Rates of single-copy DNA evolution in herons

DNA-DNA hybridization was used to discover the extent of single-copy DNAsimilarity among 13 species of herons and one ibis. Genetic distances amongtaxa were summarized as Tm values in a folded matrix. From this matrix,trees with the same branching pattern were constructed by least squaresunder one of two assumptions: (1) that sister branches are equal in lengthand (2) that sister branches are not necessarily equal in length. Theresidual sums of squares of these trees were compared by F-test to seewhether the branches of the tree built under assumption (2) fit the matrixdata significantly better than those of the tree built under assumption(1). By this method the existence of different rates of DNA evolution indifferent heron lineages was established. Bittern single-copy DNA hasevolved at a rate approximately 25% faster, and boat-billed heron(Cochearius) and rufescent tiger heron (Tigrisoma lineatum) DNA has evolvedapproximately 19% slower, than that of day and night herons. It appearsthat the differences in rates of DNA evolution may increase proportionallywith genealogical distance.