For all practical purposes, I've stopped posting to this blog. This is partly because I've now been writing quite a lot over at Denim and Tweed for some time, including notes about scientific papers I've read and updates about the most recent results of my own research. That site, not this, will probably be the forum I use for the foreseeable future. With that in mind, I'm retaining this blog on my personal site purely as a record of previous posting.

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

Pink Menno Campaign is organizing people to support broader (and officially-sanctioned) inclusion of LGBTQ people in the Mennonite Church by wearing pink at the upcoming biennial convention of Mennonite Church USA.

Mennonites are in a slightly unusual position w/r/t sexual orientation -- the Confession of Faith in a Mennonite Perspective accepts only heterosexual marriage -- but the CoF is more a descriptive than a prescriptive document, and because MCUSA lacks some sort of centralized doctrinal enforcement, a few individual congregations do welcome LGBTQ folks and even perform same-sex marriage ceremonies. Sometimes such congregations and/or their pastors are "disciplined" in various ways by the local-level church authorities that can do such things, and the results are never happy.

I thought it was a big deal when, as a delegate at the last MCUSA conference, I was involved in preparing a statement on behalf of young Mennos that included a very brief nod to broader inclusion; much more recently, a group of Mennonite pastors signed an open letter to the church calling for an end to the exclusion of LGBTQ folks. (An article in Mennonite Weekly Review covers both the letter and its context.) Progress? Hard to say. A Delegate Assembly full of pink t-shirts is a mighty appealing image, though.

(Cross-posted at Denim and Tweed.)

Labels: church, Mennonites, sexuality

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 website for the Evolution 2009 meetings, to be held right here at the University of Idaho this spring, is officially live, although issues remain with our domain registration (eventually, evolutionmeetings09.org is supposed to forward to this page). Graphic design for the conference logo is by Christian Blackman, a UI Art and Design student; HTML coding and layout by yours truly.

Labels: Evolution2009, professional

All Israelis, men and women, are required to serve in the national military when they turn 18. That's a hard social background within which to be a conscientious objector, even before you account for the fact that refusal to serve means jail time. Yet there are Israeli COs. On the God's Politics blog, Howard Zinn introduces a campaign on behalf of one cohort of teenage COs, the Shministim. (That's Hebrew for "twelfth-grader" - can you imagine going to jail for your beliefs as a high school senior? Yeah, neither can I.) The American-based Jewish Voice for Peace is looking for people to sign a statement calling for the Shminstim to be released, to be delivered to the Israeli Minister of Defense as one big pile of postcards on 18 December. Sign the statement here.

Labels: Isreal, peace

Labels: Seattle, travel