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Clare D. Marsden,
Anthony Cornel,
Yoosook Lee,
Michelle R. Sanford,
Laura C. Norris,
Parker B. Goodell,
Catelyn C. Nieman,
Sarah Han,
Amabelia Rodrigues,
Joao Denis,
Ahmed Ouledi,
Gregory C. Lanzaro
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Clare D. Marsden,
Anthony Cornel,
Yoosook Lee,
Michelle R. Sanford,
Laura C. Norris,
Parker B. Goodell,
Catelyn C. Nieman,
Sarah Han,
Amabelia Rodrigues,
Joao Denis,
Ahmed Ouledi,
Gregory C. Lanzaro
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ABSTRACT: Considerable technological advances have been made towards the generation of genetically modified mosquitoes for vector control. In contrast, less progress has been made towards field evaluations of transformed mosquitoes which are critical for evaluating the success of, and hazards associated with, genetic modification. Oceanic islands have been highlighted as potentially the best locations for such trials. However, population genetic studies are necessary to verify isolation. Here, we used a panel of genetic markers to assess for evidence of genetic isolation of two oceanic island populations of the African malaria vector, Anopheles gambiae s.s. We found no evidence of isolation between the Bijagós archipelago and mainland Guinea-Bissau, despite separation by distances beyond the known dispersal capabilities of this taxon. Conversely, the Comoros Islands appear to be genetically isolated from the East African mainland, and thus represent a location worthy of further investigation for field trials. Based on assessments of gene flow within and between the Comoros islands, the island of Grande Comore was found to be genetically isolated from adjacent islands and also exhibited local population structure, indicating that it may be the most suitable site for trials with existing genetic modification technologies.
Evolutionary Applications 02/2013; · 4.92 Impact Factor
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ABSTRACT: The African malaria vector, Anopheles gambiae, is characterized by multiple polymorphic chromosomal inversions and has become widely studied as a system for exploring models of speciation. Near complete reproductive isolation between different inversion types, known as chromosomal forms, has led to the suggestion that A. gambiae is in early stages of speciation, with divergence evolving in the face of considerable gene flow. We compared the standard chromosomal arrangement (Savanna form) with genomes homozygous for j, b, c, and u inversions (Bamako form) in order to identify regions of genomic divergence with respect to inversion polymorphism. We found levels of divergence between the two sub-taxa within some of these inversions (2Rj and 2Rb), but at a level lower than expected and confined near the inversion breakpoints, consistent with a gene flux model. Unexpectedly, we found that the majority of diverged regions were located on the X chromosome, which contained half of all significantly diverged regions, with much of this divergence located within exons. This is surprising given that the Bamako and Savanna chromosomal forms are both within the S molecular form that is defined by a locus near centromere of X chromosome. Two X-linked genes (a heat shock protein and P450 encoding genes) involved in reproductive isolation between the M and S molecular forms of A. gambiae were also significantly diverged between the two chromosomal forms. These results suggest that genes mediating reproductive isolation are likely located on the X chromosome, as is thought to be the case for the M and S molecular forms. We conclude that genes located on the sex chromosome may be the major force driving speciation between these chromosomal forms of A. gambiae.
PLoS ONE 01/2013; 8(3):e57887. · 4.09 Impact Factor
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Clare D Marsden,
Rosie Woodroffe,
Michael G L Mills,
J Weldon McNutt,
Scott Creel,
Rosemary Groom,
Masenga Emmanuel,
Sarah Cleaveland,
Pieter Kat,
Gregory S A Rasmussen,
Joshua Ginsberg,
Robin Lines,
Jean-Marc André,
Colleen Begg,
Robert K Wayne,
Barbara K Mable
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ABSTRACT: Deciphering patterns of genetic variation within a species is essential for understanding population structure, local adaptation and differences in diversity between populations. Whilst neutrally evolving genetic markers can be used to elucidate demographic processes and genetic structure, they are not subject to selection and therefore are not informative about patterns of adaptive variation. As such, assessments of pertinent adaptive loci, such as the immunity genes of the major histocompatibility complex (MHC), are increasingly being incorporated into genetic studies. In this study, we combined neutral (microsatellite, mtDNA) and adaptive (MHC class II DLA-DRB1 locus) markers to elucidate the factors influencing patterns of genetic variation in the African wild dog (Lycaon pictus); an endangered canid that has suffered extensive declines in distribution and abundance. Our genetic analyses found all extant wild dog populations to be relatively small (N(e) < 30). Furthermore, through coalescent modelling, we detected a genetic signature of a recent and substantial demographic decline, which correlates with human expansion, but contrasts with findings in some other African mammals. We found strong structuring of wild dog populations, indicating the negative influence of extensive habitat fragmentation and loss of gene flow between habitat patches. Across populations, we found that the spatial and temporal structure of microsatellite diversity and MHC diversity were correlated and strongly influenced by demographic stability and population size, indicating the effects of genetic drift in these small populations. Despite this correlation, we detected signatures of selection at the MHC, implying that selection has not been completely overwhelmed by genetic drift.
