Meeting Abstract

13.4  Jan. 4  Myodocopid ostracods (Crustacea) as models for studies of eye evolution RIVERA, Ajna S.*; OAKLEY, Todd H.; Univ of California, Santa Barbara; Univ of California, Santa Barbara arivera@lifesci.ucsb.edu

Ostracod crustaceans are a valuable group for studying evolutionary biology in general, and developmental constraints on evolution in particular. Contrary to previous ideas concerning eye evolution, myodocopid ostracods have evolved compound eyes independently from other arthropods. While this does not seem parsimonious, there are several mechanisms by which compound eyes could have evolved at least twice within the arthropods. One possibility is that of switchback evolution, wherein a latent developmental program is retained and re-emerges to produce a �lost� trait. A remnant of this may be seen in the presence of dramatic sexual dimorphism in eye morphology in certain myodocopid taxa. In these groups, males have large compound eyes with 20-30 ommatidia while females have only rudimentary eyes lacking ommatidia. If the developmental differences between males and females of these species can be understood, a testable mechanism for eye evolution in ostracods will emerge. To this end, we are constructing a phylogenetic tree using both molecular and morphological data for a group of myodocopids showing sexual dimorphism of some species, the Philomedidae. Using this tree, we will be performing a character analysis of the sexual dimorphism to test if it has evolved separately or is present in the ancestral Philomedidae. In parallel, we are testing various eye-development genes for differential expression in the larvae of male and female philomdedids for later testing on the resolved character analysis. In this way, by studying the evolution of myodocopid compound eyes, we will gain understanding of the ways in which evolutionary trajectories are constrained by history and development.