A new Joshua tree study is just out in the current issue of New Phytologist, presenting an analysis of the environments occupied by the two different types of Joshua tree. The results demonstrate that the two tree types mostly grow in similar climatic conditions [PDF], which suggests that coevolution with its pollinators, not natural selection from differing environments, is responsible for the evolution of the two different tree types.

The Pellmyr Lab has been studying the two types of Joshua tree, which are pollinated by two separate, highly specialized moths, for several years now. Previous papers have shown that the two types of Joshua tree, first described in the 1970s based only on their vegetative features, are most strongly differentiated by the shape of their flowers [$-a]; and that, although the two moths are separate species, the two tree types are not fully genetically differentiated [PDF].

The latest paper is a chapter from the dissertation of Will Godsoe, who just received his doctorate last week. It presents an analysis that sidesteps a fundamental problem with studying long-lived, specialized organisms -- they're hard use in fully controlled experiments. To determine whether the two types of Joshua tree really evolved as a result of coevolution with their pollinators, we'd like to be able to eliminate the alternative hypothesis that the two types evolved in response to different environmental conditions. Except for a small contact zone in central Nevada, each tree type occurs in a different part of the Mojave desert, and the two regions do have some broad-scale differences in when they receive precipitation.

Ideally, to determine whether two plants have different environmental needs, you just perform an experimental transplant, growing each plant in the other's environment to see whether it fares as well as it does at home. This isn't really possible with Joshua trees, which are pretty tricky to sprout from seeds (I've tried), and which, in any event, take something like twenty years to mature. So Will proposed to use niche modeling methods instead. Niche models are statistical descriptions of environments where an organism is known to live, often used to predict where it could live. To build niche models for each type of Joshua tree, Will assembled location data we'd collected over several field seasons in the Mojave, then spent another field trip driving around the desert some more to fill in the gaps -- he wanted locations where Joshua trees were definitely growing and where they definitely weren't, to fully "inform" the models.

Using the location data, it was possible to determine what kinds of climates each Joshua tree type tended to occupy by cross-referencing with existing climate databases, then fitting statistical models to the results. The models produced for each tree type could then be compared -- and, for the most part, they're similar. That is, if you collected seeds from one tree type, planted them where the other type grows, and waited around for a few decades to check the result, you'd probably find that it grew as well as it did in its home range.

So, if differing climates don't explain the origin of the two types of Joshua tree, does that leave no other possibility but the pollinating moths? Not exactly -- there are lots of environmental variables that weren't available for Will's niche models, for instance, or there could be a third, completely unknown factor. But this does make coevolution with the moths a more plausible explanation. In light of some of our very latest results -- which should be going to press fairly soon -- coevolution is looking like a better and better possibility.

Reference

Godsoe, W., Strand, E., Smith, C.I., Yoder, J.B., Esque, T., & Pellmyr, O. (2009). Divergence in an obligate mutualism is not explained by divergent climatic factors New Phytologist, 183 (3), 589-99 DOI: 10.1111/j.1469-8137.2009.02942.x

Godsoe, W., Yoder, J.B., Smith, C.I., & Pellmyr, O. (2008). Coevolution and divergence in the Joshua tree/yucca moth mutualism The American Naturalist, 171 (6), 816-23 DOI: 10.1086/587757

Smith, C.I., Godsoe, W., Tank, S., Yoder, J.B., & Pellmyr, O. (2008). Distinguishing coevolution from covicariance in an obligate pollination mutualism: Asynchronous divergence in Joshua tree and its pollinators. Evolution, 62 (10), 2676-87 DOI: 10.1111/j.1558-5646.2008.00500.x

Labels: Joshua tree, science

Just back from a week and a half of attempted fieldwork in Nevada, with a hiatus to Southern California for a lecture to a Desert Institute class. Very few Joshua trees were in flower; so the trip was kind of a bust. But still a nice break.

Labels: Joshua tree, science, travel

The latest results from the Pellmyr Lab's ongoing study of Joshua tree and its pollinators are online as part of the new October issue of Evolution. It's the cover article, no less. The study, whose lead author is Chris Smith (now on the faculty at Willamette University) compares patterns in the population genetics of Joshua trees and the moths that pollinate them, and shows that although the moths have become two separate species, the trees may not have followed suit [PDF].

