Mol Biol Evol. 2013 Jul;30(7):1574-87. doi:10.1093/molbev/mst066
Roux C, Tsagkogeorga G, Bierne N, Galtier N.
Crossing the species barrier: genomic hotspots of introgression between two highly divergent Ciona intestinalis species.
Speciation during the Pliocene (≈ 3.8 Ma) and then recent introgression 15,000 years ago.