Population genetics of Plasmodium resistance genes in Anopheles gambiae: no evidence for strong selection

Abstract

Anopheles mosquitoes are the primary vectors for malaria in Africa, transmitting the disease to more than 100 million people annually. Recent functional studies have revealed mosquito genes that are crucial for Plasmodium development, but there is presently little understanding of which genes mediate vector competence in the wild, or evolve in response to parasite-mediated selection. Here, we use population genetic approaches to study the strength and mode of natural selection on a suite of mosquito immune system genes, CTL4, CTLMA2, LRIM1, and APL2 (LRRD7), which have been shown to affect Plasmodium development in functional studies. We sampled these genes from two African populations of An. gambiae s.s. , along with several closely related species, and conclude that there is no evidence for either strong directional or balancing selection on these genes. We highlight a number of challenges that need to be met in order to apply population genetic tests for selection in Anopheles mosquitoes; in particular the dearth of suitable outgroup species and the potential difficulties that arise when working within a closely-related species complex.

The Anopheles gambiae 2La chromosome inversion is associated with susceptibility to Plasmodium falciparum in Africa

“…The 2La inversion assay yields standard amplicons of 207 bp (2L+ a allele) and 492 bp (2La allele). Non-standard amplicons of 672, 687, 760 and 1020 bp were described, which result from insertion of mobile elements into the breakpoint regions (Ng'habi et al, 2008; Obbard et al, 2007, 2009). These larger bands are interpretable derivatives of the standard amplicon sizes and therefore can be assigned to one of the two inversion alleles.…”

Exploring the Molecular Landscape of Host-Parasite Coevolution

“…This problem, for example, is particularly acute in the study of mosquitoes, which tend to form species flocks with little diversity within flocks but substantial (too substantial for outgroup comparisons) divergence between flocks (Obbard et al 2007(Obbard et al , 2009). The number and average genetic distance separating Daphnia species suggest that this is unlikely to be a problem in this genus (Colbourne et al 1998).…”

Adaptive Evolution of a Stress Response Protein

“…A hallmark of genes involved in host-pathogen interactions is an exceptionally fast rate of protein evolution (corrected for mutation rate) [14], [15], [16], [17], [18]. This arises because fighting pathogens leads to arms races: a series of selective sweeps caused by repeated adaptation and counteradaptation between host and pathogen.…”