A history of invasion: COI phylogeny of Manila clam Ruditapes philippinarum in Europe

tThe Manila clam Ruditapes philippinarum – synonym Venerupis philippinarum (Adams and Reeve, 1850)is now one of the top 5 most commercially valuable bivalve species worldwide. Originally from the Indo-Pacific region, it has been introduced in many countries for fisheries and aquaculture, including estuarineenvironments along Atlantic and Mediterranean European coasts. Yet despite its commercial value andwidespread distribution, the precise origins of stocks remain speculative and the genetic diversity ofintroduced populations is poorly known. Thus, the aim of this work was to collect mtDNA COI (Cytochromeoxidase I) gene sequences from 5 European countries with Manila clam stocks and compare them withnative Asian populations to evaluate their genetic diversity and identify possible routes of invasion.The COI gene sequencing supported a strong founder effect in the European populations with 3 mainhaplotypes occurring at high frequencies, derived from Japan. However, high haplotype diversity wasalso observed due to the occurrence of 10 rare haplotypes. This supports hypotheses (i) there have beenadditional, previous unrecorded, introductions as previously hypothesized by analysis of 16S rDNA, and(ii) there has been a limited loss of genetic diversity in introduced populations, as previously suggestedby microsatellite data. This is the first genetic comparison of Manila clam populations introduced in toEurope with native clams. Genetic data herein presented are fundamentally important for the traceabilityof clam products and stock management programmes and will also inform discussion on the potentialresilience of exploited Manila clam populations.