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Weetman D, Steen K, Rippon EJ, Mawejje HD, Donnelly MJ, Wilding CS. Contemporary gene flow between wild An. gambiae s.s. and An. arabiensis. Parasit Vectors 2014; 7:345. [PMID: 25060488 PMCID: PMC4124135 DOI: 10.1186/1756-3305-7-345] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Accepted: 07/21/2014] [Indexed: 11/10/2022] Open
Abstract
Background In areas where the morphologically indistinguishable malaria mosquitoes Anopheles gambiae Giles and An. arabiensis Patton are sympatric, hybrids are detected occasionally via species-diagnostic molecular assays. An. gambiae and An. arabiensis exhibit both pre- and post-reproductive mating barriers, with swarms largely species-specific and male F1 (first-generation) hybrids sterile. Consequently advanced-stage hybrids (back-crosses to parental species), which would represent a route for potentially-adaptive introgression, are expected to be very rare in natural populations. Yet the use of one or two physically linked single-locus diagnostic assays renders them indistinguishable from F1 hybrids and levels of interspecific gene flow are unknown. Methods We used data from over 350 polymorphic autosomal SNPs to investigate post F1 gene flow via patterns of genomic admixture between An. gambiae and An. arabiensis from eastern Uganda. Simulations were used to investigate the statistical power to detect hybrids with different levels of crossing and to identify the hybrid category significantly admixed genotypes could represent. Results A range of admixture proportions were detected for 11 field-collected hybrids identified via single-locus species-diagnostic PCRs. Comparison of admixture data with simulations indicated that at least seven of these hybrids were advanced generation crosses, with backcrosses to each species identified. In addition, of 36 individuals typing as An. gambiae or An. arabiensis that exhibited outlying admixture proportions, ten were identified as significantly mixed backcrosses, and at least four of these were second or third generation crosses. Conclusions Our results show that hybrids detected using standard diagnostics will often be hybrid generations beyond F1, and that in our study area around 5% (95% confidence intervals 3%-9%) of apparently ‘pure’ species samples may also be backcrosses. This is likely an underestimate because of rapidly-declining detection power beyond the first two backcross generations. Post-F1 gene flow occurs at a far from inconsequential rate between An. gambiae and An. arabiensis, and, especially for traits under strong selection, could readily lead to adaptive introgression of genetic variants relevant for vector control. Electronic supplementary material The online version of this article (doi:10.1186/1756-3305-7-345) contains supplementary material, which is available to authorized users.
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Affiliation(s)
| | | | | | | | | | - Craig S Wilding
- Department of Vector Biology, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UK.
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O'Loughlin SM, Magesa S, Mbogo C, Mosha F, Midega J, Lomas S, Burt A. Genomic analyses of three malaria vectors reveals extensive shared polymorphism but contrasting population histories. Mol Biol Evol 2014; 31:889-902. [PMID: 24408911 PMCID: PMC3969563 DOI: 10.1093/molbev/msu040] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Anopheles gambiae s.l. are important malaria vectors, but little is known about their genomic variation in the wild. Here, we present inter- and intraspecies analysis of genome-wide RADseq data, in three Anopheles gambiae s.l. species collected from East Africa. The mosquitoes fall into three genotypic clusters representing described species (A. gambiae, A. arabiensis, and A. merus) with no evidence of cryptic breeding units. Anopheles merus is the most divergent of the three species, supporting a recent new phylogeny based on chromosomal inversions. Even though the species clusters are well separated, there is extensive shared polymorphism, particularly between A. gambiae and A. arabiensis. Divergence between A. gambiae and A. arabiensis does not vary across the autosomes but is higher in X-linked inversions than elsewhere on X or on the autosomes, consistent with the suggestion that this inversion (or a gene within it) is important in reproductive isolation between the species. The 2La/2L+(a) inversion shows no more evidence of introgression between A. gambiae and A. arabiensis than the rest of the autosomes. Population differentiation within A. gambiae and A. arabiensis is weak over approximately 190-270 km, implying no strong barriers to dispersal. Analysis of Tajima's D and the allele frequency spectrum is consistent with modest population increases in A. arabiensis and A. merus, but a more complex demographic history of expansion followed by contraction in A. gambiae. Although they are less than 200 km apart, the two A. gambiae populations show evidence of different demographic histories.
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Affiliation(s)
- Samantha M O'Loughlin
- Department of Life Sciences, Imperial College London, Silwood Park, Ascot, United Kingdom
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3
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Lee Y, Marsden CD, Norris LC, Collier TC, Main BJ, Fofana A, Cornel AJ, Lanzaro GC. Spatiotemporal dynamics of gene flow and hybrid fitness between the M and S forms of the malaria mosquito, Anopheles gambiae. Proc Natl Acad Sci U S A 2013; 110:19854-9. [PMID: 24248386 DOI: 10.1073/pnas.1316851110] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
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.
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Gómez G, Jaramillo L, Correa MM. Wing geometric morphometrics and molecular assessment of members in the Albitarsis Complex from Colombia. Mol Ecol Resour 2013; 13:1082-92. [PMID: 23702155 DOI: 10.1111/1755-0998.12126] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2012] [Accepted: 04/14/2013] [Indexed: 01/07/2023]
Abstract
Malaria parasites are transmitted to humans by female mosquitoes of the genus Anopheles. The Albitarsis Complex harbours at least eight species not readily differentiable by morphology. This complicates the determination of those species involved in malaria transmission and the implementation of targeted and effective vector control strategies. In Colombia, there is little information about the identity and distribution of the Albitarsis Complex members. In this work, COI DNA barcoding was used to assign specimens Anopheles albitarsis s.l. to any of the previously designated species of the Albitarsis Complex. Two molecular operational taxonomic units (MOTUs), differentially distributed in Colombia, were detected, A. albitarsis I in the NW and NE, and A. albitarsis F, E and NE Colombia. In contrast, nuclear white gene and ITS2 sequence analyses did not allow differentiating between the MOTUs. Wing landmark-based geometric morphometrics applied to explore intertaxa phenotypic heterogeneity showed a subtle but significant difference in size, while shape did not allow the separation of the MOTUs. In general, the multiple marker analysis was not supportive of the existence in Colombia of more than one species of the Albitarsis Complex.
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Affiliation(s)
- G Gómez
- Grupo de Microbiología Molecular, Escuela de Microbiología, Universidad de Antioquia, Calle 67 No. 53-108, off. 5-430, Medellín, Colombia
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Yaro AS, Traoré AI, Huestis DL, Adamou A, Timbiné S, Kassogué Y, Diallo M, Dao A, Traoré SF, Lehmann T. Dry season reproductive depression of Anopheles gambiae in the Sahel. J Insect Physiol 2012; 58:1050-1059. [PMID: 22609421 PMCID: PMC4789105 DOI: 10.1016/j.jinsphys.2012.04.002] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Revised: 03/26/2012] [Accepted: 04/02/2012] [Indexed: 05/30/2023]
Abstract
The African malaria mosquito, Anopheles gambiae, is widespread south of the Sahara including in dry savannahs and semi-arid environments where no surface water exists for several months a year. Adults of the M form of An. gambiae persist through the long dry season, when no surface waters are available, by increasing their maximal survival from 4 weeks to 7 months. Dry season diapause (aestivation) presumably underlies this extended survival. Diapause in adult insects is intrinsically linked to depressed reproduction. To determine if reproduction of the Sahelian M form is depressed during the dry season, we assessed seasonal changes in oviposition, egg batch size, and egg development, as well as insemination rate and blood feeding in wild caught mosquitoes. Results from xeric Sahelian and riparian populations were compared. Oviposition response in the Sahelian M form dropped from 70% during the wet season to 20% during the dry season while the mean egg batch size among those that laid eggs fell from 173 to 101. Correspondingly, the fraction of females that exhibited gonotrophic dissociation increased over the dry season from 5% to 45%, while a similar fraction of the population retained developed eggs despite having access to water. This depression in reproduction the Sahelian M form was not caused by a reduced insemination rate. Seasonal variation in these reproductive parameters of the riparian M form population was less extreme and the duration of reproductive depression was shorter. Blood feeding responses did not change with the season in either population. Depressed reproduction during the dry season in the Sahelian M form of An. gambiae provides additional evidence for aestivation and illuminates the physiological processes involved. The differences between the Sahelian and riparian population suggest an adaptive cline in aestivation phenotypes between populations only 130 km apart.
