It's really just a social construct.

seanc• 10 years ago

My understanding was that they might be able to crossbreed, but offspring are not fertile, e.g. hybrids such as mules and ligers.

alexbock• 10 years ago

Two individuals may be capable of breeding and reliably producing fertile offspring but still be considered different species if they would never mate "naturally". This may be due to geography, different mating seasons, different songs or appearances, etc.

dschiptsov2• 10 years ago

So, are there different species of people?)

openasocket• 10 years ago

If only it was! But then we discovered "ring species" (https://en.wikipedia.org/wiki/Ring_species) which threw a monkey wrench into what was once a simple definition. Basically, there are populations of animals A, B and C, where A and B can inter-breed, B and C can inter-breed, but A and C can't. So our definition of species no longer satisfies the transitive property, and it all falls apart. As far as I know, this issue hasn't yet been satisfactorily answered in the case of ring species.

danieltillett2• 10 years ago

A species is just a human construct to make it easier to understand biological diversity. In the real world living things are never black and white.

Dylan168072• 10 years ago

We discovered setups where A, B, and C exist at the same time in different places. That's interesting, but it's not a new challenge. The very simplest version of evolution also involves A, B, and C, existing at different times in the same place. The difference with a ring species is that you can't dodge the complexity by ignoring extinct things. But the complexity was always there.

thaumasiotes• 10 years ago

then we discovered "ring species" (https://en.wikipedia.org/wiki/Ring_species) which threw a monkey wrench into what was once a simple definition

Well, ok, we documented some ring species. That had no effect on the biological species concept, though. It never satisfied the transitive property.

bfuller• 10 years ago

Giraffes? Giraffes!

Myrmornis• 10 years ago

A few comments on the academic field that this paper lies in. The aim is to use DNA sequences to make inferences about the history of the populations. It's a really vexed area. The core objective is to make statistical inferences about whether giraffes are one "species" or multiple based on observed DNA sequences. The core problem is that we can't easily know or approximate the relevant probability distributions. Compare species-level giraffe taxonomy with a classification problem in which a large training data set is available, like determining whether a speech recording is male or female. For speech we can collect an arbitrarily large training data set. But for giraffes, the equivalent would be to find a large sample of biological lineages which are in all other respects like giraffes but differ in that some of them are one "species" and some multiple, and collect DNA sequences from each of these. It's fantasy -- it doesn't exist.

To go into a bit more detail: to do the inference task we would need at least three things:

1. A definition of "species"

2. The probability distribution of DNA sequences under the null hypothesis

3. (For Bayesian approaches) The probability distribution of DNA sequences under the alternate hypotheses

(1) Is a huge problem because many biologists don't think it's necessary to worry about the definition. Putting that aside temporarily:

(2). If Giraffes are a single species, what is the probability distribution from which our observed DNA sequences were sampled? The answer is that it depends critically on all sorts of other things: social and reproductive biology of giraffes, giraffe demographics, giraffe post-natal dispersal patterns. Maybe the most important is that it depends on the geographic distribution of savanna vegetation types over the past few million years in sub-saharan Africa. We do not know the effects of any of these on the relevant probability distributions. The field of population genetics does allow us to define probability distributions over sampled DNA sequences, but you have to specify the model. And all the above-listed unknowns and more are relevant to the model. From a formal statistical point of view you could place priors on these unknown things and simulate from the marginal distribution of interest, but in practice that is of course fantasy: there's no convincing way to choose priors for such things, and there's no way to test it because giraffe evolution happened once only.

(3). See (2).

The upshot of all this is that while making evolutionary inferences from DNA sequences is a fascinating discipline, it has some serious challenges and limitations: we need to recognize that it is not in as happy a place as other sorts of statistical inferences for which arguments can be made about the relevant probability distributions needed to make the inference. There is a huge disconnect between the statistical and theoretical machinery used in the field, and the ability of practitioners to understand that material. This is absolutely fair enough: people publishing papers on a particular species are likely to be ecologists and conservation biologists; but to understand coalescent theory and the statistical inference techniques used requires graduate-level understanding of stochastic processes, statistical inference theory, computational statistics and other stuff from discrete math etc. But that's not to imply that it would all be fine if people publishing the papers were professional computational statisticians. The real problem is that while we wish that we had the ability to make, and more importantly test, these inferences, the truth is that it's a wildly ambitious inference problem. Throwing fancy math and computational statistics algorithms at it will get some people tenure, and will make graduate students in organismal biology feel intimidated, but it doesn't change that problem.

sndean• 10 years ago

I'm pretty happy with a (the?) species definition in microbiology:

<97% 16S rRNA gene sequence identity? You're a different species [0].

It's a little more complicated than that, and some important people (especially in the older generation) don't like it, but it's a good / quick standard.

[0] http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1764935/

benkuykendall• 10 years ago

Presumably a "species" should be an equivalence class, right? So the relation "A and B are of the same species" should be transitive, symmetric, and reflexive. Symmetry is easy (an organism shares 100% of its genome with itself) as is reflexivity (A shares n% with B iff B shares n% with A). However, transitivity does not follow obviously: for example, A and B could share 98%, B and C could share 98%, but A and C could share 96%. Which species(es) do the three belong to?

rcthompson2• 10 years ago

Unfortunately, speciation is mostly a continuous process, so there's no way to define species by some kind of "degree of similarity/dissimilarity" metric and have it be a transitive relationship. Any species definition that is completely transitive will necessarily have edge cases where two extremely similar organisms fall on different sides of an arbitrary threshold and are declared to belong to two different species.

The classic example of non-transitive species relationships from sexually reproducing organisms is a "ring species": https://en.wikipedia.org/wiki/Ring_species

DNA analysis reveals there are four distinct giraffe species, not one

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