As I've probably written about before, Joshua trees are exclusively pollinated by yucca moths. Female yucca moths carry pollen between Joshua tree flowers in special mouthparts. When she arrives at a new flower, the female moth lays her eggs inside it, then deliberately applies pollen to the flower's receptive surface. When the fertilized flower develops into a fruit, the moth eggs hatch, and the larvae eat some of the seeds inside the fruit.

Among the yuccas, Joshua trees are unique because they're pollinated by two species of moths, which are each other's closest evolutionary relative. One species is found in the eastern part of Joshua tree's range, the other in the west. Joshua trees from the east and west have differently-shaped flowers [PDF], which is consistent with the hypothesis that coevolution between moths and trees has driven both toward an evolutionary split.
The new study goes deeper to look at genetic relationships between different populations of the moths and the trees, and what it finds isn't as tidy as the earlier work might suggest: While Joshua trees' morphology corresponds nicely to the split in the pollinators, the patterns visible in their chloroplast DNA does not. In some populations, trees look "eastern," but have chloroplast DNA more closely related to "western" populations. This suggests that, although the moths have become separate species, they're still moving between the two kinds of Joshua tree frequently enough that the trees haven't quite split. Why do the two tree types look different, then? One possibility is coevolution with the two moth species, which might exert selection the trees in different ways.

There's still a lot of work to do before we fully understand what's going on here. Will Godsoe, the other doctoral student in our lab, is doing some intensive niche modeling to see how much environmental differences might be contributing to the patterns we see here. My own dissertation will look at whether the same incongruities turn up in nuclear DNA, which can have a different evolutionary history than that in the chloroplast.

References

W. Godsoe, J.B. Yoder, C.I. Smith, O. Pellmyr (2008). Coevolution and Divergence in the Joshua Tree/Yucca Moth Mutualism The American Naturalist, 171 (6), 816-23 DOI: 10.1086/587757

C.I. Smith, W.K.W. Godsoe, S. Tank, J.B. Yoder, O. Pellmyr (2008). Distinguishing coevolution from covicariance in an obligate pollination mutualism: asynchronous divergence in Joshua tree and its pollinators. Evolution, 62 (10), 2676-87 DOI: 10.1111/j.1558-5646.2008.00500.x

Labels: coevolution, science

Back in March, Science ran a Perspectives piece in which computer scientist Ben Shneiderman suggested that the wealth of new data on human interactions provided by the Internet (Facebook, Amazon.com customer records, &c.) would require a new approach to science, which he called "Science 2.0" [subscription]:

... the Science 2.0 challenges cannot be studied adequately in laboratory conditions because controlled experiments do not capture the rich context of Web 2.0 collaboration, where the interaction among variables undermines the validity of reductionist methods (7). Moreover, in Science 2.0 the mix of people and technology means that data must be collected in real settings ... Amazon and Netflix became commercial successes in part because of their frequent evaluations of incremental changes to their Web site design as they monitored user activity and purchases.

Science 2.0 sounded, to me, a lot like what ecologists and evolutionary biologists often do - hypothesis testing based on observations, manipulations of whole natural systems in the field, and the clever use of "natural experiments" sensu Diamond [subscription]. I said as much in a post shortly after Shneiderman's article ran, and also wrote a brief letter to Science.

And now it turns out they've published it! My letter, along with a response from Shneiderman, is in the 6 June issue [subscription]. You can read it in PDF format here. In very short form, I say:

... what Shneiderman calls Science 1.0 has always included methods beyond simple controlled experiments, such as inference from observation of integrated natural systems and the careful use of "natural experiments" (1) to test and eliminate competing hypotheses.

Shneiderman's response concedes the point on natural experiments, but says he was actually talking about manipulative experiments conducted on large online social networks

Amazon and NetFlix designers conduct many studies to improve their user interfaces by making changes in a fraction of accounts to measure how user behaviors change. Their goal is to improve business practices, but similar interventional studies on a massive scale could develop better understanding of human collaboration in the designed (as opposed to natural) world ...

That still sounds to me like ecological experimentation, but with people's Facebook accounts instead of (to pick an organism at random) yucca moths. Maybe I'm just not getting it, but I don't see anything in Shneiderman's description that qualifies as a new kind of science.

References
Shneiderman B. 2008. Science 2.0. Science 319:1349-50.

Diamond J. 2001. Dammed experiments! Science 294:1847-8.