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Affiliation(s)
- Alpha S Yaro
- Malaria Research and Training Center/Faculty of Medicine, Pharmacy and Odonto-Stomatology, Bamako, Mali.
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Alquezar DE, Hemmerter S, Cooper RD, Beebe NW. Incomplete concerted evolution and reproductive isolation at the rDNA locus uncovers nine cryptic species within Anopheles longirostris from Papua New Guinea. BMC Evol Biol 2010; 10:392. [PMID: 21184676 PMCID: PMC3022607 DOI: 10.1186/1471-2148-10-392] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2010] [Accepted: 12/24/2010] [Indexed: 11/20/2022] Open
Abstract
Background Nuclear ribosomal DNA (rDNA) genes and transcribed spacers are highly utilized as taxonomic markers in metazoans despite the lack of a cohesive understanding of their evolution. Here we follow the evolution of the rDNA second internal transcribed spacer (ITS2) and the mitochondrial DNA cytochrome oxidase I subunit in the malaria mosquito Anopheles longirostris from Papua New Guinea (PNG). This morphospecies inhabits a variety of ecological environments indicating that it may comprise a complex of morphologically indistinguishable species. Using collections from over 70 sites in PNG, the mtDNA was assessed via direct DNA sequencing while the ITS2 was assessed at three levels - crude sequence variation through restriction digest, intragenomic copy variant organisation (homogenisation) through heteroduplex analysis and DNA sequencing via cloning. Results Genetic evaluation of over 300 individuals revealed that A. longirostris comprises eight ITS2 PCR-RFLP genotypes and nine ITS2 heteroduplex genotypes showing distinct copy variant organization profiles after PCR amplification. Seven of these nine genotypes were found to be sympatric with other genotypes. Phylogenetic analysis of cloned ITS2 PCR products and mtDNA COI confirmed all nine clades with evidence of reproductive isolation at the rDNA locus. Compensatory base changes in the ITS2 secondary structure or in pseudoknots were absent when closely related species were assessed. Individuals from each ITS2 genotype showed the same copy variant heteroduplex profile suggesting that the rDNA array is fixed within each genotype. Conclusion The centromere-proximal position of the rDNA array in Anopheles mosquitoes has probably reduced interchromosomal recombination leaving intrachromosomal events responsible for the observed pattern of concerted evolution we see in these mosquitoes. The stability of these intragenomic ITS2 copy variants within individuals and interbreeding populations suggests that rDNA is moving as a single evolutionary unit through natural populations to fixation and has provided a complementary diagnostic tool to the restriction digest for studying genetic discontinuities and species boundaries. In this, the utility of the ITS2 as a universal taxonomic marker is probably contingent on several factors pertaining to spacer dimensions and the genomic location of the rDNA array with respect to recombination and proximity to regions potentially under selection.
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Affiliation(s)
- David E Alquezar
- Institute for the Biotechnology of Infectious Disease, University of Technology, Sydney. Australia
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7
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Linton Y, Smith L, Koliopoulos G, Zounos AK, Samanidou‐Voyadjoglou A, Patsoula E, Harbach RE. TheAnopheles (Anopheles) maculipenniscomplex (Diptera: Culicidae) in Greece. J NAT HIST 2010. [DOI: 10.1080/00222930701403255] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Abstract
Anopheles gambiae is a primary vector of Plasmodium falciparum, a human malaria parasite that causes over a million deaths each year in sub-Saharan Africa. Population genetic tests have been employed to detect natural selection at suspected A. gambiae antimalaria genes, but these tests have generally been compromised by the lack of demographically correct null models. Here, we used a coalescent simulation approach within a maximum likelihood framework to fit population growth, bottleneck, and migration models to polymorphism data from Cameroonian A. gambiae. The best-fit models for both the "M" and the "S" molecular forms of A. gambiae included ancient population growth and a high rate of migration from an unsampled subpopulation. After correcting for differences in effective population size, our models suggest that the molecular forms expanded at different times and both expansions significantly predate the advent of agriculture. We show that correcting null models for demography increases the power to detect natural selection in A. gambiae.
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9
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Herrera-aguilar M, Be-barragán LA, Ramirez-sierra MJ, Tripet F, Dorn P, Dumonteil E. Identification of a large hybrid zone between sympatric sibling species of Triatoma dimidiata in the Yucatan peninsula, Mexico, and its epidemiological importance. Infection, Genetics and Evolution 2009; 9:1345-51. [DOI: 10.1016/j.meegid.2009.09.009] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/02/2009] [Revised: 09/14/2009] [Accepted: 09/21/2009] [Indexed: 11/23/2022]
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10
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Wilkins EE, Marcet PL, Sutcliffe AC, Howell PI. Authentication scheme for routine verification of genetically similar laboratory colonies: a trial with Anopheles gambiae. BMC Biotechnol 2009; 9:91. [PMID: 19849838 PMCID: PMC2772846 DOI: 10.1186/1472-6750-9-91] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2009] [Accepted: 10/22/2009] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND When rearing morphologically indistinguishable laboratory strains concurrently, the threat of unintentional genetic contamination is constant. Avoidance of accidental mixing of strains is difficult due to the use of common equipment, technician error, or the possibility of self relocation by adult mosquitoes ("free fliers"). In many cases, laboratory strains are difficult to distinguish because of morphological and genetic similarity, especially when laboratory colonies are isolates of certain traits from the same parental strain, such as eye color mutants, individuals with certain chromosomal arrangements or high levels of insecticide resistance. Thus, proving genetic integrity could seem incredibly time-consuming or impossible. On the other hand, lacking proof of genetically isolated laboratory strains could question the validity of research results. RESULTS We present a method for establishing authentication matrices to routinely distinguish and confirm that laboratory strains have not become physically or genetically mixed through contamination events in the laboratory. We show a specific example with application to Anopheles gambiae sensu stricto strains at the Malaria Research and Reference Reagent Resource Center. This authentication matrix is essentially a series of tests yielding a strain-specific combination of results. CONCLUSION These matrix-based methodologies are useful for several mosquito and insect populations but must be specifically tailored and altered for each laboratory based on the potential contaminants available at any given time. The desired resulting authentication plan would utilize the least amount of routine effort possible while ensuring the integrity of the strains.
