Evolution of low-copy number and major satellite DNA sequences coexisting in two Pimelia species-groups (Coleoptera)

Satellite DNA sequence evolution has been studied in several insect species from the genus Pimelia (Tenebrionidae, Coleoptera). Low-copy number homologs of the previously characterized major satellite DNA from P. monticola (PMON) have been cloned and sequenced from six congeneric species belonging to two species groups: Ibero-Balearic and Moroccan. Sequence analysis of a sample of low-copy number repeats revealed two subfamilies, differing on average 17.5% due to randomly spread single point mutations. Each subfamily is specific for a group of taxa in congruence with their biogeography. Within each group, there is no significant species-specific clustering of the sequences. These results suggest that the two satellite subfamilies arose after the split of an ancestral lineage into the North African and Ibero-Balearic Pimelia species-groups, but before their subsequent radiation. Rate heterogeneity tests suggest that PMON sequences have evolved faster in the lineage leading to the Moroccan group. Comparison of sequence divergences between minor PMON and the previously characterized major PIM357 satellite obtained from the same taxa, points to similar evolutionary dynamics. Both sequences are evolving in parallel accumulating mutations in a gradual manner irrespectively of significant differences in abundance. These data show that copy number of the sequence families does not necessarily affect the sequence change dynamics of satellite repeats.