How I spent another morning at SICB

Everyone can stop now, my brain is full. Seriously, this is a painful meeting: my usual strategy at science meetings is to be picky and see just a few talks in a few sessions, to avoid burnout…but at this one, I go to one session and sit through the whole thing, and at the breaks I look at the program and moan over the concurrent sessions I have to be missing. I have to come to SICB more often, that's for sure.

I do have one major complaint, though: PowerPoint abuse. The evolution of slides has continued apace since my graduate school days, when one slide was one photograph, developed in a darkroom ourselves, and then carefully labeled with letraset lettering, photographed again on a copy stand with slide film, and then sent off for processing (usually the day before the meeting, so there was no slack for redoing anything.) Now the slides are all huge multipaneled affairs with data packed into tiny little boxes that fade in as the speaker does a tarantella on the keyboard, and it's getting a little irritating. Most of the talks this morning would, at some point, throw up a gigantic, intricately detailed cladogram with 50 taxa and branch points all labeled and circles and arrows and scary tiny lettering all around. Any one slide legitimately represents something that the speaker could talk about for an hour, no problem, but wham-bam-zoom, they'll run through 20 of them in 20 minutes. If the information density is going to be this high, they ought to set it up so they can beam these monster slides to our laptops over the wireless network, so we can actually try to absorb it into our heads in some way other than being battered about the cranium with it.

I spent Friday morning at the Key Transitions in Animal Evolution symposium.

• F. Boero: Cnidarian milestones in metazoan evolution. This talk was a bit thin on the data, but it was presented more as a conceptual overview, so I let it go. The idea was simple: it was an anti-Great Chain of Being talk, pointing out that sponges and especially cnidarians were darned important creatures that ought to be appreciated for the fact that they bear the seeds of everything we consider especially essential to the bilateria. They have bilateral symmetry, many have supporting skeletons, polyp buds have an internal mass that corresponds in many ways to mesoderm, they have body cavities, the modularity of their development has affinities to bilaterian metamery, and most interestingly, cnidarian planula larvae have specialized concentrations of nerve cells that resemble a brain. One weird twist (I love weird twists) was the idea that the cnidocyst was such an incredibly potent adaptation that the cnidaria didn't need all the elaborate complexity of the bilateria to succeed, and that maybe an important milestone that was a precursor to our evolution was the loss of cnidocysts.

• B. F. Lang: The evolutionary transition from protists to Metazoa: mitochondrial genome organization and phylogenomic analyses based on nuclear and mitochondrial genes. I was rather far over my head in this talk; it was hardcore phylogenetic analysis of really distant branch points in our evolutionary history—this fellow is trying to puzzle out the branch point between fungi and animals. I mainly just jotted down a few names I'll have to look up later: the Ichthyosporia, which are fungal-like cells with amoeboid stages, the Nuclearia, which are low on the branch leading to the fungi, the Capsaspora, which similarly lie on a branch leading to the animals, and the Apusozoa, bikont flagellates that have been poorly characterized so far.

• D.K. Jacobs: Origins of sensory and neural organization in basal metazoa. The cnidarian fan club was out in force in this session. This was a talk on the identification of cnidarian genes usually associated with nervous system and sensory organ development and function, the point being that all of the precursors to our rather more elaborate neural processing system are there in jellyfish. There were a few places where I wondered if he was going a little too far—there's no reason to assume that finding a gene that is used in the vertebrate brain in a cnidarian means that gene has a similar function there—but still an interesting talk. One cute idea was that the choanocytes of sponges can also be thought of as sensory organs, and also that neural genes seem to share functions with nephridia/kidneys, too, raising the possibility of a primitive link between excretion and the origins of the nervous system. (Watch Fox News, and this possibility will seem even more likely).

• G. Wagner: Do genome duplications play a role in key transitions? This is the second time I've heard this Wagner fellow talk, and he keeps making me think. He brought up a familiar correlation: in vertebrate evolution, we see signs that there are major gene duplications at the same time that we see major radiations. In the vertebrate lineage, for instance, we see two whole genome duplications, and the conceit is that these increases in genetic material provided the substrate for more sophisticated developmental events that were the source of our success; similarly, the even more successful teleosts show signs of a third round of duplications. Wagner objected, pointing out that there are many highly successful groups that did not exhibit these duplications (arthropods, insect, mammals, and birds, for instance), and that others, such as plants and sturgeon, have duplications but no subsequent radiation. He argued that it was an artifact, not evidence of a causal relationship. The rapid expansion of a lineage during an adaptive radiation would act to preserve and propagate any genetic quirks of the founding population. The duplications are neither necessary nor sufficient to instigate a key transition. One point that came up very briefly in the Q&A was that we developmental biologists are a bit obsessive about regulatory genes like the Hox genes and think those are indicative of importance, but that there are also duplications in, for instance, the glyocolytic enzymes that also correspond to the major transitions.

