Ecological Genomics of the Malaria Mosquito Anopheles gambiae

Doctoral Dissertation

Abstract

Anopheles gambiae is the primary mosquito vector of malaria in sub-Saharan Africa. It has adapted to thrive in contrasting ecological conditions from the humid rainforests of central Africa to the near desert-like conditions of the northern Sahel. Within a single location, it survives extreme seasonal fluctuations in rainfall and temperature. This ecological adaptation has driven incipient speciation into two forms, termed M and S, which exploit permanent and temporary larval habitats, respectively. Polymorphic chromosomal inversions shared between forms are non-randomly associated with multiple environmental factors further promoting adaptation. A long-term goal is to determine the genetic basis of ecological adaptation in An. gambiae. Chapter 2 reports a molecular diagnostic of the 2La inversion that will enhance both phenotypic and genetic studies of this rearrangement. Traditional cytogenetic karyotyping is labor-intensive, requires rare skills, and is limited to semi-gravid females. This new PCR (polymerase chain reaction) for determining 2L karyotype is accurate, simple, and can be utilized on mosquitoes of any development stage and either sex.
In Chapter 3 and 4, an oligonucleotide microarray platform was used to map genome wide divergence between Malian An. gambiae carrying alternative chromosomal arrangements. Divergence mapping between alternative arrangements of five common, polymorphic inversions revealed three regions of elevated differentiation. Two of the regions are located within the 2La inversion and appear to contain at least some of the genes responsible for the selective maintenance of this polymorphic inversion. The other four inversions Ì¢âÂ" all on the right arm of chromosome 2 Ì¢âÂ" exhibited substantially less differentiation, confounding the genome scans. Possible explanations for the contrasting patterns of evolution seen between these different inversions systems are discussed.
In Chapters 5 and 6, the same microarray platform was used to map divergence between the M and S Forms of An. gambiae. Three rangewide islands of genomic divergence were discovered between nascent species; one at the pericentromeric region of each chromosome. Whether these islands are incidental or instrumental to speciation remains an open question. A fourth island, on chromosome 3 and distant from the centromere, is likely due to recent geographically-restricted selection within the M Form at the TEP1 immunity gene. The diverse pathogen community in the permanent larval sites utilized by the M Form may have driven a novel TEP1 allele (TEP1rB) to fixation in this form. Intriguingly, this derived allele may inadvertently increase resistance to Plasmodium.
While each region of elevated divergence needs to be further investigated, these studies represent a crucial first step in connecting genetic polymorphisms to adaptive phenotypic diversity in this medically important species.

Attributes

Attribute NameValues
URN
  • etd-04202010-155930

Author Bradley Jourdan White
Advisor Nora Besansky
Contributor Nora Besansky, Committee Chair
Contributor Frank Collins, Committee Member
Contributor Jeffrey Feder, Committee Member
Contributor David Severson, Committee Member
Degree Level Doctoral Dissertation
Degree Discipline Biological Sciences
Degree Name PhD
Defense Date
  • 2010-02-22

Submission Date 2010-04-20
Country
  • United States of America

Subject
  • evolution

  • sympatric speciation

  • drosophila

  • adaptation

  • inversion

  • gene flow

Publisher
  • University of Notre Dame

Language
  • English

Record Visibility Public
Content License
  • All rights reserved

Departments and Units

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