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Title: Microsatellite genotypes reveal some long distance gene flow in Perkinsus marinus, a major pathogen of eastern oysters

Author
item Thompson, Peter
item Rosenthal, Benjamin
item HARE, M - Cornell University

Submitted to: Journal of Shellfish Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2014
Publication Date: 4/30/2014
Publication URL: http://handle.nal.usda.gov/10113/59401
Citation: Thompson, P.C., Rosenthal, B.M., Hare, M.P. 2014. Microsatellite genotypes reveal some long distance gene flow in Perkinsus marinus, a major pathogen of eastern oysters. Journal of Shellfish Research. 33(1):195-206.

Interpretive Summary: The agent of Dermo disease, Perkinsus marinus, causes disease and death in oysters. Passive dispersal of P. marinus between hosts maybe limited to local oysters connected by common water currents. Marked genetic distinctions among local parasite populations would provide evidence in favor of limited dispersal. Here genetically variable loci were characterized from 15 oyster populations from the Gulf of Mexico and Atlantic coasts of the United States. Allele frequencies were found to differ significantly among most locales, but there was no indication that the populations separated by the greatest distances were least closely related, genetically. One genetic lineage occurred in many locations, while the others were limited to a particular region or disjunct locations. Two lineages were associated with recent range expansion. Altogether, local assemblages of P. marinus were found to be comprised of mixtures of distinct parasite types that undergo only infrequent recombination. By mixing divergent strains, long distance dispersal may play an important role in the evolution of P. marinus and spread of Dermo disease, whereas locally, high frequency strains may represent focal epizootics. This information will be of interest to fisheries managers and those attempting to restore estuary habitats, as well as parasitologists, epidemiologists, and population geneticists.

Technical Abstract: As the agent of Dermo disease, Perkinsus marinus causes significant mortality and reduced fecundity in host populations. Passive dispersal of P. marinus between hosts subjects parasite movements to control by water currents in estuarine systems, potentially limiting connectivity among parasite populations in different estuaries. Given recent evidence for sexual reproduction in P. marinus, estimates of gene flow among locations may provide insights into this parasite’s epidemiology. Here, seven P. marinus microsatellite loci were amplified from 374 individuals collected from 2002 to 2008 at 15 geographic locations encompassing 4800 km of the Gulf of Mexico and Atlantic coasts of the United States. Among 1082 oysters sampled, 374 were determined to be infected by a single parasite genotype and therefore amenable to analysis. Allele frequencies differed significantly among most locales, but there was no indication of isolation by distance. Nor were populations subdivided into three genetic regions, as previously hypothesized. Four distinct clusters of multi-locus genotypes were identified by analyzing genetic distances among individuals and using Bayesian assignment tests. One lineage occurred in many locations, while the others were limited to a particular region or disjunct locations. Two lineages were associated with recent range expansion. Altogether, local assemblages of P. marinus are characterized by mixtures of distinct sympatric populations that undergo only infrequent recombination. By mixing divergent strains, long distance dispersal may play an important role in the evolution of P. marinus and spread of Dermo disease, whereas locally, high frequency strains may represent focal epizootics.