A Third-Year Study of Continuity of Taxa and Reproductive Status of Cytoforms of the Simulium arcticum Complex at the Clearwater River, Montana

Abstract

The purpose of this study is to 1) investigate the reproductive status of the two most prevalent taxa, IIL-3 and IIL-22 of the Simulium arcticum complex at the Clearwater River in 2009 and 2) determine whether the distribution and frequencies of cytotypes are similar from year to year when compared with previous analyses in 2007 and 2008. Larvae were collected and cytogenetic analysis was used to do the following: identify banding patterns and inversions of polytene chromosomes and identify distinct cytotypes and siblings, as well as determine the reproductive status of the types through the use of the autosomal polymorphism, IS-1, and perform equilibrium analysis. The data from 2009 revealed that these two taxa are in genetic equilibrium, suggesting that they are not reproductively isolated. These data serve as the fourth positive test of the Geographic Distribution/Taxon Age Continuum hypothesis (Shields, 2006), which suggests that taxa with broad geographic distributions may be evolutionarily old and therefore are expected to be reproductively isolated in sympatry, while presumably younger taxa which have more restricted distributions are not reproductively isolated. When compared with the data from 2007 and 2008, there is great similarity in the types and frequencies from year to year.