Q: When is a species not a species?

A: When it’s a subspecies. While there are many other potential answers to the question I posed, this is the answer I’m going to explore today.

As a taxonomist, I got quite upset yesterday by the many news outlets describing Lonesome George’s death as “the end of a species”. Because it wasn’t and it is not correct to say so. This isn’t really surprising though, given that sub-editors who write headlines on science articles often aren’t fussed with accuracy. Lonesome George was a particular subspecies of Galapagos tortoise (Chelonoidis nigra abingdonii (Gunther, 1877)). While it was almost certainly the end of a subspecies, the species proper will continue as long as there are Galapagos tortoises to propagate it.

Firstly, the reason why Lonesome George was (is?) important is more to do with history, than anything that George himself had to offer. The Galapagos tortoises, Chelonoidis nigra (Quoy and Gaimard, 1824), as a group, helped Charles Darwin figure out the theory of natural selection. They are fairly important creatures from that point of view. Put very simply, Darwin noticed that the tortoises on different islands of the Galapagos group had distinctly different physical characteristics (traits). But as they must have come from a common ancestor or geographical place, how did these changes happen?

When can we have a subspecies?

We know now that evolution is a continuous process, and we apply artificial dividers to designate species that are all, really, in a state of flux. New species are the result of different traits being selected for via breeding, over a very long time (or not, if the organism reproduces quickly). As generations of tortoises are born with particular traits, their overall appearance changes and they begin to look less like their ancestors and more like their own version. When they are deemed to be different enough, they are designated as their own species. But it’s the intermediate part that gets a bit weird, and has been subject to a range of controversy over the years. The arguing about species has resulted in two camps of taxonomists: the ‘lumpers’, who don’t like subspecies and prefer to bunch all together under species level regardless of population variation; and the ‘splitters’, who do the opposite of the lumpers.

A subspecies is a valid form of taxonomy. It is the name given to a species that has two or more discernible versions (‘races’) but that aren’t morphologically or genetically distinct enough to warrant separate species status. Often subspecies are the result of geographical boundaries, for example the water between all the Galapagos islands. There can never be one subspecies though. It’s either one species, or two or more subspecies. There is no real limit to the number of subspecies that can be recognised, as long as there is enough valid evidence to support the designation (Mallet 2001). Modern molecular techniques can reveal a new level of difference between races of a species, and is a major driver in the increase in species complexes (or often called cryptic species) being discovered.

The tortoise case study

Phylogenetic analysis of the Galapagos tortoises revealed that there is three distinct lineages within the subspecies found on Santa Cruz, which was already part of a species complex. The combination of morphological characters and genetic data indicated that one of these lineages should be described as a new taxon (presumably at subspecies level) (Russello et al. 2005). Interestingly, however, I found a paper from 2012 where each subspecies of Galapagos tortoise had been raised to species level (Poulakakis et al. 2012). While this arrangement may suit sub-editors who write bad news headlines, it is not correct, though. Consultation with the most recent annotated checklist of turtle taxonomy (van Dijk et al. 2011) revealed that the Galapagos tortoises are still being treated as a species complex – i.e., a species that comprises numerous subspecies.

Is it the end?

Yes. The world has indeed lost a subspecies – but it’s not really a big deal and we lose subspecies all the time. For this reason, incidentally, you don’t hear much about ‘species conservation’ anymore. The loss of a subspecies means even less to the public than the loss of a species, despite each subspecies contributing to biodiversity. However, with increasing sophistication and precision of molecular techniques, we may find more subspecies of Galapagos tortoises within the extant and extinct populations. Lonesome George may have had more cousins that we originally thought.

References:

Mallet (2001) Subspecies, semispecies, superspecies. In: Encyclopedia of biodiversity. SA Levin (ed). Academic Press.

Poulakakis et al. 2012. Unravelling the peculiarities of island life: Vicariance, dispersal and the diversification of the extinct and extant giant Galapagos tortoises. Molecular Ecology 21, 160-173.

Russello et al. 2005. A Cryptic taxon of Galapagos tortoise in conservation peril. Biology Letters 1, 287-290.

van Dijk et al. 2011. Turtles of the world, 2011 update: Annotated checklist of taxonomy, synonymy, distribution, and conservation status. Chelonian Research Monographs no. 5.

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Lonesome George died.

Lonesome George (image via ABC news)

News outlets are reporting on the death of Lonesome George. He was the last known individual of the Pinta Island subspecies of Galapagos tortoise (Chelonoidis nigra abigdonii). While there are still several other extant subspecies from different islands, the abingdonii subspecies is now no more. The Galapagos tortoises were made famous by Charles Darwin, along with the Galapagos finches, because each island has tortoises (and finches) with distinctly different sets of features. These are excellent examples of adaptation, and by extrapolation, evolution. Darwin also found that they were quite tasty, and the several that rattled around the decks of The Beagle to be taken back to London as biological specimens never made it home alive.

George was discovered in the 1970s as the last remaining tortoise on Pinta Island, and relocated to a breeding facility in Ecuador. But it was always going to be an uphill battle because he didn’t have a mate of the same subspecies. He did not produce any viable offspring on the couple of occasions that his mates laid eggs. The females who were potential mates were different subspecies of Galapagos tortoise, so maybe they were just too different at a genetic level.

Galapagos tortoises of all subspecies have been in decline as the result of prolific hunting in the late 19th and early 20th centuries. Apart from being easy to catch, their longevity meant that they did not breed quickly so could not replace their populations at a fast enough rate to cope with the reduction caused by hunting. They have also been under threat by the destruction of their habitat by introduced species.

