Mitochondrial DNA polymorphism in a black fly, Simulium vittatum (Diptera: Simuliidae)

Abstract

Mitochondrial DNA (mtDNA) was extracted from pooled field-collected samples representing six species of black flies (Cnephia dacotensis, Simulium bivittaum, S. johansenni, S. luggeri, S. piperi, S. vittatum) and compared by restriction fragment length polymorphism (RFLP) analysis. Morphospecies were molecularly distinct, with few shared restriction fragments. Eleven populations of S. vittatum were found that appeared to be homogeneous for a single mitochondrial haplotype. Ten other populations of S. vittatum showed extensive mitochondrial heterogeneity. In part, these samples contained mixtures of two cytologically recognized siblings: IIIL-1 and IS-7. About 70% of the mitochondrial genome of a population pure for sibling IIIL-1 was cloned as five HindIII fragments, which were used as hybridization probes to examine individual black flies. Thirteen mtDNA haplotypes involving permutations of 10 HindIII restriction sites were identified in individual black flies examined from 26 populations. DNA from 168 larvae cut with both EcoR1 and HindIII revealed five additional haplotypes. One HindIII haplotype was present in 84% of 390 larvae examined and predominated in every population examined from New York to California and in both the IIIL-1 and IS-7 siblings. Nebraska populations had individuals with nearly all known haplotypes. The most common haplotype was usually the only form present in warm, silty streams with organic enrichment. Rarer haplotypes were found in cool, spring-fed streams but without clear geographic or phylogenetic components.