Thursday, September 11, 2014

How new colors evolve

Lately, we've been looking at macroevolutionary patterns and asking about the origin(s) and loss(es) of interesting traits. We've had exciting discussions about the lability of these traits and the problem of identifying cause and effect. So maybe it's a good time to look in more detail at one such trait and ask how does novelty arise? This is a bit old, but attempts to offer a compelling mechanism for the evolution of new pigments in Heliconius butterflies. What do you think?

Positive selection of a duplicated UV-sensitive visual pigment coincides with wing pigment evolution in Heliconius butterflies

Authors: Adriana D. Briscoe, Seth M Bybee, Gary D. Bernard, Furong Yuan, Marilou P. Sison-Mangus, Robert D. Reed, Andrew D. Warren, Jorge Llorente-Bousquets, and Chuan-Chin Chiao

Time: Tuesday September 16th at 10:30 in Argumentet

Abstract:The butterfly Heliconius erato can see from the UV to the red part of the light spectrum with color vision proven from 440 to 640 nm. Its eye is known to contain three visual pigments, rhodopsins, produced by an 11-cis-3-hydroxyretinal chromophore together with long wavelength (LWRh), blue (BRh) and UV (UVRh1) opsins. We now find that H. erato has a second UV opsin mRNA (UVRh2)—a previously undescribed duplication of this gene among Lepidoptera. To investigate its evolutionary origin, we screened eye cDNAs from 14 butterfly species in the subfamily Heliconiinae and found both copies only among Heliconius. Phylogeny-based tests of selection indicate positive selection of UVRh2 following duplication, and some of the positively selected sites correspond to vertebrate visual pigment spectral tuning residues. Epi-microspectrophotometry reveals two UV-absorbing rhodopsins in the H. erato eye with λmax = 355 nm and 398 nm. Along with the additional UV opsin, Heliconius have also evolved 3-hydroxy-DL-kynurenine (3-OHK)-based yellow wing pigments not found in close relatives. Visual models of how butterflies perceive wing color variation indicate this has resulted in an expansion of the number of distinguishable yellow colors on Heliconius wings. Functional diversification of the UV-sensitive visual pigments may help explain why the yellow wing pigments of Heliconius are so colorful in the UV range compared to the yellow pigments of close relatives lacking the UV opsin duplicate.

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