Among the sibling species of the Afrotropical Anopheles gambiae complex, the nominal taxon (An. gambiae s.str.) is the major malaria vector. Its bionomics suggest a man-dependent speciation process which involves, in West Africa, various incipient species chromosomally recognized by different combinations of 2R paracentric inversions. One of the most recent evolutionary steps of such a speciation process appears to be the chromosomal form Mopti, which is associated with dry season irrigation in arid zones, and is characterized by a remarkable ecological flexibility related to three 2R alternative arrangements, namely bc, u and +, whose expected karyotypes are found in Hardy-Weinberg equilibrium. The study of this chromosomal polymorphism in samples from a 16-locality transect in Mali shows wide variations and highly significant correlation with both temporal and spatial climatic differences. Mosquitoes homokaryotypic for 2Rbc are the actual dry season and arid areas breeders. The regular rise of 2Rbc frequency, up to fixation, during each dry season, corresponds to the South-North clinal increase of the same arrangement along the transect, from about 30% in the humid savanna to near fixation in the South-Saharan zone. This coherent ecological genetics case provides full support to the hypothesis of the adaptive nature of paracentric inversions. Moreover, the very peculiar system of combinations of contiguous 2R inversions, utilized by Mopti as well as by other chromosomal forms of An. gambiae, suggests a process of polygenic reorganization based on linkage disequilibria and involving the inversions as driving selection units.

Recent advances have demonstrated that, in the absence of postmating barriers to hybridization, reproductive isolation between different forms of Anopheles gambiae sensu stricto is maintained by strong assortative mating. The forms of An. gambiae s.s. and the sister species An. arabiensis commonly form mixed swarms in which they mate. This raises the question as to how individuals recognize mates of their own species or form within swarms. It has been proposed that wingbeat frequency is used as a cue to discriminate potential mates. This has important implications for prospective genetic control programs. We used a photosensor to record the transient waveforms generated by individuals An. arabiensis and from the M and S molecular forms of An. gambiae s.s. as they flew through a beam of light. We found no significant between-species or between-form differences in the fundamental harmonic--equivalent to wingbeat frequency--either in males or females collected from sympatric populations in Mali, West Africa. However, there were significant differences in the amplitude of the first and third harmonics in females and of the first and second harmonics in males. Whereas these results suggest some morphological or behavioral differences between species and forms, the extensive overlap in the distributions of harmonic amplitudes does not point to them as reliable cues for assortative mating. Combining all waveforms parameters into a discriminant analysis did not yield characteristic scores either for males or females. Thus, our results do not support the wingbeat hypothesis of premating isolation in the An. gambiae complex.

We studied a Malian family with parental consanguinity and two of eight siblings affected with late-childhood-onset progressive myoclonus epilepsy and cognitive decline, consistent with the diagnosis of Lafora disease. Genetic analysis showed a novel homozygous single-nucleotide variant in the NHLRC1 gene, c.560A>C, producing the missense change H187P. The changed amino acid is highly conserved, and the mutation impairs malin's ability to degrade laforin in vitro. Pathological evaluation showed manifestations of Lafora disease in the entire brain, with particularly severe involvement of the pallidum, thalamus, and cerebellum. Our findings document Lafora disease with severe manifestations in the West African population.Electronic supplementary materialThe online version of this article (doi:10.1007/s10048-009-0190-4) contains supplementary material, which is available to authorized users.