Generic affinities among crocodilians as revealed by DNA fingerprinting with a Bkm-derived probe

Genetic fingerprint profiles have been successfully used for establishing biological relationships, in linkage analysis, and in studies of population structure but have not so far been used for ascertaining phylogenetic relationships among related groups of species and genera. This is largely because these profiles are thought to evolve too rapidly to be informative over large time intervals. However, we show here that among the Crocodilia, whose phylogeny is a debated issue, these profiles can provide phylogenetically useful information. By using the probe Bkm-2(8), DNA fingerprints with distinct bands distributed in the size range 0.5-23.0 kb were obtained for individuals of 18 species belonging to seven of the eight genera of crocodilians. These genetic profiles showed individual-, species-, and restriction enzyme-specific patterns. In addition, striking differences were observed in the copy number of Bkm-related sequences in genomes of different crocodilian species. The qualitative data from DNA fingerprint profiles, and quantitative data on copy number variation in Bkm-related sequences, suggest that these genera belong to two distinct groups, one of which includes Alligator, Paleosuchus, and Caiman; the other includes Crocodylus, Osteolaemus, Tomistoma, and Gavialis. A close relationship between Tomistoma and Gavialis is also suggested by these results.