Genetic diversity and population structure of Glossina pallidipes in Uganda and western Kenya.

Background: Glossina pallidipes has been implicated in the spread of sleeping sickness from southeastern Uganda into Kenya. Recent studies indicated resurgence of G. pallidipes in Lambwe Valley and southeastern Uganda after what were deemed to be effective control efforts. It is unknown whether the G. pallidipes belt in southeastern Uganda extends into western Kenya. We investigated the genetic diversity and population structure of G. pallidipes in Uganda and western Kenya.

Results: AMOVA indicated that differences among sampling sites explained a significant proportion of the genetic variation. Principal component analysis and Bayesian assignment of microsatellite genotypes identified three distinct clusters: western Uganda, southeastern Uganda/Lambwe Valley, and Nguruman in central-southern Kenya. Analyses of mtDNA confirmed the results of microsatellite analysis, except in western Uganda, where Kabunkanga and Murchison Falls populations exhibited haplotypes that differed despite homogeneous microsatellite signatures. To better understand possible causes of the contrast between mitochondrial and nuclear markers we tested for sex-biased dispersal. Mean pairwise relatedness was significantly higher in females than in males within populations, while mean genetic distance was lower and relatedness higher in males than females in between-population comparisons. Two populations sampled on the Kenya/Uganda border, exhibited the lowest levels of genetic diversity. Microsatellite alleles and mtDNA haplotypes in these two populations were a subset of those found in neighboring Lambwe Valley, suggesting that Lambwe was the source population for flies in southeastern Uganda. The relatively high genetic diversity of G. pallidipes in Lambwe Valley suggest large relict populations remained even after repeated control efforts.

Conclusion: Our research demonstrated that G. pallidipes populations in Kenya and Uganda do not form a contiguous tsetse belt. While Lambwe Valley appears to be a source population for flies colonizing southeastern Uganda, this dispersal does not extend to western Uganda. The complicated phylogeography of G. pallidipes warrants further efforts to distinguish the role of historical and modern gene flow and possible sex-biased dispersal in structuring populations.