THE BAG320 SATELLITE DNA FAMILY IN BACILLUS STICK INSECTS (PHASMATODEA) - DIFFERENT RATES OF MOLECULAR EVOLUTION OF HIGHLY REPETITIVE DNA IN BISEXUAL AND PARTHENOGENETIC TAXA

The Bag320 satellite DNA (satDNA) family was studied in seven populati ons of the stick insects Bacillus atticus (parthenogenetic, unisexual) and Bacillus grandii (bisexual). It was characterized as widespread i n all zymoraces of B. atticus and in all subspecies of B. grandii. The copy number of this satellite is higher in the bisexual B. grandii (1 5%-20% of the genome) than in the parthenogenetic B. atticus (2%-5% of the genome). The nucleotide sequences of 12 Bag320 clones from B. att icus and 17 from B. grandii differed at 13 characteristic positions by fixed nucleotide substitutions. Thus, nucleotide sequences from both species cluster conspecifically in phylogenetic dendrograms. The nucle otide sequences derived from B. grandii grandii could be clearly discr iminated from those of B. grandii benazzii and B. grandii maretimi on the basis of 25 variable sites, although all taxa come from Sicily. In contrast, the Bag320 sequences from B. atticus could not be discrimin ated accordingly, although they derive from geographically quite dista nt populations of its three zymoraces (the Italian and Greek B. atticu s atticus, the Greek and Turkish B. atticus carius, and the Cyprian B. atticus cyprius). The different rate of evolutionary turnover of the Bag320 satDNA in both species can be related to their different modes of reproduction. This indicates that meiosis and chromosome segregatio n affect processes in satDNA diversification.