Current reproductive isolation between ancestors of natural hybrids in Bacillus stick insects (Insecta: Phasmatodea)

Interspecific hybrids raise a variety of developmental, reproductive, and evolutionary issues. In Sicily, geographically and chronologically distinct hybridizations between the highly differentiated Bacillus rossius and B. grandii have produced hybridogenetic strains and clonal parthenogenetic species. In northern Sicily, all-female populations of facultatively parthenogenetic B. rossius and bisexual B. grandii benazzii co- occur and we could test their current hybridization through electrophoretic marker analyses; control crosses with allopatric males were also carried out. Hybrid female progeny percentages ranged from 0 to 74 being fewer in egg batches laid by parthenogenetic mothers than in those of amphimictic females; no difference was noticed between sympatric and allopatric pairs. F1 hybrids of both sexes proved sterile; although some eggs started cleaving, no hemiclonal or clonal progeny hatched, only rare androgenetics being obtained. In currently produced hybrids a complete disruption of gametogenesis occurs, so that genetic constraints between parental taxa appear stronger now than in the past, most likely the result of ancestor evolution.