Resolving a Cryptic Species Complex: Application and Utility of Mitochondrial 16S and Nuclear Its1 Molecular Markers in Pyrgulopsis Micrococcus


Steven Kepes

Date of Graduation

Spring 2003


Master of Science in Biology



Committee Chair

John Heywood


Pyrgulopsis micrococcus (Hydrobiidae: Nymphophilinae) is a cryptic species complex found among three river drainages in the Death Valley system. Jennings (2001) used mitochondrial cytochrome c oxidase subunit I (mtCOI) DNA sequences to examine intra-and inter- population genetic variation in 13 populations of Pyrgulopsis micrococcus. Jennings (2001) concluded that at least five cryptic species existed in the P. micrococcus species complex. However, these conclusions were based on analysis of a single mitochondrial marker and a small sample size per population. To better delineate this species complex, phylogenetic analyses based on the partial mitochondrial 16S ribosomal DNA region (16S) and the complete first nuclear internal transcribed spacer region (ITS1) were performed for multiple individuals from each of thirteen populations of P. micrococcus, ten other Pyrgulopsis species, and an outgroup species from the genus Nymphophilus. Neighbor-joining and maximum parsimony analyses depicted a poloyphyletic P. micrococcus with five major clades. Genetic variation was lower within clades (16S, 0%-0.9%; ITS1, 0%-1.8%) than between clades (16S, 0.4%-3.7%; ITS1, 4.3%-12.8%). The genetic distance between P. micrococcus and other ingroup species was similar to, and in some cases lower than the genetic distance between clades of P. micrococcus (16S, 0.4%-4.6%; ITS1, 4.5%-14.9%). Furthermore, in nearly all phylogenetic reconstructions at least one ingroup species nested within P. micrococcus. This evidence supports the recognition of at least five new species from the P. micrococcus species complex.

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