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Affiliation(s)
- Elien E Wilkins
- Entomology, Centers for Disease Control and Prevention (CDC), Atlanta GA, USA
| | - Paula L Marcet
- Entomology, Centers for Disease Control and Prevention (CDC), Atlanta GA, USA
| | - Alice C Sutcliffe
- Entomology, Centers for Disease Control and Prevention (CDC), Atlanta GA, USA
- Atlanta Research & Education Foundation (AREF), Veterans Affairs, Atlanta GA, USA
| | - Paul I Howell
- Entomology, Centers for Disease Control and Prevention (CDC), Atlanta GA, USA
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Diabaté A, Dao A, Yaro AS, Adamou A, Gonzalez R, Manoukis NC, Traoré SF, Gwadz RW, Lehmann T. Spatial swarm segregation and reproductive isolation between the molecular forms of Anopheles gambiae. Proc Biol Sci 2009; 276:4215-22. [PMID: 19734189 PMCID: PMC2821344 DOI: 10.1098/rspb.2009.1167] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Anopheles gambiae, the major malaria vector in Africa, can be divided into two subgroups based on genetic and ecological criteria. These two subgroups, termed the M and S molecular forms, are believed to be incipient species. Although they display differences in the ecological niches they occupy in the field, they are often sympatric and readily hybridize in the laboratory to produce viable and fertile offspring. Evidence for assortative mating in the field was recently reported, but the underlying mechanisms awaited discovery. We studied swarming behaviour of the molecular forms and investigated the role of swarm segregation in mediating assortative mating. Molecular identification of 1145 males collected from 68 swarms in Donéguébougou, Mali, over 2 years revealed a strict pattern of spatial segregation, resulting in almost exclusively monotypic swarms with respect to molecular form. We found evidence of clustering of swarms composed of individuals of a single molecular form within the village. Tethered M and S females were introduced into natural swarms of the M form to verify the existence of possible mate recognition operating within-swarm. Both M and S females were inseminated regardless of their form under these conditions, suggesting no within-mate recognition. We argue that our results provide evidence that swarm spatial segregation strongly contributes to reproductive isolation between the molecular forms in Mali. However this does not exclude the possibility of additional mate recognition operating across the range distribution of the forms. We discuss the importance of spatial segregation in the context of possible geographic variation in mechanisms of reproductive isolation.
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Affiliation(s)
- Abdoulaye Diabaté
- Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA
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Abstract
Understanding nucleotide variation in natural populations has been a subject of great interest for decades. However, many taxonomic groups, especially those with atypical life history attributes remain unstudied, and Drosophila is the only arthropod genus for which DNA polymorphism data are presently abundant. As a result of the recent release of the complete genome sequence and a wide variety of new genomic resources, the Daphnia system is quickly becoming a promising new avenue for expanding our knowledge of nucleotide variation in natural populations. Here, we examine nucleotide variation in six protein-coding loci for Daphnia pulex and its congeners with particular emphasis on D. pulicaria, the closest extant relative of D. pulex. Levels of synonymous intraspecific variation, pi(s), averaged 0.0136 for species in the Daphnia genus, and are slightly lower than most prior estimates in invertebrates. Tests of neutrality indicated that segregating variation conforms to neutral model expectations for the loci that we examined in most species, while K(a)/K(s) ratios revealed strong purifying selection. Using a full maximum-likelihood coalescent-based method, the ratio of the recombination rate to the mutation rate (c/u), averaged 0.5255 for species of the Daphnia genus. Lastly, a divergence population-genetics approach was used to investigate gene flow and divergence between D. pulex and D. pulicaria.
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Oliveira E, Salgueiro P, Palsson K, Vicente JL, Arez AP, Jaenson TG, Caccone A, Pinto J. High levels of hybridization between molecular forms of Anopheles gambiae from Guinea Bissau. J Med Entomol 2008; 45:1057-1063. [PMID: 19058629 DOI: 10.1603/0022-2585(2008)45[1057:hlohbm]2.0.co;2] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
In the malaria vector Anopheles gambiae Giles sensu stricto, two molecular forms denoted M and S are considered units of incipient speciation within this species. Very low hybrid frequencies and significant genetic differentiation have been found in sympatric M- and S-form populations. We studied the molecular form composition and the degree of genetic differentiation at 15 microsatellites in two samples of An. gambiae collected in two consecutive years from Bissau, Guinea Bissau. High frequencies of M/S hybrids (19-24%) were found in this area. Coincidently, very low levels of genetic differentiation were detected between forms when analysis involved microsatellites mapped at chromosome-3 (mean Fst, 0.000-0.002). The single exception was the X-linked AGXH678, for which high differentiation was measured (Fst, 0.158-0.301). This locus maps near the centromere of chromosome X, a low recombination region in which selection is likely to promote divergence between M and S forms. These results strongly suggest that the degree of isolation between M and S forms, considered the units of incipient speciation within An. gambiae, is not homogenous throughout the species distribution range.
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Affiliation(s)
- E Oliveira
- Centro de Malária e outras Doen as Tropicais, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa, 1349-008 Lisbon, Portugal
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14
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Marshall JC, Pinto J, Charlwood JD, Gentile G, Santolamazza F, Simard F, Della Torre A, Donnelly MJ, Caccone A. Exploring the origin and degree of genetic isolation of Anopheles gambiae from the islands of São Tomé and Príncipe, potential sites for testing transgenic-based vector control. Evol Appl 2008; 1:631-44. [PMID: 25567803 PMCID: PMC3352388 DOI: 10.1111/j.1752-4571.2008.00048.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Accepted: 08/27/2008] [Indexed: 01/11/2023] Open
Abstract
The evolutionary processes at play between island and mainland populations of the malaria mosquito vector Anopheles gambiae sensu stricto are of great interest as islands may be suitable sites for preliminary application of transgenic-based vector control strategies. São Tomé and Príncipe, located off the West African coast, have received such attention in recent years. This study investigates the degree of isolation of An. gambiae s.s. populations between these islands and the mainland based on mitochondrial and ribosomal DNA molecular data. We identify possible continental localities from which these island populations derived. For these purposes, we used FST values, haplotype networks, and nested clade analysis to estimate migration rates and patterns. Haplotypes from both markers are geographically widespread across the African continent. Results indicate that the populations from São Tomé and Príncipe are relatively isolated from continental African populations, suggesting they are promising sites for test releases of transgenic individuals. These island populations are possibly derived from two separate continental migrations. This result is discussed in the context of the history of the African slave trade with respect to São Tomé and Príncipe.
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Affiliation(s)
- Jonathon C Marshall
- Department of Zoology, Weber State University, 2505 University Circle Ogden, UT, USA
| | - João Pinto
- Centro de Malária e Outras Doenças Tropicais, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa Lisbon, Portugal
| | | | - Gabriele Gentile
- Dipartimento di Biologia, Università di Roma "Tor Vergata" Rome, Italy
| | | | - Frèdèric Simard
- Laboratoire de l'Institut de Recherche Pour le Developpement (IRD), UR 016, Organisation de Coordination Pour la Lutte Contre les Endémies en Afrique Centrale (OCEAC) Yaoundé, Cameroun
| | | | - Martin J Donnelly
- Vector Group, Liverpool School of Tropical Medicine Pembroke Place, Liverpool, UK
| | - Adalgisa Caccone
- Department of Ecology and Evolutionary Biology, Yale University New Haven, CT, USA
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Lehmann T, Diabate A. The molecular forms of Anopheles gambiae: a phenotypic perspective. Infect Genet Evol 2008; 8:737-46. [PMID: 18640289 DOI: 10.1016/j.meegid.2008.06.003] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2008] [Revised: 06/11/2008] [Accepted: 06/12/2008] [Indexed: 11/18/2022]
Abstract
The African malaria mosquito Anopheles gambiae is undergoing speciation, being split into the M and S molecular forms. Speciation is the main process promoting biological diversity, thus, new vector species might complicate disease transmission. Genetic differentiation between the molecular forms has been extensively studied, but phenotypic differences between them, the evolutionary forces that generated divergence, and the mechanisms that maintain their genetic isolation have only recently been addressed. Here, we review recent studies suggesting that selection mediated by larval predation and competition promoted divergence between temporary and permanent freshwater habitats. These differences explain the sharp discontinuity in distribution of the molecular forms between rice fields and surrounding savanna, but they can also explain the concurrent cline between humid and arid environments due to the dependence on permanent habitats in the latter. Although less pronounced, differences in adult body size, reproductive output, and longevity also suggest that the molecular forms have adapted to distinct niches. Reproductive isolation between the molecular forms is achieved by spatial swarm segregation, although within-swarm mate recognition appears to play a role in certain locations. The implications of these results to disease transmission and control are discussed and many of the gaps in our understanding are highlighted.
