The genetic structure of the exotic ascidian Styela plicata (Tunicata) from Italian ports, with a re‐appraisal of its worldwide genetic pattern

Abstract

The pleated ascidian Styela plicata (Lesueur, 1823) is a solitary species commonly found in ports and marinas around the world. It has been recorded in the Mediterranean region since the mid-19th century. In the present work, the species' genetic diversity was analysed, employing a 613-bp portion of the mitochondrial cytochrome c oxidase subunit I (COI) gene from 149 individuals collected in 14 ports along Italian coasts at spatial scales ranging from 1 to approximately 2200 km. Haplotype and nucleotide diversity values were h = 0-0.933 (total h = 0.789) and p = 0-0.145 (total p = 0.0094), respectively. A general southward trend of increasing within-population genetic diversity was observed. Analysis of molecular variance revealed significant genetic structuring but no significant differences were detected among basins, and no isolation by distance was found. Our data were integrated with the COI sequences available from previous studies and re-analysed in order to investigate the possible

Stochasticity in space, persistence in time: genetic heterogeneity in harbour populations of the introduced ascidianStyela plicata

“…In further instances, a wide range of genetic diversities has been found among introduced populations of some species (e.g., Styela clava , Goldstien et al, 2011 ). In Styela plicata , low values of diversity, similar to those found here, were reported for populations from Australia and New Zealand ( Torkkola, Riginos & Liggins, 2013 ), while in a study of 15 harbours in Italy (including some big ports with international traffic), widely different values of haplotype diversity were found ( Maltagliati et al, 2015 ). The low genetic diversity observed here is consistent with the idea that the studied populations are seeded by small number of individuals, likely associated to local boating activities.…”

“…New haplotypes were labelled from 23 onwards, as there were 22 haplotypes described in Pineda, López-Legentil & Turon (2011) . Six of our sequences (haplotypes 1, 2, 3, 4, 5 and 9) were already identified by Pineda, López-Legentil & Turon (2011) , of which 5 (haplotypes 1, 2, 3, 4 and 5) were also found by Maltagliati et al (2015) in Italian waters (from both eastern and western shores). Haplotype frequencies per population and year are presented in Supplemental Information ( Table S1 ).…”

“…Two major clades of COI have been described for Styela plicata ( Pineda, López-Legentil & Turon, 2011 ) and most of our sequences belonged to haplogroup 1. The divergent haplotype 5 was the only representative of haplogroup 2, confirming its presence in the Mediterranean Sea ( Maltagliati et al, 2015 ). Overall, some geographically close localities displayed very different haplotype composition (e.g., Vilanova i la Geltrú and Arenys de Mar), while some widely separated populations were genetically similar.…”

“…Our finding of a significant spatial component is consistent with results obtained in previous studies (e.g., Styela clava , Dupont et al, 2009 ; Dupont et al, 2010 ; Botryllus schlosseri , López-Legentil, Turon & Planes, 2006 ), while other introduced ascidians did not show spatial differentiation at regional scales (e.g., Ciona spp., Zhan, Macisaac & Cristescu, 2010 , Microcosmus squamiger , Rius, Pascual & Turon, 2008 ; Ordóñez et al, 2013 ). In Styela plicata , previous studies have shown significant spatial structure between harbour populations ( Torkkola, Riginos & Liggins, 2013 ; Maltagliati et al, 2015 ), although the degree of differentiation could vary latitudinally as a function of temperature ( David, Marshall & Riginos, 2010 ).…”

Habitat niche breadth predicts invasiveness in solitary ascidians

“…In the Mediterranean, we categorized the species as nonindigenous or indigenous (see Table ). We included Styela plicata with the indigenous species of the Mediterranean for analysis although it possibly invaded from the Atlantic Ocean (Maltagliati, Lupi, Castelli, & Pannacciulli, ; Pineda, López‐Legentil, & Turon, ) as it is clearly not of tropical origin, unlike the rest of the nonindigenous species, and has been found in the Mediterranean for at least a century (de Barros, da Rocha, & Pie, ).…”