Phylogenetic Utility of Partial Dna Sequences of G6pdh at Different Taxonomic Levels in Hexapoda with Emphasis on Diptera

Abstract

A given gene may be phylogenetically informative at one taxonomic level but uninformative at another. Thus, candidate genes should be evaluated for phylogenetic usefulness before any major project is initiated. We evaluated the utility for insect systematics of an ≈480-bp fragment of the coding region of the gene G6pdh, which encodes the pentose phosphate shunt enzyme glucose-6-phosphate dehydrogenase (E.C. 1.1.1.49). Sequences were obtained for 12 species of hexapods at taxonomic levels ranging from class to sibling species. Two additional insect sequences and five sequences from distantly related taxa (bacteria, yeast, rat, and human) were obtained from the literature. Sequences were obtained from cloned polymerase chain reaction (PCR) products; in most cases, sequences had to be obtained from complementary DNA rather than genomic DNA. The failure to obtain PCR products from genomic DNA may have been the result of unexpectedly long introns in the amplified region. DNA sequences were analyzed using parsimony methods of phylogeny reconstruction. Comparison of DNA trees with generally accepted phylogeny indicates that G6pdh exon sequence may not be useful phylogenetically for closely related sibling species (e.g., Rhagoletis pomonella species group), but could be useful in insects from generic to ordinal levels. For example, G6pdh supports a proposal by Crampton (Crampton, G. C. 1944. A comparative morphological study of the terminalia of male calyptrate cyclorrhaphous Diptera and their acalyptrate relatives. Bull. Brooklyn Entomol. Soc. 34: 1-34) suggesting that the sister group relationship Sarcophagidae + Tephritidae is more likely than Sarcophagidae + Drosophilidae or Drosophilidae + Tephritidae. The advantages and disadvantages of protein coding regions and ribosomal DNA sequences for phylogenetic purposes are discussed in terms of ease of alignment, division of sequences into subsets subject to different selection pressures and rates of evolution, ease of amplification, and feasibility of study of individual variation.