EXPERIMENTAL-EVIDENCE OF HYBRID BREAKDOWN BETWEEN GENETICALLY DISTINCT POPULATIONS OF ECHINOSTOMA-CAPRONI

In this paper we investigate whether the assortative mating between in dividuals of the same genetic entity (i.e. coming from the same geogra phical area) of Echinostoma caproni, reported in a previous paper, may be explained by a post-zygotic isolating mechanism. The fecundity of the adults of 2 parental genetic entities and of their hybrids (i.e. F 1, F2, F3) was quantified through 3 successive generations. Whereas th e number of eggs released by Fl hybrids is similar to that of the mid- parent, that of recombinant hybrids (F2-3 hybrids) is significantly lo wer than that of F1 and that of the mid-parent. Since these results se em to demonstrate hybrid breakdown, 2 important factors maintaining re productive isolation, i.e. pre-mating reproductive isolation and low h ybrid fecundity, may influence the evolution of E. caproni.