Genetic structure of Carcinus maenas within its native range: larval dispersal and oceanographic variability

Abstract

Unravelling the interactions between life-history strategies and oceanography is central to our understanding of gene flow and connectivity in the marine environment. In the present study, we investigated the population genetic structure of the shore crab in its native range in relation to oceanographic characteristics and dispersal potential. Using 10 microsatellite markers over 2 yr, we surveyed 18 locations distributed along ~4200 km within the species native range, from Sweden to Morocco, assessed the population structure by means of F ST and Bayesian clustering analysis and tested the hypothesis of isolation-by-distance (IBD) with a Mantel test. We focused particular attention along a 1200 km stretch of the Iberian Peninsula. We found no evidence of genetic structure (F ST = 0.0001, p > 0.05) along the Iberian coast, and patterns were temporally stable over 2 yr. Across the more extensive geographic spatial scale, overall genetic differentiation was low (F ST = 0.001) but statistically significant (p < 0.001). Furthermore, clustering analysis grouped the samples into 3 genetic units from (1) Sweden, (2) Wales and the Iberian Peninsula and (3) Morocco. While the correlation between genetic and geographic distances was significant, the pattern was not consistent with an IBD pattern. Results suggests that, in the absence of barriers to gene flow, shore crab populations are genetically similar across thousands of kilometres, but isolated populations still may occur within the species native range. Local oceanography and larval behaviour may have a significant influence on the structuring of the populations under study.

Temporal genetic homogeneity among shore crab (Carcinus maenas) larval events supplied to an estuarine system on the Portuguese northwest coast

“…In addition, the species' type III survivorship characteristics may result in the recruitment of genetically variable larval patches that can potentially contribute to transitory genetic differences among populations. These differences are illustrated by the divergence in the results observed by Pascoal et al (2009) and Domingues et al (2010), for the same geographical region. Finally, the oceanographic conditions along the western Iberian Peninsula ecosystem are variable throughout the year, and more unstable than previously thought (reviewed in Relvas et al, 2007).…”

“…Microsatellite DNA is a powerful genetic tool to detect differentiation and provenance of individuals recruiting to a given population (Selkoe and Toonen, 2006), even in species exhibiting high dispersal capacity, as in the shore crab C. maenas. An intensive sampling, over two years, of 14 C. maenas populations distributed along southern, western and northern Iberian Peninsula found genetically homogeneous populations (Domingues et al, 2010), and it is thus not possible to assign larvae recruiting to a particular estuary to putative source populations. We would expect a reduction of genetic diversity within larvae arriving at a given location relative to the adult source populations if only a small proportion of adult crabs contribute to reproduction at each spawning event.…”

“…Each event lasted 3 to 5 days and, whenever possible, 80-100 megalopae per event were randomly selected, proportionally to abundance in the surface and bottom nets, from the day of maximum supply, or from proximate days in events with a low number of larvae (Table 1). Genetic variation of megalopae was compared with 1262 previously analysed adult crabs collected from 14 estuaries along a 1200 km stretch of the Iberian Peninsula in the summer of (Domingues et al, 2010, pooled in a single sample, referred to as 'Iberian Peninsula' adult population (Table 1).…”

“…DNA was resuspended in a volume of 100 ml of 1 Â TE buffer (10 mM Tris-Cl, 1 mM EDTA, pH 8.0) and stored at À20 1C. The samples were genotyped using the same ten species-specific microsatellite loci selected by Domingues et al (2010) (Supplementary Table 1), to allow comparisons with results from adult population: Cma01EPA, Cma03EPA, Cma04EPA, Cma05EPA, Cma08EPA, Cma09EPA, Cma10EPA, Cma14EPA (Tepolt et al, 2006), SP107 and SP495 (Pascoal et al, 2009). Microsatellite loci were amplified in two multiplex PCR performed in 10 ml reactions containing 1 ml of the template DNA, 1 Â QIAGEN Multiplex PCR Master Mix (Qiagen, Crawley, West Sussex, UK) and 0.1À0.3 mM of each primer (forward 6-FAM, VIC, NED or PET fluorescently labelled primers).…”

“…High dispersal potential would contribute to maintain genetically homogeneous populations connected through larval dispersal along the Iberian Peninsula (Domingues et al, 2010). Despite this fact, it is reasonable to expect high variance in reproductive success, given that only a few individuals may successfully reproduce each year, genetic differences of which might be enough to cause genetic structure among larval events but not sufficient to impact adult population structure.…”