Fecundity, growth rate and survivorship at the interface between two contiguous genetically distinct groups of Semibalanus balanoides

Abstract

On the western coast of the Atlantic, according to the literature, 2 distinct groups of Semibalanus balanoides occur with a distinct interface near the Miramichi Estuary, New Brunswick, in the Gulf of St. Lawrence. On each side of this interface, the groups are characterized by clinal variations for MPI (mannose-6-phosphate isomerase) and GPI (glucose-6-phosphate isomerase). The present study was carried out to determine whether selection occurs at this interface, to establish how early in the sessile life period it occurs and to examine the selecting forces involved. Reciprocal transplant experiments of newly settled individuals to both sides of the interface were carried out. No significant differences specifically linked to source or destination were observed in growth or fecundity for the 2 groups at the sites studied for either control or transplanted individuals. However, differences in survival were observed; individuals transplanted south of the estuary showed lower survival than individuals transplanted north. An allozyme analysis of barnacle survivors for MPI and GPI, 2 alleles whose frequencies are known to vary abruptly in this region, indicated a change of allele frequency in transplanted individuals. The transplants' allele frequencies came to resemble those of adults from target sites, while no change occurred in transplanted individuals at control sites. Taken together with previous results, our study suggests that selection occurs very early in the newly settled individuals (spat).

Regional variation in the spatial scale of selection at MPI* and GPI* in the acorn barnacle Semibalanus balanoides (Crustacea)

“…We also observed that genotype frequency at a given site did not vary significantly at older life stages. In a recent transplant experiment conducted in the same study area than our study, Brind'Amour et al. (2002) also reported that the crucial period for selection was in the early phases shortly after settlement (spat stage), and lasted <5 days, the maximal age of the barnacles that were experimentally transplanted.…”

“… a: This article; b: Flowerdew (1983); c: Holm & Bourget (1994); Brind'Amour et al. (2002); Drouin et al.…”

Genetic differentiation, hybridization and adaptive divergence in two subspecies of the acorn barnacle Tetraclita japonica in the northwestern Pacific

“…Barnacles exhibit strong postsettlement mortality (Barnes 1999), and selection against maladapted genotypes is strong in newly settled individuals (Schmidt et al . 2000; Brind’Amour et al . 2002; Drouin et al .…”

Physiological stress and the fitness effects of Mpi genotypes in the acorn barnacle Semibalanus balanoides

“…MPI and GPI are commonly polymorphic enzymes in barnacles, and the acorn barnacle Semibalanus balanoides has emerged in the past decade as a model system for testing how balancing selection may act to maintain polymorphism at these loci (Hedgecock 1986, Holm & Bourget 1994, Schmidt & Rand 1999, Rand et al 2002, Véliz et al 2004. S. balanoides is unique because it is one of few systems where balancing selection has been implicated by static sampling of defined microhabitats, experimental manipulations in the field and laboratory manipulation (Schmidt 2001, Schmidt & Rand 2001, Brind'Amour et al 2002. Nevertheless, conflicting results about the nature of selection on metabolic enzymes has led to questions about extending results from one geographic region to other populations over the entire species range.…”