Elsevier

Fisheries Research

Volume 110, Issue 2, July 2011, Pages 259-267
Fisheries Research

The invasive Manila clam Ruditapes philippinarum (Adams and Reeve, 1850) in Northern Adriatic Sea: Population genetics assessed by an integrated molecular approach

https://doi.org/10.1016/j.fishres.2011.04.013Get rights and content

Abstract

The coastal lagoons of the Northern Adriatic Sea are among the most worldwide productive locations of Manila clam Ruditapes philippinarum. Although introduced in Italy in 1983 from the Indo-Pacific, fishing and exploitation of Manila clam improved during the years as Italy became the leading country in Europe for production of this shellfish.

Despite its commercial importance, genetic structure of R. philippinarum in Northern Adriatic Sea has not been previously investigated. Here we present the first genetic study on Manila clam populations inhabiting a Mediterranean area, assessed by both mitochondrial (16S rDNA) and nuclear DNA (microsatellite loci). Our study showed that this species has a limited genetic differentiation at the mitochondrial level, but a higher rate of genetic diversity can be identified by polymorphic markers as microsatellites. In particular, out of 28 alleles, 7 private ones were recorded for the Venice Lagoon populations, 2 for those of Scardovari and one for the Po River Delta populations. These molecular markers suggest the occurrence of at least two different introduction events from different recruitment stocks, representing a powerful tool not only to assess genetic diversity of an introduced species, but also helpful information to manage aquaculture and fishery stocks, and to warrant food quality, safety and for the authentication of shellfish products, and traceabilty path.

Highlights

Ruditapes philippinarum in Northern Adriatic Sea is an important economic source. ► Genetic structure of this successful invader was never investigated. ► We studied both 16S rDNA and microsatellites. ► Multiple introduction events from different recruitment stocks occurred. ► Molecular data are useful for food quality, safety and for the authentication of shellfish products, and also for traceability path.

Introduction

For more than a decade, biological invasions have been considered to be one of the “big five” issues in conservation biology worldwide (Sala et al., 2000). This is particularly true for aquatic ecosystems where most introduced species rapidly form self-sustaining populations and pose major threats to the invaded communities (Kolar and Lodge, 2001). Invasive exotic species are affecting virtually all major rivers, lakes and coastlines in both tropical and temperate zones (McNeely and Schutyser, 2003) and one of the main vectors of aquatic invasive species is undoubtedly aquaculture (Wonham and Carlton, 2005).

Among invertebrates, bivalves are one of the most invasive group, as many species became successful invaders and they can occur at remarkably high densities accounting for the major proportion of the benthic faunal biomass (Sousa et al., 2009). Examples are multiple (Sousa et al., 2009): Corbicula fluminea (Müller, 1774) (Sousa et al., 2008), Crassostrea gigas (Thunberg, 1793) (Ruesink et al., 2005), Dreissena polymorpha (Pallas, 1771) (Strayer et al., 1999), Limnoperna fortunei (Dunker, 1857) (Boltovskoy et al., 2006), Musculista senhousia (Benson in Cantor, 1842) (Crooks and Khim, 1999), Mytilus galloprovincialis (Lamark, 1817) (Branch and Steffani, 2004) and Perna viridis (Linnaeus, 1758) (Rajagopal et al., 2006). These bivalve invasions are widespread but with a few exceptions (D. polymorpha, C. fluminea and C. gigas) invasive bivalves have received little attention relative to other faunal groups (Sousa et al., 2009).

Manila clam Ruditapes philippinarum (Adams and Reeve, 1850) belongs to the family Veneridae (Rafinesque, 1815) and its natural range is located into the Indo-Pacific region Japan, Korea and China (Gosling, 2003). It was introduced into the west coast of North America, Hawaii, Portugal, French Atlantic coast, French Mediterranean coast (Thau Lagoon), Italy (Adriatic Sea and Sardinia) and Ireland (Gosling, 2003) due to its acclimatization and fast population spreading. In Italy, Manila clam was intentionally introduced in Northern Adriatic Sea for aquaculture purposes in 1983 to support a clam fishery suffering a crisis due to overexploitation of native clam Tapes decussatus (Linnaeus, 1758) (Breber, 1985, Pellizzato et al., 1989). Manila clam showed a great capacity to adapt to the new environment (Solidoro et al., 2000) not only for growth rate, but also for natural reproduction of populations spreading into the Venice Lagoon and other shallow lagoons of Northern Adriatic Sea (Pranovi et al., 2006). According to the hypothesis that alien species invasions could be favored by an altered ecological, chemical or physical state of the system induced by anthropogenic disturbance, R. philippinarum turned out to be commercially ‘the right species at the right moment’ (Pranovi et al., 2006). It rapidly became invasive, affecting the native Mediterranean species T. decussatus which actually has a fragmented distribution (Pranovi et al., 2006).

