Population genetics of the American lobster, Homarus americanus, and its phylogenetic relationships with other clawed lobsters

Population genetics of the American lobster, Homarus americanus has been examined using samples from four areas: inshore and offshore Gulf of Maine, Gulf of St. Lawrence, and Long Island Sound. Both microsatellite and mitochondrial DNA markers were employed. Three highly variable microsatellite markers (Hom3-2, Hom7-1, Hom8-1) have been isolated from the American lobster. These markers revealed extensive polymorphism in all samples, with expected heterozygosities ranging from 0.55 to 0.95. Breeding studies demonstrated Mendelian inheritance of codominant alleles for each marker and the absence of linkage between markers; null alleles were observed for Hom3-2 and Hom8-1. The frequencies of two haplotypes of the lobster mitochondrial genome were distinguished by amplification of a portion of the mitochondrial ND2 gene followed by restriction digestion using XcmI. Both molecular approaches revealed homogeneous genetic composition among all studied populations, suggesting extensive gene flow in the Gulf of Maine and nearby regions. Inshore and offshore lobsters in the Gulf of Maine belong to the same panmictic population. Thus, these findings suggest that management of the lobster fishery cannot use stocks defined on genetic differences. Other population studies of American lobsters are reviewed, and the impact of transplantation of lobsters is discussed. About 350 base pairs of the mitochondrial 16S rRNA gene were used to study the phylogenetic relationships among five genera of the clawed lobster family Nephropidae, including Homarus, Homarinus, Metanephrops, Nephrops, and Nephropsis. Tree topologies obtained from maximum-parsimony, neighbor-joining, and maximum-likelihood analyses demonstrated that Homarus and Nephrops consistently formed a well-supported clade that excluded Homarinus. Some morphological characters, which appear synapomorphic for Homarus and Homarinus, and also those shared by Nephrops and Metanephrops, may thus be due to convergence or symplesiomorphy. These findings suggest that the current taxonomy does not reflect the phylogeny of clawed lobsters. More molecular data and studies using homologous morphological characters are needed to improve the resolution of the phylogeny of clawed lobsters.