High connectivity and directional gene flow in European Atlantic and Mediterranean populations ofCiona intestinalissp. A

Abstract

Understanding the factors that cause population divergence has long been of interest to marine biologists in their attempts to interpret the effect of human‐mediated vectors. Broadcast‐spawning species with limited dispersal capability are excellent candidates to measure the present‐day patterns of genetic diversity. The tunicate Ciona intestinalis (Ascidiacea) is comprised of a complex of morphologically cryptic species that form vigorous aggregates in eutrophic habitats (harbors, gulfs and lagoons) where they can compete with the epibenthic community and cause biofouling problems. This study investigated biogeographic variability and migration patterns of C. intestinalis sp. A along Northeast Atlantic and Mediterranean coasts using microsatellite markers. Data presented here on 371 specimens collected from 17 populations reveal high genetic polymorphism, but with a deficit of heterozygote deficiency. Absence of evidence for isolation by distance suggests that the genetic patterns do not reflect the geographic distribution of sampled populations. Substantial gene flow and artificial potential for dispersal boost high levels of within‐population genetic variability and prevent genetic differentiation within and between seas. A predominant eastward migration pattern was revealed by the data set, with very limited opportunity for C. intestinalis sp. A to travel westward. This directional movement indicates that other properties (e.g. habitat quality, genetic traits, mating system, life cycle) may cause adaptive divergence at a large biogeographic scale.

Distinguishing contemporary hybridization from past introgression with post-genomic ancestry-informative SNPs in strongly differentiatedCionaspecies

“…This finding differed from several published studies of C. robusta and C. intestinalis based on microsatellite loci. Heterozygote deficiencies have indeed been regularly reported (Caputi et al 2007;Sordino et al 2008;Zhan et al 2010;Zhan et al 2012;Affinito et al 2014). This discrepancy can be explained by the choice of marker used (microsatellite versus SNPs); null alleles are a known pitfall of microsatellite loci (Dakin & Avise 2004;Chapuis & Estoup 2007).…”

Temporal correlation of population composition and environmental variables in the marine invader Ciona robusta

“…A total of 769 individuals were genotyped using eight microsatellite loci previously developed for C. intestinalis sp. A (now known as C. robusta ) (Cin‐1, Cin‐2, Cin‐5, Cin‐7, Cin‐9, Cin‐4, Cin‐49, and Cin‐67) (Affinito et al, ; Andreakis, Caputi, & Sordino, ). All loci were amplified in a single multiplex PCR, using the Qiagen Multiplex PCR Kit with the same condition as in type I PCR in Affinito et al ().…”

“…Finally, few 100 m from FPR and close to the Foce di Mezza Chiaja canal, C. robusta grows on vertical concrete rock docks at 0.5-1.5 m depth in the FFM site. Previous data indicate that a single population with high internal genetic diversity inhabits the Fusaro Lagoon (Affinito et al, 2015;Caputi et al, 2015;Sordino et al, 2008). Specimen sampling was carried out manually in randomly selected and unmanipulated 15 × 15 cm (0.44 m 2 ) areas on artificial structures at ca.…”

“…A (now known as C. robusta) (Cin-1, Cin-2, Cin-5, Cin-7, Cin-9, Cin-4, Cin-49, and Cin-67) (Affinito et al, 2015;. All loci were amplified in a single multiplex PCR, using the Qiagen Multiplex PCR Kit with the same condition as in type I PCR in Affinito et al (2015). The forward primer was always la- [1996][1997][1998][1999][2000][2001][2002][2003][2004], and their significance was tested with 10,000 bootstrap replicates.…”

“…The first records of C. robusta in the Mediterranean basin date to the second half of the 19th century (reviewed in Hoshino & Nishikawa, 1985). Large-scale genetic patterns in the English Channel and Mediterranean populations show high levels of within-population genetic variability and low levels of genetic differentiation among large geographical distances, in the absence of isolation by distance (Affinito et al, 2015;Hudson, Viard, Roby, & Rius, 2016). A longitudinal pattern of gene flow that follows a predominant eastward migration pattern indicates active recruitment from the Atlantic to the Mediterranean Sea (Affinito et al, 2015;Procaccini, Affinito, Toscano, & Sordino, 2011).…”