Relationship Between Two Androgenetic Clam Species,Corbicula leanaandCorbicula fluminea, Inferred from Mitochondrial Cytochrome b and Nuclear 28S rRNA Markers

Abstract

Two shell color types, yellow (type I) and brown (type II), of hermaphrodite Corbicula fluminea clams from Ritto, Shiga Prefecture, Japan, are sympatric with both male and hermaphrodite Corbicula leana. In the present study, the mitochondrial DNA (mtDNA) cytochrome b and nuclear 28S rRNA genes of C. fluminea were sequenced to construct a haplotype network in order to investigate the genetic relationship with C. leana. Ninety C. fluminea samples revealed only two cytb haplotypes; the majority (97.8%) were CB7, while the remainder were CB1. In C. leana, only CB1 was detected in hermaphrodites, but both CB1 and CB7 were detected in males. Nuclear 28S rRNA haplotypes of C. fluminea type I individuals were divergent from those of hermaphrodite C. leana. However, C. fluminea type I clams shared haplotypes with male C. leana individuals, whereas C. fluminea type II individuals shared haplotypes with both hermaphrodite and male C. leana samples. These results suggest that it may be difficult to define a clear genetic border between these species.

Genetic characterization of the Asian clam species complex (Corbicula) invasion in the Iberian Peninsula

“…The most unexpected result of the 28S sequencing is the extremely high presence of heterozygotes (162 out of 175). This feature could be due to multiple copies of the 28S gene in the genome (Lee et al, 2005;Komaru et al, 2013). However, cloning results suggested that multi-copy probably explains only the low occurrence of rare haplotypes, while 'true heterozygosity' originated from sexual reproduction should be assumed for the most common alleles.…”

“…Only 2 out of the 10 haplotypes (S5, S10) were novel. The remaining eight matched either with our reference haplotypes (S1 = SR1, RA lineage; S6 = SR2, RlcB lineage; S8 = SR4, SC lineage; Table 2), with other haplotypes previously found in invaded regions (S3 corresponded to RA lineage, GenBank accession EU090403; Hedtke et al, 2008), or with Japanese native haplotypes (S2, S4, S7, and S9 matched to Japanese C. fluminea, GenBank numbers AB736282, AB736278, AB736287, and AB736291, respectively; Komaru et al, 2013).…”

“…However, cloning results suggested that multi-copy probably explains only the low occurrence of rare haplotypes, while 'true heterozygosity' originated from sexual reproduction should be assumed for the most common alleles. In this same sense, Komaru et al (2013) reported intra-individual sequence variation of the 28S gene in the hermaphrodite C. leana and in the dioecious C. japonica and C. sandai, all 3 having 2 predominant haplotypes in most clones, with less frequent haplotypes found only in a single clone. The high level of fixed heterozygosis suggests a possible advantage of possessing diverse copies of the gene (either because of multi-copy or 'real heterozygosity') in invasive regions, which could buffer the inbreeding depression linked to asexual reproduction.…”

“…The genetic characterization of these taxa is still scarce and does not always match with morphological traits. In Japan, the invasive C. fluminea was classified based on shell color types in Type I (yellow) and Type II (brown) (Komaru et al, 2013). However, haplotype distributions of mitochondrial Cytochrome oxidase I (COI) gene and nuclear ribosomal gene 28S did not match the distribution of shell color types (Wang et al, 2014).…”

Morphological and molecular differentiation of genus Corbicula suggests that two species are sympatrically distributed in Datong Lake in the Central Yangtze River Basin

“…Although its invasion and rapid expansion have been of intensive research topic in freshwater ecology, the taxonomy and systematic status of freshwater clam Corbicula in its native range is still not clearly resolved (Park and Kim 2003). Several systematic uncertainties using molecular methods were clarified in the last decades, such as mitochondrial and nuclear marks (Hedtke et al 2008;Komaru et al 2012Komaru et al , 2013. However, it still remained confusing, mainly due to the polymorphism of the morphology, color of the shell, and complex reproduction modes.…”