Phenotypic divergence of Glossina morsitans (Diptera: Glossinidae)
populations in Zambia: Application of landmark-based wing geometric
morphometrics to discriminate population-level variation
Abstract
An important consequence of the discontinuous distribution of insect
populations within their geographic range is phenotypic divergence.
Detection of this divergence can be challenging when it occurs through
subtle shifts in morphological traits with complex geometries, such as
insect wing venation. Here, we used landmark-based wing geometric
morphometrics to investigate the population-level phenotypic variation
of the two subspecies of Glossina morsitans, G. m. centralis Machado and
G. m. morsitans Westwood that occur in Zambia. Twelve homologous
landmarks digitized on the right wings of 720 specimens collected from
four and five sites (80 per site with 1:1 sex ratio) within the G. m.
centralis and G. m. morsitans range respectively, were subjected to
generalised Procrustes analysis to obtain wing centroid size (CS) and
wing shape variable. Linear permutation models were then used to compare
CS and wing shape between male and female G. morsitans, the two
subspecies G. m. centralis and G. m. morsitans, and between sample
locations within each subspecies range. Significant differences in CS
and wing shape were observed between G. morsitans sexes, subspecies and
sample locations within each subspecies range. Neighbour-joining trees
derived from the analysis of Procrustes distances showed that tsetse
within each subspecies range were highly divergent. We conclude that G.
morsitans populations in Zambia exhibit significant population-level
variation in fly size and wing shape which suggests high levels of
population structuring. The main drivers of this structuring could be
adaptation to local climatic condition, especially temperature and
random genetic drift. We therefore recommend molecular studies to
estimate the levels of gene flow between these populations and determine
their levels of genetic isolation.