Molecular Ecology 03/2012; 21(6):1379-93. · 5.52 Impact Factor
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ABSTRACT: The suggestion that genetic divergence can arise and/or be maintained in the face of gene flow has been contentious since first proposed. This controversy and a rarity of good examples have limited our understanding of this process. Partially reproductively isolated taxa have been highlighted as offering unique opportunities for identifying the mechanisms underlying divergence with gene flow. The African malaria vector, Anopheles gambiae s.s., is widely regarded as consisting of two sympatric forms, thought by many to represent incipient species, the M and S molecular forms. However, there has been much debate about the extent of reproductive isolation between M and S, with one view positing that divergence may have arisen and is being maintained in the presence of gene flow, and the other proposing a more advanced speciation process with little realized gene flow because of low hybrid fitness. These hypotheses have been difficult to address because hybrids are typically rare (<1%). Here, we assess samples from an area of high hybridization and demonstrate that hybrids are fit and responsible for extensive introgression. Nonetheless, we show that strong divergent selection at a subset of loci combined with highly asymmetric introgression has enabled M and S to remain genetically differentiated despite extensive gene flow. We propose that the extent of reproductive isolation between M and S varies across West Africa resulting in a 'geographic mosaic of reproductive isolation'; a finding which adds further complexity to our understanding of divergence in this taxon and which has considerable implications for transgenic control strategies.
Molecular Ecology 11/2011; 20(23):4983-94. · 5.52 Impact Factor
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ABSTRACT: The M and S molecular forms of Anopheles gambiae s.s. have been considered incipient species for more than ten years, yet the mechanism underlying assortative mating of these incipient species has remained elusive. The discovery of the importance of harmonic convergence of wing beat frequency in mosquito mating and its relation to wing size have laid the foundation for exploring phenotypic divergence in wing size of wild populations of the two forms. In this study, wings from field collected mosquitoes were measured for wing length and wing width from two parts of the sympatric distribution, which differ with respect to the strength of assortative mating. In Mali, where assortative mating is strong, as evidenced by low rates of hybridization, mean wing lengths and wing widths were significantly larger than those from Guinea-Bissau. In addition, mean wing widths in Mali were significantly different between molecular forms. In Guinea-Bissau, assortative mating appears comparatively reduced and wing lengths and widths did not differ significantly between molecular forms. The data presented in this study support the hypothesis that wing beat frequency may mediate assortative mating in the incipient species of A. gambiae and represent the first documentation of a morphological difference between the M and S molecular forms.
PLoS ONE 01/2011; 6(11):e27920. · 4.09 Impact Factor
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ABSTRACT: The major histocompatibility complex (MHC) is a set of highly polymorphic genes involved in the immune response. Extensive research on the canid MHC has found moderate-to-high levels of diversity at the DLA-DRB1, DLA-DRA, DLA-DQA1, and DLA-DQB1 class II loci with frequent transspecific polymorphism among Canis species. In this study, we assessed MHC variation in the more distantly related and highly endangered African wild dog (Lycaon pictus). We screened 168 African wild dogs from Eastern and Southern Africa as well as 200 samples from the European captive population for variation at MHC class II loci. As for all other canids screened to date, we found a single allele at DLA-DRA, which was the same as that found in Canis species. In contrast, we found 17 DLA-DRB1 alleles, one DLA-DQA1 allele, and two DLA-DQB1 alleles, all of which were unique to African wild dogs. At DLA-DRB1, African wild dogs were found to have comparable numbers of alleles but less overall amino acid variation than other canids. However, the low numbers of alleles at DLA-DQA1 and DLA-DQB1 are surprising, given that in other canids, these loci are also highly variable. Overall, our data suggest that African wild dogs are genetically depauperate at the MHC relative to other canids. These data are indicative of a loss of genetic variation, possibly as a result of population bottlenecks and declines experienced by this species.
The Journal of heredity 07/2009; · 2.05 Impact Factor
