Hi Juan and Philippe,
Meyer, A., W. Salzburger, and M. Schartl. 2006. Sexual selection driven hybrid origin of a new species of swordtail (Xiphophorus clemenciae, Pisces). Molecular Ecology 15: 721-730.
http://www.evolutionsbiologie.uni-konst ... 05de85721c
Stupid as I am I mixed up the species name for the Neolamprologus (those Africans remain a mystery for me anyway). Of course, Philippe is right.
Salzburger W., Baric S. & Sturmbauer C. (2002) Speciation via introgressive hybridization in East African cichlids? Molecular Ecology, 11, 619-625.
I just want to mention at the end that reproductive isolation in the biological species concept does not mean that two separate species cannot produce viable hybrids! Reproductive isolation may be maintained in a natural situation by prezygotic barriers (e.g. sexual selection).