SATELLITE SEQUENCE TURNOVER IN PARTHENOGENETIC SYSTEMS - THE APOMICTIC TRIPLOID HYBRID BACILLUS-LYNCEORUM (INSECTA, PHASMATODEA)

In the genus Bacillus (Insecta, Phasmatodea) the Bag320 satellite DNA family is present in the bisexual B. grandii and in the related automi ctic nonhybrid B. atticus, it is lacking in the other bisexual taxon o f the genus, B. rossius. This family of highly repeated sequences was analyzed for 11 populations of the apomictic triploid hybrid B. lynceo rum. In the neighbor-joining dendrogram, B. lynceorum nucleotide seque nces distribute, regardless of geographical origin, among two clusters , one also including all clones of the three B. atticus races, and the other including sequences of the B. grandii grandii subspecies. Thus, B. lynceorum is a trihybrid taxon: as the molecular approach definiti vely demonstrates, it embodies one haploid complement each of both B. grandii grandii and B. atticus, which must be added to that of B. ross ius. The contribution of the latter species has already been assessed on karyological and allozymic grounds. A statistical analysis performe d on p-distances shows that for the parental taxa, nucleotide substitu tion values are of comparable magnitudes at the population level but d iffer at the subspecific level, being higher for the bisexual taxon. I n the apomictic hybrid, atticus- and grandii grandii- like sequences c oexist with significantly different p-distance values. For three clone s, the nucleotide compositions at the diagnostic loci suggest that gen e conversion can occur between atticus- and grandii grandii-like monom ers. On the whole, this supports bisexuality as a driving force in var iant fixation and suggests that in Bacillus, different gametogenetic p rocesses and different origins of the unisexuals are mirrored in genom ic turnover rates of satellite DNA.