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Affiliation(s)
- Tovi Lehmann
- Laboratory of Malaria and Vector Research, NIAID, NIH, MS 8132, 12735 Twinbrook Parkway, Rockville, MD, USA.
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Esnault C, Boulesteix M, Duchemin JB, Koffi AA, Chandre F, Dabiré R, Robert V, Simard F, Tripet F, Donnelly MJ, Fontenille D, Biémont C. High genetic differentiation between the M and S molecular forms of Anopheles gambiae in Africa. PLoS One 2008; 3:e1968. [PMID: 18414665 DOI: 10.1371/journal.pone.0001968] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2007] [Accepted: 03/07/2008] [Indexed: 11/19/2022] Open
Abstract
Background Anopheles gambiae, a major vector of malaria, is widely distributed throughout sub-Saharan Africa. In an attempt to eliminate infective mosquitoes, researchers are trying to develop transgenic strains that are refractory to the Plasmodium parasite. Before any release of transgenic mosquitoes can be envisaged, we need an accurate picture of the differentiation between the two molecular forms of An. gambiae, termed M and S, which are of uncertain taxonomic status. Methodology/Principal Findings Insertion patterns of three transposable elements (TEs) were determined in populations from Benin, Burkina Faso, Cameroon, Ghana, Ivory Coast, Madagascar, Mali, Mozambique, Niger, and Tanzania, using Transposon Display, a TE-anchored strategy based on Amplified Fragment Length Polymorphism. The results reveal a clear differentiation between the M and S forms, whatever their geographical origin, suggesting an incipient speciation process. Conclusions/Significance Any attempt to control the transmission of malaria by An. gambiae using either conventional or novel technologies must take the M/S genetic differentiation into account. In addition, we localized three TE insertion sites that were present either in every individual or at a high frequency in the M molecular form. These sites were found to be located outside the chromosomal regions that are suspected of involvement in the speciation event between the two forms. This suggests that these chromosomal regions are either larger than previously thought, or there are additional differentiated genomic regions interspersed with undifferentiated regions.
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Diabaté A, Dabiré RK, Heidenberger K, Crawford J, Lamp WO, Culler LE, Lehmann T. Evidence for divergent selection between the molecular forms of Anopheles gambiae: role of predation. BMC Evol Biol 2008; 8:5. [PMID: 18190719 PMCID: PMC2217532 DOI: 10.1186/1471-2148-8-5] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2007] [Accepted: 01/11/2008] [Indexed: 11/17/2022] Open
Abstract
BACKGROUND The molecular forms of Anopheles gambiae are undergoing speciation. They are characterized by a strong assortative mating and they display partial habitat segregation. The M form is mostly found in flooded/irrigated areas whereas the S form dominates in the surrounding areas, but the ecological factors that shape this habitat segregation are not known. Resource competition has been demonstrated between species undergoing divergent selection, but resource competition is not the only factor that can lead to divergence. RESULTS In a field experiment using transplantation of first instar larvae, we evaluated the role of larval predators in mediating habitat segregation between the forms. We found a significant difference in the ability of the molecular forms to exploit the different larval sites conditioned on the presence of predators. In absence of predation, the molecular forms outcompeted each other in their respective natural habitats however, the developmental success of the M form was significantly higher than that of the S form in both habitats under predator pressure. CONCLUSION Our results provide the first empirical evidence for specific adaptive differences between the molecular forms and stress the role of larval predation as one of the mechanisms contributing to their divergence.
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Affiliation(s)
- Abdoulaye Diabaté
- Laboratory of Malaria and Vector Research, NIAID, National Institute of Health, 12735 Twinbrook Parkway, Room 2W13A, Rockville MD 20852 USA
- IRSS/Centre Muraz, Laboratoire de Parasitologie/Entomologie BP 390 Bobo Dioulasso, Burkina Faso
| | - Roch K Dabiré
- IRSS/Centre Muraz, Laboratoire de Parasitologie/Entomologie BP 390 Bobo Dioulasso, Burkina Faso
| | - Kyle Heidenberger
- Laboratory of Malaria and Vector Research, NIAID, National Institute of Health, 12735 Twinbrook Parkway, Room 2W13A, Rockville MD 20852 USA
| | - Jacob Crawford
- Laboratory of Malaria and Vector Research, NIAID, National Institute of Health, 12735 Twinbrook Parkway, Room 2W13A, Rockville MD 20852 USA
| | - William O Lamp
- Department of Entomology University of Maryland College Park, MD 20742-4454 USA
| | - Lauren E Culler
- Department of Entomology University of Maryland College Park, MD 20742-4454 USA
| | - Tovi Lehmann
- Laboratory of Malaria and Vector Research, NIAID, National Institute of Health, 12735 Twinbrook Parkway, Room 2W13A, Rockville MD 20852 USA
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Slotman MA, Reimer LJ, Thiemann T, Dolo G, Fondjo E, Lanzaro GC. Reduced recombination rate and genetic differentiation between the M and S forms of Anopheles gambiae s.s. Genetics 2006; 174:2081-93. [PMID: 17057242 PMCID: PMC1698612 DOI: 10.1534/genetics.106.059949] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2006] [Accepted: 10/01/2006] [Indexed: 11/18/2022] Open
Abstract
Genetic differentiation between the largely sympatric molecular forms M and S of Anopheles gambiae appears mostly limited to division 6 and part of division 5 of the X chromosome. This region is adjacent to the centromere and includes the rDNA that was used to define these forms. This localized differentiation between populations that experience gene flow strongly suggests that this region contains genes responsible for reproductive isolation. Regions adjacent to centromeres are known to experience less recombination in several species and it has recently been suggested that low recombination rates can facilitate the accumulation and maintenance of isolation genes in partially isolated populations. Therefore, we measured the recombination rate in division 5D/6 directly and estimate that it is at least 16-fold reduced across this region compared to the remainder of the X chromosome. Additionally, sequence data from four loci from field-collected mosquitoes from several West African countries show very strong differentiation between the molecular forms in division 5D/6, whereas none was observed in two loci elsewhere on the X chromosome. Furthermore, genetic variation was substantially lower in division 5D/6 compared to the two reference loci, and the inferred genealogies of the division 5D/6 genes show patterns consistent with selective sweeps. This suggests that the reduced recombination rate has increased the effect of selection on this region and that our data are consistent with the hypothesis that reduced recombination rates can play a role in the accumulation of isolation genes in the face of gene flow.
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Affiliation(s)
- Michel A Slotman
- Department of Entomology, University of California, Davis 95616, USA.
