thinkevolution.net

Illustration by Beto Alvarez, Inquirer Staff Artist

Yesterday the Philadelphia Inquirer profiled an article just published by my lab, which demonstrates the role of a gene called couch potato in determining reproductive diapause in fruit flies. Genes in flies are named after their mutant phenotype; when this gene is disrupted, the animals lie around like lazy couch potatoes.

The nifty thing about this new work is that it demonstrates how a single gene—and more specifically, a single nucleotide site within that gene—affects a major phenotype under strong selection in natural populations. Diapause is a physiological state which permits flies to withstand long periods of stress. Flies are more likely to survive winter if they are in diapause, but not all flies are capable of entering diapause. This paper demonstrates that a single nucleotide polymorphism, which is located within the couch potato gene, determines whether flies are diapause-capable or not. From Florida to Maine, natural populations of fruit flies have gradually increasing frequencies of the nucleotide that confers diapause capability—almost all Maine flies, which must survive long winters, carry the diapause allele. Evidence suggests that this polymorphism affects other traits, like lifespan and reproduction, as well. So it’s likely that this single mutation has significant effects on the evolution of many traits. A tidy example of evolution at work (for those keeping track).

The article was published yesterday in PNAS.

A donkeycorn in a water garden. Photograph by Mary Schwalm.

There’s been a lot of coverage of Richard Lenski’s citrate-metabolizing bacteria this summer, and it’s pretty entertaining. Lenski is a biologist at Michigan State and has been maintaining populations of E. coli bacteria in his lab for two decades. Bacteria rapidly divide, grow and die; they acquire random mutations, and lose them; it’s called evolution, and it happens. Over the years Lenski has published numerous papers on his experimental bacterial evolution project, all of which describe the populations, you know, changing over time.

Probably nothing would have happened if science writer Carl Zimmer hadn’t profiled Lenski’s work. Zimmer is one of the best science writers out there, transforming basic science research findings into fascinating tales of biological anomalies and unlikely plot twists, and he’s devoted a lot of attention to Lenski’s evolving bacteria. Last year he wrote about the work in The New York Times and he also described it in his book Microcosm, published this past May. Lenski was recently inducted in the National Academy of Sciences—a big honking deal: Congratulations, Dr. Lenski!—and his inaugural publication in the Academy’s scientific journal describes a discovery having to do with the bacteria evolving the ability to metabolize citrate. These results were also presented by graduate student Zachary Blount at the evolution conference in Minnesota this June, to an entertained audience who watched a video of what it took to analyze the 40 trillion cells in the experiment. Zimmer also wrote, eloquently, about this finding, and why it’s cool, in a June 2 post on his blog. (Recommended reading if you’re interested in the details of the actual science.) With an interested reception in the scientific community and national attention in the popular media, Lenski and his well-adapted cells were, obviously, ripe targets for an outraged rejection by the anti-evolution people.

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A graduate student of evolutionary biology at UC Berkeley corrected columnist Pam Peirce today in her weekly gardening column in the San Francisco Chronicle. Peirce had originally described an insect pest as “developing” a resistance to pesticides, but the correct term is “evolve.” The difference: both describe change, but development is change over an organism’s lifetime while evolution is change over generations, in this case in response to environmental pressure. (A more complete explanation of how evolution is change and how this terminology can be used can be found here.)

The correction tidily dispenses with a common blurring of concepts. Evolution of pesticide resistance is an everyday example of natural selection, one obviously well established in the popular imagination. It’s satisfying to see the practical importance of understanding the process, even if it comes as a correction.