Allozyme variation in the marine fanworm Sabella spallanzanii:comparison of native European and introduced Australian populations

Abstract

Three Austral~an (Cockburn Sound, Western Australia, Adelaide, South Australia. Port Ph~llip Bay, Victoria) and four European (Roscoff, Atlantic; Alicante, Carteau, and Marseille, all from the Mediterranean Sea) populations of Sabella spallanzanii were e x a m ~ n e d for variation at 23 allozyme loci. Levels of genetlc variation were high, with average heterozygosities per locus ranging from 0.20 to 0.21 for the Australian collections, and from 0.23 to 0.27 for the European collections. The 3 Australian collections were genetically very closely related to one another, with no s ta t~s t~cal ly significant differences at any of the 15 variable locl. This suggests either an introduction to one port, with a subsequent spread to other areas, or separate introductions with subsequent extensive gene flow. The 4 European collections showed I ~ m ~ t e d , but significant, d~fferent~ation among themselves at 10 of 18 variable l o c ~ Much of the: heterogeneity reflected differences betlveen the Roscoff (Atlantic) collection and the 3 Mediterranean collect~ons. The Koscoff collect~on was Iess variable, In terms of both heterozygos~ty and mean numbers of allelrs, than the hiled~terranean collections The Australian collect~ons were more closely rclated to the Xlrditerranean collections (mean Nei distance = 0.040) than to the Roscoff collection (mean Nei distance = 0.084). If a Mediterranean origin is assumed, then the introduction to Australia was accompanied by the loss of about 18% of the original variation. Flnally, the high genetic similarity of the Australian to the European collections of S. spallanzanii, and the very clear genetic separation of S. pavonina (mean Nei distance = 0.996), reaffirms that the Australian collections are truly S. spallanzanii and not an undescribed native species. K E Y WORDS: Sabella . Allozyme . Polymorphism . Genetic d i f ferent~at~on Founder effect Intro duction