Meeting Abstract

97.5  Monday, Jan. 6 14:30  Influence of zooplanktivory on retinal ganglion cell topography in labrid reef fishes COHN, BRIAN*; COLLIN, SHAUN; WAINWRIGHT, PETER; SCHMITZ, LARS; W.M. Keck Science Department, Claremont McKenna, Pitzer, and Scripps Colleges; School of Animal Biology and the Oceans Institute, The University of Western Australia; Department of Evolution and Ecology, University of California Davis; W.M. Keck Science Department, Claremont McKenna, Pitzer, and Scripps Colleges bcohn12@BrianCohn.com

While the majority of labrid reef fishes prey on bottom-dwelling invertebrates, this very speciose and ecologically diverse clade contains multiple independent evolutionary transitions to a plankton-based diet. These zooplanktivores hunt mainly on small, partially transparent copepods drifting above the reef, posing a visual challenge for these predators. We hypothesized that retinas of zooplanktivores are modified to meet the requirements of plankton-feeding, with higher visual acuity and a centrally located peak in retinal cell density. We sampled retinas of two zooplanktivores and each of their closest phylogenetic relatives for a total of 15 species, yielding spatial density measurements of ganglion cells. In order to achieve a precise visualization of ganglion cell maps, we developed an R code that projects the density surface onto an easily readable polar heat-map. We also utilized a new retrotransformation program to ‘retistruct’ the hemispherical nature of RGC data and applied thin plate spline interpolation for contour smoothing. While there is only a weak indication of interspecific variation in the total number and peak density of RGCs, their distribution across the retina varies between zooplanktivores and others. Transitions to plankton-feeding coincide with the presence of only one spatial retinal peak in acuity, while other labrids have two retinal peaks. Our results support the hypothesis that zooplanktivory is a major axis of diversification in visual morphology.