Meeting Abstract
Eye evolution is a classic system for studying origins of morphological complexity. Eyes with lenses that focus light onto photoreceptor cells have evolved at least 11 times in metazoans. Although many of these lens eyes have Cambrian origins, some, such as the unique aragonite lens of polyplacophoran molluscs, may have evolved as recently the Eocene. Here, we address the question of when in evolutionary time these independent origins occurred. In the case of vertebrates, arthropods, cephalopods, bivalves, and gastropods, we estimated an age range based on published data. We evaluated evidence for homology of lens eyes within each lineage to correct for the possibility of multiple origins. Using published phylogenies and fossil-calibrated time trees, we determined a maximum (age of MRCA without eyes) and minimum age of origin (age of crown group with lens eyes). In some cases, as in Cubozoa, we estimated time trees using multilocus datasets compiled from NCBI and fossil calibrations. Our preliminary estimates of eight lens eyes indicate that these structures evolved in the Precambrian, Cambrian, or as recently as the late Devonian. Some taxa present unique challenges due to the paucity of their fossil records (i.e. Nemertea), the variable nature of their photoreceptor structures (i.e. sabellid polychaetes) or the absence of robust phylogenetic hypotheses (i.e. Polyplacophora). These three lineages are candidates for the most recent independent origin of a metazoan lens eye. To estimate the age of origin of chiton aragonite lens eyes, we are using target-capture phylogenomic methods to generate a time-calibrated phylogeny. Together, our timeline of lens eye origins will provide a valuable temporal context forfurther comparative research on evolution of complex structures.
