PHYLOGENETIC ANALYSIS OF SLIPPAGE-LIKE SEQUENCE VARIATION IN THE V4 RIBOSOMAL-RNA EXPANSION SEGMENT IN TIGER BEETLES (CICINDELIDAE)

Sequence variation in the middle part of the small-subunit rRNA was st udied for representatives of the major groups in the family Cicindelid ae (Coleoptera). All taxa exhibited a much expanded segment in variabl e region V4 compared to D. melanogaster. This expanded segment was not found in other groups of beetles, including three taxa in the closely related Carabidae. Secondary structure predictions indicate that the expanded segment folds into a single stem-loop structure in all taxa. Despite its structural conservation, the fragment differs strongly in primary sequence, even between closely related sister taxa. Several fe atures of these sequences are consistent with slippage replication as the mechanism that has generated this sequence variation: the level of internal sequence repetition as measured by the relative simplicity f actor (RSF), its variation in length between close relatives, and the strong nucleotide bias compared to the remainder of the gene. With few exceptions, there was also a correlation between sequence length and the level of sequence repetition, frequently interpreted as the result of slippage. Phylogenies inferred from the expansion segment were not consistent with existing hypotheses from other molecular data for the group. This indicates that DNA sequences in this region are not homol ogous throughout the entire Cicindelidae, but it leaves open the possi bility that this expansion segment can be used for phylogeny reconstru ction within subgroups. The implications of a phylogenetic approach to the understanding of slippage-like evolution are discussed.