Countering morphological ambiguities: development of a PCR assay to assist the identification of Tubifex tubifex oligochaetes

Abstract

The freshwater oligochaete, Tubifex tubifex, is a common resident of organic-rich sediments worldwide. Although it is a familiar species to fish enthusiasts, toxicologists and parasitologists, T. tubifex often confounds definitive identification due to the similarity that immature specimens bear to several other common oligochaetes, and given the degree of plasticity of key morphological characters due to environmental conditions and/or age of specimen. To solve this identity crisis, we used a polymerase chain reaction based molecular approach and developed a T. tubifex specific assay with primers that amplify a 192 bp fragment of the internal transcribed spacer region 1 ribosomal DNA. We tested these primers on four T. tubifex mitochondrial genotypes, and on other oligochaete species from nine genera. The primers amplified all specimens identified morphologically as T. tubifex. They did not amplify any other species, including morphologically similar worms possessing hair chaetae (Dero digitata, Ilyodrilus templetoni, Tubifex ignotus or Rhyacodrilus spp.) or other oligochaetes often found with T. tubifex (Lumbriculus variegates, Limnodrilus hoffmeisteri, Stylodrilus heringianus or Trichodrilus sp.). This technique should remove the uncertainties all too often associated with identification of T. tubifex.