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Molecular population genetics of Drosophila immune system genes.

ABSTRACT: A striking aspect of many vertebrate immune system is the exceptionally high level of polymorphism they harbor. A convincing case can be made that this polymorphism is driven by the diversity of pathogens that face selective pressures to evade attack by the host immune system. Different organisms accomplish a defense against diverse pathogens through mechanisms that differ widely in their requirements for specific recognition. It has recently been shown that innate defense mechanisms, which use proteins with broad-spectrum bactericidal properties, are common to both primitive and advanced organisms. In this study we characterize DNA sequence variation in six pathogen defense genes of Drosophila melanogaster and D. mauritiana, including Andropin; cecropin genes CecA1, CecA2, CecB, and CecC; and Diptericin. The necessity for protection against diverse pathogens, which themselves may evolve resistance to insect defenses, motivates a population-level analysis. Estimates of variation levels show that the genes are not exceptionally polymorphic, but Andropin and Diptericin have patterns of variation that differ significantly from neutrality. Patterns of interpopulation and interspecific differentiation also reveal differences among the genes in evolutionary forces.

SUBMITTER: Clark AG

PROVIDER: S-EPMC1208192 | biostudies-other | 1997 Oct

REPOSITORIES: biostudies-other

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Molecular population genetics of Drosophila immune system genes.

Clark A G AG Wang L L

Genetics 19971001 2

A striking aspect of many vertebrate immune system is the exceptionally high level of polymorphism they harbor. A convincing case can be made that this polymorphism is driven by the diversity of pathogens that face selective pressures to evade attack by the host immune system. Different organisms accomplish a defense against diverse pathogens through mechanisms that differ widely in their requirements for specific recognition. It has recently been shown that innate defense mechanisms, which use ...[more]

PMID: 9335607

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Project description:Natural selection is expected to drive adaptive evolution in genes involved in host-pathogen interactions. In this study, we use molecular population genetic analyses to understand how natural selection operates on the immune system of Anopheles coluzzii (formerly A. gambiae "M form"). We analyzed patterns of intraspecific and interspecific genetic variation in 20 immune-related genes and 17 nonimmune genes from a wild population of A. coluzzii and asked if patterns of genetic variation in the immune genes are consistent with pathogen-driven selection shaping the evolution of defense. We found evidence of a balanced polymorphism in CTLMA2, which encodes a C-type lectin involved in regulation of the melanization response. The two CTLMA2 haplotypes, which are distinguished by fixed amino acid differences near the predicted peptide cleavage site, are also segregating in the sister species A. gambiae ("S form") and A. arabiensis. Comparison of the two haplotypes between species indicates that they were not shared among the species through introgression, but rather that they arose before the species divergence and have been adaptively maintained as a balanced polymorphism in all three species. We additionally found that STAT-B, a retroduplicate of STAT-A, shows strong evidence of adaptive evolution that is consistent with neofunctionalization after duplication. In contrast to the striking patterns of adaptive evolution observed in these Anopheles-specific immune genes, we found no evidence of adaptive evolution in the Toll and Imd innate immune pathways that are orthologously conserved throughout insects. Genes encoding the Imd pathway exhibit high rates of amino acid divergence between Anopheles species but also display elevated amino acid diversity that is consistent with relaxed purifying selection. These results indicate that adaptive coevolution between A. coluzzii and its pathogens is more likely to involve novel or lineage-specific molecular mechanisms than the canonical humoral immune pathways.

Dataset Information

Molecular population genetics of Drosophila immune system genes.

Publications

Molecular population genetics of Drosophila immune system genes.

Similar Datasets

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