Conceived and designed the experiments: JB MJBV PS TDM. Performed the experiments: NK JB SR KTD SC. Analyzed the data: JB PS TDM. Contributed reagents/materials/analysis tools: SR TDM. Wrote the paper: NK JB SR MJBV KTD SC PS TDM.
The authors have declared that no competing interests exist.
African animal trypanosomosis is a major obstacle to the development of more efficient and sustainable livestock production systems in West Africa. Riverine tsetse species such as
In the present study, genetic variation at microsatellite DNA loci was used to examine the population structure of
Therefore, potential re-invasion of flies from adjacent river basins will have to be prevented by establishing buffer zones between the Mouhoun and the other river basin(s), in the framework of the PATTEC (Pan African Tsetse and Trypanosomosis Eradication Campaign) eradication project that is presently targeting the northern part of the Mouhoun River Basin. We argue that these genetic analyses should always be part of the baseline data collection before any tsetse control project is initiated.
Tsetse flies are insects that transmit trypanosomes to humans (sleeping sickness) and animals (nagana). Controlling these vectors is a very efficient way to control these diseases. In Burkina Faso, a tsetse eradication campaign is presently targeting the northern part of the Mouhoun River Basin. To attain this objective, the approach has to be area-wide, i.e. the control effort targets an entire pest population within a circumscribed area. To assess the level of this isolation, we studied the genetic structure of
Tsetse flies (Diptera: Glossinidae) are the sole cyclical vectors of human and animal trypanosomoses, two major plagues that are seriously impeding African development. African animal trypanosomosis (AAT) is a major obstacle to the development of more efficient and sustainable livestock production systems in West Africa. Since 2008, the Government of Burkina Faso has embarked on an ambitious tsetse eradication campaign that targets the northern Mouhoun River Basin for its first phase (
In the Mouhoun River Basin,
Control of tsetse can be achieved through a variety of techniques
In Burkina Faso,
The present study includes
The study area is located in South-Western Burkina Faso (latitude 10.2 to 12.2 N; longitude −5.5 to −2.0°W) and encompassed the Mouhoun River Basin (8 sampling sites) and three neighbouring river basins, i.e. the Comoe (3 sampling sites), the Sissili and the Niger (1 sampling site each) River Basins (
River basin | Site | Females | Males | Total | Number of trap sites | Mean distance between trap sites | Total river length sampled |
Comoe | Degue Degue | 18 | 17 | 35 | 3 | 212 | 424 |
Fandiora | 16 | 19 | 35 | 3 | 2830 | 5660 | |
Toussiana | 25 | 10 | 35 | 2 | 210 | 210 | |
Mouhoun | Darsalamy | 24 | 10 | 34 | 4 | 327 | 980 |
Dialé | 36 | 20 | 56 | 9 | 264 | 2115 | |
Dingasso | 19 | 20 | 39 | 5 | 70 | 280 | |
Niafongo | 17 | 25 | 42 | 4 | 130 | 391 | |
Sissili | Yalé | 15 | 5 | 20 | 9 | 540 | 4316 |
All | 170 | 126 | 296 | 39 | 464 | 14376 |
River basin | Site | Females | Males | Total | Number of trap sites | Mean distance between trap sites (m) | Total river length sampled (m) |
Comoe | Toussiana | 12 | 12 | 24 | 2 | 210 | 210 |
Mouhoun | Darsalamy | 18 | 15 | 33 | 4 | 320 | 960 |
Minsin(pindia) | 15 | 11 | 26 | 4 | 110 | 330 | |
Niafongon | 13 | 15 | 28 | 4 | 135 | 404 | |
Rz banzon | 20 | 10 | 30 | 6 | 88.2 | 441 | |
Samandeni | 24 | 12 | 36 | 2 | 73 | 73 | |
Zamakologo | 23 | 12 | 35 | 3 | 145 | 290 | |
Niger | Bleni | 20 | 10 | 30 | 6 | 79 | 395 |
All | 145 | 97 | 242 | 31 | 135 | 3103 |
A total of 296
Three legs of each individual tsetse fly were removed, transferred to a tube to which 200 µl of 5% Chelex chelating resin was added
All datasets were processed with Create V 1.1
Wright's
The significant departure from 0 of these parameter estimates was tested by randomisation procedures under Fstat. For this, alleles are randomly exchanged between individuals in each subsample and the proportion of times when a
Linkage disequilibrium (LD) between loci was also tested through randomising association between each locus pair. For each pair of loci the tests were combined across subsamples with the
For LD, there were as many tests as there were loci pairs (here possibly 36), we therefore tested the probability of obtaining a proportion higher than the expected one (5%) with a binomial test with
