Microsatellite and mitochondrial DNA based evidence reveals a single horseshoe crab (Limulus polyphemus) population on the northern Yucatan Peninsula, Mexico

In Mexico, the American horseshoe crab, Limulus polyphemus, is regarded as in danger of extinction, with a distribution range limited to the Yucatan Peninsula. Population genetics knowledge of this species in Mexico is incipient. We conducted a base-line genetic survey of eight localities on the northern coast of the Yucatan Peninsula to assess patterns of genetic structure, genetic variation, and gene flow among these localities. We analyzed DNA samples from 190 L. polyphemus specimens using 14 nuclear-encoded microsatellites and a region of the mitochondrial Cytochrome Oxidase I (COI) gene. Total allelic richness was 5.432, similar to previous figures for populations at the northern and southern extremes of the species' global distribution. Observed heterozygosities (Ho) were 0.540-0.590, while expected heterozygosities (He) were 0.479-0.532, and there was no evidence of population bottlenecks. We found 129 mtDNA haplotypes (121 of which were found in single individuals) and 275 polymorphic sites, and the mean haplotype diversity among sites was high (0.852 +/- 0.027 SD). AMOVAs based on both microsatellite and mtDNA data revealed that L. polyphemus from the northern Yucatan Peninsula show low genetic structure (Fst < 0.05, p > 0.05) and high gene flow (Nm = 10.967) favored by the absence of geographic barriers between coastal lagoons, suggesting that they constitute a single popu-lation. This was further confirmed by discriminant analyses of principal components using microsatellite data. This information is useful in establishing coordinated conservation efforts among federal and state protected areas.