Satellite sequence turnover in parthenogenetic systems: the apomictic triploid hybrid Bacillus lynceorum (Insecta, Phasmatodea)

In the genus Bacillus (Insecta, Phasmatodea) the Bag320 satellite DNAfamily is present in the bisexual B. grandii and in the related automicticnonhybrid B. atticus; it is lacking in the other bisexual taxon of thegenus, B. rossius. This family of highly repeated sequences was analyzedfor 11 populations of the apomictic triploid hybrid B. lynceorum. In theneighbor-joining dendrogram, B. lynceorum nucleotide sequences distribute,regardless of geographical origin, among two clusters, one also includingall clones of the three B. atticus races, and the other including sequencesof the B. grandii grandii subspecies. Thus, B. lynceorum is a trihybridtaxon: as the molecular approach definitively demonstrates, it embodies onehaploid complement each of both B. grandii grandii and B. atticus, whichmust be added to that of B. rossius. The contribution of the latter specieshas already been assessed on karyological and allozymic grounds. Astatistical analysis performed on p-distances shows that for the parentaltaxa, nucleotide substitution values are of comparable magnitudes at thepopulation level but differ at the subspecific level, being higher for thebisexual taxon. In the apomictic hybrid, atticus- and grandii grandii- likesequences coexist with significantly different p-distance values. For threeclones, the nucleotide compositions at the diagnostic loci suggest thatgene conversion can occur between atticus- and grandii grandii-likemonomers. On the whole, this supports bisexuality as a driving force invariant fixation and suggests that in Bacillus, different gametogeneticprocesses and different origins of the unisexuals are mirrored in genomicturnover rates of satellite DNA.