Phylogeography of the invasive polychaete Sabella spallanzanii (Sabellidae) based on the nucleotide sequence of internal transcribed spacer 2 (ITS2) of nuclear rDNA

Abstract

Genetic relationships between different populations of the invasive species Sabella spallanzanii (Gmelin, 1791) (Polychaeta, Sabellidae) are investigated through the use of the internal transcribed spacer 2 (ITS2) of the nuclear ribosomal DNA (285 bp). Samples were taken from South Australian waters (3 populations), the Mediterranean Sea (8 populations) and the French Atlantic coast (1 population). The ITS2 sequences were analyzed using both maximum parsimony and unweighted pair-group mean analysis (UPGMA) algorithms; results showed genetic disjunction between the Australian and the Mediterranean populations. Within the Mediterranean populations, 3 different sub-groups, corresponding to different sub-basins, could be clearly detected (Northwest- ern, Central and Eastern basins). The Atlantic population showed strong differences with the Mediterranean and Australian populations, but did not allow the identification of the source of intro- duction from Europe to Australia. Data also suggest the occurrence of a reduced genetic variability of the Australian populations, probably due to the 'founder effect' of one introduction, either via ballast waters or hull fouling. The recent description of the life cycle and larval development of S. spallan- zanii in the Mediterranean Sea, with a long pelagic larval phase and a post-settlement stage of meta- morphosis (approx. 25 d), supports the hypothesis of introduction via ballast waters (larval pool). Our data show high consistency when compared with the allozyme analysis previously performed by Andrew & Ward (1997; Mar Ecol Prog Ser 152:131-143) on a reduced number of populations and emphasize the importance and suitability of ITS sequences as markers to study the genetic structure at the population level in S. spallanzanii.