MOLECULAR EVOLUTIONARY DIVERGENCE AMONG NORTH AMERICAN CAVE CRICKETS. II. DNA-DNA HYBRIDIZATION.

Single-copy DNA divergence among 23 populations of cave crickets belonging to two genera (Euhadenoecus and Hadenoecus) has been determined by DNA-DNA hybridization employing the TEACL method. These same populations have been studied for allozyme variation (Caccone and Sbordoni, 1987). In addition, a European relative (Dolichopoda laetitiae) has been included as an outgroup for rooting the phylogeny. One of the most remarkable findings is the large degree of DNA divergence among these species and populations. A ΔTm of up to 5°C has been found between populations of the same species; even further divergence is indicated by a lowered normalized percentage of reassociation. A phylogeny was constructed and tested for synchrony of rates, i.e., a molecular clock. Statistically, we could not reject the clock hypothesis. Attempts to calibrate the clock led to the conclusion that these insects are among the fastest evolving (with respect to single-copy DNA) groups yet studied-at least as fast as Drosophila and sea urchins-where a ΔTm of 1°C indicates 0.5 to 1.5 MY since the last common ancestor. In general, the phylogeny derived from the DNA data agrees with that derived from isozymes. Nei's D and ΔTm are correlated; in this group a D of 0.1 corresponds to a ΔTm of about 1.5°C. This indicates that, relative to total single-copy DNA, the protein-coding regions of the genome are slowly evolving.