More snails

Posted on December 22, 2008 by Michael

I love me some snail.

Biologists have tracked down genes that control the handedness of snail shells, and they turn out to be similar to the genes used by humans to set up the left and right sides of the body.

The finding, reported online in advance of publication in Nature by University of California, Berkeley, researchers, indicates that the same genes have been responsible for establishing the left-right asymmetry of animals for 500-650 million years, originating in the last common ancestor of all animals with bilateral body organization, creatures that include everything from worms to humans.

“Previous studies indicated that the methods for breaking left-right symmetry in animals seem to differ widely, so there was nothing suggesting that the common ancestor of humans, snails and other bilateral organisms had a common strategy for left-right asymmetry,” said Nipam H. Patel, UC Berkeley professor of integrative biology and of molecular and cell biology, and an investigator of the Howard Hughes Medical Institute.

“Indeed, scientists thought that one of the genes that is critical for setting up left-right asymmetry in vertebrates was only present in vertebrates and related groups and not in any other animals,” said UC Berkeley post-doctoral fellow Cristina Grande. “But we found that gene in snails, which has a lot of evolutionary implications. This cellular pathway was present already in the ancestors of most animals.”

There isn’t much I have to add to this right now. It’s just another good piece of evolutionary study. Pretty.

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How Natural Selection is Cumulative

Posted on November 8, 2008 by Michael

Tale Of Two Snails Reveals Secrets About The Biochemistry Of Evolution

In the new study, Emilio Rolán-Alvarez and colleagues note that scientists long have known that animals of the same species can have different physical characteristics enabling them to survive in different habitats. One famous example is the different beak sizes and shapes that evolved in Darwin’s finches, enabling the birds to live on different foods in different habitats on the Galapagos Islands. Until now, however, scientists knew little about the invisible biochemical changes behind such adaptations.

To help fill those gaps, the scientists studied two populations of marine snails that live only a few feet apart on the Spanish coast. One group lives on the lower shore, typically submerged in water and protected from large changes in temperature. The other group lives on the upper shore exposed to daily changes in temperature, humidity and other environmental conditions. Tests with mass spectrometry showed major differences in about 12 percent of the proteins in the snail, a subset of proteins that apparently enables the snails to survive in different environmental conditions.

This is a wonderful example of the how natural selection works in a cumulative way. Rather than the misconception that entire organs and bodily systems come into existence in one fell swoop, this study of snails offers a taste of reality.

Notice that these snails have the same set of proteins. However, between the two groups, there are differences within the proteins. Essentially, the proteins are expressed differently. At least part of the reason has to do with differing levels of ATP, or energy. That is, these proteins are regulated slightly differently, but differently enough to allow for this species of snail to live in two distinct environments. This can be important in explaining the cumulative effects of natural selection – this is still one species of snail, but they have minute differences in just 21 proteins which allow for slightly different living conditions. If the snails continue to diverge and actually fully speciate (they are in a state of sympatric incomplete speciation now) – i.e., they cannot or simply do not produce fertile offspring – then it is highly likely that such an event would be contigent upon this first deviation in protein regulation.

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