Distinguishing contemporary hybridization from past introgression with postgenomic ancestry-informative SNPs in strongly differentiated Ciona species.
Biological introductions bring into contact species that can still hybridize. The evolutionary outcomes of such secondary contacts may be diverse (e.g. adaptive introgression from or into the introduced species) but are not yet well examined in the wild. The recent secondary contact between the non-native sea squirt Ciona robusta (formerly known as C. intestinalis type A) and its native congener C. intestinalis (formerly known as C. intestinalis type B), in the Western English Channel, provides an excellent case study to examine. To examine contemporary hybridization between the two species, we developed a panel of 310 ancestry-informative SNPs from a population transcriptomic study. Hybridization rates were examined on 449 individuals sampled in eight sites from the sympatric range and five sites from allopatric ranges. The results clearly showed an almost complete absence of contemporary hybridization between the two species in syntopic localities, with only one-first-generation hybrid and no other genotype compatible with recent backcrosses. Despite the almost lack of contemporary hybridization, shared polymorphisms were observed in sympatric and allopatric populations of both species. Furthermore, one allopatric population from SE Pacific exhibited a higher rate of shared polymorphisms compared to all other C. robusta populations. Altogether, these results indicate that the observed level of shared polymorphism is more probably the outcome of ancient gene flow spread afterwards at a worldwide scale. They also emphasize efficient reproductive barriers preventing hybridization between introduced and native species, which suggests hybridization should not impede too much the expansion and the establishment of the non-native species in its introduction range.
UPMC Univ Paris 6, UMR 7144, Equipe DIVCO, Sorbonne Universités, Station Biologique de Roscoff, Place Georges Teissier, 29680, Roscoff, France.|CNRS, UMR 7144, Adaptation et Diversité en Milieu Marin, Station Biologique de Roscoff, Place Georges Teissier, 29680, Roscoff, France.
Sarah
S
Bouchemousse
Station Marine - OSU OREME, Université de Montpellier, 2 Rue des Chantiers, 34200, Sète, France.|CNRS-UM-IRD-EPHE, UMR 5554, Institut des Sciences de l'Evolution, Place Eugène Bataillon, 34095, Montpellier, France.
Cathy
C
Liautard-Haag
Station Marine - OSU OREME, Université de Montpellier, 2 Rue des Chantiers, 34200, Sète, France.|CNRS-UM-IRD-EPHE, UMR 5554, Institut des Sciences de l'Evolution, Place Eugène Bataillon, 34095, Montpellier, France.
Nicolas
0000-0003-1856-3197
N
Bierne
UPMC Univ Paris 6, UMR 7144, Equipe DIVCO, Sorbonne Universités, Station Biologique de Roscoff, Place Georges Teissier, 29680, Roscoff, France. viard@sb-roscoff.fr.|CNRS, UMR 7144, Adaptation et Diversité en Milieu Marin, Station Biologique de Roscoff, Place Georges Teissier, 29680, Roscoff, France. viard@sb-roscoff.fr.
Frédérique
F
Viard
D000818:Animals; D002938:Ciona intestinalis / Q000145:classification / Q000235:genetics*; D051456:Gene Flow; D005828:Genetics, Population; D006824:Hybridization, Genetic; D058865:Introduced Species; D020641:Polymorphism, Single Nucleotide; D017422:Sequence Analysis, DNA; D006113:United Kingdom
biological invasions; contemporary hybridization; past introgression; population genomics; secondary contacts; tunicates