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My research program focuses on the phylogeny, symbiosis, and biogeography of Photobacterium and Vibrio, clades of marine prokaryotes (family Vibrionaceae) containing luminous and non-luminous species. These bacteria, which are distributed globally in the world’s oceans, are commonly encountered in coastal, open-ocean and deep-sea habitats as free-living bacteria and as saprophytes, enteric commensals and pathogens of marine animals. Several members of the Photobacterium clade also occur in mutualistic bioluminescent associations with teleost fishes and loliginid and sepiolid squids; the animal harbors a dense population of its specific Photobacterium species in a complex gland-like light organ and uses the bacterial light for luminescence displays associated with sex-specific signaling, predator avoidance, and predation. Bioluminescent symbiosis provides part of the ecological context for our work, and much of the source material for it, and motivates many of the questions we are addressing. Through fine-scale multilocus phylogenetic analysis, coupled with deep taxon sampling and diversity analyses based on genomic profiling, we are revealing previously unrecognized species-level clade structure within Photobacterium and Vibrio, diagnosing new species, defining the genomic structure of symbiotic and oceanic populations, and testing hypotheses for biogeographic pattern, lineage diversification and symbiont-host co-speciation. Experimental work seeks to define the process of genomotypic divergence and lineage diversification as an early step in speciation, and modeling work examines the contribution of symbiosis to the creation and maintenance of that genomotypic diversity. A foundation for our research is the Photobacterium/Vibrio Genomic Diversity Collection, with current holdings in excess of 8,000 natural isolates. In collaborative interactions, we are addressing systematics of the host animals and evolution of the light organ systems of these animals in the context of robust molecular phylogenies based on mitochondrial and chromosomal loci.
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