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Yawson AE, Weetman D, Wilson MD, Donnelly MJ. Ecological zones rather than molecular forms predict genetic differentiation in the malaria vector Anopheles gambiae s.s. in Ghana. Genetics 2006; 175:751-61. [PMID: 17110481 PMCID: PMC1800615 DOI: 10.1534/genetics.106.065888] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The malaria mosquito Anopheles gambiae s.s. is rapidly becoming a model for studies on the evolution of reproductive isolation. Debate has centered on the taxonomic status of two forms (denoted M and S) within the nominal taxon identified by point mutations in the X-linked rDNA region. Evidence is accumulating that there are significant barriers to gene flow between these forms, but that the barriers are not complete throughout the entire range of their distribution. We sampled populations from across Ghana and southern Burkina Faso, West Africa, from areas where the molecular forms occurred in both sympatry and allopatry. Neither Bayesian clustering methods nor F(ST)-based analysis of microsatellite data found differentiation between the M and S molecular forms, but revealed strong differentiation among different ecological zones, irrespective of M/S status and with no detectable effect of geographical distance. Although no M/S hybrids were found in the samples, admixture analysis detected evidence of contemporary interform gene flow, arguably most pronounced in southern Ghana where forms occur sympatrically. Thus, in the sampled area of West Africa, lack of differentiation between M and S forms likely reflects substantial introgression, and ecological barriers appear to be of greater importance in restricting gene flow.
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Affiliation(s)
- Alexander E Yawson
- Vector Group, Liverpool School of Tropical Medicine, Liverpool L3 5QA, United Kingdom
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Kayondo JK, Mukwaya LG, Stump A, Michel AP, Coulibaly MB, Besansky NJ, Collins FH. Genetic structure of Anopheles gambiae populations on islands in northwestern Lake Victoria, Uganda. Malar J 2005; 4:59. [PMID: 16336684 PMCID: PMC1327676 DOI: 10.1186/1475-2875-4-59] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2005] [Accepted: 12/09/2005] [Indexed: 11/10/2022] Open
Abstract
Background Alternative means of malaria control are urgently needed. Evaluating the effectiveness of measures that involve genetic manipulation of vector populations will be facilitated by identifying small, genetically isolated vector populations. The study was designed to use variation in microsatellite markers to look at genetic structure across four Lake Victoria islands and two surrounding mainland populations and for evidence of any restriction to free gene flow. Methods Four Islands (from 20–50 km apart) and two surrounding mainland populations (96 km apart) were studied. Samples of indoor resting adult mosquitoes, collected over two consecutive years, were genotyped at microsatellite loci distributed broadly throughout the genome and analysed for genetic structure, effective migration (Nem) and effective population size (Ne). Results Ne estimates showed island populations to consist of smaller demes compared to the mainland ones. Most populations were significantly differentiated geographically, and from one year to the other. Average geographic pair-wise FST ranged from 0.014–0.105 and several pairs of populations had Ne m < 3. The loci showed broad heterogeneity at capturing or estimating population differences. Conclusion These island populations are significantly genetically differentiated. Differences reoccurred over the study period, between the two mainland populations and between each other. This appears to be the product of their separation by water, dynamics of small populations and local adaptation. With further characterisation these islands could become possible sites for applying measures evaluating effectiveness of control by genetic manipulation.
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Affiliation(s)
- Jonathan K Kayondo
- Center for Tropical Disease Research and Training, University of Notre Dame, Notre Dame IN 46556-0369, USA
- Department of Entomology, UgandaVirus Research Institute (UVRI), Box 49 Entebbe, Uganda
| | - Louis G Mukwaya
- Department of Entomology, UgandaVirus Research Institute (UVRI), Box 49 Entebbe, Uganda
| | - Aram Stump
- Center for Tropical Disease Research and Training, University of Notre Dame, Notre Dame IN 46556-0369, USA
| | - Andrew P Michel
- Center for Tropical Disease Research and Training, University of Notre Dame, Notre Dame IN 46556-0369, USA
| | - Mamadou B Coulibaly
- Center for Tropical Disease Research and Training, University of Notre Dame, Notre Dame IN 46556-0369, USA
| | - Nora J Besansky
- Center for Tropical Disease Research and Training, University of Notre Dame, Notre Dame IN 46556-0369, USA
| | - Frank H Collins
- Center for Tropical Disease Research and Training, University of Notre Dame, Notre Dame IN 46556-0369, USA
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Diabaté A, Dabire RK, Kim EH, Dalton R, Millogo N, Baldet T, Simard F, Gimnig JE, Hawley WA, Lehmann T. Larval development of the molecular forms of Anopheles gambiae (Diptera: Culicidae) in different habitats: a transplantation experiment. J Med Entomol 2005; 42:548-53. [PMID: 16119542 DOI: 10.1093/jmedent/42.4.548] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
We compared the development of the molecular forms of Anopheles gambiae s.s. in different larval habitats. First stage larvae (L1s) of wild-caught females were placed into cages in natural habitats of the M form (rice fields) or the S form (puddles/ quarries). Each cage was covered with cloth, allowing exchange of water, solutes, and small particles, including microorganisms, and was seeded with 100 L1s of a single form (M or S) or by a mixture of 50:50 of M and S forms. Emergence success of both forms in puddles and quarries was three-fold higher than in the rice fields. The emergence rate of the S form was higher than that of the M form in both habitats, but the form x habitat interaction was not significant. In temporary larval sites such as puddles, emergence success of the M form was lower in mixed cages than in single form cages, whereas the reverse was true for the S form, suggesting competition between the forms. The median developmental time was not significantly different between forms. Although these findings demonstrate differences between forms, they do not suggest that their spatial segregation is determined by differences in their exploitation of the physical and chemical conditions in these environments. These results should be regarded with caution because small numbers of first stage larvae could pass through the cloth of the cages.
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Affiliation(s)
- Abdoulaye Diabaté
- IRSS Centre Muraz, Laboratoire de Parasitologie Entomologie BP 390 Bobo Dioulasso, Burkina Faso
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Abstract
Emerging species within the primary malaria vector Anopheles gambiae show different ecological preferences and significant prezygotic reproductive isolation. They are defined by fixed sequence differences in X-linked rDNA, but most previous studies have failed to detect large and significant differentiation between these taxa elsewhere in the genome, except at two other loci on the X chromosome near the rDNA locus. Hypothesizing that this pericentromeric region of the X chromosome may be accumulating differences faster than other regions of the genome, we explored the pattern and extent of differentiation between A. gambiae incipient species and a sibling species, A. arabiensis, from Burkina Faso, West Africa, at 17 microsatellite loci spanning the X chromosome. Interspecific differentiation was large and significant across the entire X chromosome. Among A. gambiae incipient species, we found some of the highest levels of differentiation recorded in a large region including eight independent loci near the centromere of the X chromosome. Outside of this region, no significant differentiation was detected. This pattern suggests that selection is playing a role in the emergence of A. gambiae incipient species. This process, associated with efficient exploitation of anthropogenic modifications to the environment, has public health implications as it fosters the spread of malaria transmission both spatially and temporally.
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Affiliation(s)
- Aram D Stump
- Center for Tropical Disease Research and Training, Department of Biological Sciences, University of Notre Dame, Indiana 46556, USA.