Yoder, JB, and B Shneiderman. 2008. Science 2.0: Not So New? Science 320:1290-1.

Labels: media, publication, science, scientific methods

The New Yorker has a great essay by Jared Diamond on the role of revenge in tribal societies. It's more story-telling than the sort of rigorous comparative anthropology on display in Guns, Germs, and Steel, but it's fascinating.

Labels: Jared Diamond, science

The first publication from the Pellmyr Lab's study of Joshua trees and their pollinators, in which we demonstrate significant, potentially coevolved, morphological differences in Joshua trees pollinated by different species of yucca moths, is now online at the American Naturalist's website. My understanding is that it'll be in the print edition this June.

Godsoe W, JB Yoder, CI Smith, and O Pellmyr. 2008. Coevolution and Divergence in the Joshua Tree/Yucca Moth Mutualism. The American Naturalist 171.

Labels: coevolution, Joshua tree, science

CV update: my first paper on the Joshua tree-yucca moth mutualism, which documents phenotype matching between Joshua tree and its two pollinator species, is accepted at The American Naturalist, pending revision.

Labels: coevolution, professional, publication, science

Gore Shares Peace Prize for Climate Change Work - New York Times

Labels: politics, science

I've just discovered that my first academic publication is now available as an advanced online release. It's a review about coevolution (specifically, John Thompson's "Geographic Mosaic Theory") in the journal Heredity. I'm a very minor coauthor among a group of scientists from UI and Washington State University.

The article itself is on the journal's website here [subscription required for full text]. There's also a podcast including an interview with Dick Gomulkiewicz, the lead author.

Labels: coevolution, publication, science

On returning to Moscow after fieldwork, I learned that the UI Student Grant Program has agreed to fund a project I proposed to them just before I left, through a grant of $1500. This is the second grant I've received this year in support of work that will likely make up my dissertation, so I'm very pleased. My CV has been updated accordingly.

Labels: professional, science

I'm officially a fan of Morning Edition's Friday science report, "Krulwich on Science". It's a lighthearted look at current and past science that manages to communicate a real sense of wonder about the world around us. Today's piece, "Have you heard about B flat?" is a delightfully wonky exploration of a completely inexplicable pattern, the recurrence of a particular musical note throughout nature, that recalls Douglas Adams at his weirdest. Another favorite of mine is "Charles Darwin and the racing asparagus", in which David Quammen helps Krulwich build a playful picture of the gentleman scientist at work.

Labels: nature, science, websites

The NY Times interviews Katherine Jefferts Schori, the first woman to head the Episcopal Church, whose first career was in academic science. Pity more Christian denominations aren't headed by ex-scientists.

Labels: church, politics, science

Following up on a report of ancient human-Neanderthal interbreeding, Slate.com tackles the biological species concept and does a pretty decent job.

Labels: science

Just posted some new photos from a mini field trip I went on yesterday morning with Olle, my advisor. My new camera's "super-macro" function works pretty well, it turns out.

Labels: nature, photo, science

Just finished Stephen Jay Gould's The Structure of Evolutionary Theory (Cambridge, Massachusetts: The Belknap Press of Harvard University, 2002), and I feel like I've had a complete course in macroevolution. It was a bloody long book, all 1,343 pages of it - Gould even started to make fun of the length in the later chapters - but a bloody good read.

From the epilogue, a tribute to Charles Darwin and a discussion of evolutionary science as narrative (p. 1342):

So why fret and care that the actual version of the destined deed [the discovery of natural selection] was done by an upper class English gentleman who had circumnavigated the globe as a vigorous youth, lost his dearest daughter and his waning faith at the same time, wrote the greatest treatise ever composed on the taxonomy of barnacles, and eventually grew a white beard, lived as a country squire just south of London, and never again traveled far enough even to cross the English Channel? We care for the same reason that we love okapis, delight in the fossil evidence of trilobites, and mourn the passage of the dodo. We care because the broad events that had to happen, happened to happen in a certain particular way. And something almost unspeakably holy -- I don't know how else to say this -- underlies our discovery and confirmation of the actual details that made our world and also, in realms of contingency, assured the minutiae of its construction in the manner we know, and not in any one of a trillion other ways, nearly all of which would not have included the evolution of a scribe to record the beauty, the cruelty, the fascination, and the mystery.

Labels: science