05 November 2005

Papers read this week

I consider the writing of these posts about the papers I've recently read a good mental exercise, forcing me to go over the papers, re-read parts of them and try to distil out what I find significant in them.

Martens, K., G. Rossetti, D. J. Horne. 2003. How ancient are ancient asexuals? Proceedings of the Royal Society, Biological Sciences 270:723-729.
In a recent post on rotifers, I mentioned that bdelloid rotifers are the largest group of asexual animals. A less speciose group that is also asexual is darwinuloid ostracods (family Darwinulidae). Ostracods are microscopic crustaceans with a pair of carapaces resembling clam shells. Thanks to their carapaces that fossilize well, they have an extensive fossil record. In those species that have males, male carapaces can be distinguished from female carapaces by 3 morphological criteria: lack of a brood pouch, position of muscle scars and size dimorphism (dimensions of male and female carapaces differ). The authors analyzed fossil carapaces of a darwinuloid ostracod, Alicenula leguminella, from about 145 Myr ago and found that all the individuals were females. They also reconsidered published accounts of fossil male darwinuloids and rejected them, concluding that these ostracods have been reproducing asexually for about 200 Myr.

I have a deep interest in the evolution of terrestriality among animals, especially invertebrates. Here's a couple of papers more or less related to that topic.

K. Martens, P. De Deckker, G. Rossetti. 2004. On a new terrestrial genus and species of Scottiinae (Crustacea, Ostracoda) from Australia, with a discussion on the phylogeny and the zoogeography of the subfamily. Zoologischer Anzeiger 243:21-36.
Another paper on ostracods. This is cool, because there are terrestrial ostracods, something I didn't know before I read this paper. They apparently retain a film of water within their carapaces and breath thru that water. The appendages of terrestrial species have been modified by evolution to enable them crawl on land.

Fratini, S., M. Vannini, S. Cannicci & C.D. Schubart, 2005. Tree-climbing mangrove crabs, a case of convergent evolution. Evolutionary Ecology Research 7(2): 219-233.
Several species of semi-terrestrial crabs in the family Sesarmidae climb mangroves. These crabs have a number of common morphological characters and therefore have been assumed to have descended from a common ancestor. The authors derived a phylogeny for these crabs based on their mitochondrial DNA sequences. Their results suggest that tree-climbing species are not as closely related to each as previously thought and that their arboreal lifestyle evolved in at least 3 independent lineages.

And now for something completely different...

Graham, L.A. & P. L. Davies. 2005. Glycine-rich antifreeze proteins from snow fleas. Science 310: 461.
Snow fleas are tiny wingless insects (family Poduridae) that may be seen in winter on the surface of the snow. Not surprisingly, they produce antifreeze proteins to resist freezing. The authors isolated 2 antifreeze proteins from a species of snow flea and determined its partial amino acid sequence, which was rich in glycine. They note that the snow flea antifreeze proteins do not resemble the antifreeze proteins of moths and beetles, which are rich in another amino acid, threonine. It appears that the ability to produce antifreeze proteins evolved independently in different groups of insects.

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