Males adjust their signalling behaviour according to experience of male signals and male–female signal duets

Variation in thermal courtship activity curves across individuals exceeds variation across populations and sexes

The dynamics of mating interactions can vary in response to a wide variety of environmental factors. Here, we investigate the potential for individuals to vary consistently in the environmental conditions under which they actively engage in courtship. Specifically, we quantify variation in how courtship activity changes with environmental temperature across levels of biological organization in Enchenopa binotata treehoppers. Male E. binotata produce vibrational courtship signals and receptive females respond with their own sex-specific vibrational courtship signal. We tested each individual twice for the production of courtship signals across a range of ecologically relevant temperatures (18-36 °C). Then, we measured repeatability and variability in the resulting thermal courtship activity curves, including the temperature of peak activity and tolerance to thermal extremes. We also looked at patterns of variation across populations and sexes. We found minimal variation across populations, but significant variation across individuals. Specifically, we found prevalent repeatability in how thermally generalized or specialized individuals are. However, repeatability was limited to females only. We also found higher variability in female traits than in male traits, although patterns of variability did not always predict patterns of repeatability. These results suggest that thermal variation could alter the dynamics of mate competition and that-due to potentially different selective optima for males and females-the sexes may respond to changes in temperature in different ways. Specifically, females show a higher potential to adapt but males show a higher potential to be more robust to changes in temperature due to overall higher courtship activity across temperatures.

Effects of the maternal social environment on the mating signals and mate preferences of adult offspring in Enchenopa treehoppers

Much is known about how the maternal environment can shape offspring traits via intergenerational effects. It is less clear, however, whether such effects may reach adult offspring sexual traits, with potential consequences for sexual selection and speciation. Here, we report effects of adult female aggregation density on the mating signals and mate preferences of their offspring in an insect that communicates via plant-borne vibrational signals. We experimentally manipulated the density of aggregations experienced by egg-laying mothers, reared the offspring in standard densities, and tested for corresponding differences in their signals and preferences. We detected a strong effect in male signals, with sons of mothers that experienced low aggregation density signalling more. We also detected a weak effect on female mate preferences, with daughters of mothers that experienced low aggregation density being less selective. These adjustments may help males and females find mates and secure matings in low densities, if the conditions they encounter correspond to those their mothers experienced. Our results thus extend theory regarding adjustments to the social environment to the scale of intergenerational effects, with maternal social environments influencing the expression of the sexual traits of adult offspring.

Characterization of light-dependent rhythm of courtship vibrational signals in Nilaparvata lugens: essential involvement of cryptochrome genes

BACKGROUND

Vibrational signal plays a crucial role in courtship communication in many insects. However, it remains unclear whether insect vibrational signals exhibit daily rhythmicity in response to changes in environmental cues.

RESULTS

In this study, we observed daily rhythms of both female vibrational signals (FVS) and male vibrational signals (MVS) in the brown planthopper (BPH), Nilaparvata lugens (Stål), one of the most notorious rice pests across Asia. Notably, oscillations of FVS and MVS in paired BPHs were synchronized as part of male-female duetting interactions, displaying significant day-night rhythmicity. Furthermore, we observed light dependency of FVS emissions under different photoperiodic regimes (18 L:6 D and 6 L:18 D) and illumination intensity levels (>300 lx, 50 lx, and 25 lx). Subsequently, the potential role of circadian clock genes cryptochromes (Nlcry1 and Nlcry2) in regulating FVS daily oscillations was examined using gene knockdown via RNA interference. We observed sharp declines and disrupted rhythms in FVS frequencies when either of the Nlcrys was downregulated, with Nlcry2 knockdown showing a more prominent effect. Moreover, we recorded a novel FVS variant (with a dominant frequency of 361.76 ± 4.31 Hz) emitted by dsNlcry1-treated BPH females, which significantly diminished the impact of courtship stimuli on receptive males.

