Signal design and courtship presentation coincide for highly biased delivery of an iridescent butterfly mating signal

Abstract

Sensory drive theory contends that signaling systems should evolve to optimize transmission between senders and intended receivers, while minimizing visibility to eavesdroppers where possible. In visual communication systems, the high directionality afforded by iridescent coloration presents underappreciated avenues for mediating this trade-off. This hypothesis predicts functional links between signal design and presentation such that visual conspicuousness is maximized only under ecologically relevant settings and/or to select audiences. We addressed this prediction using Hypolimnas bolina, a butterfly in which males possess ultraviolet markings on their dorsal wing surfaces with a narrow angular reflectance function. Males bearing brighter dorsal markings are increasingly attractive to females, but also likely more conspicuous to predators. Our data indicate that, during courtship (and given the ritualized wingbeat dynamics at these times), males position themselves relative to females in such a way as to simultaneously maximize three components of known or putative signal conspicuousness: brightness, area, and iridescent flash. This suggests that male signal design and display have coevolved for the delivery of an optimally conspicuous signal to courted females. More broadly, these findings imply a potential signaling role for iridescence itself, and pose a novel example for how signal design may coevolve with the behavioral context of display.

Implications of insect responses to supernormal visual releasing stimuli in intersexual communication and flower-visiting behaviour: A review

“…In many species, UV markings on the wings are also important for intersexual communication. As recently shown by White et al (2015), the maximally bright UV refl ectance of white spots surrounded by shimmering blue scales on the black upper side of the wings of courting H. bolina males can be seen only from a very restricted angle. This has the advantage that the UV pattern of the males is clearly visible to H. bolina females, but not to avian predators.…”

“…For example, the role of male coloration in intersexual signalling studied by Rutowski (2003) and White et al (2015). In addition, UV markings can play an important role.…”

“…In the butterfl y Hypolimnas bolina (family Nymphalidae) the fl ashing UV signals from the upper surface of the four wings of courting males may act as optical stimuli for females, allowing a couple to fi nd optimal positions relative to each other and in stimulating a female's readiness to mate. The optimal position is when the male fl ies just below the female (Kemp, 2007;Rutowski et al, 2007;White et al, 2015). White and co-workers have shown that this position permits the males to enhance the fl ashing effect by increasing the brightness and wing area visible while simultaneously minimising the amount of time during each wing beat cycle in which the UV signal can be seen.…”

“…Hence, it appears that the visual system of male A. paphia can perceive a fl ickering orange stimulus up to the maximum perceptual range. This may also apply to other mating butterfl ies, as indicated for H. bolina (Rutowski, 2003;White et al, 2015). It means that the response to visual releasing signals is not detection for a potential mate may be limited to a few metres.…”

Technicolour deceit: a sensory basis for the study of colour-based lures

“…Signal presentation ( Fig. 2a, b) refers to the behavioural context of display, which includes the mechanics of how signals are presented (Dakin & Montgomerie, 2009;Sicsu, Manica, Maia, & Macedo, 2013;White, Zeil, & Kemp, 2015) as well as strategic choices about when and where to display (Endler & Thery, 1996;Endler, 1991). Reception is determined by the complex (and often little-understood) processes of vision and perception (Fig.…”