shield-backed bug (Calliphara exellens)
All across the animal kingdom, animals communicate with each other by sending signals. Many use multimodal signaling, which includes components in multiple sensory modalities, for example, both visual and auditory. It is thought that ordering multiple signals increases evolutionary fitness and augments the ability of receivers to process signals by improving signal efficacy (signal form and how effectively it is transmitted to a receiver).
Mukai et al. would like to better understand the evolution of multimodal signaling and signal order by studying the signaling of Heteroptera. Heteroptera is a taxonomic group of insects, and different species in the group exhibit a wide range of signaling behaviors. In this study, the authors set out to investigate the courtship displays of a particular species of Heteroptera, the shield-backed bug. The shield-backed bug (Calliphara exellens) is also known as the jewel bug. They hypothesized that vibrations the jewel bugs transmitted through leaves to each other would be important to their courtship displays.
Alocasia odora (AKA night-scented lily, Asian taro or giant upright elephant ear) upon which the bugs courted in the wild and lab
Researchers observed the courtship displays of pairs of jewel bugs in the wild and in the laboratory for 30 minutes or until copulation. They recorded the types and descriptions of the signals used, their duration, repetition, and the ordering of signals. They also recorded and characterized male tremulation (abdomen jerking), female tremulation, and male percussion (leaf drumming) in the laboratory with a vibrometer.
During courtship, the bugs displayed vibrational cues with tremulation and percussion, visual cues with head lowering, and possible tactile/chemical cues by touching. The behaviors were exhibited in a particular order and pattern; thus, researchers divided the courtship display into four phases: Duet I, Touch pronotum/Rub antennae (Tp/Ra), Duet II, and Precopulation. In Precopulation, all females adopted a copulation acceptance posture after the male drummed on the leaf. The three types of vibrations recorded in the lab differed in pulse duration and interval based on courtship phase. (Please see Figure 1 for a more detailed, graphical display of the results including the signal modality, behavior descriptions, duration, repetitions, and a picture of each courtship phase.)
Figure 1. Typical phases of a successful Calliphara exellens courtship display as observed on an Alocasia odora plant. Modalities potentially used as signals; Vib, Vibrational cues; Vis, Visual cues; Che, Chemical cues; and tac, Tactile cues. Black bars on the left of the figure indicate phases in which a given signal modality was observed. Gray bars indicate phases where the signal modality was absent. Phase durations and numbers of repeats are shown as means ± SEs. Solid arrows indicate the progression of steps, and dotted arrows indicate the exchange of signals between the male and female. (From: Mukai et al., 2022)
The association between male percussion and female copulation acceptance, as well as the variation in vibration pulses based on phase, provided support for the hypothesis that vibrational signals are key to the bugs’ courtship displays. Observations of the different types of cues in the courtship displays (visual, vibrational, and possible tactile/chemical) indicated the jewel bugs use multimodal signaling. Mukai et al. further inferred that jewel bug multimodal signals are ordered or hierarchical because of the perceived order to the courtship display behaviors. To summarize, this study suggests that during courtship, the jewel bugs use ordered or hierarchical multimodal signaling with vibrational signals being particularly important.
Macaranga tanarius (AKA parasol leaf tree) upon which the bugs courted in the wild
Mukai et al. wish to investigate, in the future, the rules and significance of the jewel bug signals and their order. This study initiates this investigation and fits into the larger context of interspecific comparisons of signaling in Heteroptera. The findings of this paper contribute to the field of sensory ecology by furthering our understanding of multimodal signaling and signal ordering and perhaps providing a framework for categorizing display patterns in insects. All of this work will be important to uncover insight into the evolution of multimodal signaling and signal ordering going forward.
Reference:
Mukai, H., Takanashi, T., & Yamawo, A. (2022). Elaborate mating dances: Multimodal courtship displays in jewel bugs. Ecology, 103(4). https://doi.org/10.1002/ecy.3632
Visual Source Links:
Image 1 obtained from https://upload.wikimedia.org/wikipedia/commons/9/9b/ナナホシキンカメムシ_Calliphara_exellens.jpg
Image 2 obtained fromhttps://www.longfield-gardens.com/plantname/Alocasia-Upright
Image 3 obtained from https://sown.com.au/macaranga-tanarius-euphorbiaceae-macaranga/
Figure 1 and legend are Figure 1 and legend from Mukai, H., Takanashi, T., & Yamawo, A. (2022). Elaborate mating dances: Multimodal courtship displays in jewel bugs. Ecology, 103(4). https://doi.org/10.1002/ecy.3632
