The thoracic anatomy of the male and female winter moth Nyssiodes lefuarius (Lepidoptera: Geometridae) and evolutionary changes in the thorax of moths and butterflies

The thoraces of males and flightless females of the geometrid winter moth Nyssiodes lefuarius are described, documented in detail, and compared. Morphological, functional, and evolutionary aspects of the female phenotype are discussed. The flightlessness of female N. lefuarius is linked not only with complex modifications of the skeletomuscular structure, especially elements of the flight apparatus, but also with greatly enlarged ovaries and a reduced gut. Compared with other flightless female lepidopterans, females of N. lefuarius display a specific thoracic skeletomuscular configuration, which strongly suggests independent evolution, in agreement with the phylogenetic pattern. The evolutionary scenario of flight ability enhancement in Lepidoptera is demonstrated using a combined phylogeny from recent studies based on molecular data. Thoracic skeletomuscular characters are compiled and mapped, mainly using extensive information from the literature, but also including the new morphological data obtained from the male N. lefuarius. Important changes in the thoracic character system are linked with the rise of Coelolepida, Heteroneura, and Ditrysia. Only minor changes take place in the character system in more advanced groups of Lepidoptera. A highly unusual feature is the secondarily stiff wing type in some groups of Ditrysia without the neopteran basal folding mechanism. The morphological background of the secondarily evolved palaeopteran condition is a complex of different character changes. Major problems in the reconstruction of the phylogeny are a high degree of homoplasy and missing detailed data for several crucial taxa emerging close to the root of the order.