Monday Awesome: Walking the ducks.

screenshot of the video

This was spotted over my morning coffee today and I knew it had to got straight to the Awesome post. It is a video (linky below, I can’t embed the whole thing) of a duck farmer.

A farmer in China, Hong Mingshun, takes his ducks for a walk to a new area to feed and swim. It’s sort of like a field trip I think, they do this a few times a year. He says that the ducks like to hang out somewhere new. The awesome thing about this is that he has 5000 ducks! I thought it would be like herding cats, but as you’ll see in the video, everyone’s very orderly.

http://media.theage.com.au/selections/farmer-takes-his-5000-ducks-for-a-walk-3401978.html

Science round-up: Herpetological social insights and tasty grasshoppers.

The IncreasingDisorder computer was suffering from a deficit of internet over the past week. The modem had broken AND there were problems with the line. At least I got all the problems sorted out at once. But I was severely restricted by what science bits and general browsing I could do – stabbing at an iPhone screen to browse via 3G is not as fun as it sounds.

Everything’s OK now through. So it’s high time for a science round-up. What have I found so far?

  • some lizards just like to fight
  • turtles got busted having sex – 47 million years ago!
  • stressed-out grasshoppers have a different elemental composition to laid-back ones

Them’s fightin’ words….

Dalmatian wall lizard. Image via NewScientist

From NewScientist, and published in the Journal of Zoology, we have a fun story about pugnacious lizards. Most animals do not like to fight, with notable exceptions to this convention being my cat (a feisty piece indeed), and the Dalmatian wall lizard (Podarcis melisellensis). Generally, if one must fight, it’s usually against the same species, and for reasons such as food availability or sex rivalry. But the Dalmatian wall lizard is aggressive and likes to fight – and it will fight even if unprovoked. The reasons for this behaviour is unknown, although the researcher pointed out that he’d put the wall lizards into artificial situations with other species of lizards that they normally don’t hang out with. Social etiquette be damned. Next time I’m on a bus or somewhere with a lot people I don’t know, I’ll start a fight.

Ref: Lailvaux et al. 2012 Journal of Zoology online early DOI: 10.1111/j.1469-7998.2012.00943.x

Herptile pr0n

image via Science

Various news outlets, including Science mag (ScienceNOW in fact), are reporting on the finding of a pair of turtles  caught having sex, published in Biology Letters (but not yet available to us proles who don’t work for ScienceNOW). The notable aspect of this is that the turtles are fossils and are about 47 million years old. Nine pairs of turtles have been found from the Messel pit in Germany, which was a lake a long, long time ago. The Messel pit has provided many high quality specimens of animals, but never any copulating. How did the palaeontologists know what these turtles were doing? Several things provided clues: the size of both turtles. All the pairs had a large and a small turtle, and freshwater turtles even today display sexual dimorphism, the relative positioning of the turtles to each other, and that in two pairs, the male’s tail was wrapped around that of the female’s – a turtle sex thing apparently.

The main question, however, was how did they die caught in the act? One hypothesis is that the Messel lake had anoxic (no oxygen) water in its deeper areas, and because turtle sex can take some time, pairs sinking a bit while taking a break could find themselves in depths with too little oxygen to survive. Either way, I’m sure the Science journalists had fun writing the article.

Stressed grasshoppers taste different….

Well, possibly, but that’s not the point of the article. Published in Science, is some research examining how the elemental composition of herbivore insects varies with exposure to predators, and what that means for soil community function. Grasshoppers that are stressed out because of exposure to spider predators have a higher carbon to nitrogen ratio than those that have no predators nearby. What this means is that decomposition of biomass in soils is slower in areas where herbivores are predated on because of the different chemical composition of the herbivores and the volume of herbivores returned to the soil. From the paper:

…predator-induced changes in the nutritional composition of herbivore biomass dramatically slow the decomposition of plant litter through legacy effects on soil communities.

Nifty.

Ref: Hawlena et al. 2012 Science 336, 1434-1438.

Finally:

Some cosmic prettiness in the form of an infrared photo of the Pleiades, from NASA, via the BBC website.

Image via NASA/BBC News

Tuesday Cringe: ‘Bogan’ in the dictionary.

There was nothing awesome about yesterday, so therefore no Monday Awesome. Sorry folks.

Today, however, I saw via various news sites that the Oxford English Dictionary (which is the one the Queen uses when she wants to check up on ‘her’ English) has included the word ‘bogan’ in its new edition. For the non-Aussie readers of the blog, here’s the OED definition:

a “depreciative term for an unfashionable, uncouth, or unsophisticated person, especially of low social status”

They forgot to mention that the bogan is often identified by a mullet or rat’s tail hairdo, and, increasingly, a Southern Cross tattoo, but I guess that comes under the general term ‘unfashionable’.

So, international readers, there you have it. Another insight into the rich and varied Australian lexicon. I hope you all use it in a sentence today.

Monday Awesome: Radiohead – old school style.

It’s cold outside, I’m a little bit sick and trying (with varying degrees of success) to think clever thoughts. The iPod is on random and Radiohead popped up unexpectedly. This reminded me that early Radiohead was awesome, and that it’s been too long since I listened to them. So I went digging on the’Tube and came up with this video. It’s from Jools Holland in the mid-90s, and has a very entertaining German subtitle thing going on. We get two songs – High and Dry, and The Bends.

Sit back, enjoy.