Molecular and morphological evidence of hybridization between native Ruditapes philippinarum and the introduced Ruditapes form in Japan

Abstract

Marine aquaculture and stock enhancement are major causes of the introduction of alien species. A good example of such an introduction is the Japanese shortneck clam Ruditapes philippinarum, one of the most important fishery resources in the world. To meet the domestic shortage of R. philippinarum caused by depleted catches, clams were imported to Japan from China and the Korean peninsula. The imported clam is an alien species that has a very similar morphology, and was misidentified as R. philippinarum (hereafter, Ruditapes form). We genotyped 1,186 clams of R. philippinarum and R. form at four microsatellite loci, sequenced mitochondrial DNA (COI gene fragment) of 485 clams, 34 of which were R. variegatus, and measured morphometric and meristic characters of 754 clams from 12 populations in Japan and China, including the Ariake Sea and Tokyo Bay, where large numbers of R. form were released. Our analyses confirmed that R. form was from the genus Ruditapes, and the genetic differentiation between R. philippinarum and R. form was distinct, but small, compared with five bivalve outgroups. However, R. form had distinct shell morphology, especially larger numbers of radial ribs on the shell surface, suggesting that R. form might be a new Ruditapes species or a variation of R. philippinarum that originated from southern China. A genetic affinity of the sample from the Ariake Sea to R. form was found with the intermediate shell morphology and number of radial ribs, and the hybrid proportion was estimated at 51.3 ± 4.6 % in the Ariake Sea.

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

“…Hurtado et al (2011) demonstrated that those 2 species (R. decussatus and R. philippinarum) can hybridize, and they found genetic and cytological evidence of the occurrence of hybridization between female R. decussatus and male R. philippinarum using 16S mitochondrial rDNA, ITS2, and 5SrDNA genes. Kitada et al (2013) also demonstrated hybrids of R. philippinarum and other Ruditapes forms. It is believed that hybrid swarms are a virtually intractable problem and that rapid detection of hybridization and response is critical.…”

“…have doubly uniparental inheritance (DUI) of mitochondrial DNA (mtDNA) and 2 different sex-related M-and F-type mtDNAs (Plazzi & Passamonti 2010 and references therein). These authors, and also Kitada et al (2013), recommended that DNA should be obtained from the foot or the adductor muscle, as DUI species carry very little M-type mtDNA in those tissues. We therefore used adductor muscle tissue for DNA extractions in adult individuals.…”

Morphological and Molecular Differences Between the Invasive BivalveRuditapes philippinarum(Adams & Reeve, 1850) and the Native SpeciesRuditapes decussatus(Linnaeus, 1758) from the Northeastern Adriatic Sea

“…There are various kinds of interactions between invaders and native species, including competition for resources, predation, release of toxins, disease transmission, ecosystem engineering, and hybridization between alien and native species (Hurtado et al 2011). In particular, R. philippinarum is prone to hybridize with native congeneric species (Kitada et al 2013). Hybrids between the allochthonous R. philippinarum and the autochthonous R. decussatus have been found in the north west and north of Spain (Hurtado et al 2011, Habtemariam et al 2015.…”

The application of genetics to marine management and conservation: examples from the Indo-Pacific

“…Restocking without considering wild population structure can have potentially disastrous effects on local populations. For example, the intentional stocking of the Japanese shortneck clam from China and the Korean peninsula to enhance depleted Japanese populations backfired when it turned out to be a cryptic species that is now rapidly hybridizing with the native population such that the hybrid proportion now exceeds 50% (Kitada et al 2013).…”