Regional Differentiation and Sex‐Biased Dispersal among Populations of the Horseshoe Crab Limulus polyphemus

Abstract

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.

Conservation status of the American horseshoe crab, (Limulus polyphemus): a regional assessment

“…These recent findings (King et al 2005 suggest the presence of similar levels of genetic diversity and variation among the collections, punctuated with a series of genetic discontinuities of varying ''depth'' across the species' range that could indicate demographic independence, regional adaptation, and reflect vicariant geographic events. Populations sampled within these regional groupings exhibit shallow but statistically significant differentiation.…”

“…However, close inspection has revealed the presence of considerable morphological and genetic variability (Shuster 1979;Riska 1981;Selander et al 1970;King et al 2005;Faurby et al 2010). A range of molecular genetic techniques applied across multiple studies has been utilized in attempts to assess population structure (stock identification) in horseshoe crabs.…”

“…The number of effective alleles and heterozygosity of the populations are not significantly different from published data of populations in the Greater Delaware Bay Region (Kasinak et al 2011). More recently, King et al (2005King et al ( , 2015 surveyed neutral (assumed) genetic variation at 13 microsatellite DNA markers among 1841 horseshoe crabs sampled at 35 spawning locations (Table 1) from northern Maine to the Yucatán Peninsula, México. This extensive intraspecific examination of the nuclear genome (nDNA) revealed considerable allelic diversity and differentiation (population structuring).…”

“…There is significantly more male migration between these two bays than female gene flow (King et al 2005). This sex-biased dispersal implies that should a population become extirpated, gene flow alone may not be sufficient to repopulate an area due to limited larval dispersal potential (Botton and Loveland 2003) and female migration (Swan 2005) between embayments (King et al 2005).…”

Opsin1-2, Gqα and arrestin levels at Limulus rhabdoms are controlled by diurnal light and a circadian clock

“…All previous investigations of the dynamics of the effects of clock input and light on retinular cells used animals captured off the coast of New England and maintained under natural illumination at Woods Hole, MA, or Syracuse, NY. We used animals from a different breeding population (King et al, 2005), and the dynamics of light in Florida are much different from those in Massachusetts and New York. To estimate when in our…”