High and lowland dependent wing phenotypic variation of the dark blue tiger butterfly, Tirumala septentrionis (Butler, 1874) (Lepidoptera: Nymphalidae) with FE-SEM wing scales nanomorphology

Abstract

Butterflies display remarkable variation in wing shape and size, which is associated with tremendous ecological diversity. In butterflies, wing color patterns have been extensively studied, but wing shape and size diversity is less understood. In the present study, we investigated the altitude-specific wing asymmetry (right and left wings), sexual asymmetry, and wing covariation (proximal-distal and anterior-posterior wing organization) of Tirumala septentrionis (Butler, 1874). Using the geometric morphometric (GMM) method, we discovered that broad and expanded wings were found in lowland areas, whereas long and more rounded slender wings were found in highland areas. Furthermore, the ANOVA analysis, found significant (p < 0.05) altitude-specific shape and size differences in forewings and hindwings of both sexes. Thus, compared to size variations, the shape can be utilized as a valuable tool to distinguish sex (male and female), wing asymmetry (right and left) as well as altitudes (high and lowlands) specific variations of T. septentrionis. Furthermore, we noticed that lowland butterfly population had more asymmetric wings than the highland in the wing asymmetry analysis. We suspected that the unique wing morphology observed in the highland T. septentrionis population favored long-distance flight (indication of a migratory population). In contrast, the lowland population wing morphology indicated a newly colonized butterfly population. In addition to GMM analysis, we documented the FE-SEM wing scale morphology of T. septentrionis collected from two different altitudes. Interestingly, we observed that there is no difference in scale morphology related to altitude variations. Finally, we concluded that altitude-specific variations were observed mainly on wing shape and size, rather than the wing scales. These morphological variations were primarily associated with an adaptive response like migration, host searching, flight energy management and so on.