8 December 2011

The queen of questions in evolutionary biology

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How do all-female species survive without males? And what bizarre fate did a couple of 2010's newly discovered species meet?
Monkey Rhinopithecus strykeri

Scientists first learned of 'Snubby' - as they nicknamed the species - from hunters in Myanmar. Credit: Martin Aveling/Fauna & Flora International.

whiptail lizards

Three generations of all-female A. tesselata whiptail lizards. Credit: Peter Baumann

Limestone Leaf-Warbler (Phylloscopus Calciatilis):

In January 2010, a small, distinctive bird known as the limestone leaf-warbler was found living in the rocky forests of the Annamite mountain range in Laos and Vietnam and described for the first time. Credit: Ulf Johansson/Swedish Museum of Natural History. Psychedelic

Positive news stories about animals are pretty rare. Unfortunately you’re more likely to see a story about how a certain rhinoceros species has gone extinct or a certain native bird is now critically endangered than you are a story about animals being brought back from the brink of extinction. Which is why stories about the discovery of previously unknown species – especially the discovery of a bunch of new species – are so encouraging.

The World Wildlife Fund reported today that in 2010, new species were discovered at the rate of one every two days in the Greater Mekong region that includes Cambodia, Laos, Myanmar, Thailand, Vietnam and the Yunnan Province of China. (Download a PDF of the report here.)

The 208 new species include a new snub-nosed monkey, a self-cloning skink, five carnivorous plants and a beautiful green and yellow leaf warbler (an insectivorous bird). You might remember the monkey from such comparisons as to Michael Jackson, due to its uniquely upturned nose. Locals say this kind of monkey can be spotted with its head between its knees in wet weather to avoid rain running into it. Which I guess sounds pretty cute if you like monkeys. Oh and after posing with the ghostly monkey corpse, the locals who found it ate it.

The new coning skink from Vietnam also hit the headlines in late 2010, due to the female’s ability to reproduce via cloning, which has made the males of the species embarrassingly redundant. This kind of cloning is not unique to this particular species. I wrote an article for the COSMOS print edition earlier this year about a group of lizards called whiptails. A third of the 50 known species are entirely female.

Fascinatingly enough, the researcher working on the cloning whiptails, Peter Baumann from the Stowers Institute for Medical Research in the U.S., says that unisexual lizards don’t suffer from the poor adaptability and vulnerability to disease than one would expect from an entire species that’s missing the genetic variation that comes with sexual reproduction between two organisms.

What Baumann discovered is that the lizards have evolved to clone themselves in a way that delivers enough genetic variation to their children to ensure that generation after generation of the species is just as tough as their sexually reproducing peers. In asexual whiptail reproduction, meiosis (which is the process that halves the number of chromosomes in order to create the egg or sperm cells) begins with cells containing 92 chromosomes – twice the number used in sexual meiosis. This results in eggs containing 46 chromosomes, which is twice the number of the chromosomes that end up in eggs from sexually reproducing animals. So while there is no genetic material from another animal present in the offspring, the mother has imbued her baby with a double-shot of genetic material, which seems to ensure the longevity of a unisexual species.

On discovering this, Baumann brought up the intriguing question of why the vast majority of species on Earth reproduce sexually. “Males use up resources (food, shelter, water) without contributing much to the next generation. If you do the simple maths – a unisexual species comprised of only females will grow much faster assuming that equal numbers of offspring are produced,” he told me. “Graham Bell called this ‘the queen of questions in evolutionary biology’. What is the advantage of sex that is large enough and acts on a short enough timescale to outweigh the two-fold cost of sex? Clearly 99.9% of all species reproduce sexually, but we still don’t understand why that is so.”

Sadly, as incredible as these new Vietnamese lizards are, they too suffer the same fate as our snub-nosed monkey friend – becoming someone else’s dinner. As Stuart Chapman, conservation director of WWF Greater Mekong lamented, “While the 2010 discoveries are new to science, many are already destined for the dinner table, struggling to survive in shrinking habitats and at risk of extinction.” And there’s the – very strange – kicker.

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