• N.W. Blackstone: Foods-eye view of the transition from basal metazoans to bilaterians. This was another weird talk that came from a completely different perspective and made me think. It might actually be a little too weird, but it's still provocative and interesting. Blackstone is looking at everything from the perspective of metabolic signaling—he's clearly one of those crazy people coming out of the bacterial tradition. Cells communicate with one another with the byproducts of metabolism, where the redox state of membrane proteins are read as indicators of the internal state of the cells (he later calls this "honest signaling", because there aren't any intermediates between the cell and the expression of its metabolic state). The big innovation in the eukaryotes was to escape volume constraints by folding their chemiosmotic membranes into the interior of the organism, and the major animal innovation was the evolution of the mouth, which allowed specialized acquisition and processing of food patches. Subsequent evolution was to allow the animal to sense and seek out and exploit food patches in an environment where they were dispersed in a non-uniform manner. Another interesting tangent was the question of cancer: long-lived sponges and cnidarians don't get cancer. His explanation was that it was because their cells use that "honest" metabolic signaling, so that rogue cells don't have a way to trick the organism into allowing them to use more resources than they actually need; the only way to signal is to exhibit genuine metabolic distress, and cells with metabolic problems will die. Our cells have these indirect, multi-layered signaling mechanisms that allow cancer cells to "lie" to the organism as a whole.

• P. Cartwright: Rocks and clocks: integrating fossils and molecules to date transitions in early animal evolution. Molecular phylogeny is a useful tool to find patterns, and recognize branch points; this information needs to be integrated with fossil date to calibrate the clock and anchor those events to specific dates. This work was a combined effort to put together a catalog of 18s and 28s trees, and use fossil evidence to constrain the timing of the events in a metazoan cladogram. I wasn't entirely convinced that they'd overcome the obvious problems—fossils can provide a minimum but not a maximum age—but as an excuse to show lots of pictures of Cambrian and pre-Cambrian fossils, I wasn't going to complain. In particular, they had some amazing cnidarian fossils from 500 million year old rocks in Utah that were pretty much indistinguishable from modern taxa; jellyfish definitely are in a good niche. In her final table of conclusions (which flew by much too quickly!), she pinned the origin of the metazoa to 950mya, the deuterostomes to 539mya, the lophotrochozoa to 537mya, the ecdysozoa to 541mya, and the placozoa to 61mya (!). The clustering of those significant groups to right around the Cambrian was an indication that the Cambrian explosion was real.

• M. Q. Martindale: The developmental basis of body plan organization in the Eumetazoa. Uh, Mark can talk really, really fast. My notes are a rather unreadable scrawl as I tried to keep up. A general point: he emphasized that much of what we can expect to see from developmental biologists is going to look like the intricate 'circuit diagrams' that Eric Davidson has published, where the fundamental unit is a network of gene interactions that define a cell state. He showed Davidson's endomesoderm specification kernel for echinoderms, for instance, and then went through each of the genes involved and showed that they are all also present in Nematostella, and that they are almost all involved in endomesoderm specification there, as well. While the network has not been identified in the cnidarian, only the components, I do't think we'll be too surprised to see similar interactions appear as the details are worked out.

• D.J. Miller: Implications of cnidarian gene expression data for the origins of bilaterality: is the glass half full or half empty. Where Martindale was all about the similarities, Miller was all about the differences. He's working with a cnidarian, too, but a different one, Acropora. He was also explaining the expression of important early patterning genes, but one very interesting difference is that he looked at Emx and Otx, homologs to anterior-posterior genes in the bilateria that are expressed in the anterior end of those animals—but are expressed at opposite ends of the Acropora planula from each other. While some gene functions are conserved, there is no simple correspondence along the body axis.

• J. Extavour: Urbilaterian reproduction. A different sort of talk: this one was about the nature of Urbilaterian germ cells. She made the case that one of the key steps necessary to the evolution of true multicellularity was the sequestration of a distinct stem cell population that was specialized to minimize mutation with a greatly reduced mitotic rate, reduced transcription, and with mechanisms to reduce the activity of transposable elements. This was part of the process of making the fitness of individual cells take a backseat to the overall fitness of the organism.

• P.W.H. Holland: More than one way to make a worm. This talk was fun. He started with the idea of the worm, a flexible, elongated, motile tube, and showed that "worm" was a successful form that one could find scattered across the phyla of the bilateria, and that the urbilaterian was almost certainly a worm. He then raised two questions: are there examples of more derived forms that have secondarily given up features to revert to "wormness" (he gave one example, arguing that the hagfish was basically a chordate worm); and more interestingly, are there any examples of organisms that have independently evolved into a worm? He then showed us a movie of a creature that definitely looked like a worm; on first sight, it looked like a nematode, but rather than undulating and crawling it did a strange corkscrew curl. It's called Buddenbrockia, and it's a parasite found inside bryozoans. closer examination showed that it is a sealed hollow tube, completely mouthless and without a gut, and with no sensory organs, and that its interior is lined with 4 blocks of longitudinal muscle. It looked like something from outer space, if you asked me. Inside that tube, though, can be found flagellated spores that look like myxozoans. Molecular phylogeny reveals that it is a myxozoan, and that it is nested within the cnidaria. The idea is that this wormlike animal was built by breaking down a cnidarian and building it up again, and so represents a worm that has evolved independently of the Eubilateria—a worm is apparently a kind of universally basic form to take. Very cool!