Evolutionary history and analysis of iridescent ultraviolet butterfly scales

Iridescent ultraviolet (IUV) patterns on pierid butterfly wings are
phenotypic adaptations commonly used as sexual signals, generated by
scales with ultrastructural modifications. Pierid IUV patterns are
sexually dichromatic, with reduced size in females, where conspicuous
sexual signaling balances courtship against ecological predation. There
have been no phylogenetic reconstructions of IUV within Pieridae and
little morphological characterization of phenotypic diversity. Our
genus-wide characterization of IUV revealed the uniform similarity of
stacked lamellar ridges on the dorsal surface of cover scales. We tested a
hypothesis of single versus multiple origins by reconstructing a phylogeny
of 534 species (~43.2% described species), with all genera represented,
and a trait matrix of 734 species (~59.4%) screened for IUV. A single,
early dimorphic origin of IUV followed by several losses and gains
received strong support, concluding that IUV patterns and structural
coloration are old traits. Collectively, these results support the
homology of IUV scales and patterns that diversified within several
lineages, suggesting an interplay between female-mediated sexual selection
and ecological predatory selection.