Natural hybridization between genetically differentiated populations of Crassostrea gigas and C. angulata highlighted by sequence variation in flanking regions of a microsatellite locus

Abstract

The marine environment is of special interest for studying hybridization between closely related taxa because of the high dispersal potential of planktonic larvae, such as those of most bivalve species. The oysters Crassostrea angulata and C. gigas are known to be very close genetically and entirely inter-fertile under controlled conditions. However, hybridization in the wild had not been investigated, mainly due to the lack of nuclear diagnostic markers. In the present paper, we first estimated genetic differentiation between these 2 closely related taxa using 8 microsatellite markers. Interestingly, 5 markers displayed significant differences of allele size between taxa. The subsequent sequencing of alleles of one of these microsatellites showed several mutational events, which suggested null alleles and homoplasy. The presence of 1 insertion/deletion event in its 5' flanking sequence enabled us to design a new bi-allelic ('C' and 'NC') nuclear PCR-restriction fragment length polymorphism (-RFLP) marker (CG44R). This, together with a mitochondrial DNA marker, was used to analyze populations of C. angulata and C. gigas. The CG44R allele frequencies were very different between C. angulata (f[C] = 0.91) and C. gigas (f[NC] = 0.92) populations. This analysis also provided evidence for hybridization between C. angulata and C. gigas in a wild Portuguese population where the 2 taxa are in contact due to recent transportation of C. gigas stocks for aquacultural production. Our results represent the first indication of hybridization between these 2 taxa in the natural environment, and contribute to knowledge of the evolutionary history of the Crassostrea genus.

Artificial interspecific backcrosses between the hybrid of female Crassostrea hongkongensis × male C. gigas and the two parental species

“…Although a number of oyster breeders have conducted interspecific hybridization among the Crassostrea genus Batista et al, 2007Batista et al, , 2008Gaffney and Allen, 1993;Huo et al, 2013;Huvet et al, 2002Huvet et al, , 2004Piferrer et al, 2009;Xu et al, 2009Xu et al, , 2014Zhang et al, 2012Zhang et al, , 2014, there are no reports of further utilization of the hybrids with the exception of two subspecies of C. gigas and C. angulata (Wang et al, 2008). This is the first report to describe completely fertile backcrossed progeny and F 2 hybrids; this finding differed from the F 1 hybrids (C. hongkongensis ♀ × C. gigas ♂) that exhibited high levels of sterility .…”

Impacts of supplementation aquaculture on the genetic diversity of wild Ruditapes decussatus from northern Spain

“…Huvet et al (2004) reported hybridization between introduced Crassostrea gigas (Thunberg, 1793) and the Portuguese oyster C. angulata (Lamarck, 1819), with dramatic consequences for the latter species. Another example occurs in the genus Mytilus in North America.…”

New insights about the introduction of the Portuguese oyster,Crassostrea angulata, into the North East Atlantic from Asia based on a highly polymorphic mitochondrial region

“…Several studies have reported the production of F1 hybrids between C. angulata and C. gigas under experimental conditions (Imai and Sakai 1961;Menzel 1974;Huvet et al 2002;Batista et al 2007). Hybrids between C. angulata and C. gigas have also been reported in the wild (Huvet et al 2004) and first generation hybrids were shown to be fully viable and fertile under experimental conditions . However, several phenotypic and genetic differences were also reported between C. angulata and C. gigas (for review see Batista et al 2009).…”