Isolation by distance and a chromosomal cline in the Cayapa cytospecies of Simulium exiguum, the vector of human onchocerciasis in Ecuador

Abstract

The population genetic structure of the Cayapa cytospecies of Simulium exiguum, the vector of onchocerciasis, was analysed using allozyme frequency and chromosomal inversion polymorphism data from 6 and 15 populations respectively, collected in Ecuador. Eight allozyme loci were scored. No unique allozyme markers were found enabling us to identify biting adults of the vector from the non-vector Bucay cytotype. Mannose-phosphate isomerase (Mpi) contributed largely to the significant heterogeneity in gene frequency among populations of the Cayapa cytospecies and also to the overall population structuring (F(ST) = 0.015 +/- 0.014) which fitted the isolation by distance model. However, heterozygote deficits were recorded for Mpi in four of the six populations, which could indicate that selection is acting at this locus but this hypothesis will require further convincing evidence. Furthermore the significant population structuring of allozymes was not evident when Mpi was omitted from the analysis. All inversion polymorphisms (IIS-B, IIS-F, IIL-A and IIL-B) were in Hardy-Weinberg equilibrium, showed significant heterogeneity between populations and revealed the occurrence of an altitudinal cline in inversion IIS-B frequency. The inversion polymorphisms revealed a significant degree of population structuring (F(ST) = 0.083 +/- 0.027), which can be explained by the isolation by distance model. A UPGMA cluster analysis revealed the relatively remote, high altitude Rio Mira populations to be the most genetically distinct.

Phylogenetic, Spatial, and Species‐Trait Patterns across Environmental Gradients: the Case of Hydropsyche (Trichoptera) along the Loire River

“…Consequently, genetic divergence developed across longitudinal (or altitudinal) gradients, which is perhaps the typical evolutionary pathway along running waters (CHARALAMBOUS et al, 2005;HUGHES, 2007;RAEYMAEKERS et al, 2007;ZIERITZ et al, 2010). In our Hydropsyche, the typical evolutionary step was directed downstream.…”

“…Likewise, focusing on the phylogeny of pupation, WIGGINS and WICHARD (1989) argued that the caddisflies originated from colonizers of cool running waters. Most likely, population fragmentation preceded range expansion of these ancestors (see BAKER et al, 2003 for an example) and genetic divergence developed across altitudinal (i.e., longitudinal) gradients over several dozens to hundreds of kilometers within catchments (for examples on lotic insects and other lotic animals, see CHARALAMBOUS et al, 2005;HUGHES, 2007;ZIERITZ et al, 2010).…”

Phylogeography of Simulium siamense Takaoka and Suzuki complex (Diptera: Simuliidae) in Thailand

“…2010). Irrespective of molecular markers used, low genetic differentiation between cytologically described species has been reported in many species (Feraday & Leonhardt 1989; Scarpassa & Hamada 2003; Charalambous et al . 2005; Morales‐Hojas & Krueger 2009; Conflitti et al .…”

“…2009), which can be recognized by: (i) fixed chromosome inversion differences; (ii) differences in sex‐linked inversions; and (iii) differences in floating inversions (Rothfels 1979). Molecular approaches have been used to differentiate cytospecies but most are unsuccessful (Feraday & Leonhardt 1989; Scarpassa & Hamada 2003; Charalambous et al . 2005; Morales‐Hojas & Krueger 2009).…”

Synthesising environmental, epidemiological, and genetic data to assist decision making for onchocerciasis elimination

“…However, this is a static map and ignores the 'innate' connectivity between locations mediated by the movement of the human host and the vectors. Population genetics has been used to infer the movement of pathogens, whereby pathogen movement can be measured indirectly by the genetic relatedness of parasites across locations [18][19][20][21][22][23][24][25][26][27][28]. The dispersal, and thus gene flow, of parasites and vectors, are subject to influence by the environmental features of the landscape.…”