An imperfect imago? Post-mating loss of iridescent scales in Cheimas butterflies may change female from attractive to cryptic (Lepidoptera: Nymphalidae: Satyrinae)

Abstract

Adults of both sexes of Cheimas opalinus (Staudinger), a Satyrinae butterfly occurring in the cloud forests of the Venezuelan Cordillera de Mérida, have simple wing colour patterns, dark brown dorsa marked by one conspicuous element, large greenish-blue patches in the discal area of the hind wing. It was observed that in young, freshly emerged females these patches are frequently absent. They fade away and eventually disappear during mating and nuptial flights when brushed out by lateral movements of the male’s hind wing put between folded female hind wings. The falling off of the scales is made easy because they do not adhere to the wing as firmly as brown background scales due to their particular folded extremities. We speculate that this process is related to the fitness of the females. Prior to mating, blue-green patches are advantageous because they attract the attention of the opposite sex and enhance the chances of successful mating. After mating they lose their sexual role. Females without the blue-green patches become cryptic. Thus, they are less apparent not only for the males, which helps them avoid sexual harassment, but also for potential bird predators. Additionally, the loss of blue reflecting scales may speed up the warming up of the abdomen and egg maturation. In the males, positive role of the patches (signalling), and negative (bird attraction), is balanced during their entire life span, and they fade gradually due to regular usage of wings scaling in flight. Our hypothesis is supported by morphological, optical, experimental and statistical analysis in which we used 509 individuals of both sexes. A similar ratio of young (with undamaged wing) females with or without blue patch was recorded, whereas in the males no individuals without any trace of blue patch were reported, and a correlation of age (wing damage) and gradual fading off of the patch was demonstrated. Such an adaptation involving an active change of the appearance of adults, i.e. colour patterns related to sexual selection, has not been reported previously in Lepidoptera.

KEYWORDS:

• Avian predation
• cloud forests
• infraspecific communication
• mating
• scales
• sexual selection
• signalling
• structural colours
• wing scale nanomorphology

Acknowledgements

We would like to especially thank the late professor Janusz Wojtusiak (MZUJ) who did the SEM documentation presented in this paper. We also thank professor Wojciech Witaliński (Institute of Zoology of the Jagiellonian University) for bursa copulatrix dissections.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplemental material

Supplemental material for this article can be accessed here

Additional information

Funding

The fieldwork of Tomasz W. Pyrcz in Venezuela and laboratory experiments were supported by grants from the Zoological Museum and Entomology Department of the Institute of Zoology of Jagiellonian University (Kraków, Poland). The research of Zsolt Bálint in Venezuela was supported by the BioPhot programme [EuFrame6 12915], and currently by the projects OTKA 111741 and 115724.