On the distribution and genetic differentiation of Anopheles gambiae s.s. molecular forms

Torre, Alessandra della; Tu, Zhijian; Petrarca, Vincenzo

doi:10.1016/j.ibmb.2005.02.006

Cited by 217 publications

(293 citation statements)

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“…Finally, we note that M and S are sympatric in southern Cameroon, yet in this region of West Africa both forms remain reproductively isolated and both are monomorphic for the standard (uninverted) arrangements of the inversion systems on chromosome 2 (9). Thus, it is conceivable that reduced recombination at the proximal end of the X chromosome is responsible for maintaining ecological and reproductive differences in lieu of alternative chromosomal arrangements.…”

Section: Discussionmentioning

confidence: 78%

“…The incipient species (designated molecular forms M and S) are defined by fixed sequence differences in the X-linked ribosomal DNA locus (ref. 9 and references therein), but these species do not differ by any known fixed inversion difference. The S form occurs across subSaharan Africa, where it exploits typical rain-dependent A. gambiae breeding sites.…”

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confidence: 87%

“…Nevertheless, where sympatric throughout most of west Africa (figure 1 of ref. 9), the two forms can be sampled as adults from the same houses, where females of both forms feed preferentially on human blood. Wild females are estimated to mate with males of the other form at a rate of only Ϸ1% (10), indicating strong assortative mating.…”

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confidence: 99%

“…Wild females are estimated to mate with males of the other form at a rate of only Ϸ1% (10), indicating strong assortative mating. In the laboratory, hybrids of both sexes are viable and fertile, but naturally occurring M͞S hybrids are rare (e.g., 6 of 8,000, Ͻ Ͻ1%) (9).…”

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confidence: 99%

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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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Section: Discussionmentioning

confidence: 78%

mentioning

confidence: 87%

mentioning

confidence: 99%

mentioning

confidence: 99%

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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. gambiae is the most important vector throughout Africa and the most extensively studied Anopheles species (8). The effectiveness of malaria transmission emerges from the complementary ecoclimatic attributes and seasonal patterns of both species.…”

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confidence: 99%

Population genetic structure of Plasmodium falciparum in the two main African vectors, Anopheles gambiae and Anopheles funestus

Annan

Durand

Ayala

et al. 2007

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

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We investigated patterns of genetic diversity of Plasmodium falciparum associated with its two main African vectors: Anopheles gambiae and Anopheles funestus. We dissected 10,296 wildcaught mosquitoes from three tropical sites, two in Cameroon (Simbock and Tibati, separated by 320 km) and one in Kenya (Rota, >2,000 km from the other two sites). We assayed seven microsatellite loci in 746 oocysts from 183 infected mosquito guts. Genetic polymorphism was very high in parasites isolated from both vector species. The expected heterozygosity (HE) was 0.79 in both species; the observed heterozygosities (HO) were 0.32 in A. funestus and 0.42 in A. gambiae, indicating considerable inbreeding within both vector species. Mean selfing (s) between genetically identical gametes was s ‫؍‬ 0.33. Differences in the rate of inbreeding were statistically insignificant among sites and between the two vector species. As expected, because of the high rate of inbreeding, linkage disequilibrium was very high; it was significant for all 21 loci pairs in A. gambiae and for 15 of 21 pairs in A. funestus, although only two pairwise comparisons were between loci on the same chromosome. Overall, the genetic population structure of P. falciparum, as evaluated by F statistics, was predominantly clonal rather than panmictic, a population structure that facilitates the spread of antimalarial drug and vaccine resistance and thus may impair the effectiveness of malaria control efforts. malaria ͉ epidemiology ͉ evolutionary genetics ͉ Cameroon ͉ Kenya M alaria is the most significant and widespread vectortransmitted human disease, accounting yearly for several hundred million clinical cases and Ͼ2 million deaths, mostly affecting young children and pregnant women in subSaharan Africa (1). Prevention and cure of the disease are major publichealth challenges that are tackled by using several strategies, among them vector control. The transmission of Plasmodium falciparum, the agent of malignant malaria, involves a complex vectorial system consisting of Ϸ10 Anopheles species, colonizing different ecoclimatic settings, regions, and seasons in strongly variable relative abundances (2-5).The two most important vectors of malignant malaria in Africa are Anopheles gambiae and Anopheles funestus because of their widespread distribution, highly anthropophilic and endophilic behavior, and long life spans (6, 7). A. gambiae is the most important vector throughout Africa and the most extensively studied Anopheles species (8). The effectiveness of malaria transmission emerges from the complementary ecoclimatic attributes and seasonal patterns of both species. A. funestus breeds in permanent larval sites that enable this species, in regions of seasonal transmission, to extend parasite transmission far into the dry season, after the temporary breeding pools of A. gambiae have dried out (7, 9-11).Differences in the biology and ecology of these two main vectors might entail a differential impact on the genetic composition of the P. falciparum populations they harbo...

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