A Longitudinal Analysis of the Distributions of and An Assessment of the Reproductive Status of Two Siblings of the S. arcticum Complex at Little Prickly Pear Creek

Abstract

Shields (2006) has proposed the S. arcticum Geographic Distribution/Taxon-Age hypothesis. Accordingly, cytospecies with broad, geographic distributions may be evolutionarily old and would be expected to be more reproductively isolated in sympatry than presumably younger cytotypes that have more restricted distributions. Given that no large-scale reproductive isolation test had been preformed between S. arcticum s. s. and S. apricarium, and since Little Prickly Pear Creek (LPPC) offered the opportunity for such studies, one was performed there. Accordingly, I hypothesized that the two cytospecies, S. arcticum s. s. and S. apricarium would be reproductively isolated at LPPC. Little Prickly Pear Creek was the single exception among the five drainages previously studied upon which the 5. arcticum s. s. high/ 5. apricarium low hypothesis was based. The site was unique in that the ratio of the two taxa was reversed from the previous observations at the other four drainages, i.e. S. arcticum s. s. predominated at the original low elevation site at LPPC. I therefore studied this drainage at four equally spaced locations to determine if some other abiotic factor, such as water temperature, might influence the distribution of these cytospecies. Since colder water is usually found at higher elevations and its temperature increases as it moves to lower elevations, I hypothesized that as I sampled down stream from the original site the frequency of 5. apricarium would increase. I used conventional methods of collection and cytogenetic analysis to study 1108 larvae of the Simulium arcticum complex at four sites including the original one. First, I found that S. apricarium did not increase in frequency as I sampled down stream. In fact, S. apricarium was only dominant in one of 15 collections. Therefore, I reject my first hypothesis. In addition, I found little evidence for hybridization between the two cytospecies. This observation supports the Geographic Distribution/Taxon-Age hypothesis of Shields (2006)