The mitochondrial cytochrome oxidase II gene in Bacillus stick insects: Ancestry of hybrids, androgenesis, and phylogenetic relationships

Sequencing of a cytochrome oxidase II (COII) gene fragment in Bacillus taxa provided evidence that the bisexual B. rossius is the maternal ancestor of the hybridogenetic B. rossius-grandii strains and revealed the same ancest ry for both parthenogenetic hybrids: the diploid B. whitei (B. rossius/gran dii grandii) and the triploid B. lynceorum (B. rossius/grandii grandii/ att icus). Present data clearly demonstrate that all Bacillus unisexuals arose through asymmetrical hybridization events and realized a paraphyletic deriv ation from the B. rossius redtenbacheri subspecies. The invention of B. ros sius mitochondrial DNA haplotypes in specimens with B. grandii grandii nucl ear genomes revealed the occurrence of androgenesis in nature. Natural andr ogens represent a peculiar escape from hybridity and can help maintain the hybridogenetic system through the production of the fathering taxon via hyb rid females. Results from the COII gene support the phyletic relationships among taxa suggested by previous taxonomical approaches, but also indicate a departure of B. grandii subspecies from the established taxonomy. Assumin g the existence of a molecular clock, the evaluated substitution rate bring s the splitting between B. rossius and B. granctii/B. atticus back to 22.79 +/- 2.65 myr before present, while the origin of hybrids appears to be muc h more recent (1.06 +/- 0.53 myr). (C) 2001 Academic Press.