The Sunday morning session at the Oregon evo-devo symposium

[Since I had to fly away early this morning and missed all these talks, I had to rely on regular commenter DanioPhD to fill in the gaps … so here's her summary:]

This morning's final series of talks each focused on a different phylum, but the unifying theme was one of bridging the processes of microevolution and macroevolution. The first talk after breakfast (and a long night of Scotch-drinkin' and story-swappin' prior to that) was Bernie Degnan of the University of Queensland. He summarized his work on Amphimedon queenslandica, a sponge species developed as a model of a representative primitive metazoan. Sponges diverged from the metazoan lineage ca. 700 MYA and possess the most minimalist metazoan body plan--no nervous system, muscles, nor any discernible tissues in the adult body architecture. Their embryos, however, feature robust anterioposterior patterning, distinct cell types organized into tissues, and cell morphogenesis typical of more complex metazoans. These embryonic characteristics are achieved by a regulatory network of genes, which, while inactive in the adult sponge, strongly support the presence of similar molecules in the ancestral metazoan genome. A few million years after the divergence of porifera, metazoans were able to co-opt these molecular toolkits to build the diverse, molecularly and morphologically distinct tissues common to all bilaterians. PZ has previously written up one such sponge tale here describing the molecular precursors to a nervous system in the sponge genome. Precursors to pretty much every other developmental 'big gun', e.g, Hox genes, Pax genes, Wnts, Hedgehog, etc. are also present as a basic prototype, in the Amphimedon genome.

Next up at the podium was Michael Wade, of Indiana University. He presented a model for the evolution of maternal effect genes and made predictions based on algebraic expression of the rates of maternal effect alleles within and between populations. This was a bit outside my area/interests, but for more specifics, please see (this link to the relevant paper abstract). The take-home message was that the maternal genotype has critical input into embryonic development and survival, irrespective of the zygotic genotype. The mode of transmission and expression of maternal effect genes differ from zygotic genes, in that all offspring will be influenced by the maternal genotype, but only female offspring will activate these genes from their own genome. This gives natural selection different 'access' to these genes as compared to the garden variety zygotic gene pool, thus positive selection (selecting for advantageous mutations) and purifying selection (purging deleterious mutations) will work at different rates on maternal effect genes as compared to zygotic genes.

Bill Cresko of the University of Oregon presented his work on the evolution of bone morphogenesis in sticklebacks. This was another example of a microevolution study that may have applications useful for understanding macroevolution. Briefly, there are oceanic--andromatous, actually, as they migrate to fresh water for spawning--populations of sticklebacks that have existed in roughly their present form for over 10 million years. They feature some wicked bony spikes around their pelvic region and lateral dermal bones, both of which presumably confer some protection against predators. There are several fresh water species as well, young (15,000 years or less) populations descendent from the migratory oceanic stock who were trapped in fresh water by receding glaciers. The key feature of these new stickleback populations is their rapid (in evolutionary time) and repeated loss of both the pelvic spikes and the body armor. It happens in isolated freshwater stickle populations all over the world, over and over again. Bill's group has been intercrossing the oceanic and freshwater stocks to identify the genes responsible for these changes. Mapping has revealed that the genetic regulators of pelvic spines are independent of those that regulate the lateral plates. From the gene clusters implicated in the latter, several interesting candidates with roles in mineralization, osteoblast function, and Calcium ion processing have been identified. Intriguingly, it's not clear at all that selection is acting on the bony plate factors at all. It's just as likely that some other linked factor is the real target of this rapid and repeated selection, and the bony plate genes on the same chromosome are just along for the ride.

Kevin Peterson, a paleontologist from Dartmouth College was the final speaker. He gave a broad and engaging summary of recent work on the evolution of microRNAs. microRNAs (miRs) are short (22-mer) RNA sequences which, after several steps of post-transcriptional modification to their shape and configuration, have precise, cell-specific effects on mRNA, either by degrading it altogether or inhibiting translation. Described as the 'dark matter' of the genome, these tiny, unassuming molecules were largely overlooked until recent investigations revealed their hitherto unknown importance in gene regulation. Peterson's angle was to apply the known data on miRs across the phyla and take a novel look at the macroevolution of these factors. For years, evolutionary biologists have sought to explain the explosions of diversity and complexity seen in the vertebrate clade.

