Terrapins' light displays, a natural fish experiment and how a variety of eye colors persist in white Europeans, presented June 21-25 in Snowbird, Utah
Terrapins show off
Human eyes may not do justice to the spectacle of terrapins flirting. Male and female diamondback terrapins (Malaclemys terrapin) in eastern North America gather in shallow water during breeding season. The first study of how these terrapins might perceive their potential mates finds that, unlike humans, terrapins see ultraviolet wavelengths as well as blue, green and red, reported Abby Dominy of Drexel University in Philadelphia on June 22. Terrapin shells don’t reflect UV, but the reptiles’ skin does. In shallow water enough UV penetrates for terrapins to show off their contrasting patches of shell and skin. Whether terrapins find the displays alluring is Dominy’s next question.
Might be giants
By getting creative in defining “island,” scientists have found a new way to test why creatures evolve giant forms when they move onto islands. Brian Langerhans of North Carolina State University and his colleagues studied the Bahamas mosquitofish (Gambusia hubbsi) around Andros Island. During the last 15,000 years or so, sea level changes let offshore mosquitofish colonize what are today small, isolated inland bodies of water called blue holes. The 23 blue holes in the study show how body size changed in repeated natural experiments of islandlike isolation. On average, mosquitofish in blue holes are now nearly 20 percent longer than their offshore relatives. Analyzing how fish size varies with other factors, Langerhans dismisses three of the proposed explanations for island supersizing: denser island populations, fewer predators and more productive ecosystems. Instead, he says, milder competition may have made a difference. The mosquitofish tended to evolve larger bodies in blue holes with fewer other kinds of fish competing for food or other resources. Langerhans presented the work June 23.
What lovely eyes
There’s been more talking than testing about why white Europeans and their far-flung descendants maintain a variety of eye colors, says Ashley Carter of California State University Long Beach. Ideas proposed include early attachment to parental eye color or, in contrast, distaste for parental eye color as a bit of evolutionary discouragement for inbreeding. But parental eye color may turn out to have little to do with it, Carter reported June 22. He and his colleagues asked men and women of various ancestries to rank the attractiveness of faces in sets of photos. No parental effects showed up in any group of people. However, white women tended to favor faces with an eye color that was rare within a particular set of photos. A bias for whatever eye color happens to be unusual could preserve variety by favoring any variation on the wane.
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A. Carter and A. Uhl. Why do Europeans Have so many Different Eye Colors? Evidence for Negative Frequency Dependent Sexual Selection on Eye Color in Europeans. Evolution 13, Snowbird, Utah, June 22, 2013.
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