Selection for Size in Tsetse Flies

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Abstract
Species of Glossina each have a characteristic size which is little variable; low variability is imposed by the method of reproduction, adenotrophic viviparity, but there are examples in the literature of differential mortality causing samples of wild flies to be even less variable than samples emerging from wild puparia, and some cases examined in present investigation conform to this pattern. Large samples of wild G. morsitans and wild G. swynnertoni were compared with samples emerging from puparia collected in same areas. For 4 months populations of wild male G. morsitans were losing their smallest members to the extent of about 12% of the total, the effect disappearing towards the end of the dry season. The cause of this loss was not established. Only small numbers of wild female G. morsitans were examined and no conclusions were drawn. Male G. swynnertoni were not undergoing differential mortality, and 34 taken as prey of 2 species of Asilidae showed no size bias. Female G. swynnertoni on the other hand suffered from differential mortality throughout their lives; both larger and smaller individuals were eliminated by unidentified causes so that a female of mean size had the greatest expectation of life.

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