Meeting Abstract

S3-1.2  Jan. 4  Evolution of High-Acuity Vision in Coleoid Cephalopods SWEENEY, A*; JOHNSEN, S; Duke University; Duke University

Spherical lenses with a graded refractive index design are required for camera-like vision in aquatic animals. In cephalopods, these lenses are made of a group of closely related proteins collectively called S-crystallins. Our earlier work has shown that an adaptive radiation these S-crystallin genes and positive selection on the electrostatic properties of S-crystallin proteins led to a graded refractive index lens capable of forming high-resolution images in the squid Loligo opalescens. In the L. opalescens lens, S-crystallins with high charge stabilize the optical properties of regions of low refractive index in peripheral layers, and S-crystallins with lower charge are tightly packed in the high refractive index cortex. The mechanistic link between S-crystallin sequence, biochemistry and refractive index allows us to understand in molecular detail the optical evolution of a camera-like eye in cephalopods. To understand the transition from ancestral cephalopod vision to extant camera-like vision in coleoid cephalopods, we used techniques from molecular evolution, biochemistry, molecular dynamics, optical modeling and image analysis. We sequenced 600 S-crystallin genes from most major coleoid taxa, constructed a gene tree from these sequences and analyzed it for patterns of charge evolution. We also measured the optical quality of these lenses by calculating their modulation transfer functions (MTFs). Our gene tree suggests that high-resolution lenses evolved from a low-resolution ancestor multiple times within the coleoid cephalopods. Consistent with our gene tree data, our MTF data show that there is taxonomic variation in lens quality within coleoid cephalopods. We will discuss the correlations between independent adaptive radiations of S-crystallin molecules, high acuity vision in cephalopods and possible evolutionary scenarios in which these changes in visual acuity may have been occurring during the Jurassic radiation of squid.