Different rates of mitochondrial DNA sequence evolution in Kirk's dik-dik (Madoqua kirkii) populations.

We have investigated evolutionary rates of the mitochondrial genome among individuals of Madoqua kirkii using the relative rate test. Our results demonstrate that individuals of two chromosome races, East African cytotype A and Southwest African cytotype D, evolve about 2.3 times faster than East African cytotype B. Cytogenetic changes, DNA repair efficiency, mutagens, and more likely, hitherto unrecognized factors will account for the rate difference we have observed. Our results suggest additional caution when using molecular clocks in the estimation of divergence time, even within lineages of closely related taxa. Rate heterogeneity in microevolutionary timescales represents a potentially important aspect of basic evolutionary processes and may provide additional insights into factors which affect genome evolution.