The Simulium arcticum Complex: Environmental Effects on Distribution of Taxa at Trout Creek and Reproductive Status of Taxa at the Blackfoot River

Abstract

This study had two major objectives: 1) To determine if elevation correlated with sibling distribution within the Simulium arcticum complex at Trout Creek, Lewis and Clark County, Montana, a previously unstudied drainage, and 2) to determine the reproductive status of siblings and cytotypes at the Blackfoot River, Missoula County, Montana, as a test of the Shields Geographic Distribution/Taxon Age Continuum Hypothesis. In both studies I used cytogenetic analysis to: compare the banding patterns of polytene chromosomes of salivary glands of larvae of the S. arcticum complex, identify larvae to sibling and cytotype, and score autosomal polymorphisms that could be used to determine reproductive status. For the elevational study, frequencies of siblings at three different elevations along Trout Creek, Lewis and Clark County, Montana, were compared. Based on previous collections in different drainages, it was hypothesized that Simulium apricarium would be found predominately at lower elevations while Simulium arcticum sensu stricto would be found at higher elevations. Data collected in the present study supported this hypothesis with the caveat that S. arcticum s. s. was quite rare in the drainage. A new cytotype, S. arcticum IIL-68, was also discovered at Trout Creek. For the study of reproductive status, the Blackfoot River at Russell Gates Campground, Missoula County, Montana, was chosen. Previous analysis of this site showed the presence of a sufficient number of siblings and cytotypes, as well as numerous autosomal polymorphisms within the 5. arcticum complex so that a determination of reproductive status could be made. The Shields Geographic Distribution/Taxon Age Continuum Hypothesis suggests that if a cytotype and a sibling occurred in sympatry, they should be reproductively isolated from one another. The data supported this hypothesis, as analysis of autosomal polymorphisms within the S. negativum and S. arcticum IIL-9 populations suggest that these populations are both temporally and genetically reproductively isolated. Additionally, the data suggest that two Y-chromosomes, IL-3.4 and IL-3.4 + IS-1, exist within the S. negativum population at the Blackfoot River.