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 ro ssius and B. grandii have produced hybridogenetic strains and clonal p arthenogenetic species. In northern Sicily, all-female populations of facultatively parthenogenetic B. rossius and bisexual B. grandii benaz zii co-occur and we could test their current hybridization through ele ctrophoretic marker analyses; control crosses with allopatric males we re also carried out. Hybrid female progeny percentages ranged from 0 t o 74 being fewer in egg batches laid by parthenogenetic mothers than i n those of amphimictic females; no difference was noticed between symp atric and allopatric pairs. F-1 hybrids of both sexes proved sterile; although some eggs started cleaving, no hemiclonal or clonal progeny h atched, 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 pas t, most likely the result of ancestor evolution.