Molecular identification of sympatric chromosomal forms of Anopheles gambiae and further evidence of their reproductive isolation

Abstract

Three chromosomal forms of Anopheles gambiae s.s., designated as Bamako, Mopti and Savanna, were studied for diagnostic PCR assays based on the analysis of the X-linked ribosomal DNA (rDNA). The study was performed on a 1.3 kb fragment containing part of the 28S coding region and part of the intergenic spacer region. The amplified material was cut with fourteen restriction enzymes to detect Restriction Fragment Length Polymorphisms (RFLPs). The enzymes Tru9I and HhaI produced patterns of DNA bands which differentiated Mopti from Savanna and Bamako; moreover, a distinct 'hybrid' pattern was recognized in the F1 female progeny from the cross of Mopti with either one of the other two chromosomal forms. The diagnostic significance of the PCR-RFLP assay was verified on 203 karyotyped females from field samples collected in two villages in Mali and one village in Burkina Faso. Agreement was observed between the chromosomal and the molecular identifications. No 'hybrid' molecular patterns were detected even among carriers of rare heterokaryotypes hypothetically produced by crosses between Mopti and Savanna. The results confirm previous observations indicating barriers to gene flow within An. gambiae s.s. and supporting the specific status of the taxonomic units proposed on cytogenetic ground.

The role of agricultural use of insecticides in resistance to pyrethroids in Anopheles gambiae s.l. in Burkina Faso.

“…In tropical areas, the molecular study of natural populations support the stability of genetic differentiation and the existence of effective isolation barriers, presumably acting at the premating level. 17,19 However, in southern Benin, the kdr mutation was recently detected in the M population. 20,21 The low genetic diversity in the sodium channel introns of the resistant M and S mosquitoes suggests that a genetic sweep has occurred through an introgression from the S form.…”

“…11 Anopheles gambiae s.s. mosquitoes were identified as being the M or S form by polymerase chain reaction-restriction fragment length polymorphism. 17 …”

Revisiting the role of introgression vs shared ancestral polymorphisms as key processes shaping genetic diversity in the recently separated sibling species of the Anopheles gambiae complex

“…Recent work suggests that there are two forms of uncertain taxonomic status within A. gambiae, which may be characterised by their rDNA molecular type (Favia et al, 1997;Wondji et al, 2002). All the samples used in this study are the S rDNA type except samples from Senegal and Ghana, which are from populations that only exhibit the M form and the sample from Sao Tome and Principe which is also M form (Pinto et al, 2003).…”

When genetic distance matters: Measuring genetic differentiation at microsatellite loci in whole-genome scans of recent and incipient mosquito species

“…Furthermore, even within A. gambiae s.s., cytologically defined chromosomal forms (e.g., Mopti, Savanna, and Bamako) are reproductively isolated in the northern dry areas of West Africa, including Mali and Burkina Faso, and may represent emerging species with different disease transmission characteristics (5,6). Although many DNA regions have been recently analyzed to examine genetic differentiation within A. gambiae s.s, the only fixed molecular differences found so far that consistently discriminate chromosomal forms are in the X-linked ribosomal (r)DNA region (1)(2)(3)(4)7). In Mali and Burkina Faso, these markers distinguish Mopti from Savanna and Bamako chromosomal forms; however, when the analysis is extended to additional populations in West Africa, two nonpanmictic units are identified even in the absence of chromosomal differentiation.…”