Morphological change plotted against time reveals that the biggest degree of change happened early in our lineage, and subsequent increases in complex phenotypes have been relatively miniscule. When the molecular era revealed the genome duplication phenomenon, many pinned their hopes on this as the explanation for complexity, but this rationale fails under further scrutiny. Similarly, as we learned from the Coyne-Wray duel on Friday night, Cis-regulatory elements were enthusiastically embraced as a key factor behind evolutionary complexity in vertebrates, but again, this explanation alone cannot account for many of the observed changes. Peterson and others have shown that miR gene families are present throughout all phyla, and have continued to evolve throughout evolution. There is a very low rate of secondary loss of miRs, once they appear, and sequence divergence is restricted due to the required nucleotide specificity of the recognition sequences which anneal to the target transcripts. These characteristics lend themselves to the creation of a robust phylogeny, which, in addition to clarifying some controversial assignments between morphological and molecular phylogenies, shows an acquisition of new miR families at a rate which largely overlaps that of the morphological changes noted in vertebrate evolution. Thus, the fine-tuning of cell-specific gene regulation conferred by the evolution of novel miRs may be an important mechanism in generating complexity.


[So now everyone has to tell DanioPhD to start her own blog!]

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DanioPhD - Thanks for the wonderful summary. You really should start your own blog!!!

Ok, well, I made up a word: "andromatous" should be "anadromous" of course--yikes!

The Michael Wade link is here if you want it. Sorry!

Very well done, thanks much Danio.

Danio, don't you know that when the Almighty PZ says jump, you must clear 4.8m in a standing leap? Start your own blog.

I don't suppose you mentioned another toiler at the University of Queensland to the first speaker?

By John S. Wilkins (not verified) on 06 Apr 2008 #permalink

I rarely comment on any site and maybe only once here but I read your site "religiously" so to speak. I am an attorney. I am a liberal. I am a Democrat. I have an empirically demanding mind. I am an agnostic (at best or worst depending on your perspective) and have been, I think, throughout my lifetime although I have tried my best in the past to join the "moral majority" through religion here in Texas. I have found humor and support for my beliefs in most that I read here, however I am disappointed by your apparent contempt of attorneys and the legal process. I do not intend this comment to chastise but rather to encourage perspective.
I interpret most that I read here to be politically liberal. Am I mistaken? Do you not realize your rights here in this country to pursue your beliefs through the justice system enables you to speak freely here as you do. I respect your opinion that scientists should not be diverted from their endeavors to testify in a pharmaceutical case but isn't it the legal process that guarantees your right to this forum? Yes some lawyers maybe financially motivated to pursue questionable scientific claims but isn't that the very process that guarantees our rights to everything we hold dear. If the theocrats have their way free speech will not be free, just ask the Dixie Chicks. I know this will seem like a lawyer defending his profession to you but I intend it to be a defense of what you are doing here. I have seen other posts you have made containing derision of lawyers and I am writing this because I believe that your positions about religious influence on our government and the legal process itself are inconsistent. Casting all attorneys as unscrupulous money hungry shysters perpetuates the religious right's arguments (and the corporate opportunists taking advantage of it) against the very thing you do here. Yes there are questionable legal actions from your perspective and mine. Are they truly frivolous? Maybe, but that is not the point. My father ,a lawyer for 38 years, I think defined it best, "a frivolous lawsuit is someone else's lawsuit." You may think this warrants no consideration at all but I was about to delete your site from my favorites and I thought what the hell, if I can't persuade you about the integral importance of the legal system in our country then I am sure not going to convince people here in Texas.
William Shakespeare in his play Henry the VI paid respect and homage to what we lawyers do. It has been a greatly maligned quote through misunderstanding, or not, but it does conversely illustrate the importance of lawyers, like them or not. "THE FIRST THING WE DO, LET'S KILL ALL THE LAWYERS." This is how you allow the majority to control. I think your tendency to deride all lawyers helps the very theocracy I believe you rail against. Richard Dawkins's book lead me to you and I do enjoy your knowledge and perspective, it is refreshing, but I think you undermine your right to deliver it to us by disparaging lawyers. I know this comment is not responsive to this post but I hoped you would more readily notice it here. Keep up the fight for reality, thank you.

"Microevolution" and "macroevolution"? What is this heresy? You're using the language of the creationists!

It's all just evolution, baby.

Cyde Weys, these are real phenomenon that fully vested evolutionary biologists debate over at length--an explicit aim, in fact of this particular Symposium, entitled: "From Patterns to Process: Bridging Micro- and Macroevolutionary Concepts through Evo-Devo"

The creationists aren't creative enough to make up their own terminology, silly! They just borrow ours and dress it up in a clown suit.

Phenomenon should be Phenomena (doo doo do do do...)

Oh how I need to sleep.

Sweet dreams, Danio. :-)

Clay: repost that over on the Seidel thread... I think it's quite relevant

I think there is a tendency to blame lawyers for America's litigious culture, and I don't think all lawyers are the only people to blame for that. The fight against cretinism has largely been fought in the courts and we need to remember that.

Also, Danio, great post!

How refreshing to find some developmental biology on here for a change! And the upside is, fewer comments!

miRNAs are kind of the latest vogue in epigenetics. Why not? but I wouldn't attribute them with superpowers, either.

