Disentangling wing shape evolution in the African mayfly, Teloganodidae (Ephemeroptera)

Abstract

Wings are one of the most important structures in the evolution of insects and winged insects are widely accepted as being monophyletic. In Ephemeroptera, wing structure and shape is important for interpreting taxonomic relationships. Morphological variation in wing shape of 14 distinct operational taxonomic units (OTUs) of South African Teloganodidae mayfly was examined using landmark-based geometric morphometric methods and molecular phylogenetics to determine evolutionary shape change and allometry. Fore and hind wing shape data were tested for phylogenetic structure using an independently derived molecular phylogeny, which were then mapped into PCA shape space. The effect of evolutionary allometry as a factor contributing to shape change was examined and quantified. Significant phylogenetic signal was found in fore and hind wing shape, and evolutionary allometry was found to have a significant effect on fore wing but not hind wing shape variation. In the fore wing, evolutionary allometry was removed to explore the non-allometric component of shape variation and discuss possible implications on flight performance. The principal findings of this research show that the relationships between wing shape and size are complex and taxon-specific. We have revealed that evolutionary size changes have a considerable effect on the evolutionary shape changes of Teloganodidae fore wings, however this does not account for all the variation in shape. An increased fore wing size is associated with a broader wing base and narrower, raked wing apex, promoting less-energetically demanding flight, possibly with a higher range of speeds. The smaller species have a relatively narrow wing base and increased wing area at the apex, suggesting a slower flight with more agility, which is more energetically costly. The non-allometric variation involves similar, but less distinct shape changes compared to the allometric component, indicating that other processes must also contribute to the same features of evolutionary shape variation.