Geometric morphometrics as a tool for interpreting evolutionary transitions in the black fly wing (Diptera: Simuliidae)

Abstract

A geometric morphometric analysis was conducted on wing-vein landmarks on exemplar species of the family Simuliidae of the following genera: Parasimulium, Gymnopais, Twinnia, Helodon, Prosimulium, Greniera, Stegopterna, Tlalocomyia, Cnephia, Ectemnia, Metacnephia, Austrosimulium, and Simulium. Generalized least squares superimposition was performed on landmarks, followed by a principal component analysis on resulting Procrustes distances. Patterns of shape change along the principal component axes were visualized using the thin-plate spline. The analysis revealed wing shape diversity through (1) the insertion points of the subcosta and R1, resulting in the terminus of the costa exhibiting a trend towards a more apical position on the wing, and (2) the insertion point of the humeral cross vein, resulting in the anterior branch of the media exhibiting a trend toward a more basal position on the wing. Canonical variates analysis of Procrustes distances successfully assigned all exemplar species into their a priori taxonomic groupings. The diversity in wing shape reveals a trend towards decreased length of basal radial cell and increased costalization of anterior wing veins in the evolutionary transition from plesiomorphic prosimuliines to more derived simuliines. The functional significance of these evolutionary transitions is discussed.