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Tripet F, Dolo G, Lanzaro GC. Multilevel analyses of genetic differentiation in Anopheles gambiae s.s. reveal patterns of gene flow important for malaria-fighting mosquito projects. Genetics 2005; 169:313-24. [PMID: 15677750 PMCID: PMC1448890 DOI: 10.1534/genetics.104.026534] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2004] [Accepted: 07/09/2004] [Indexed: 11/18/2022] Open
Abstract
Malaria control projects based on the introduction and spread of transgenes into mosquito populations depend on the extent of isolation between those populations. On the basis of the distribution of paracentric inversions, Anopheles gambiae has been subdivided into five subspecific chromosomal forms. Estimating gene flow between and within these forms of An. gambiae presents a number of challenges. We compared patterns of genetic divergence (F(ST)) between sympatric populations of the Bamako and Mopti forms at five sites. We used microsatellite loci within the j inversion on chromosome 2, which is fixed in the Bamako form but absent in the Mopti form, and microsatellites on chromosome 3, a region void of inversions. Estimates of genetic diversity and F(ST)'s suggest genetic exchanges between forms for the third chromosome but little for the j inversion. These results suggest a role for the inversion in speciation. Extensive gene flow within forms among sites resulted in populations clustering according to form despite substantial gene flow between forms. These patterns underscore the low levels of current gene flow between chromosomal forms in this area of sympatry. Introducing refractoriness genes in areas of the genome void of inversions may facilitate their spread within forms but their passage between forms may prove more difficult than previously thought.
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Affiliation(s)
- Frédéric Tripet
- Vector Genetics Lab, Department of Entomology, University of California, Davis, California 95616, USA.
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Slotman M, della Torre A, Powell JR. FEMALE STERILITY IN HYBRIDS BETWEEN ANOPHELES GAMBIAE AND A. ARABIENSIS, AND THE CAUSES OF HALDANE'S RULE. Evolution 2005. [DOI: 10.1554/04-640] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Van Bortel W, Trung HD, Roelants P, Backeljau T, Coosemans M. Population genetic structure of the malaria vector Anopheles minimus A in Vietnam. Heredity (Edinb) 2004; 91:487-93. [PMID: 14576742 DOI: 10.1038/sj.hdy.6800313] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Anopheles minimus A, a major malaria vector in Southeast Asia, is the main target of vector control in this area. The impact of these control measures can be influenced by the population structure of the target species. In rural areas, An. minimus breeds along the banks of small clear-water streams, yet in the suburbs of Hanoi, northern Vietnam, there is an An. minimus population whose immature stages develop in water tanks. This study uses allozyme data (1) to assess the population structure of An. minimus A and (2) to evaluate the taxonomic status of the urban An. minimus population from Hanoi. The population from the suburbs of Hanoi was identified as An. minimus A. Although significant genetic differentiation was observed between rural and urban An. minimus A populations, they have not differentiated substantially by genetic drift. Limited macrogeographical differentiation was observed between two rural populations at distances of more than 1000 km. Consequently, geographical distance is not the primary factor in differentiating An. minimus A populations having the typical breeding ecology. The estimated effective population size is consistent with the moderate macrogeographical differentiation. Furthermore, no genetic structuring was observed between adult mosquitoes having different behaviour. The macrogeographical population structure indicates that genes may spread over large areas, whereas the presence of an 'urban' An. minimus A population shows the ability of this species to adapt to anthropogenic environmental changes.
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Affiliation(s)
- W Van Bortel
- Department of Parasitology, Prince Leopold Institute of Tropical Medicine, Nationalestraat 155, B-2000 Antwerpen, Belgium.
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Besansky NJ, Krzywinski J, Lehmann T, Simard F, Kern M, Mukabayire O, Fontenille D, Touré Y, Sagnon N. Semipermeable species boundaries between Anopheles gambiae and Anopheles arabiensis: evidence from multilocus DNA sequence variation. Proc Natl Acad Sci U S A 2003; 100:10818-23. [PMID: 12947038 PMCID: PMC196886 DOI: 10.1073/pnas.1434337100] [Citation(s) in RCA: 164] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2003] [Indexed: 11/18/2022] Open
Abstract
Attempts to reconstruct the phylogenetic history of the Anopheles gambiae cryptic species complex have yielded strongly conflicting results. In particular, An. gambiae, the primary African malaria vector, is variously placed as a sister taxon to either Anopheles arabiensis or Anopheles merus. The recent divergence times for members of this complex complicate phylogenetic analysis, making it difficult to unambiguously implicate interspecific gene flow, versus retained ancestral polymorphism, as the source of conflict. Using sequences at four unlinked loci, which were determined from multiple specimens within each of five species in the complex, we found contrasting patterns of sequence divergence between the X chromosome and the autosomes. The isolation model of speciation assumes a lack of gene flow between species since their separation. This model could not be rejected for An. gambiae and An. arabiensis, although the data fit the model poorly. On the other hand, evidence from gene trees supports genetic introgression of chromosome 2 inversions between An. gambiae and An. arabiensis, and also points to more broad scale genetic exchange of autosomal sequences between this species pair. That such exchange has been relatively recent is suggested not only by the lack of fixed differences at three autosomal loci but also by the sharing of full haplotypes at two of the three loci, which is in contrast to several fixed differences and considerably deeper divergence on the X. The proposed acquisition by An. gambiae of sequences from the more arid-adapted An. arabiensis may have contributed to the spread and ecological dominance of this malaria vector.
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Affiliation(s)
- N J Besansky
- University of Notre Dame, Center for Tropical Disease Research and Training, Department of Biological Sciences, Notre Dame, IN 46556, USA.
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Abstract
Human malaria is truly a disease of global proportions and is one of the most broadly distributed vector-borne infections. Anopheline mosquitoes are the exclusive vectors of human malaria. A handful of species predominate as the most notorious malaria vectors, but the species and forms involved in the transmission of human malaria world-wide are incredibly diverse. Many of the anophelines that vector malaria exist as members of species complexes that often contain vector and non-vector species. Additionally, single anopheline species often exhibit significant heterogeneity across the species' range. This phenotypic and genotypic plasticity exacerbates the difficulties in identification of vector populations and implementation of effective surveillance and control strategies. Polytene chromosome investigations were among the first to provide researchers with tangible genetic markers that could be used to differentiate between what are now recognised as species and chromosomal forms of anopheline mosquitoes. The advent of the polymerase chain reaction gave access to the molecular genetics of genomes and the techniques that followed have facilitated investigation of the genetics of individual specimens or population size samples. The variety and number of genetic markers available for the study of malaria vectors has literally exploded in the last 10 years. Markers have expanded from the 'traditional tools' to include a vast array of molecular markers. Contemporary markers range from what are now referred to as 'classical genetic markers' to methods used to detect and identify single nucleotide polymorphisms and finally to highly polymorphic markers. One of the greatest advantages of this wide variety of genetic markers is that researchers may choose to utilise any combination of markers or techniques to address multifaceted questions relating to malaria transmission. These molecular markers have proven useful in a wide variety of applications including molecular taxonomy, evolutionary systematics, population genetics, genetic mapping, and investigation of defined phenotypes.
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Affiliation(s)
- Douglas E Norris
- W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Johns Hopkins Malaria Research Institute, Baltimore, MD 21205, USA.
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Leo NP, Barker SC. Intragenomic variation in ITS2 rDNA in the louse of humans, Pediculus humanus: ITS2 is not a suitable marker for population studies in this species. Insect Mol Biol 2002; 11:651-657. [PMID: 12421423 DOI: 10.1046/j.1365-2583.2002.00367.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The two internal transcribed spacers (ITS) of ribosomal DNA are often used as markers of populations of insects. We studied the ITS2 of the head lice and body lice of humans, to determine whether this gene is a suitable marker of populations of these insects. ITS2 sequences were amplified by PCR from lice from four different countries: Australia, China, Japan and the USA. Direct cycle-sequencing of some of these PCR products gave equivocal nucleotide chromatograms. This indicated that some lice had more than one ITS2 sequence, so we cloned PCR products from these lice. Temperature gradient gel electrophoresis (TGGE) revealed that 50 of the 67 clones we screened had different nucleotide sequences. All lice had several ITS2 types, including those with unequivocal chromatograms. A phylogenetic tree of 15 different ITS2 sequences showed that the sequences from individual lice were not monophyletic. We conclude that the ITS2 is not a useful marker of populations for Pediculus humanus.
