Ambient light and mimicry as drivers of wing transparency in Lepidoptera

Abstract

Transparency is common in aquatic environments where it reduces detectability by predators. Transparency degree (the proportion of transmitted light) varies under water and is higher as light availability increases. Transparency is rare on land and poorly studied. Recent studies have shown that Lepidoptera – a group in which transparency has independently evolved multiple times – also display large variation in transparency degree. The large diversity encompasses different types of clearwing species, such as bee/wasp mimics and death leaf mimics. This study explores how the evolution of different transparency degree could be related to habitat openness, and to mimicry syndrome, through two complementary approaches. First, by exposing artificial moth-like prey to wild avian predators in open and closed habitats, our fieldwork experiment shows an increase in prey survival at higher transparency degrees in open compared to closed habitats. Second, by analysing the evolution of wing characteristics and ecological traits in 107 clearwing species, comparative analyses show that instead, open habitat species show in average similar or slightly lower transparency degree than closed habitat species. We also find that bee/wasp mimics have highest and least varying transparency degrees and are more often diurnal. Compared to bees/wasp mimics, leaf mimics have lower but more varying transparency degree and are more often nocturnal. High transparency degree likely reduces detectability in open habitats, as shown by field experiments and comparative analyses of optical measurements on bee/wasp mimics. Our results suggest that habitat openness, and species interactions play a crucial role in determining transparency design.

Mimicry can drive convergence in structural and light transmission features of transparent wings in Lepidoptera

“…Nevertheless, convergence in properties of transparent patches may also result from other selective processes. Transparency is also involved in crypsis ( Arias et al, 2020b ), even in aposematic prey ( Arias et al, 2019 ; McClure et al, 2019 ), and the degree of transparency needed to achieve crypsis may depend on the ambient light ( Johnsen and Widder, 1998 ; Arias et al, 2020a ). Specifically, in bright environments only highly transparent prey are cryptic, whereas in darker environments moderately transparent prey can be cryptic.…”

Mimicry drives convergence in structural and light transmission features of transparent wings in Lepidoptera

“…Nevertheless, convergence in properties of transparent patches may also result from other selective processes. Transparency is also involved in crypsis , even in aposematic prey (Arias et al, 2019;McClure et al, 2019), and the degree of transparency needed to achieve crypsis may depend on the ambient light (Arias, Barbut, et al, 2020;Johnsen & Widder, 1998). Specifically, in bright environments only highly transparent prey are cryptic, whereas in darker environments moderately transparent prey can be cryptic.…”