Abstract
The basket clam genus, Corbicula, commonly known as the Asian clam, has become one of the most internationally high-profile and widespread aquatic invasive species. This genus is now considered to comprise a polymorphic species complex. The international invasion of Corbicula is characterised by four lineages, each fixed for one morphotype, genotype and haplotype combination: the American form (A) and European round form (R), the American form (C) and European saddle from (S), American form B, form round light colour (Rlc) and an intermediate between forms R and S known as Int. We investigated the genetic and morphometric makeup of each Irish population in order to establish which invasive lineages were present so as to identify the number of introductions to Ireland. A combination of morphometric, mitochondrial cytochrome oxidase subunit I (mtCOI) gene analysis and microsatellite markers were used to determine the invasive form at each Irish site. All Irish Corbicula samples conformed morphometrically to the invasive form A/R. All mtCOI sequences retrieved for 25 Irish individuals were identical to the international A/R form, while microsatellite markers again showed a common clustering with the international A/R forms of Corbicula. The combined approach of morphometries, total genomic DNA and microsatellite markers indicate only one form of Corbicula invaded Ireland; the international A/R form.
Highlights
Corbicula is a freshwater bivalve genus, commonly known as basket clams
This study aimed to demonstrate the effectiveness of combined morphological and genetic approaches in resolving invasive bivalve identification
All Irish Corbicula clams were visually determined as the European form R as described in [19,23] with a round deep shell that may range from externally dark to golden, heavy ridges and a generally white interior (Figure 2)
Summary
Corbicula clams are native to Asia, Australia, Middle East and Africa, and have become invasive in Europe and the Americas [1,2,3,4]. Invasive Corbicula clams, as well as most native lineages, reproduce through a peculiar and rare asexual reproductive mode, i.e., androgenesis or strict paternal inheritance. Androgenesis in Corbicula occurs through the expulsion of maternal nuclear chromosomes after obligatory fertilization of an oocyte by an unreduced biflagellate androgenetic spermatozoa [5,6,7]. In North America, the first record of an invasive lineage of Corbicula was made in 1924 in British Columbia [8], with subsequent spread through many parts of the continent (reviewed in [9]). Corbicula has spread across much of Central and South America during the 1970s and
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