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Affiliation(s)
- N P Leo
- Department of Microbiology and Parasitology, University of Queensland, Brisbane 4072, Queensland,
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Abstract
Restrictions to gene flow among molecular forms of the mosquito Anopheles gambiae sensu stricto reveal an ongoing speciation process affecting the epidemiology of malaria in sub-Saharan Africa.
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Affiliation(s)
- A della Torre
- Parasitology Unit, Department of Public Health, University of Rome "La Sapienza," P.le Aldo Moro 5, 00185 Rome, Italy.
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Gentile G, Della Torre A, Maegga B, Powell JR, Caccone A. Genetic differentiation in the African malaria vector, Anopheles gambiae s.s., and the problem of taxonomic status. Genetics 2002; 161:1561-78. [PMID: 12196401 PMCID: PMC1462204 DOI: 10.1093/genetics/161.4.1561] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Of the seven recognized species of the Anopheles gambiae complex, A. gambiae s.s. is the most widespread and most important vector of malaria. It is becoming clear that, in parts of West Africa, this nominal species is not a single panmictic unit. We found that the internal transcribed spacer (ITS) of the X-linked rDNA has two distinct sequences with three fixed nucleotide differences; we detected no heterozygotes at these three sites, even in areas of sympatry of the two ITS types. The intergenic spacer (IGS) of this region also displays two distinct sequences that are in almost complete linkage disequilibrium with the distinct ITS alleles. We have designated these two types as S/type I and M/type II. These rDNA types correspond at least partly to the previously recognized chromosomal forms. Here we expand the geographic range of sampling to 251 individuals from 38 populations. Outside of West Africa, a single rDNA type, S/type I, corresponds to the Savanna chromosomal form. In West Africa, both types are often found in a single local sample. To understand if these findings might be due to unusual behavior of the rDNA region, we sequenced the same region for 46 A. arabiensis, a sympatric sibling species. No such distinct discontinuity was observed for this species. Autosomal inversions in one chromosome arm (2R), an insecticide resistance gene on 2L, and this single X-linked region indicate at least two genetically differentiated subpopulations of A. gambiae. Yet, rather extensive studies of other regions of the genome have failed to reveal genetic discontinuity. Evidently, incomplete genetic isolation exists within this single nominal species.
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Affiliation(s)
- Gabriele Gentile
- Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520-8106, USA
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Thomasova D, Ton LQ, Copley RR, Zdobnov EM, Wang X, Hong YS, Sim C, Bork P, Kafatos FC, Collins FH. Comparative genomic analysis in the region of a major Plasmodium-refractoriness locus of Anopheles gambiae. Proc Natl Acad Sci U S A 2002; 99:8179-84. [PMID: 12060762 PMCID: PMC123041 DOI: 10.1073/pnas.082235599] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have sequenced six overlapping clones from a library of bacterial artificial chromosome (BAC) clones derived from a laboratory strain of the mosquito, Anopheles gambiae, the major vector of human malaria in Africa. The resulting uninterrupted 528-kb sequence is from the 8C region of the mosquito 2R chromosome, at or very near the major refractoriness locus associated with melanotic encapsulation of parasites. This sequence represents the first extensive view of the mosquito genome structure encompassing 48 genes. Genomic comparison reveals that the majority of the orthologues are found in six microsyntenic clusters in Drosophila melanogaster. A BAC clone that is wholly contained within this region demonstrates the existence of a remarkable degree of local polymorphism in this species, which may prove important for its population structure and vectorial capacity.
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Affiliation(s)
- Dana Thomasova
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
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Abstract
The century-old discovery of the role of Anopheles in human malaria transmission precipitated intense study of this genus at the alpha taxonomy level, but until recently little attention was focused on the systematics of this group. The application of molecular approaches to systematic problems ranging from subgeneric relationships to relationships at and below the species level is helping to address questions such as anopheline phylogenetics and biogeography, the nature of species boundaries, and the forces that have structured genetic variation within species. Current knowledge in these areas is reviewed, with an emphasis on the Anopheles gambiae model. The recent publication of the genome of this anopheline mosquito will have a profound impact on inquiries at all taxonomic levels, supplying better tools for estimating phylogeny and population structure in the short term, and ultimately allowing the identification of genes and/or regulatory networks underlying ecological differentiation, speciation, and vectorial capacity.
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Affiliation(s)
- Jaroslaw Krzywinski
- Department of Biological Sciences, Center for Tropical Disease Research and Training, University of Notre Dame, Notre Dame, Indiana 46556, USA.
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Wondji C, Simard F, Fontenille D. Evidence for genetic differentiation between the molecular forms M and S within the Forest chromosomal form of Anopheles gambiae in an area of sympatry. Insect Mol Biol 2002; 11:11-19. [PMID: 11841498 DOI: 10.1046/j.0962-1075.2001.00306.x] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We studied genetic variation at ten microsatellite DNA loci in Anopheles gambiae populations from the Forest chromosomal form collected in four villages in Cameroon (Central Africa). Both recently described M and S molecular forms occur in sympatry in this area. Geographic differentiation within form was low (Fst < 0.017) despite geographical distance between collection sites ranging from 35 to 350 km. However, higher (Fst > 0.035) and statistically significant levels of genetic differentiation were observed between forms, being the highest between sympatric M and S populations collected within the same village. Results were consistent across all loci spread throughout the genome, therefore reflecting a genome-wide pattern. Considering previous findings of strong assortative mating within forms and general lack of hybrids in areas of sympatry, we propose that there is now sufficient direct and indirect evidence to consider both M and S molecular forms of An. gambiae as distinct species that have probably speciated recently.
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Affiliation(s)
- C Wondji
- Laboratoire de l'Institut de Recherche pour le Développement (IRD), Organisation de Coordination pour la Lutte Contre les Endémies en Afrique Centrale (OCEAC), Yaoundé, Cameroun
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Abstract
Gene flow was investigated in Anopheles gambiae from eight localities that span the ecological zones of Nigeria (arid savanna zones in the north gradually turn into humid forest zones in the south). Genetic differentiation was measured over 10 microsatellite loci and, to determine any effects of selection, five loci were located within chromosome inversions and the other five were outside inversions. Over all loci, the largest estimates of differentiation were in comparisons between localities in the savanna vs. forest zones (range FST 0.024-0.087, Nm 2.6-10.1; RST 0.014-0.100, Nm 2.2-16.4). However, three loci located within inversions on chromosome II, whose frequencies varied clinically from north to south, were responsible for virtually all of the differentiation. When the three loci were removed, genetic distances across the remaining seven loci were markedly reduced even between localities in the forest and savanna zones (range FST 0.001-0.019, Nm 12.7-226.1) or no longer significant (P > 0.05) in the case of RST. Although tests of isolation by distance gave seemingly equivocal results, geographical distance does not appear to limit gene flow. These observations suggest that gene flow is extensive across the country but that selection on genes located within some inversions on chromosome II counters the homogenizing effects of gene flow.
