New study on ring species

Ring species are really quite startling evidences of biological change. A classic ring species is a single species that is distributed around some kind of geographic barrier to dispersion. Around the barrier, the species populations have differentiated into varieties or subspecies. Most of the adjacent subspecies are interfertile, except for one pair that is either reproductively isolated or experiences reduced fitness. For those of you who just tuned out from all the biology jargon, here's a simpler explanation based on what we think ring species are: Imagine a species spreading out (dispersing) from a location, say in northern California. This species (say it's a salamander) is a mountain species and doesn't like the lower elevations. As this salamander spreads southward over many generations, it will avoid California's central valley and spread down the hills and mountains that run around the central valley. Since salamanders don't really move very fast, spreading through California takes many generations, and during that time, the salamander populations become slightly different as they (presumably) adapt to local conditions. Finally, when the salamanders finish dispersing around the central valley, they come into contact again in the south, around Frazier Park. One set of salamanders went east around the central valley, and one went west. When they meet in the south, though, these salamanders are no longer able to interbreed normally, but if you test adjacent populations along the eastern dispersal route, you'll find that they interbreed just fine. Likewise with the western route. It's only the salamanders from the very southern ends of the dispersion routes that can't interbreed normally. If you're looking to reproductive capabilities to define what is a species (the biological species concept), these salamanders are kind of weird. As you might have guessed already, evolutionary biologists think that these salamanders (and other ring species like them) are examples of speciation in progress. I agree.

A new paper from Monahan et al. takes a different approach to studying ring species. Rather than looking for the species, they instead looked at geographic barriers that would be conducive to the formation of ring species. They found that these barriers are pretty rare, which could explain why there are so few examples of ring species. The paper is open access, and I definitely recommend you check it out, if you're into that sort of thing.

Monahan et al. 2012. Ring distributions leading to species formation: a global topographic analysis of geographic barriers associated with ring species. BMC Biology 10:20.

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Origins Exhibit opens at Southern Adventist University

For several years now, Southern Adventist University in Collegedale, TN has been turning the halls of the Hickman Science Center into a beautiful new exhibit, with the intention of explaining our origins from a creationist worldview. The last time I saw it, they were working on the geologic column exhibit, having finished an amazing mural depicting the structure of a cell. I got to watch as they uncrated their Dunkleosteus replica (that's a really nifty kind of fish).

Now comes word that the work is finished and the exhibit is open to the public. You can find out more about the exhibit at their website:
SAU Faith & Science

After the somewhat discouraging reports in the latest NCSE Reports, it's nice to see Southern Adventist still taking a firm stand on creation. Congratulations to Lee Spencer, Keith Snyder, and all our friends and colleagues at Southern!

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Reminder CBS/CGS call for abstracts

Just a quick reminder that the deadline to submit biology and geology abstracts to the annual conference of the Creation Biology Society and Creation Geology Society is less than three weeks away on April 1.  See the full call for abstracts here:

2012 Call for Abstracts

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An intermediate euglena?

You might remember euglena from your biology days peering at tiny critters under the microscope. Euglena was that weird one-celled organism that could swim around like an animal but photosynthesize like a plant. Turns out there are a number of euglena-like organisms (euglenids) that are also photosynthetic but appear to have evolved from one-celled organisms that are "phagotrophic." Phagotrophic is a fancy word that basically means that the non-photosynthetic euglenids get their energy from eating other stuff. The question is how do you evolve from one to the other? Seems like a big change in lifestyle. Imagine if I suddenly stopped eating, turned green, and started laying out in the sun in my underpants. OK, maybe you don't want to imagine that, but that's the kind of change we're talking about.

In a recent paper from BMC Evolutionary Biology, Yamaguchi et al. report the discovery of a euglenid named Rapaza viridis that appears to be able to get energy in two different ways. It's capable of eating, and it needs to eat a particular kind of algae in order to survive. Rapaza cells also possess the ability to photosynthesize, and they cannot survive longer than a week in the dark even when supplied with plenty of algae to eat. What's even weirder is that Rapaza appears to have two types of chloroplasts, the cellular structures where photosynthesis takes place. One chloroplast from Rapaza looks like a regular photosynthetic euglenid chloroplast, but the other looks like a chloroplast from the algae that it eats. I'm sure there's a very interesting story going on at the molecular level, regulating the appropriation of chloroplasts and possibly other items from the algae that Rapaza eats. Hopefully, future research will illuminate this fascinating relationship.

Rapaza makes a fascinating intermediate form between the eating and photosynthesizing euglenids. It's like the photosynthesizing euglenids because it needs to get its energy from photosynthesis, but it's like the eating euglenids because it can eat algae. What makes it even more interesting is that a molecular phylogeny puts Rapaza on a branch between the eating and the photosynthetic euglenids (that means it looks very much like a "transitional form"). Like some other intermediate forms, though, Rapaza has traits from two different groups rather than intermediate traits (I should note that that's not true for all intermediates): it has euglenid and algal chloroplasts, not something "in between." Does this mean we should view all euglenids as members of the same created kind? Time will tell, but Rapaza definitely stands as a great example of the kind of complicated, symbiotic relationships found among one-celled organisms.

Yamaguchi et al. 2012. Morphostasis in a novel eukaryote illuminates the evolutionary transition from phagotrophy to phototrophy: description of Rapaza viridis n. gen. et sp. (Euglenozoa, Euglenida). BMC Evol Biol 12:29.

(photo from wikipedia)

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Gorilla genome and fossil fleas

Just a quick note to alert readers to two interesting items in this week's Nature. First up is the publication of the gorilla genome. Pieces and drafts of this have been available for years, but this is the first (to my recollection) summary of the entire genome project. Scally et al. (the authors) aligned the human, chimp, gorilla, and orangutan genomes and reported a mean difference of 1.37% between human and chimp, 1.75% between human and gorilla, and 3.4% between human and orangutan. No surprises there, although I am quite certain there are probably denials of these results already being written. Scally et al. also reported that

In 30% of the genome, gorilla is closer to human or chimpanzee than the latter are to each other; this is rarer around coding genes, indicating pervasive selection throughout great ape evolution, and has functional consequences in gene expression.

For an evolutionary explanation of this result, I recommend Dennis Venema's essay on Speciation and Incomplete Lineage Sorting. It is not yet clear to me exactly what significance this would have for a creationist model, but I have some research going that should shed some light on that question. Meanwhile, the gorilla genome paper is open access, so you can read it for yourself:

Scally et al. 2012. Insights into hominid evolution from the gorilla genome sequence. Nature 483:169-175.

In other news, Huang et al. report newly discovered Chinese fossils from Jurassic and Cretaceous sediments showing really large fleas with siphoning mouthparts but no powerful, jumping hindlegs. Interesting stuff, and possibly relevant for understanding the origin of these ectoparasites. Check it out (if you have a Nature subscription):

Huang et al. 2012. Diverse transitional giant fleas from the Mesozoic era of China. Nature 483:201–204.

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