Analysis of the spatial and temporal dynamics of marine bivalve evolution: Combining molecular and densely-sampled fossil data

Clams are diverse and abundant in both modern and ancient freshwater and marine environments, and today more than 9,000 species exist. Modern marine clams are economically very important not only as food for humans but also because they serve as food for other animals that humans depend on, like fish. In spite of this diversity and importance, the evolutionary history of the group is not well understood, and this project will develop a more detailed understanding of the 500-million-year evolutionary history of clams.

This project will use information from DNA sequences as well as from the anatomy of modern and fossil species to reconstruct evolutionary patterns. Moreover, this information will be employed to consider various key questions such as how the pace of evolution in the group has varied through time, and further the extent to which information on rates of evolution derived from the study of DNA sequences differs from that information gathered from the study of fossils.

The project will also consider why clam species in the tropics are more diverse than those found in polar regions, and how differences in ecology influence rates of evolution. This research will provide training for undergraduates, graduate students, and a postdoctoral scholar, and the results will be used to develop high school lesson plans that focus on the causes and consequences of extinction.

This project aims to reconstruct evolutionary patterns in the highly diverse bivalve clade using information from the rich marine bivalve fossil record, along with genetic information from extant species. This group, since it evolved in the Cambrian period, has fluctuated significantly in species diversity and provides an exceptional opportunity to consider how information from fossil and extant taxa can be incorporated into phylogenetic studies.

The project will also focus on how various ecological traits, including larval type, have influenced rates of speciation and extinction in the group through time. The project will first involve developing a hypothesis of relationship for all extant bivalve families using information on DNA sequences housed in GenBank, along with information from morphology.

Then, building on the family-level phylogeny, a species-level phylogeny spanning all of Bivalvia will be developed with an especial focus on marine and fossil taxa. Tests will be conducted to ascertain differences in diversification rates under alternative evolutionary models applied to genetic and fossil-based phylogenies. An additional element will be to use these phylogenies to test hypotheses on why bivalves, like most other groups, show latitudinal diversity gradients.

Previous studies of these diversity gradients have primarily focused on extant terrestrial taxa. This study will provide an opportunity to consider this issue in greater detail in marine organisms. Further, the study, through incorporation of fossil taxa, will consider how latitudinal diversity gradients have changed through time, adding an important temporal component not often considered.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.