Population genetics of Glossina palpalis palpalis from central African sleeping sickness foci

Abstract

Background: Glossina palpalis palpalis (Diptera: Glossinidae) is widespread in west Africa, and is the main vector of sleeping sickness in Cameroon as well as in the Bas Congo Province of the Democratic Republic of Congo. However, little is known on the structure of its populations. We investigated G. p. palpalis population genetic structure in five sleeping sickness foci (four in Cameroon, one in Democratic Republic of Congo) using eight microsatellite DNA markers.

Results: A strong isolation by distance explains most of the population structure observed in our sampling sites of Cameroon and DRC. The populations here are composed of panmictic subpopulations occupying fairly wide zones with a very strong isolation by distance. Effective population sizes are probably between 20 and 300 individuals and if we assume densities between 120 and 2000 individuals per km2, dispersal distance between reproducing adults and their parents extends between 60 and 300 meters.

Conclusions: This first investigation of population genetic structure of G. p. palpalis in Central Africa has evidenced random mating subpopulations over fairly large areas and is thus at variance with that found in West African populations of G. p. palpalis. This study brings new information on the isolation by distance at a macrogeographic scale which in turn brings useful information on how to organise regional tsetse control. Future investigations should be directed at temporal sampling to have more accurate measures of demographic parameters in order to help vector control decision.

Figure 1

Map showing the geographic location of samples in Cameroon and DRC.

Figure 2

Individual fixation index (F_IS) of G. palpalis palpalis from Cameroon and DRC from individual traps, computed for each locus and overall (All). For each locus, the 95% confidence intervals were obtained by Jackknife over subsamples (individual traps) while it was obtained by bootstrap over loci for the overall mean. The P-value obtained while testing for significant deviation from panmixia are indicated between brackets.

Figure 3

Individual fixation index (F_IS) as function of the number of blank genotypes found per locus over all sub-samples. The equation of the regression, the determination coefficient R² and the significance of the F test (P-value) are also given.

Figure 4

Isolation by distance between the different G. palpalis palpalis captured in georeferenced traps in Cameroon and DRC. The regression equation of Rousset's model and significance of Mantel test are indicated. The thick line is the mean model and the two thin lines correspond to those obtained from the 95% confidence intervals of the slope. More details can be found in the text.