Did Bill Cresko mention if those pelvic spikes and body armor are from somites or from neural crest populations, like the turtle plastron may be? Neural crest is evolutionarily far more plastic and has led to great adaptations in head morphology; it would be interesting to know if in teleosts these cells kept a chondrogenic program that they no longer use in amniotes, at least in the trunk. (Trunk neural crest cells keep that capacity in vitro).

Danio, your most important sentence to me is here: "Metazoans were able to co-opt these molecular toolkits to build the diverse, molecularly and morphologically distinct tissues common to all bilaterians."

Co-option is what my research is all about. I do think that evolution is parsimonious, and I love the mix-and-match aspect of gene expression control elements. [miRNAs are part of that, too, of course.]

I hereby declare that DanioPhD must, and without delay, start her own blog so that I, gentle enthusiast, will be able to read more of this 'ere interesting verbiage.

Thanks, Danio.

"fully vested evolutionary biologists"

What, we are supposed to get vests?? I think there has been some oversight, I haven't received mine yet. I am assuming it's at least in black leather and says "Charlie Darwin's Angels" in the back?

John@#7: Nope, but he did have some highly entertaining shark stories to tell from your part of the globe.

Alethea@#14: These are dermal bones, of course, so I wouldn't be surprised if crest played a role at some stage. The armor doesn't actually develop until rather late--ca. 30 days post fertilization, with mineralization beginning around the neuromasts. This is after the fish has already been hatched, swimming around and eating for several weeks. Are there other examples of crest-derived cell populations hanging around uncommitted for so long? Another cool thing he mentioned was that one of the genes of interest, a LIM mineralization protein, has multiple splice forms, some of which are specific to the armor formation, and others specific to the muscle that articulates with this dermal bone and pelvic spines, indicating a degree of crosstalk between those groups of progenitors.

Windy@#16: Yes, and it's lined with cozy finch feathers.

Thanks all, for the positive feedback. Find me another 10 (15? 20?) hours a week and I'll happily start a blog. It's tempting as it is.

Amphimedon queenslandica

Is -medon really feminine?

Next up at the podium was Michael Wade, of Indiana University. He presented a model for the evolution of maternal effect genes and made predictions based on algebraic expression of the rates of maternal effect alleles within and between populations. This was a bit outside my area/interests, but for more specifics, please see (this link to the relevant paper abstract).

This link still doesn't work.

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Perhaps this will help you remember the "anadromous": it literally means "uprunning". Compare anabolism vs catabolism, and Dromaius (the emu) and Dromaeosaurus.

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Did Bill Cresko mention if those pelvic spikes and body armor are from somites or from neural crest populations, like the turtle plastron may be?

No idea, but the turtle plastron consists of the clavicles, the interclavicle, and a few pairs of gastralia. The latter are homologous to "fish" (and probably caecilian) scales. Is it known where zebrafish scales come from? Also, I suppose zebrafish, having cleithra, also have clavicles and an interclavicle?

By David Marjanović, OM (not verified) on 07 Apr 2008 #permalink

The cooption thing was obvious from years ago, where every single Northern had a column for Brain and over 90% of genes were expressed there even if they were only otherwise on in one other tissue. it became a cliche.

It is of course quite obviously how you get a human brain from essentially the same set* of genes that a mouse has. You use far more of them to build the brain.

*yes, I know there are a few novel genes in humans that operate in brains but that can never be the whole story.

By Peter Ashby (not verified) on 07 Apr 2008 #permalink

David, please see comment #4 for the link. Thanks for the etymology lesson. Ichthyic will probably never speak to me again, and I definitely won't be able to show my beet-red face around Bill Cresko's lab anytime soon :)

Peter, co-option is certainly not a novel concept, but it's continually astounding how far back in evolutionary history these things are found, as more genomic information from diverse phyla is revealed. The new genomic information obtained from basal metazoans and bilaterians presented at this conference complemented the spirited debates over the origins of cellular complexity quite nicely.

Amphimedon queenslandica

Is -medon really feminine?

Next up at the podium was Michael Wade, of Indiana University. He presented a model for the evolution of maternal effect genes and made predictions based on algebraic expression of the rates of maternal effect alleles within and between populations. This was a bit outside my area/interests, but for more specifics, please see (this link to the relevant paper abstract).

This link still doesn't work.

-----------------

Perhaps this will help you remember the "anadromous": it literally means "uprunning". Compare anabolism vs catabolism, and Dromaius (the emu) and Dromaeosaurus.

-----------------

Did Bill Cresko mention if those pelvic spikes and body armor are from somites or from neural crest populations, like the turtle plastron may be?

No idea, but the turtle plastron consists of the clavicles, the interclavicle, and a few pairs of gastralia. The latter are homologous to "fish" (and probably caecilian) scales. Is it known where zebrafish scales come from? Also, I suppose zebrafish, having cleithra, also have clavicles and an interclavicle?

By David Marjanović, OM (not verified) on 07 Apr 2008 #permalink