conservation

This week's Nature has a news article by Emma Marris about bison conservation and genomics. I've been very interested in cattle and bison as an example of introgression in large mammals; in this case between two genera separated by over a million years of divergence. Possibly all, and certainly most of the bison left today have cattle genes in them. The article profiles geneticist James Derr, who sees these cattle genes as a conservation problem:

Wildlife managers have considered the genetic diversity of animals for some time, and animals in captivity have often been bred to preserve genetic diversity. But those were blunt approaches. Now, armed with genomic tools, researchers are starting to look at specific sequences in the genome, and are raising questions about what the fundamental unit of conservation should be. Most people see preserving wildlife as a matter of saving individuals; if all the individuals die out, the species becomes extinct. But that reasoning looks simplistic when considered at the genomic level. If the genes of a species change enough — through interbreeding, for example — that species will cease to exist even if individuals that look something like the original continue to thrive.

This issue is quite threatening to the entire idea of endangered species preservation. One argument for extending protection to multiple populations of species like chimpanzees is that you are preserving gene pools that have unique evolutionary histories. You can't just preserve one tiny corner of a species and expect to retain the genetic diversity that was present in the whole species' range.

But if your species' genetic diversity is already compromised by introgression, either from within the same species or from other more distant lineages, this argument is weakened. And if it's OK to preserve a fragment of diversity in an interbred population, then why not simply introgress the endangered species' genes into a more common, cosmopolitan relative. That is, why save the wolf, if you've already got lots of dogs with wolf genes in them? Why save the polar bear, when its genes will continue to exist in brown bears?

As the article notes, this question is really academic for most threatened species, whose population histories may not lend themselves to such promiscuous gene mixing. But bison are an interesting case nonetheless --

In 1905, then US President Theodore Roosevelt and William Hornaday, head of the New York Zoological Society (now known as the Wildlife Conservation Society), founded the American Bison Society, which collected bison and established herds in a few reserves in Montana, Oklahoma and South Dakota. A small herd, perhaps 30 in number, was still roaming Yellowstone National Park. According to Derr, all the bison in the United States today — there are now up to a million of them, mostly on private ranches — can probably be traced back to fewer than 200 bison.

Other scientists argue that the most important thing may not be unique genes, but instead unique cultural inheritance and status within ecological communities:

"There are more important things than genes," says Rurik List, an ecologist at the National Autonomous University of Mexico, who works with a herd that spans the US–Mexico border. These bison have some cattle genes, but they also have institutional memory. If List were to remove them and replace them with pure animals, would the bison still be able to find the water holes that the current herd knows so well? "They have been behaving like bison for 80 years," says List. "They have been fulfilling an ecological role."

So far all the genetic estimates of introgression are based on only 14 markers -- probably good enough as a test for the fraction of introgression dating back within the last 150 years, but it's not going to give any information about the dynamics or even the identity of genes that have moved into bison. Many more markers are going to be necessary in this and other cases of reintroductions and hybridization with domesticated varieties.

References:

Marris E. 2009. Conservation: The genome of the American West. Nature 457:950-952. doi:10.1038/457950a

Scientific American reports on a taxonomic auction by Purdue University:

Naming your kid after you is one thing. But imagine if an entire species were named for you.

This week, Purdue University is auctioning off the rights to name seven newly discovered bats and two turtles, the Associated Press is reporting. The winners — who will shell out a minimum of $250,000 for at least one of the bats, a Purdue spokesman told ScientificAmerican.com — can link their own name or that of a pal to the animal’s scientific name.

"Unlike naming a building or something like that, this is much more permanent. This will last as long as we have our society," John Bickham, who co-discovered the nine species, told the AP.

I don't think there's anything wrong in principle with selling the naming rights to your new species. Heck, I'd be happy to name a new species after a donor, if I had either. I don't even think there's anything wrong with consistently adopting a splitter's viewpoint on new species, keeping in mind that you have many donors and other people that you might honor with your work.

But it seems to me there is a truth-in-advertising problem here. Species names are not eternal. They are hypotheses. We re-evaluate the relations between living populations and fossil populations all the time. The scientific community ignores ("sinks") taxonomic names that they come to believe are synonymous with existing taxa. So there is an obvious question: what are you really paying for, if you bid on naming rights for a species?

Naturally, it will depend on the investigators. Are they credible? Do they have a good record in the practice of taxonomy?

