Scale granules and colours: Sexual dimorphism in Trichonis (Lepidoptera: Lycaenidae, Theclinae)

Zsolt Bálint,Andrew Parker,Abigail Ingram,Krisztián Kertész,Gábor Piszter,Zsolt E Horváth,Levente Illés,László Péter Biró

doi:10.1016/j.asd.2021.101113

Abstract

A large fraction of dorsal wing surface ground scales show an unusual granulated nature, composed of material apparently extruded from the scale lumen in male individuals of both Trichonis Hewitson, 1865 species in the tribe Eumaeini, a rare Guyanian–Amazonian genus. Only a few not-granulated male specimens are known, females are not granulated. The granulated scales are investigated by various microscopic (optical, scanning and transmission electron microscopy, focused ion beam lamella cutting) and spectroscopic (optical reflectance, energy-dispersive X-ray (EDS), Raman) techniques. The characteristic blue colour unique in the South American representatives of the tribe is documented and analysed. EDS spectra show that the granules contain additional calcium and oxygen as compared with the un-granulated regions of the same scale. Electron diffraction (inside the TEM) did not reveal any crystalline component in the granules. The granulated wing surfaces of the males exhibit a UV absorption band at 280 nm, characteristic for biogenic CaCO3; therefore, the material of the granules is tentatively identified as CaCO3. It is shown that the granules influence the optical properties of the dorsal wing surface resulting in a characteristic spectrum.

Highlights

Papilionoid lepidopterans, especially members of the family Lycaenidae, are well known because of frequently encountered sexual dimorphism
Optical microscopy lamella extracted using Focused ion Beam (FIB) sculpting from a granule located inside the combined Scanning electron microscopy (SEM)/FIB microscope (Zeiss LEO 1540 XB (Jena, Germany)) were inspected with a Philips CM20 (Eindhoven, The Netherlands) at 200 kV
Inside this apparatus the energy-dispersive Xray spectroscopy (EDS) investigation and the preparation of Transmission electron microscopy (TEM) lamella were carried out using FIB

Summary

Introduction

Papilionoid lepidopterans, especially members of the family Lycaenidae, are well known because of frequently encountered sexual dimorphism This is expressed in various ways from wing shape and venation, via colouration and pattern, to the scale macroand micromorphology (Vertesy et al, 2006). The sexual dimorphism of the very rare Neotropical eumaeine lycaenid butterfly genus Trichonis Hewitson, 1865 (type species: Papilio theanus Cramer, 1777, by original designation) is expressed in all the above-mentioned ways. These are so remarkable that the opposite sexes of the Trichonis type species were described as representing different species by the same classical worker Pieter Cramer (1721e1776) (Cramer, 1775, 1777). Later it was pointed out that this „female” was an undescribed species' male, which belonged to the genus Trichonis (Lathy, 1930). Robbins (1986) monographing Trichonis pointed out and briefly described the remarkable male secondary sexual characters expressed by highly specialized scales found on the ventral wing surface of the forewings and dorsal wing surface of the hindwing as large scent pads. Robbins (1986) documented first the female of Trichonis immaculata Lathy (1930), a very rare jewel of the lowland Lycaenidae fauna in the Amazonian basin and the Guyana shield

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