Genetic structure and phylogeographic evolution of the West African populations of Sitophilus zeamais (Coleoptera, Curculionidae)

Delimiting populations of a species in space and assessing the degree of connectivity between them are essential steps to the development of management scenarios. Populations more or less spatially isolated and reproductively independent should be considered because local genetic luggage allows adaptation to specific conditions. This is especially true in beetles such as Sitophilus zeamais (Motschulsky, 1855), which have an extraordinary plasticity and potential destruction of stored cereals. The objective of this study was to characterize genetic structure and phylogeographic evolution of S. zeamais populations associated with maize in two biogeographical regions of Africa, using genetic markers (sequencing) associated with Bayesian approaches. Portions of mitochondrial gene were sequenced from individuals sampled in West and Central Africa. A total of 112 (Cytochrome B), 109 (Cytochrome oxidase I) and 99 (concatenated matrix) sequences were used for analysis. An analysis of sequences revealed the presence of 30 haplotypes. The analyses of sequences exhibited a rather high level of polymorphism (Hd = 0.789 ± 0.039; Pi = 0.005 ± 0.001). A high level of haplotype diversity and low nucleotide diversity were observed in West Africa (Hd = 0.922 ± 0.023; π = 0.007.0012). These both parameters were twice lower in Central Africa populations (Hd = 0.512 ± 0.085; π = 0.003 ± 0.001). The results indicated also a genetic structure without phylogeographic pattern. Most of molecular variances were due to individual characteristics in a population; whereas a little molecular divergence was related to a differentiation between the biogeographical regions in West and Central Africa. These populations were characterized by private and common haplotypes. The combined analyses of Bayesian phylogenetic, molecular dating and neutrality tests have suggested the existence of 4 main clusters that separated from themselves from a bottleneck followed by a moderate demographic expansion since Pleistocene period.