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

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

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