Spatial distribution patterns of larval cytotypes of the Simulium venustum/verecundum complex (Diptera: Simuliidae) on the Avalon Peninsula, Newfoundland: factors associated with cytotype abundance and composition

Abstract

Using principal component analysis and cluster and regression analyses, larval macrodistribution of Simulium venustum/verecundum complex cytotypes within a drainage basin and along a stream continuum was investigated. Cytotypes included ACD (= Simulium rostratum Lundström) and AA from the verecundum line of the complex and EFG/C (= Simulium truncatum Lundström), AC(gb) and CC2-3 (combined CC2 and CC3) from the venustum line. Abundance of both AC(gb) and CC2-3 increased with increasing stream size. The abundance of CC2-3 also increased at sites with warmer temperatures and lower conductivity, dissolved oxygen, and pH levels. Cytotype composition changed in a continuous, directional, and predictable (R2 = 52.4–92.2%) manner with increased distance from outlets. It is argued that changes in cytotype composition must be considered in future sampling protocols, as quantitative and qualitative changes in the cytotype assemblage can occur over distances as short as 100 m. Discontinuity in the frequency of the IIL-4 polymorphism suggested restricted gene flow due to limited adult AA dispersal over distances greater than 12 km.