Cytogenetic analysis of a new subcomplex of Simulium exiguum (Diptera: Simuliidae) in amazonian Ecuador

Abstract

AbstractTwo new cytotypes of the onchocerciasis vector blackfly Simulium exiguum Roubaud are described from amazonian Ecuador. As transmission of the disease does not occur in the region, the two cytotypes are not currently vectors, The Napo form (N = 113) differs cytologically from the chromosomal standard of the species, the Cayapa form, through possession of the fixed paracentric inversions IL-E and IIIL-L; the Huatarac form (N = 22) differs by the fixed inversions IL-L and IIIL-D + L. Both forms form a subcomplex, termed the ‘amazonian’ subcomplex, through sharing the fixed inversion IIIL-L. They also share a number of polymorphic inversions, but neither form possesses sex-linked inversions. The fixed and sex-linked inversions of the previously described Aguarico form were found to be polymorphic and autosomal in the Napo and Huatarac forms, suggesting a close genetic relationship among these forms. The Napo form is distributed throughout the Napo river system (except in the Rio Huatarac) and found in the Rio Aguarico, whereas the Huatarac form is unique to the Rio Huatarac. As their distributions in this study were allopatric, the species status of the two cytotypes could not be tested. The Aguarico form was not found in the Rio Aguarico, nor in any of the other rivers sampled. Whether the Napo form has replaced the Aguarico form in the Rio Aguarico, or whether its absence is due to seasonal variation requires further investigation.