My brain is most wonderfully agitated, which is the good thing about going to these meetings. Scientists are perverse information junkies who love to get jarred by new ideas and strong arguments, and meetings like this are intense and challenging. I’ve only got a little time here before the next session, so let me rip through a short summary of my morning.
Hopi Hoekstra talked about Golden mice in them thar hills: the molecular basis of crypsis in Nebraskan deermice. This was an excellent example of the kind of approach Coyne advocated the previous evening: she has a very cool system in mice of the genus Peromyscus in which populations living in the Sand Hills of Nebraska have a more golden fur color than those living in nearby regions, and they have a handle on the genetic mechanism behind this. So on the one hand they have a trove of deep molecular information — the wideband mutation in the golden mice is a variant of the very well known agouti locus — and on the other they are looking at its distribution in wild populations. She’s able to cover quite a bit of breadth, talking about both the sequences and molecular consequences of different alleles in promoter regions of the gene, and looking at the golden, brown, and intermediate populations along the borders of the Sand Hills.
Leonie Moyle talked about plants (and I think she’s the only plant evo-devo person talking this weekend; sorry, vegetableophiles) in Attack of the tomato killers: genetics of reproductive isolation in Solanum. I did not know tomatoes were so interesting and so relevant to evolution. Their native source is on the steep Pacific side of South America, and there are 10-13 closely related species, all diploid, and all intercrossable. This means that they represent an opportunity to study mechanisms of speciation. What genetic mechanisms are responsible for the reproductive isolation of these species? She’s been doing quantitative trait locus (QTL) mapping, identifying regions of the tomato genome that are responsible for reduced viability or fertility in hybrids, and has been working through combinations of hybrid QTLs to identify more specific interactions that are responsible for the problems. It was a bit preliminary, but one of the important points she made was a comparison with similar work that has been done in Drosophila, and finding some significant differences; for instance, the plants tended to have small numbers of QTLs associated with sterility, each with fairly modest effects, while Drosophila QTLs associated with barriers to hybridization tended to be more numerous, and more likely to be found in males. The differences are likely to be a consequence of different reproductive strategies in plants and animals, with these plants being hermaphrodites with low levels of sperm competition.
Stephan Schneider discussed Annelids, ancestors, and asymmetries:
Reconstructing bilaterian evolution in a talk that was a fairly conventional representative of the evo-devo tradition: lots of comparisons of patterns of molecular expression in diverse groups, used to reconstruct a likely distant ancestral form. In particular, he described β-catenin and the Wnt genes. The Wnt genes are important cell signaling genes that play a role in multiple events in embryogenesis; the Wnt family contains 13 canonical members, a diverse group that arose long, long ago in the metazoan ancestor. Schneider was studying an annelid worm, Platynereis, which seems to be genomically conserved, retaining 12 Wnt genes (many other species have lost individual members of the Wnt family, for instance, so it’s a bit unusual). The coolest part of this talk was that he followed β-catenin expression through the early developmental lineage of the dividing Platynereis embryo, and observed a consistent pattern: it formed a binary cell fate specification system. At each division, the more vegetal daughter cell would retain or switch on β-catenin, while the more animal side of the division would switch it off. It formed a kind of simple system for distinguishing sister cell fates in an embryonic lineage, with the idea being that maybe this was the original function of this molecule, which has since become an important determinant of vegetal fates in even us organisms that don’t rely on a well-defined cell lineage.
Mark Martindale talked about Developmental changes associated with
body plan evolution, but it was largely about smacking us around with a metaphorical clue-bat to correct some bad practices in evo-devo (Mark is always an entertaining and iconoclastic speaker, so don’t miss opportunities to listen to him when you get a chance). He railed against attempts to define the properties of the ancestral urbilaterian from 600 million years ago by comparing the genes of a fruit fly and a mouse and basing our models on that highly limited comparison. He turned Dobzhansky’s dictum on its head and told us that “nothing in evolution makes sense except in the light of biology”, and that what we need to do is identify the common properties of all nodes of the metazoan cladogram before leaping from a few extant forms directly to the last common ancestor.
He described the project of a large group of protostome biologists to assemble a more diverse and more accurate collection of genomic data to make better predictions. As an example, he described the work on Nematostella (I’ve mentioned some of this before), a cnidarian. He pointed out that one of the implications of that work is that there was a reversal of the site of gastrulation at some distant point in the past; Nematostella gastrulates at the animal pole, not the vegetal pole, as both deuterostomes and protostomes do. He also argued that the urbilaterian was probably less like the segmented worm that people like Gerhart and Kirschner have popularized, and more like a ctenophore. But really, the main point of his talk is that evo-devo people need to consider more diverse forms and avoid getting hung up on misleading interpretations drawn from a very small set of model organisms.
By the way, one of the emerging conventions that was a source of some amusement is that just about every talk begins with a slide illustrating organismal diversity — that’s definitely a theme. We build a stronger case that we’re getting at general principles if we’re building from a foundation that includes tomatoes and flatworms and cnidarians in addition to flies, mice, and zebrafish.
OK, gotta run now … the afternoon session begins in a few minutes. Don’t you wish you were here?
(By the way, there is a long break between 4 and 6 today. If any Eugenians wanted to join me, I might just hang out at the bar at the Valley River Inn at that time — look for the guy with the laptop trying to condense his notes into a short blog post.)