Comparative phylogenetics of Papilio butterfly wing shape and size demonstrates independent hindwing and forewing evolution

The complex forces that shape butterfly wings have long been a subject of
experimental and comparative research. Butterflies use their wings for
flight, camouflage, mate recognition, warning and mimicry. However,
general patterns and correlations among wing shape and size evolution are
still poorly understood. We collected geometric morphometric measurements
from over 1400 digitized museum specimens of Papilio swallowtails and
combined them with phylogenetic data to test two hypotheses: 1) forewing
shape and size evolve independently of hindwing shape and size, and 2)
wing size evolves more quickly than wing shape. We also determined the
major axes of wing shape variation and discovered that most shape
variability occurs in hindwing tails and adjacent areas. We conclude that
forewing shape and size are functionally and biomechanically constrained,
while hindwings are more labile, perhaps in response to disruptive
selective pressure for Batesian mimicry or against predation. The
development of a significant, re-usable, digitized data resource will
enable further investigation on tradeoffs between flight performance and
ecological selective pressures, along with the degree to which
intraspecific, local-scale selection may explain macroevolutionary
patterns.