Meeting Abstract

46.4  Saturday, Jan. 5  Sarsielloid ostracods (Crustacea) as models for eye evolution and development RIVERA, Ajna S*; OAKLEY, Todd H; Univ. of California, Santa Barbara; Univ. of California, Santa Barbara arivera@lifesci.ucsb.edu

Switchback evolution is the re-emergence of a trait that has been lost in a specific lineage via the reactivation of a developmental program. As such, it specifically relates evolution to developmental constraints and plasticity. One possible example of switchback evolution is seen in sarsielloid ostracods, where it appears that some groups have lost and then regained compound eyes. In Euphilomedes carcharodonta and E. morini, in particular, phylogenetic evidence indicates that the regain of compound eyes has only occurred in the males. This extreme sexual dimorphism represents a developmental plasticity that could be key in a switchback evolution event. We show evidence for a novel developmental mechanism for generating extreme dimorphism – field splitting. Here, embryos and hatchlings have a single eye field on each side. Later in juvenile development, this field splits in males only. One of the resultant fields produces the compound eye while the second field, and the single field in females, produce a non-image forming rudiment (as judged by lack of ommatidia). These results suggest that the developmental and historical constraints on building an eye (e.g. eye-development gene networks) have shaped the evolution of compound eyes in the euphilomedids. Specifically, developmental constraints on eye formation in males may result in the retention of a vestigial eye field in the adults of both males and females. The presence of this eye may also represent a historical constraint – as the remnant of an eye loss event in the lineage leading to Euphilomedes.