My research interests center on evolution and ecology. I have long been interested in the evolution of breeding systems, working with both branchiopod crustaceans and livebearing fish. Currently, my research has focused on delineating the factors allowing the coexistence of male and hermaphrodite (termed "androdioecy") freshwater shrimp in ponds across the world, as well as how the evolution of hermphroditism unfolded in the Spinicaudata. Over the years of studying these questions, my research has evolved into an interdisciplinary (or "integrative") set of projects that combine to approach the complex question of how breeding systems have evolved in these crustaceans. Several graduate students and I are studying a variety of ecological, phylogenetic and genetic aspects of the unique breeding system found in these shrimp (e.g., Eulimnadia), seeking to discern the costs and benefits of hermaphroditism vs. androdioecy vs. dioecy (separate males and females) in this interesting system. Since this early work on Eulimnadia, we have expanded to study breeding system evolution across the family Limnadiidae using phylogeographic, ecological, behavioral, and genetic approaches. We published a paper establishing that shrimp in the genus Eulimnadia have reproduced via androdioecy for 24-180 million years, which is orders of magnitude longer than predicted by models of this mating system and the only system in which androdioecy is known to be this long-lived. We also published a review outlining the various androdioecious animals described to date, and noted that our clam shrimp are the most specious taxon known that is entirely androdioecious. We are now pursuing another dimension to this research which will add a paleontological aspect to our comparisons. We have teamed up with Dr. Lisa Park to explore our ability to assess breeding system type using only fossilized carapaces of Limnadiidae. We have shown that we can reliably ascertain breeding systems from the fossil record, which opens up a broad range of research possiblities that allows us to explore the evolution of breeding systems over deep time. Additional previous research on breeding system evolution in Eulimnadia has focused on inbreeding depression, relative survival of males and hermaphrodites, and the effectiveness of males in fertilizing hermaphrodites (including the competitiveness of their sperm).
Our behavioral work centers on the mating behavior of clam shrimp. We are particularly interested in a type of behavior termed "mate guarding" in which males hold ("clasp") onto hermaphrodites for up to two hours before mating. This type of mating sets up an intersexual conflict in that the optimal timing of such mate guarding is often longer for males than it is for hermaphrodites. A former PhD student (Chiara Benvenuto) explored the effects of various social environments on the timing of mate guarding to test how such environments might influence such intersexual conflict.
Along with our evolutionary questions involving E. texana, we are additionally interested in understanding its basic biology. We are currently working on understanding the reproductive system of these crustaceans, using both genetic and histological methods to understand whether these shrimp can store sperm, how hermaprhoditism may have evolved, the ultrastructure of the male gonad, and where and when fertilization takes place. The evolutionary research on mating systems has logically led us to reconstruct the phylogeny of the Limnadiidae, in collaboration with Dr. Randy Hoeh of Kent State University and Christopher Rogers of Kansas Biological Survey. We are also exploring the population genetics of these shrimp by genetically typing individuals from a number of natural populations and comparing these genetic metrics to those of a closely related congener (E. diversa). Additionally, we are documenting the extent of inbreeding in these natural populations using genetic techniques.
I am starting two new research directions as a result of interactions in our new Integrated Bioscience PhD program. The first is a collaboration with Dr. Lisa Park. Dr. Park is an expert in ostracod evolution and thus has background in inferring evolutionary relationships among species on the basis of carapace shape and ornamentation. We are teaming up to use the broad array of clam shrimp samples that we have accumulated across the planet to refine our understanding of the fossil records of conchostracans. We then plan to use this new understanding of these fossil clam shrimp to test ideas on long-term breeding system evolution in these crustaceans.
The second collaboration is with Dr. Anthony Long and his graduate student Jim Baldwin-Brown of University of California, Irvine. Eulimnadia texana's genome is being sequenced at UCI's genomics cluster and we are working on determining the sequence of the sex chromosomes. Because of the unique sex determining system of these crustaceans, we can compare androdioecious to dioecious species in this family to assess the predicted processes of sex chromosome degregation. No other system allows such a comparison, and thus we plan to develop a comparative genomics data set to allow us to test various ideas on the evolution of the non-recombining regions of clam shrimp sex chromosomes.
If any of the above research topics interests you, please link to my bibliography page for access to the abstracts of this work and requests for reprints. If you are a student interested in possibly working on these or related topics, please e-mail me at the following address: SCWeeks@uakron.edu.
E-mail address : SCWeeks@uakron.edu.