More than three levels (i.e. individuals, sub-populations and total) exist within the samples of each tsetse species. Individuals were caught in different traps, in different sites (i.e. locations) within three different river basins (Comoé, Mouhoun and Sissili for
Some microsatellite loci, noted with an X as last letter, are X linked. These loci were coded as missing data for
Significant
Confidence intervals (CI) were obtained using the standard error of estimates obtained by jackknife over subsamples or by bootstrap over loci, using Fstat, as described in
Sex-biased dispersal was assessed using three tests implemented in Fstat. First, Weir and Cockerham's estimate of
Isolation by distance was inferred with Rousset's procedure
Effective population sizes were estimated following Waples and Do's method based on linkage disequilibrium and implemented in LDNe
For
HierFstat analysis only found one significant hierarchical level of population structure in the
For
For
There was a strong and highly significant heterozygote deficit (
Heterozygote deficits (
Locus | Sex | N | Blanks | Brookfield 2 | van Oosterhout | Stuttering |
pGp17 | 296 | 51 | 76 (0.0003) | 38 (0.9896) | 8 | |
pGp20X | F | 170 | 45 | 39 (0.8713) | 2 (1 ) | 1 |
pGp20X | M | 126 | 33 | 44 (0.0233) | 11 (1 ) | NA |
pGp24 | 296 | 137 | 134 (0.6378) | 5 (1 ) | 0 | |
pGp28 | 296 | 24 | 24 (0.5340) | 2 (1 ) | 0 | |
B104X | F | 170 | 25 | 22 (0.7656) | 4 (1 ) | 0 |
B104X | M | 126 | 17 | 38 (0.0001) | 16 (0.6758) | NA |
Results are given for the loci displaying a significant departure from proportions expected under panmixia (see
For
See legend of
Locus | Sex | N | Blanks | Brookfield 2 | van Oosterhout | Stuttering |
L55-3X | F | 108 | 4 | 4 (0.5326) | 3 (0.8336) | 0 |
L55-3X | M | 58 | 5 | 6 (0.5020) | 7 (0.3475) | 0 |
pGp24 | 166 | 18 | 17 (0.6536) | 3 (1 ) | 0 | |
A10 | 166 | 30 | 28 (0.6749) | 3 (1 ) | 1 | |
B110X | F | 108 | 12 | 11 (0.7048) | 1 (1 ) | 0 |
B110X | M | 58 | 9 | 14 (0.0967) | 4 (0.9946) | 0 |
As can be seen from
|
|
|
|
Females | 0.0417 | 0.24373 | 5.83009 |
Males | 0.0241 | −0.32884 | 9.53443 |
0.1494 | 0.0869 | 0.003 | |
|
|
|
|
Females | 0.0417 | 0.24373 | 5.83009 |
Males | 0.0241 | −0.32884 | 9.53443 |
0.1494 | 0.0869 | 0.003 |
Results were assessed between samples from different river basins (m
For
Analysis |
|
Sex |
|
|
|
Over all sites (1F,1M/trap, 8 sites) | 27 | F | − |
|
0.040 |
23 | M | 0.595 | 7.337 | − |
|
Over all Mouhoun (1F,1M/trap, 6 sites) | 22 | F | − |
|
0.031 |
18 | M | 0.731 | 8.537 | − |
|
Darsalamy (4 traps) | 18 | F | − |
|
|
15 | M | 1.513 | 6.435 | 0.104 | |
Minsin (2 traps) | 15 | F | 0.123 |
|
− |
8 | M | − |
3.009 | 0.202 | |
Mouhoun (18 traps) | 106 | F | − |
|
|
72 | M | 0.329 | 7.769 | 0.043 | |
RzBanson (3 traps) | 13 | F | − |
|
0.014 |
10 | M | 0.447 | 7.642 | − |
|
Samandeni (2 traps) | 24 | F | 0.029 | 10.846 |
|
12 | M | − |
|
0.025 | |
Zamakologo (3 traps) | 23 | F | 0.254 |
|
− |
12 | M | − |
5.353 | 0.029 |
Results were assessed between traps in the Mouhoun River Basin or between sites from different river basins (m
There was a highly significant isolation by distance across traps over the total
For
Using the island model of migration with even sex ratio, published by Vitalis
The population genetics data presented here suggest that the savannah area of the watershed divide between two adjacent river basins does not seem to represent a significant barrier to gene flow for the two riverine tsetse species studied. The results corroborate data from an earlier preliminary study that assessed gene flow (but without clear quantification) between three populations of
The analysis presented here showed that dispersal of
Tsetse flies are polygynous where the reproductive investment of female flies far outreaches that of the male flies. As such and according to the three main asymmetries of dispersal/philopatry costs between genders favouring biased dispersal (i.e. the resource-competition hypothesis, the local mate competition hypothesis and the inbreeding hypothesis) a sex biased dispersal in tsetse flies (should it exist) would be biased towards greater mobility of the male sex (see
In conclusion, the data presented here, combined with those from earlier studies
(XLS)
We want to thank B. Cene and A. Sana for their technical assistance during the field work, and M. Koffi for his advices in the laboratory. TDM would like to thank Anne Isette for her strong support during data analyses.