Since introduction, production of Manila clam improved as Italy became the leading country in Europe, and the second in the world after China, with mean landing values of 50,000 tons/year, followed by Spain (4000 tons/year) and France (1000 tons/year) (Turolla, 2008). The Italian production comes exclusively from the highly eutrophic Northern Adriatic Sea, particularly from Venice and other coastal lagoons, Marano, Scardovari and Goro, where the most of production derives from aquaculture-controlled activities (Turolla, 2008) managed by local fishermen (Solidoro et al., 2000). It is worth noting that harvesting of wild populations is much more frequent in the Venice Lagoon where R. philippinarum is the subject of intensive and illegal fishing in highly polluted areas (Solidoro et al., 2000). Due to the lack of control and management planning many problems remain unsolved (Solidoro et al., 2003): use of illegal fishing tools, overfishing, health risks for consumers, polluted sediments resuspension, ecological disturbance, reduced price. These factors produce a high social cost which cannot be internalized. This dramatic situation is also reflected by the decreasing values of landing shellfish: from 40,000 tons in years 1996–1999, to 17,000 tons in 2002 (Turolla, 2008). Fisheries are based on exploitation of natural reproduction and harvesting of restocked juveniles. The recruitment of juveniles for restocking of aquaculture areas is still a problem: in fact, despite few exceptions, the 95% of recruitment stocks themselves come from natural populations (Turolla, 2008). The lack of control and management programs, combined to the exploitation of natural juveniles, led to a general decrease of population density in recruitment areas (Pellizzato et al., 2005). In short, the need for a better management of the resource is clear. Stock traceability would assist with both the optimization of the clam market and to preserve the ecosystem (Melaku Canu et al., 2000).

Surprisingly, genetic structure of this successful invader was never investigated. Genetic issues in invasion biology are multiple, regarding the chances of detection and identification of an invasive species (Darling and Blum, 2007), the chances of introduced species to become invasive, the prospect of controlling them, the evolutionary changes in invasive species and their impact on evolutionary processes in affected native species (Frankham et al., 2009). Genetic markers can be helpful to identify the source population from which an invasive species has come (Frankham et al., 2009, Geller et al., 2010) considering a wide range of molecular parameters. The genetic structure of an invasive population depends on several factors, including the effective population size at the time of introduction and the genetic diversity of the source population (Holland, 2000). Predictions of genetic diversity and population structure of non-indigenous taxa are impossible in the absence of genetic data, most importantly, the level of polymorphism, the structure of source populations and the effective population size of the introduction stock (Holland, 2000). Moreover, although the European Union law EC No. 2065/2001 requests appropriate species traceability and labelling, the tracing and tracking of seafood products is often difficult, and many scientists are looking for innovative and safe technologies to assess species identification and authenticity testing (Dawnay et al., 2007, Maldini et al., 2006, Filonzi et al., 2010).

To our knowledge, here we present the first molecular investigation on R. philippinarum populations inhabiting a Mediterranean area, assessed by both mitochondrial and nuclear DNA. An integrated molecular approach is potentially useful to investigate the composite relationships among species/subspecies and populations instead of a single locus analysis (Galtier et al., 2009). Reconstructing population history from a single locus could lead to an incomplete understanding of population histories (Freeland, 2005). Therefore, we combined the usefulness of 16S rRNA sequencing for phylogenetics of Venerids (Canapa et al., 2003, Kappner and Bieler, 2006, Mikkelsen et al., 2006), with the well documented potential of the highly polymorphic microsatellite loci to assess genetic diversity of bivalves (Sobolewska et al., 2001, Presa et al., 2002, Astanei et al., 2005, Sobolewska and Beaumont, 2005, Li et al., 2006, Yasuda et al., 2007, Gosling et al., 2008, An et al., 2009).

Section snippets

Collecting samples

Forty seven samples of Manila clam collected from 6 different sampling sites were analyzed. Sampling sites were distributed in Northern Adriatic Sea from the Venice Lagoon (Busa, Palude del Monte, Fusina) to the River Po Delta (Porto Levante, Porto Caleri) and Sacca di Scardovari (Fig. 1a and b). Detailed information on sampling locations are reported in Table 1. In addition, native T. decussatus sampled in the Venice Lagoon was included as out-group for both the mitochondrial and

Mitochondrial DNA

Alignments of 16S sequences were based on 407 bp fragments. Eight mutational steps were detected among the overall aligned sequences of R. philippinarum, with 4 transversions and 4 transitions. The frequency of detected mutations was 0.019, and most of polymorphic sites were C-T transitions (Fig. 2). The number of nucleotide substitutions (considering both transitions and transversions) between R. philippinarum and the outgroup T. decussatus was more than sixty, and mutation frequency between

Discussion

The present investigation is the first assessment of population genetics of R. philippinarum in Europe, based on combined 16S rRNA gene sequences and microsatellite analysis. In fact, very limited data on population genetics are available to make comparison of results with other Mediterranean or Indo-Pacific areas (Liu et al., 2007).

