Speciation Within
            <i>Anopheles gambiae</i>
            -- the Glass Is Half Full

Torre, Alessandra della; Costantini, Carlo; Besansky, Nora J.; Caccone, Adalgisa; Petrarca, V.; Powell, Jeffrey R.; Cóluzzi, M.

doi:10.1126/science.1078170

Cited by 193 publications

(177 citation statements)

References 16 publications

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“…Consistent with small amounts of ongoing gene flow, most previous investigations of genetic diversity in A. gambiae have reported no or only slight differentiation between the two forms (11,12). Aside from sequences adjacent to the centromere of chromosome 2L and a small region of 2R (13,14), the most significant differentiation found to date has been at the centromeric end of the X chromosome (14,15).…”

mentioning

confidence: 65%

Centromere-proximal differentiation and speciation in Anopheles gambiae

Stump

Fitzpatrick

Lobo

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

109

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The M and S molecular forms of Anopheles gambiae are undergoing speciation as they adapt to heterogeneities in the environment, spreading malaria in the process. We hypothesized that their divergence despite gene flow is facilitated by reduced recombination at the centromeric (proximal) end of the X chromosome. We sequenced introns from 22 X chromosome genes in M and S from two locations of West Africa where the forms are sympatric. Generally, in both forms nucleotide diversity was high distally, lower proximally, and very low nearest the centromere. Conversely, differentiation between the forms was virtually zero distally and very high proximally. Pairwise comparisons to a close relative, the sibling species Anopheles arabiensis, demonstrated uniformly high divergence regardless of position along the X chromosome, suggesting that this pattern is not purely mechanical. Instead, the pattern observed for M and S suggests the action of divergent natural selection countering gene flow only at the proximal end of the X chromosome, where recombination is reduced. Comparison of sites with fixed differences between M and S to the corresponding sites in A. arabiensis revealed that derived substitutions had been fixed in both forms, further supporting the hypothesis that both have been under selection. These derived substitutions are fixed in the two West African samples and in samples of S from western and coastal Kenya, suggesting that selection occurred before the forms expanded to their current ranges. Our findings are consistent with a role for suppressed genetic recombination in speciation of A. gambiae.R educed recombination contributes to the persistence of species or emerging species in the face of gene flow (1, 2). Despite some interbreeding and hybrid formation, species-specific regions of the genome can be preserved from introgression and homogenization of different genetic backgrounds if they are not subject to crossing over. Recent elaborations of this concept in organisms as diverse as humans, sunflowers, fruit flies, and mosquitoes invoke chromosomal inversions because recombination is effectively suppressed between the break points of chromosomal inversion heterozygotes (3-6). If captured by inversions, genes involved in assortative mating and species-specific ecological adaptations would remain associated longer relative to the case of free recombination. For pairs of species that have diverged in parapatry or sympatry, these models predict (i) that they are likely to differ by fixed inversions, (ii) that genes involved in reproductive isolation and species-specific adaptations should preferentially map to these inversions, and (iii) that significantly greater genetic divergence will accumulate in rearranged versus colinear regions. These predictions seem to be upheld for the group of mosquito sibling species known as the Anopheles gambiae complex (7, 8) but not for A. gambiae itself.A. gambiae, the primary vector of malaria in subSaharan Africa, is undergoing speciation. The incipient species (designate...

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mentioning

confidence: 65%

Centromere-proximal differentiation and speciation in Anopheles gambiae

Stump

Fitzpatrick

Lobo

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

109

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“…A long-standing debate has centered on the level of gene flow between forms. On one side many authors consider that RI between the two is complete or nearly complete (7,8,45,46) and that the two forms represent distinct species (29). On the other side are those who argued that RI, even if recent, cannot explain the "mosaic" pattern of genome divergence, and that it is selection operating on a few genomic regions in the face of gene flow that shapes this pattern (13,16,47).…”

Section: Discussionmentioning

confidence: 99%

Spatiotemporal dynamics of gene flow and hybrid fitness between the M and S forms of the malaria mosquito, Anopheles gambiae

Marsden²,

Norris

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

103

171

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The M and S forms of Anopheles gambiae have been the focus of intense study by malaria researchers and evolutionary biologists interested in ecological speciation. Divergence occurs at three discrete islands in genomes that are otherwise nearly identical. An "islands of speciation" model proposes that diverged regions contain genes that are maintained by selection in the face of gene flow. An alternative "incidental island" model maintains that gene flow between M and S is effectively zero and that divergence islands are unrelated to speciation. A "divergence island SNP" assay was used to explore the spatial and temporal distributions of hybrid genotypes. Results revealed that hybrid individuals occur at frequencies ranging between 5% and 97% in every population examined. A temporal analysis revealed that assortative mating is unstable and periodically breaks down, resulting in extensive hybridization. Results suggest that hybrids suffer a fitness disadvantage, but at least some hybrid genotypes are viable. Stable introgression of the 2L speciation island occurred at one site following a hybridization event.reproductive isolation | population structure | Anopheles coluzzii

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“…gambiae complex and An. gambiae s.s. are showing (Black & Lanzaro 2001, della Torre et al 2002, Besansky et al 2003, Donnelly et al 2004, Tripet et al 2005, Slotman et al 2005, Stump et al 2005, Turner et al 2005.…”

Section: Lu Longipalpis In Brazil a Complex Of Incipient Species?mentioning

confidence: 99%