Undergraduate Honors Thesis Projects

Date of Award

Spring 5-4-2025

Document Type

Honors Paper

Degree Name

Biology-BA

Department

Biology & Earth Science

Advisor

Jeffrey S. Lehman

First Committee Member

Jeffrey S. Lehman

Second Committee Member

Brandon Sinn

Third Committee Member

John Tansey

Keywords

Entomology, Lepidoptera, Structural coloration, Lycaenidae, Spectroscopy, Morphology

Subject Categories

Biophysics | Entomology | Higher Education | Structural Biology | Zoology

Abstract

Sexually dimorphic patterns and coloration are common in Lepidoptera. In addition to differences in scale pigmentation, Lepidopterans are also known to exhibit varying degrees of sexually dimorphic structural coloration. In such cases, it is hypothesized that dimorphic scale architecture results in the differential reflectance of blue, violet, or ultraviolet light. In this study, we examined variations in microstructural morphology and reflective capabilities of cover scales from a sexually dimorphic wing region of Celastrina neglecta (W. H. Edwards, 1862) (Lycaenidae: Polyommatinae) to determine the microanatomical basis of sexually dimorphic structural coloration in the species. The reflective properties of regional and single cover scales and the cover scale morphology of C. neglecta specimens (n = 29) were compared based on spectrometry and scanning electron and light microscopy. Regional analyses revealed that males and females possess statistically different regional reflectance values (P < 0.0001). Males exhibit a high reflectance (%) of violet light (380-450 nm) and low reflectance of light in the 451-730 nm range (80% and 40%, respectively), while females exhibit a lower reflectance of violet light and higher reflectance of light in the 451-730 nm range when compared to males (60% and 50%, respectively). Single scale analyses revealed the presence of both reflective and non-reflective cover scales in the region of interest. While male and female cover scales exhibit similar reflective properties (P ≥ 0.076), females possess a higher concentration of non-reflective scales in the dimorphic region than males. These results indicate that observed differences in regional reflectance are caused by the ratio of reflective to non-reflective cover scales. Morphological analyses of reflective and non-reflective cover scales indicate that the ridges and cross-ribbing of non-reflective scales are more densely packed than their reflective counterparts (P < 0.0001). The average distances between ridges and the distance between cross-ribbing were 1.92 μm and 1.03 μm and 1.57 μm and 0.79 μm for reflective and non-reflective scales, respectively. Additionally, reflective scales exhibit a fully developed lattice of pepper-pot photonic structures between the upper and lower lamina of the scale, while non-reflective scales possess an underdeveloped lattice that is irregular and, at times, absent from the intertrabecular space. These results suggest that observed differences in violet reflectance may result from differential lattice development and that females exhibit arrested maturation of cover scales in the region of interest.

Licensing Permission

Copyright, all rights reserved. Fair Use

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Acknowledgement 2

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