Concerning the mtDNA analysis, we identified four major haplogroups, but only two groups were separated by significant bootstrap values. Most of the analyzed

Acknowledgements

This work was supported by G.R.A.L. (Gestione Risorse Alieutiche Lagunari) of Venice Lagoon and by Veneto Region – FSE (European Social Fund) Project No. 101_006. Authors would like to thank Nicola Penzo for help with collecting samples in Venice Lagoon, and Paola Peresin for supporting information. Moreover, we would like to thank Marco Milia and Consorzio Cooperative Pescatori del Polesine for samples of Po River Delta.

References (79)

  • J. Roman et al.

    Paradox lost: genetic diversity and the success of aquatic invasions

    Trends Ecol. Evol.

    (2007)
  • C. Solidoro et al.

    Ecological and economic considerations on fishing and rearing of Tapes philippinarum in the lagoon of Venice

    Ecol. Model.

    (2003)
  • E.R. Alvarez-Buylla et al.

    Population genetic structure of Cecropia obtusifolia, a tropical pioneer tree species

    Evolution

    (1994)
  • H.S. An et al.

    Isolation and characterization of microsatellite markers for the clam Ruditapes philippinarum and cross-species amplification with the clam Ruditapes variegate

    Conserv. Genet.

    (2009)
  • I. Astanei et al.

    Genetic variability and phylogeography of the invasive zebra mussel, Dreissena polymorpha (Pallas)

    Mol. Ecol.

    (2005)
  • S. Barbaresi et al.

    Genetic variability in European populations of an invasive American crayfish: preliminary results

    Biol. Inva.

    (2003)
  • K. Belkhir et al.

    GENETIX 4.01, Logiciel sous windows pour la genetique ses populations

    (2000)
  • N. Bierne et al.

    Early effect of inbreeding as revealed by microsatellite analyses on Ostrea edulis larvae

    Genetics

    (1998)
  • D. Boltovskoy et al.

    Dispersion and ecological impact of the invasive freshwater bivalve Limnoperna fortunei in the Río de la Plata watershed and beyond

    Biol. Inva.

    (2006)
  • I.F.Y. Brookfield

    A simple new method for estimating null allele frequency from heterozygote deficiency

    Mol. Ecol.

    (1996)
  • A. Canapa et al.

    Molecular data from the 16S rRNA gene for the phylogeny of Veneridae (Mollusca: Bivalvia)

    Mar. Biol.

    (2003)
  • L. Cao et al.

    Differential segregation patterns of sperm mitochondria in embryos of the blue mussel (Mytilus edulis)

    Genetics

    (2004)
  • Consorzio Turistico CARD del PO....
  • J.A. Darling et al.

    DNA-based methods for monitoring invasive species: a review and prospectus

    Biol. Inva.

    (2007)
  • J.A. Darling et al.

    Genetic patterns across multiple introductions of the globally invasive crab genus Carcinus

    Mol. Ecol.

    (2008)
  • T.F. Duda

    Genetic population structure of the recently introduced Asian clam, Potamocorbula amurensis, in San Franscisco Bay

    Mar. Biol.

    (1994)
  • J. Felsenstein

    PHYLIP-phylogeny inference package version 3.6

    Cladistics

    (1995)
  • D. Frankham et al.

    Introduction to Conservation Genetics

    (2009)
  • J.R. Freeland

    Molecular Ecology

    (2005)
  • N. Galtier et al.

    Mitochondrial DNA as a marker of molecular diversity: a reappraisal

    Mol. Ecol.

    (2009)
  • M.S. Garrido-Ramos et al.

    The distribution of male-transmitted and female-transmitted mitochondrial DNA types in somatic tissues of blue mussels: implications for the operation of doubly uniparental inheritance of mitochondrial DNA

    Genome

    (1998)
  • J.B. Geller et al.

    Genetic perspectives on marine biological invasions

    Annu. Rev. Mar. Sci.

    (2010)
  • N.K. Gillis et al.

    Higher genetic diversity in introduced than in native populations of the mussel Mytella charruana: evidence of population admixture at introduction sites

    Divers. Distrib.

    (2009)
  • E. Gosling

    Bivalve Molluscs: Biology, Ecology and Culture

    (2003)
  • E. Gosling et al.

    Genetic variability in Irish populations of the invasive zebra mussel, Dreissena polymorpha: discordant estimates of population differentiation from allozymes and microsatellites

    Freshw. Biol.

    (2008)
  • S. Guerzoni et al.

    Atlante della Laguna

    Venezia tra terra e mare

    (2006)
  • D. Hedgecock et al.

    Widespread null alleles and poor cross-species amplification of microsatellite DNA loci cloned from the Pacific oyster, Crassostrea gigas

    J. Shellfish Res.

    (2004)
  • G. Hoarau et al.

    Population structure of plaice (Pleuronectes platessa L.) in northern Europe: microsatellites revealed large-scale spatial and temporal homogeneity

    Mol. Ecol.

    (2002)
  • B.S. Holland

    Genetics of marine bioinvasions

    Hydrobiologia

    (2000)
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