The enormous biodiversity on earth not only provides humans valuable biological resources, but also serves as a crucial component of our highly interdependent ecosystem. How this great biodiversity is generated remains a central question of biology. While much of the tree of life can be generated through abiotic (non-living) processes, such as climate change or tectonic movements, some of the most striking diversities arise from biotic interactions between species. Evolutionary studies of contemporary marine lineages are typically framed within abiotic hypothesis-testing contexts and have collectively lagged behind terrestrial studies in developing an integrated framework that includes a meaningful biotic perspective. The proposed research addresses this deficiency by studying the evolution of the hyperdiverse clam group Galeommatoidea. It is a particularly apt group because it contains large numbers of free-living as well as symbiotic (living with a host) species and is therefore amenable to comparative approaches. The evolutionary pathways of both free-living and symbiotic clams are affected by abiotic factors, but the symbiotic species are influenced by an additional biotic factor: their ecological interactions with hosts. By comparing the evolutionary patterns of the two groups, the relative roles of abiotic and biotic factors in driving the diversification of this species-rich marine lineage can be assessed.
The proposed research complements the NSF-funded ?Assembling the Bivalve Tree of Life? initiative and involves extensive collaboration with national and international museum collections. One graduate student is receiving in-depth research training in phylogenetic, morphological and macroevolutionary analysis. Four undergraduate students have been receiving training in molecular phylogenetic techniques. Many specimens involved in the project will be deposited into the Museum of Zoology, Ecology and Evolutionary Biology, University of Michigan. The graduate student and two other undergraduate students will be trained to computerize museum collections and manage electronic taxonomic databases. In addition, biodiversity data of selected galeommatoidean clams will be contributing to the Animal Diversity Web (ADW), a premier source of public biodiversity information that also directly feeds into the online Encyclopedia of Life. The ADW also serves as a free biodiversity database that allows students/researchers to conduct comparative meta-analysis across the tree of life.
The enormous biodiversity on earth is crucial to our highly interdependent ecosystem and provides valuable biological resources. How this amazing diversity is originated and maintained is a central question of biology. While much of the "tree of life" can be generated through abiotic (non-living) processes, such as climate change and tectonic movements, some of the most striking diversities arise from biotic interactions between species, such as competition, predation, and symbiosis. The role of biotic factors in driving species evolution has been extensively studied in terrestrial systems. Unfortunately, their impact on marine life is much less understood, even though 71% of the earth's surface is covered by the ocean. This award enabled us to study how biological interactions affect marine evolution using a group of intriguing animals: the galeommatoid clams. They are one of the most diverse bivalve groups in the ocean and they exhibit extraordinary morphologies, such as colorful tentacles and reduced or internalized shells. Some members in the group live a commensal life with many other marine invertebrates: the clams live together with burrowing animals (sea urchins, shrimps, crabs, etc.) in order to obtain food and shelter from the hosts. In collaboration with international biodiversity expedition teams, we have collected hundreds of galeommatoid clams species from all major ocean basins. We used molecular and statistical methods to study their diversification and morphological evolution patterns - in particular, how commensal associations and marine habitat types affect their evolutionary dynamics. The results from this research gave us a number of new insights into mechanisms that govern evolution of marine organisms. We learned that biologically complex coral reef habitats can promote rapid diversification of marine lineages. We also found that symbiotic associations such as commensalism can greatly affect tempo and mode of the clams' morphological evolution. In summary, research funded by this award has greatly expended our knowledge on the evolution of the taxonomically, morphologically and ecologically diverse galeommatoid clams. It has also deepened our understanding of the fundamental processes that influences the generation of marine biodiversity. Results from the study have been contributed to the NSF-supported Animal Diversity Web (ADW), a premier source of public biodiversity information that also directly feeds into the Encyclopedia of Life. During the award period, four undergraduate students have gained training in marine ecology, molecular biology, and statistical inferences, including one underrepresented minority student who is now perusing a PhD degree in the field of ecology and evolutionary biology. One graduate student (the co-PI) has successfully defended the dissertation (funded by this award) and obtained a competitive postdoctoral fellowship.
