download report - Istituto Pasteur

Della Torre - Petrarca - Bionomical, genetical and molecular characterization of populations of the Anopheles gambiae complex
Furthermore, we analysed a database of all A. gambiae
s.s. karyotyped by the group in the last 30 years, to
evaluate evolutionary patterns based on rare chromosomal
inversions (RCIs), which were recorded but not
specifically analysed so far. Among >7,300 females
from 16 Afrotropical countries, 82 RCIs were recorded
in 160 specimens: 23% were found repeatedly, in
the same sample and/or at the same sampling location
across different years and/or in different sampling
locations, while the others only once in single
specimens. The analysis of breakpoint distribution of
RCIs showed that these, like common inversions, are
disproportionately clustered on 2R, which may indicate
that this chromosomal arm is especially prone to
breakages. However, RCIs were equally frequent
across biomes and on both sides of the Great Rift
Valley (GRV), whereas common inversions predominated
in arid ecological settings and west of the GRV.
We propose that RCIs are subject mainly to drift
under unperturbed ecological conditions, but may
represent an important reservoir of genetic variation
for A. gambiae in response to environmental changes.
Molecular karyotyping of chromosomal
inversions in A. gambiae
We developed 2 PCR-based approaches allowing the
identification of the alternative arrangements of 2La
and 2Rj polymorphic inversions of A. gambiae s.s. The
first method was validated on 765 specimens sampled
across Africa and was shown to be specific and efficient,
thus providing groundwork for future studies
on the non-random distribution of 2La-carriers. The
second method was validated on >700 field specimens:
it was shown to be robust and accurate on 2R+ j and
2Rj homozygotes, thus providing the first molecular
approach for the rapid identification of the BAMAKO
form across developmental stages and sexes, opening
new perspectives for studies on the bionomics of this
A. gambiae chromosomal form.
Molecular characterization of A. gambiae
molecular forms
We analysed the insertion polymorphism of a nearly
200 bp-long SINE (SINE200) within genome areas
of high differentiation (i.e. “speciation islands”) of M
and S A. gambiae molecular forms. SINEs (Short
INterspersed Elements) are homoplasy-free and codominant
genetic markers which represent useful
tools for population genetic studies. Eight loci were
successfully amplified and found to be specific for A.
gambiae s.s.: 5 on chromosome 2L and one on Xchromosome
turned out to be monomorphic, while
two loci were found to be polymorphic. 1) S200
128
2R12D was homozygote for the insertion in most Sform
samples, while intermediate levels of polymorphisms
were shown in M-form, resulting in an overall
high degree of genetic differentiation between
molecular forms (Fst=0.46, P