Evolution of wing shape in geometrid moths: phylogenetic effects dominate over ecology

Locomotory performance is an important determinant of fitness in most
animals, including flying insects. Strong selective pressures on wing
morphology are therefore expected. Previous studies on wing shape in
Lepidoptera have found some support for hypotheses relating wing shape to
environment-specific selective pressures on aerodynamic performance. Here,
we present a phylogenetic comparative study on wing shape in the
lepidopteran family Geometridae, covering all 374 species of the northern
European fauna. We focused on eleven wing traits including aspect ratio,
wing roundness, and the pointedness of the apex, as well as the ratio of
forewing and hindwing areas. All measures were taken from images available
on the internet, using a combination of tools available in Fiji software
and in R. We found that wing shape demonstrates a phylogenetically
conservative pattern of evolution in Geometridae, showing similar or
greater phylogenetic signal than many of its potential predictors. Several
wing traits showed statistically significant associations with predictors
such as body size, flight phenology, and preference for forest habitats.
Overall, however, all of these associations remained notably weak, with no
wing shape being excluded for any value of the predictors, including body
size. We conclude that, in geometrids, wing traits do not readily respond
to selective pressures optimising aerodynamic performance of the moths in
different environments. Selection on wing shape may nevertheless operate
through other functions of the wings, with the effectiveness of crypsis at
rest being a promising candidate for further studies.