Fourteen microsatellite DNA loci were surveyed in 892 horseshoe crabs Limulus polyphemus collected from 21 sites ranging from Franklin, Maine, to the Yucatán Peninsula, Mexico. This rangewide survey revealed a high degree of genetic diversity (up to 50 alleles per locus) and heterozygosity (up to 97.2%). There appears to be substantial gene flow between each population and its nearest neighbors. The correlation of genetic distance and geographic distance supports isolation by distance as a mechanism underlying the structure of L. polyphemus along the Atlantic coast of North America. Two statistical descriptors, mean assignment percentage and assignment variance, suggested the presence of male-biased dispersal throughout the study area. Within the continuum of isolation by distance and in the presence of male-biased dispersal, the clustering of specific collections on a tree of genetic distances and hierarchical gene diversity analyses demonstrate discrete regional units. These results suggest defining four management units within the United States: the Gulf of Maine, mid-Atlantic, Atlantic Florida, and Gulf Florida. Further sampling is needed, particularly from North Carolina to the southernmost tip of Atlantic Florida, to test this hypothesis. Multilocus assignment tests indicate a high probability of correctly assigning individuals to the proposed management unit from which they were collected and could serve as a useful tool for identifying the source of animals that are caught at sea.
All Science Journal Classification (ASJC) codes
- Ecology, Evolution, Behavior and Systematics
- Aquatic Science