Genetic association of physically unlinked islands of genomic divergence in incipient species of Anopheles gambiae.
Previous efforts to uncover the genetic underpinnings of ongoing ecological speciation of the M and S forms of the African malaria vector Anopheles gambiae revealed two centromere-proximal islands of genetic divergence on X and chromosome 2. Under the assumption of considerable ongoing gene flow between M and S, these persistently divergent genomic islands were widely considered to be 'speciation islands'. In the course of microarray-based divergence mapping, we discovered a third centromere-associated island of divergence on chromosome 3, which was validated by targeted re-sequencing. To test for genetic association between the divergence islands on all three chromosomes, SNP-based assays were applied in four natural populations of M and S spanning West, Central and East Africa. Genotyping of 517 female M and S mosquitoes revealed nearly complete linkage disequilibrium between the centromeres of the three independently assorting chromosomes. These results suggest that despite the potential for inter-form gene flow through hybridization, actual (realized) gene flow between M and S may be substantially less than commonly assumed and may not explain most shared variation. Moreover, the possibility of very low gene flow calls into question whether diverged pericentromeric regions-characterized by reduced levels of variation and recombination-are in fact instrumental rather than merely incidental to the speciation process.
White
Bradley J
BJ
Department of Biological Sciences, Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN 46556, USA.
Cheng
Changde
C
Simard
Frederic
F
Costantini
Carlo
C
Besansky
Nora J
NJ
D000818:Animals; D000852:Anopheles / Q000235:genetics*; D002503:Centromere / Q000235:genetics; D002874:Chromosome Mapping; D019143:Evolution, Molecular; D005260:Female; D051456:Gene Flow; D005828:Genetics, Population; D049750:Genome, Insect; D044404:Genomic Islands; D005838:Genotype; D016013:Likelihood Functions; D015810:Linkage Disequilibrium; D020411:Oligonucleotide Array Sequence Analysis; D020641:Polymorphism, Single Nucleotide; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA