A contribution to the phylogeography ofPinctada imbricata radiata(Leach, 1814) (Bivalvia: Pteriidae) from the Eastern Mediterranean Sea by means of the mitochondrialCOImarker

Abstract

Pinctada imbricata radiata (Leach, 1814) was the first Lessepsian bivalve reported in the Mediterranean Sea where it is progressively expanding westward. Its native range includes the Indian Ocean and western Atlantic. The present study provides the first insight into the species' phylogeographic structure, by analysing sequences of a 385-bp region of the mitochondrial gene coding for the subunit I of the cytochrome c oxydase (COI). Sixty-four individuals collected at seven Mediterranean localities were sequenced; in addition, eight COI sequences of individuals from the species' native range (Persian Gulf) were retrieved from GenBank. Overall, we detected 10 haplotypes. Samples from both the native range and invaded localities were characterised by low levels of haplotype and nucleotide diversity (total h = 0.351, total π = 0.0013). Significant genetic divergence was found between Persian Gulf and Mediterranean Sea samples, whereas very shallow genetic structuring was observed within the Mediterranean study area. Moreover, no pattern of isolation by distance was detected in the Mediterranean. From a historical demography perspective, our results on Mediterranean samples were consistent with a very recent, or even ongoing, demographic expansion. Range expansion of exotic thermophilic species in this area is a widely observed phenomenon that many authors have related to global warming.

Are Pinctada radiata (Leach, 1814) and Pinctada fucata (Gould, 1850) (Bivalvia Pteriidae) only synonyms or really different species? The case of some Mediterranean populations

“…The disagreement of the present conclusions with previous molecular studies ( Barbieri et al, 2015) according to us is attributable to the low number of specimens tested in these latter.…”

“…But the genetic diversity of populations of this species in the basin seems to exhibit low values, as reported by Barbieri et al (2015).…”

“…After a critical evaluation of the morphological characters observed in very abundant amount of specimens of the two different forms of Pinctada, despite a high variability in both and the genetic studies of mainly Eastern Mediterranean specimens (Barbieri et al, 2015), we concluded that two different species are involved The first, attributable to P. radiata, on account of a bigger shell in full grown specimens, rounded in outline (Fig. 25), almost entirely red-brownish with darker radial strips, sculpture of dense and pointed process, organized in numerous rows, soft parts mainly orange (see Table 1).…”

Marine bivalves voucher DNA barcoding from Eastern Mediterranean, with evidence for Ostrea stentina invasion

“…Although these sequences were not analysed in comparison to our haplotypes owing to their much shorter available sequences, our results are in total agreement with these inferences concerning haplotype and nucleotide diversity. BLAST results of the P. radiata COI sequence obtained from the three locations of Greece were 99.22-100% similar to the ten haplotypes reported by Barbieri et al (2016) from the Eastern Mediterranean, while the haplotype H2 from these authors which was the prevalent haplotype among seven geographic areas of the Eastern Mediterranean was 100% similar to our haplotype. The low level of population subdivision seems to be mainly assigned to the long pelagic larval stage of this bivalve.…”

“…In our study this species was found panmictic at three sampling geographic areas, presenting zero differences in the both sequences of COI and 18S rRNA. Other authors also detected low haplotype and nucleotide diversity in P. radiata specimens among different sampling areas (Meyer et al, 2013;Barbieri et al, 2016) while at Adriatic Sea (Sobra Bay) and at United Arab Emirates high haplotype along with low nucleotide diversity was found by Gavrilović et al (2017) and Cunha et al (2011) respectively. Although these sequences were not analysed in comparison to our haplotypes owing to their much shorter available sequences, our results are in total agreement with these inferences concerning haplotype and nucleotide diversity.…”