Résumé
Between plagues, the solitarious desert locust (Schistocerca gregaria) is
generally thought to exist as small populations, which are particularly
prone to extinction events in arid regions of Africa and Asia. Given the
high genetic structuring observed in one geographical area (the Eritrean
coast) by former authors, a metapopulation dynamics model involving
repeated extinction and colonization events was favored. In this study, we
assessed the validity of a demographic scenario involving temporary
populations of the solitarious phase of the desert locust by analyzing
large-scale population genetic data. We scored 24 microsatellites in 23
solitarious population samples collected over most of the species range
during remission. We found very little genetic structuring and little
evidence of declining genetic diversity. A Bayesian clustering method
distinguished four genetically differentiated units. Three groups were
largely consistent with three population samples which had undergone
recent bottleneck events. Nevertheless, the last genetically homogeneous
unit included all individuals from the remaining 18 population samples and
did not show evidence of demographic disequilibrium. An approximate
Bayesian computation treatment indicated a large population size for this
main genetic group, moderately reduced between plague and remission but
still containing tens of thousands of individuals. Our results diverge
from the hypothesis of a classical metapopulation dynamics model. They
instead support the scenario in which large populations persist in the
solitarious phase of the desert locust.