Genomic evolution in parental and hybrid taxa of the genus Bacillus (Insecta Phasmatodea)

Fifteen-year-long investigations have demonstrated that bisexual Bacillus s pecies (B. rossius and B. grandii), although sharply differentiated for all ozyme genes (Nei's D, 1.23-1.62), have hybridized several times in Sicily, generating hybridogenetic strains (B. rossius-grandii) and parthenogenetic taxa, the diploid B. whitei (B. rossius/B. grandii) and, together with the telytokous taxon B. atticus, the triploid trihybrid B, lynceorum (B. rossiu s/B. grandii/B. atticus). B. atticus is much closer to B. grandii (D, 0.31- 0.36) than to B. rossius (D = 1.82). Furthermore, SEM and allozymatic inves tigations allowed it to be established that body and egg characters are mor e conserved than gene-enzyme systems. Recently, satellite DNA sequences (th e Bag320 family) and a mitochondrial coding gene (COII) were also analysed. It could be noticed that Bag sequences provided differentiation values amo ng taxa higher than coding nuclear genes. Furthermore, it was discovered th at, while parthenogenesis in B. atticus leaves random levels of individual variability of repeats - likely due to the absence of chromosome shuffling in the progeny -, the nucleotide sequences of B. grandii split into subspec ific clusters, indicating that sequence variant homogenization/fixation are at work in Mendelian reproducing species. In B. whitei and B. lynceorum, o nly a limited sequence variability of grandii-like repeats was observed, th at suggested a rather recent origin for them, although sufficiently old to allow gene-conversion to start between grandii-like and atticus-like sequen ces in B. lynceorum. The invention of both grandii-like and atticus-like Ba g 320 clones also established beyond doubt the B. atticus contibution to th e structure of this triploid hybrid. MtDNA of the COII gene gave indication s of a more homogeneous degree of differentiation among taxa than that sugg ested by nuclear compartments, since B. rossius, B. grandii, and B. atticus appear to be differentiated from each other to a similar degree. Furthermo re, COII unexpectedly demonstrated that, in addition to hybridogens and B. whitei, also B. lynceorum has B. rossius as the maternal ancestor, thus ind icating a hybridization route different from that previously thought for th is hybrid. Finally, mtDNA served as a genetic marker to demonstrate that an drogenesis does occur in nature, since from hybridogenetic females, B. gran dii specimens were produced, carrying mtDNA of B. rossius. Androgens provid e an unusual opportunity of genome evolution since gene-size fragments of D NA can escape from mitochondria and migrate to the nucleus.