Inter- and intraspecific variation in restriction maps of Drosophila mitochondrial DNAs

Abstract

Mitochondrial (mt) DNAs have been observed to be polymorphic for cleavage sites of various restriction endonucleases^1–4. Although these studies involved a variety of organisms, they were insufficient for the estimation of the level of genetic variation in natural populations. mtDNAs of various Drosophila species are heterogeneous in length, with molecular weights (MWs) ranging from 9.90 to 12.35×10⁶. The mtDNA molecule of Drosophila melanogaster contains a long A + T-rich region representing 25% of the circle length^5,6. A comparison of mtDNAs from different species of Drosophila by electron microscope partial denaturation mapping has shown that the size of the A + T-rich region varies among different species⁵. We have previously presented electron microscope heteroduplex analysis of the mtDNAs of D. melanogaster, Drosophila simulans and Drosophila virilis and showed that the sequence divergence was apparently greatest in the A + T-rich region, whereas the remainder of the molecule was much more evolutionarily conserved. The cleavage map of the D. melanogaster mtDNA molecule has been established using various restriction endonucleases^6–8. The ribosomal RNA genes (rRNAs) and the A + T-rich region have been positioned on this map. We now present the restriction endonuclease maps of the mtDNAs of three species of Drosophila. We also report the results of a systematic survey of restriction site variation in the mtDNAs of natural populations of these species and make a preliminary comparison with the level of variation of nuclear genes. Our data suggest that the mitochondrial genome may evolve in a similar way to allozymic variation.