A RE-EXAMINATION OF CONCHOSTRACANS AS MODEL FOSSIL TAXA: AN INTEGRATED BIOLOGICAL AND PALEONTOLOGICAL APPROACH

Sexual reproduction and sexual mating systems are some of the most important areas of inquiry within evolutionary biology, yet the fossil record contains relatively few examples of sexual reproductive characteristics. Finding a fossil system that allows for a comprehensive examination of mating systems over time would be invaluable in understanding one of the most important evolutionary selective forces shaping the history of life.

One taxonomic group that has been particularly useful for studies of breeding system evolution are the freshwater “clam shrimp” or “conchostracan” crustaceans, extant forms exhibiting dioecious, hermaphroditic and androdioecious populations. These crustacea inhabit temporary freshwater pools in habitats on every continent except Antarctica and have a fossil record extending back to the Devonian (370 mya). In the fossil record these shrimp are almost exclusively preserved via their carapace: a flexible and resistant, bivalved, chitinous “shell” which is not lost in ecdysis. In this study, preliminary morphometric analyses of carapaces from several extant and fossil taxa indicate that sex assignment based on carapace shape is not only possible but highly efficient.

Within the conchostracans, we have a unique opportunity to assess environment/mating system associations in a set of species that are phylogenetically closely related. By combining this opportunity with the broad fossil record of these crustaceans, we will be able to examine the evolution of a variety of mating systems over a broad time span. This would be the first study system of its kind, combining examinations of contemporary mating system evolution with a robust examination of the evolution of these systems from the fossil record.