A Cytogenetic Analysis of the Simulium arcticum Complex at the Little Blackfoot River, Powell County, Montana
This two-year study of the chromosome diversity within the Simulium arcticum complex within the Little Blackfoot River Drainage addressed the following study objectives: 1) determination of the distribution and frequency of 5. arcticum s. s., S. brevicercum, S. apricarium, and S. arcticum IIL-18 at high, intermediate, and low elevation sites; 2) investigation of the reproductive status of these taxa at the Elliston site where they were relatively abundant; and 3) investigation of sibling-specific criteria for S. brevicercum to determine the status of IIL-st/st males at Elliston. Regarding the first objective, the null hypothesis suggests that these siblings would be distributed evenly in the drainage. However, it was observed that S. arcticum s. s. occurred in abundance at the high and intermediate locations whereas S. apricarium was only found at the low elevation site. S. brevicercum and S. arcticum IIL-18 were abundant at the intermediate location. Based on this, the null hypothesis was rejected. Elevation seemed to influence the distribution of these siblings. I was unable to address the second objective because the low frequency of autosomal polymorphisms at Elliston precluded determination of the reproductive status of IIL-18, S. arcticum s. s. and IIL-st/st males. For the third objective, the criteria for identification were compared among standard males of S. brevicercum, S. arcticum s. s., and S. arcticum IIL-18. The criteria for identification of S. brevicercum were not unique to the standard males; therefore, they could either be sex-exceptional males or more plausibly, a divergent type of S. brevicercum with the characteristics being variable within the species.