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Affiliation(s)
- D Y Onyabe
- Department of Biology, The University of Vermont, 321 Marsh Life Science Building, Burlington, VT 05405, USA
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Wang R, Zheng L, Touré YT, Dandekar T, Kafatos FC. When genetic distance matters: measuring genetic differentiation at microsatellite loci in whole-genome scans of recent and incipient mosquito species. Proc Natl Acad Sci U S A 2001; 98:10769-74. [PMID: 11553812 PMCID: PMC58550 DOI: 10.1073/pnas.191003598] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Genetic distance measurements are an important tool to differentiate field populations of disease vectors such as the mosquito vectors of malaria. Here, we have measured the genetic differentiation between Anopheles arabiensis and Anopheles gambiae, as well as between proposed emerging species of the latter taxon, in whole genome scans by using 23-25 microsatellite loci. In doing so, we have reviewed and evaluated the advantages and disadvantages of standard parameters of genetic distance, F(ST), R(ST), (delta mu)(2), and D. Further, we have introduced new parameters, D' and D(K), which have well defined statistical significance tests and complement the standard parameters to advantage. D' is a modification of D, whereas D(K) is a measure of covariance based on Pearson's correlation coefficient. We find that A. gambiae and A. arabiensis are closely related at most autosomal loci but appear to be distantly related on the basis of X-linked chromosomal loci within the chromosomal Xag inversion. The M and S molecular forms of A. gambiae are practically indistinguishable but differ significantly at two microsatellite loci from the proximal region of the X, outside the Xag inversion. At one of these loci, both M and S molecular forms differ significantly from A. arabiensis, but remarkably, at the other locus, A. arabiensis is indistinguishable from the M molecular form of A. gambiae. These data support the recent proposal of genetically differentiated M and S molecular forms of A. gambiae.
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Affiliation(s)
- R Wang
- European Molecular Biology Laboratory, Meyerhofstrasse 1, 69012 Heidelberg, Germany
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Tripet F, Touré YT, Taylor CE, Norris DE, Dolo G, Lanzaro GC. DNA analysis of transferred sperm reveals significant levels of gene flow between molecular forms of Anopheles gambiae. Mol Ecol 2001; 10:1725-32. [PMID: 11472539 DOI: 10.1046/j.0962-1083.2001.01301.x] [Citation(s) in RCA: 148] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Anopheles gambiae populations in west Africa are complex, being composed of multiple, sympatric subpopulations. Recent studies have failed to reveal significant genetic differences among subpopulations, stimulating a debate regarding the levels of gene flow among them. The observed homogeneity may be the consequence of substantial contemporary gene flow or it may be that reproductive isolation is complete, but too recent for the accumulation of significant levels of genic divergence. Here, we report the results of a study estimating contemporary levels of gene flow between An. gambiae subpopulations by analysing females and transferred sperm removed from their reproductive systems. A total of 251 female and associated sperm extracts was analysed from a single site in Mali. Two molecular forms of An. gambiae, the M- and S-forms, occurred in sympatry at this site. Overall, we found very strong positive assortative mating within forms, however, we did observe significant hybridization between forms. In the M subpopulation 2/195 females (1.03%) contained sperm from S-form males and in 55 S-form females we found one female containing M-form sperm (1.82%). We also identified a mated M xS hybrid adult female. From mating frequencies, we estimate the Nem between the M- and S-form at 16.8, and from the adult hybrid frequency at 5.6. These values are consistent with our earlier estimate, based on FST for 21 microsatellite loci in which Nem = 5.8. We conclude that the general lack of genetic divergence between the M and S subpopulations of An. gambiae can be explained entirely by contemporary gene flow.
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Affiliation(s)
- F Tripet
- Department of Pathology and Center for Tropical Diseases, University of Texas Medical Branch, Galveston, TX 77555-0609, USA
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Abstract
Analyses of inversions in polytene chromosomes indicate that, in West Africa, Anopheles gambiae (sensu stricto) may be a complex of more than a single taxonomic unit, and these units have been called chromosomal forms. In order to determine whether this genetic discontinuity extends to the rest of the genome, as would be expected if reproductive isolation exists, we have sequenced several regions of both the nuclear and mitochondrial genomes. With one exception, we were unable to identify any nucleotide sites that differentiate the chromosomal forms. The exception was the internal transcribed spacer (ITS) of the ribosomal DNA (rDNA). Three sites in this region distinguish Mopti chromosomal form from Savanna and Bamako in Mali and Burkina Faso. However, outside these two countries, the association between chromosomal form and rDNA type does not always hold. Together with the variants in the rDNA intergenic spacer (IGS) described in the accompanying papers (della Torre et al., 2001; Favia et al., 2001), we can recognize two major types of rDNA, Type I and Type II (corresponding to molecular forms S and M in della Torre et al., 2001). Type I is widespread in West Africa and is the only type found outside of West Africa (i.e. Tanzania and Madagascar). Type II is confined to West Africa. We were unable to detect any heterozygosity for the ITS types even in five collections containing both types. A sample from the island of São Tomé could not be classified into either Type I or Type II as the rDNA had characteristics of both. In general, our results confirm that An. gambiae is not a single pan-mictic unit, but exactly how to define any new taxa remains problematic. Finally, we have found minor variants of the major rDNA types fixed in local populations; contrary to most previous studies, this suggests restricted gene flow among populations of this species.
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Affiliation(s)
- G Gentile
- Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect St., New Haven, CT 06520-8106, USA
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della Torre A, Fanello C, Akogbeto M, Dossou-yovo J, Favia G, Petrarca V, Coluzzi M. Molecular evidence of incipient speciation within Anopheles gambiae s.s. in West Africa. Insect Mol Biol 2001; 10:9-18. [PMID: 11240632 DOI: 10.1046/j.1365-2583.2001.00235.x] [Citation(s) in RCA: 235] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
We karyotyped and identified by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) analysis Anopheles gambiae s.s. samples collected in several African countries. The data show the existence of two non-panmictic molecular forms, named S and M, whose distribution extended from forest to savannahs. Mosquitoes of the S and M forms are homosequential standard for chromosome-2 inversions in forest areas. In dry savannahs, S is characterized mainly by inversion polymorphisms typical of Savanna and Bamako chromosomal forms, while M shows chromosome-2 arrangements typical of Mopti and/or Savanna and/or Bissau, depending on its geographical origin. Chromosome-2 inversions therefore seem to be involved in ecotypic adaptation rather than in mate-recognition systems. Strong support for the reproductive isolation of S and M in Ivory Coast comes from the observation that the kdr allele is found at high frequencies in S specimens and not at all in chromosomal identical M specimens. However, the kdr allele does not segregate with molecular forms in Benin.
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Affiliation(s)
- A della Torre
- Istituto di Parassitologia, Fondazione Pasteur - Cenci Bolognetti, Università di Roma La Sapienza, Piazzale Aldo Moro 5, 00185, Rome, Italy.
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Black WC, Lanzaro GC. Distribution of genetic variation among chromosomal forms of Anopheles gambiae s.s: introgressive hybridization, adaptive inversions, or recent reproductive isolation? Insect Mol Biol 2001; 10:3-7. [PMID: 11240631 DOI: 10.1046/j.1365-2583.2001.00234.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
A series of four papers in this issue explores the reproductive status of the five chromosomal forms of An. gambiae s.s. using molecular techniques to examine the variation among twelve different genes located throughout the An. gambiae s.s. genome. Results of these and previous studies are consistent with a hypothesis of at least partial barriers to gene flow between some chromosomal forms in the Ivory Coast and other West African countries to the north and west, but introgression between S and M types in Benin and countries to the east. Collectively, these studies indicate the need for a broader geographical sampling of An. gambiae s.s., increased research on mechanisms of prezygotic reproductive isolation and field-based studies of survival and fecundity in hybrids to test for postzygotic reproductive isolation.
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Affiliation(s)
- W C Black
- Department of Microbiology, Colorado State University, Fort Collins, CO 80523-1677, USA.
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