Tsetse flies: genetics, evolution, and role as vectors

Abstract

Tsetse flies (Diptera: Glossinidae) are an ancient taxon of one genus, Glossina, and limited species diversity. All are exclusively haematophagous and confined to sub-Saharan Africa. The Glossina are the principal vectors of African trypanosomes Trypanosoma sp. (Kinetoplastida: Trypanosomatidae) and as such, are of great medical and economic importance. Clearly tsetse flies and trypanosomes are coadapted and evolutionary interactions between them are manifest. Numerous clonally reproducing strains of Trypanosoma sp. exist and their genetic diversities and spatial distributions are inadequately known. Here I review the breeding structures of the principle trypanosome vectors, G. morsitans s.l., G. pallidipes, G. palpalis s.l. and G. fuscipes fuscipes. All show highly structured populations among which there is surprisingly little detectable gene flow. Rather less is known of the breeding structure of T. brucei sensu lato vis à vis their vector tsetse flies but many genetically differentiated strains exist in nature. Genetic recombination in Trypanosoma via meiosis has recently been demonstrated in the laboratory thereby furnishing a mechanism of strain differentiation in addition to that of simple mutation. Spatially and genetically representative sampling of both trypanosome species and strains and their Glossina vectors is a major barrier to a comprehensive understanding of their mutual relationships.

Figure 1

Distribution of Morsitans group tsetse flies predicted from satellite imagery (courtesy of ERGO Ltd and TALA, Oxford, with permission. Available from <http://ergodd.zoo.ox.ac.uk/tseweb/distributions.htm>.

Figure 2

Predicted (grey) and observed (hatched) distribution of G. pallidipes, from Rogers and Robinson (2004) with permission.

Figure 3

Pair-wise Cavalli-Sforza and Edwards chord genetic distances among G. pallidipes populations regressed on corresponding geographic distances. Note the slope for allozyme loci is much shallower than for mitochondrial and microsatellite loci (from Krafsur, 2002).

Figure 4

Lineage (haplotype) through time plots showing temporal increases in mitochondrial diversities. Note the small number of lineages (12) in Zimbabwe and Zambia and the rapid increases in diversities 300 – 400 generations ago in each region.

Figure 5

Distribution of Palpalis group tsetse flies predicted from satellite imagery (courtesy of ERGO Ltd and TALA, Oxford, with permission. Available from <http://ergodd.zoo.ox.ac.uk/tseweb/distributions.htm>.

Figure 6

Distribution of Fusca group tsetse flies predicted from satellite imagery (courtesy of ERGO Ltd and TALA, Oxford, with permission. Available from <http://ergodd.zoo.ox.ac.uk/tseweb/distributions.htm>.