In the end, you're taking a bet: A bet against future discoveries. A bet that today's knowledge is the best there will be, at least where taxonomy is concerned. A bet that today's fashion won't reverse itself -- where the fashion is to recognize lots and lots of species, which helps to promote conservation goals tied to Endangered Species status.

Well, I suppose we can say that the people who would splurge for more than $250,000 for a name don't really care if the name sticks. They probably want something else -- let's say, a story. That might include a motive to fund research on bats (in this case) or some other group of organisms, or just to fund conservation work generally. Or it might just be a line at a cocktail party -- hey, my wife has a species named after her. Or in the case of a recent taxon sale, good advertising for a casino.

But maybe the people who bid on species naming rights ought to be made aware that it is a bet. Not eternal glory, just a chance at it.

(via Sandwalk)

In last week's Science, Stanislas Dehaene and colleagues describe the relation of cultural invention to "universal intuition" about mathematical logic:

The mapping of numbers onto space is fundamental to measurement and to mathematics. Is this mapping a cultural invention or a universal intuition shared by all humans regardless of culture and education? We probed number-space mappings in the Mundurucu, an Amazonian indigene group with a reduced numerical lexicon and little or no formal education. At all ages, the Mundurucu mapped symbolic and nonsymbolic numbers onto a logarithmic scale, whereas Western adults used linear mapping with small or symbolic numbers and logarithmic mapping when numbers were presented nonsymbolically under conditions that discouraged counting. This indicates that the mapping of numbers onto space is a universal intuition and that this initial intuition of number is logarithmic. The concept of a linear number line appears to be a cultural invention that fails to develop in the absence of formal education (Dehaene et al. 2008:1217).

The idea is that children in Western societies have to learn that a number line is a linear representation; they begin by compressing the space devoted to large numbers:

When asked to point toward the correct location for a spoken number word onto a line segment labeled with 0 at left and 100 at right, even kindergarteners understand the task and behave nonrandomly, systematically placing smaller numbers at left and larger numbers at right. They do not distribute the numbers evenly, however, and instead devote more space to small numbers, imposing a compressed logarithmic mapping. For instance, they might place number 10 near the middle of the 0-to-100 segment. This compressive response fits nicely with animal and infant studies that demonstrate that numerical perception obeys Weber's law, a ubiquitous psychophysical law whereby increasingly larger quantities are represented with proportionally greater imprecision, compatible with a logarithmic internal representation with fixed noise (7, 20, 21). A shift from logarithmic to linear mapping occurs later in development, between first and fourth grade, depending on experience and the range of numbers tested (17-19).

They note that there's a problem testing these ideas in Western children, who are surrounded throughout their development by numbers -- in books, "elevators" and other places. Most of these numbers are small ones -- especially one through ten -- so they might naturally accentuate the ones they know.

They found when testing the Mundurucu that both adults and children tended to compress the high end of the number scale, even testing numbers between one and ten. This compression is logarithmic -- they accentuate contrasts between small numbers disproportionately. It makes sense logically -- we care more about detailed contrasts between small numbers than large numbers. They don't give an idea of which logarithm people are using; and in fact it may be different ones for different people. The important fact is the small number/large number contrast.

Dehaene and colleagues attribute this scaling to mapping at the neural level:

What are the sources of this universal logarithmic mapping? Research on the brain mechanisms of numerosity perception have revealed a compressed numerosity code, whereby individual neurons in the parietal and prefrontal cortex exhibit a Gaussian tuning curve on a logarithmic axis of number (27). As first noted by Gustav Fechner, such a constant imprecision on a logarithmic scale can explain Weber's law -- the fact that larger numbers require a proportional larger difference in order to remain equally discriminable. Indeed, a recent model suggests that the tuning properties of number neurons can account for many details of elementary mental arithmetic in humans and animals (21). In the final analysis, the logarithmic code may have been selected during evolution for its compactness: Like an engineer's slide rule, a log scale provides a compact neural representation of several orders of magnitude with fixed relative precision.

From that perspective, the Western conception of the number line appears as a very distinctive invention, capable of adjusting the logarithmic encoding to arrive at faster and more accurate mathematical conclusions about large numbers. The authors speculate that addition and subtraction (which display invariance between large and small numbers) and experience with measurement underlay the development of the linear concept in Western children.

References:

Dehaene S, Izard V, Spelke E, Pica P. 2008. Log or linear? Distinct intuitions of the number scale in Western and Amazonian indigene cultures. Science 320:1217-1220. doi:10.1126/science.1156540