Morphometric analysis of nymphalid butterfly wings: number, size and arrangement of scales, and their implications for tissue-size determination

Animal body size and tissue size depend on genetic and environmental factors, but the precise mechanisms of how tissue size is determined in proportion to body size remain unknown. Here we focused on wings from three nymphalid butterflies, Junonia orithya (Linnaeus), Vanessa cardui (Linnaeus) and Danaus chrysippus (Linnaeus) (Lepidoptera: Nymphalidae), to examine the contributions of the number and size of scales to macroscopic structures, represented by wing compartments, and to investigate the positional dependence of scale size, density and arrangement. The whole wing area and wing compartment area exhibited a high correlation in all three species. Similarly, the wing compartment area and the blue or orange area showed a high correlation in three species, indicating isometric relationships among wings of different sizes. However, only in J. orithya, the blue area was highly correlated with the number of constituent scales and, to a lesser extent, with scale size. In contrast, reasonable correlations were obtained between the blue or orange area and the number of rows in all three species. These results suggest that variations of the background area accompany changes in the number of scales through changes in the number of rows. In a background region of the compartment, scale size gradually decreased and scale density increased from the proximal to the distal side in all three species. Our findings suggest that butterfly wing tissue size is determined primarily by the number of scale cells and secondarily by the size change of scale cells before or during the period of row arrangement.