Judson on sticklebacks

Olivia Judson's blog, "The Wild Side" has quickly become a worthwhile weekly stop. This week, she describes some stickleback developmental biology.

Now, you may not get that excited about sticklebacks, but there have been a lot of cool parallels between stickleback and human evolution during the past couple of years. For one thing, as sticklebacks invaded the post-glacial lakes of British Columbia after the last ice age, they repeatedly differentiated in parallel into different ecological morphs. Is this like the differentiation of robust and non-robust australopithecines in different regions of Africa? Could be -- it certainly provides a possible model of parallel niche construction.

Judson features a couple of other interesting aspects of their biology. She mentions a pigmentation gene, KITLG, that has undergone adaptive changes in both sticklebacks and recent humans. Most of her story is devoted to a developmental regulation gene, Pitx1:

There are a couple of interesting things about this discovery. The first is that the molecular basis of the change from pelvis to no pelvis does not involve a mutation to the protein-coding region of the Pitx1 gene itself. In other words, the protein made from the gene hasnt changed. What has changed is the way the gene is expressed. This is in contrast to the sorts of mutations one often reads about as being involved in evolution, which typically involve changes to the protein itself.
A second interesting feature of the stickleback pelvis is that -- unlike the armor plates -- the loss is probably due to mutations having occurred independently in the different populations. Whats more, changes to the use of Pitx1 are also implicated in pelvic loss in nine-spine sticklebacks (Pungitius pungitius) -- yet nine-spine and three-spine sticklebacks have been going their own evolutionary ways for at least 10 million years.

This "parallel regulatory mutation" story has been told a number of times for different systems in the last few years -- Sean Carroll in particular tells several in his recent book, The Making of the Fittest -- which I recommend. But for a short version, Judson's post is a good read.