CONCLUSION

We observed light-dependent daily rhythms of substrate-borne vibrational signals (SBVS) in BPH and demonstrated essential yet distinct roles of the two Nlcrys. These findings enhanced our understanding of insect SBVS and illustrated the potential of novel precision physical control strategies for disrupting mating behaviors in this rice pest. © 2023 Society of Chemical Industry.

Social Plasticity Enhances Signal-Preference Codivergence

AbstractThe social environment is often the most dynamic and fitness-relevant environment animals experience. Here we tested whether plasticity arising from variation in social environments can promote signal-preference divergence-a key prediction of recent speciation theory but one that has proven difficult to test in natural systems. Interactions in mixed social aggregations could reduce, create, or enhance signal-preference differences. In the latter case, social plasticity could establish or increase assortative mating. We tested this by rearing two recently diverged species of Enchenopa treehoppers-sap-feeding insects that communicate with plant-borne vibrational signals-in treatments consisting of mixed-species versus own-species aggregations. Social experience with heterospecifics (in the mixed-species treatment) resulted in enhanced signal-preference species differences. For one of the two species, we tested but found no differences in the plastic response between sympatric and allopatric sites, suggesting the absence of reinforcement in the signals and preferences and their plastic response. Our results support the hypothesis that social plasticity can create or enhance signal-preference differences and that this might occur in the absence of long-term selection against hybridization on plastic responses themselves. Such social plasticity may facilitate rapid bursts of diversification.

Plasticity of signaling and mate choice in a trilling species of the Mecopoda complex (Orthoptera: Tettigoniidae)

Abstract

Males of a trilling species in the Mecopoda complex produce conspicuous calling songs that consist of two motifs: an amplitude-modulated motif with alternating loud and soft segments (AM-motif) and a continuous, high-intensity trill. The function of these song motifs for female attraction and competition between males was investigated. We tested the hypothesis that males modify their signaling behavior depending on the social environment (presence/absence of females or rival males) when they compete for mates. Therefore, we analyzed acoustic signaling of males in three different situations: (1) solo singing, (2) acoustic interaction with another male, and (3) singing in the presence of a female. In addition, the preference of females for these song motifs and further song parameters was studied in two-choice experiments. As expected, females showed a preference for conspicuous and loud song elements, but nevertheless, males increased the proportion of the AM-motif in the presence of a female. In acoustic interactions, males reduced bout duration significantly compared to both other situations. However, song bouts in this situation still overlapped more than expected by chance, which indicates intentionally simultaneous singing. A multivariate statistical analysis revealed that the proportion of the AM-motif and the duration of loud segments within the AM-motif allow a reliable prediction of whether males sing in isolation, compete with another male, or sing in the presence of a female. These results indicate that the AM-motif plays a dominant role especially in close-range courtship and that males are challenged in finding a balance between attracting females and saving energy during repeated acoustic interactions.

Significance statement

Males of acoustic insects often produce conspicuous calling songs that have a dual function in male-male competition and mate attraction. High signal amplitudes and signal rates are associated with high energetic costs for signal production. We would therefore predict that males adjust their signaling behavior according to their perception of the social context. Here we studied signal production and mate choice in a katydid, where males switch between loud and soft song segments in a dynamic way. Additionally, we examined the attractiveness of different song elements in female choice tests. Our results show how males of this katydid deal with the conflict of remaining attractive for females and competing with a costly signal with rivals.

Biotremology

Animal communication, including that among humans, is fascinating in its efficiency, diversity and its complexity. The evolution of a communication signal requires that the encoded content sent by an organism (sender) is detected and decoded by a receiver, who then must respond in such a way that the fitness of the sender is increased. The signal could be visual, such as bright coloration or some stereotypical movement that attracts attention through the sense of sight. It could be chemical, such as a pheromone we detect by smell or taste, or it could be tactile, involving direct physical touch. It could be an acoustic wave, detected by an auditory organ as sound and perceived through the sense of hearing, or it could be a vibrational wave detected by a vibration receiver of another sort. The medium through which the signal is transmitted could be any that exists on the Earth (solid, liquid or gas), and each type of medium influences the type of signal that is able to most efficiently move through it.

The Elaborate Postural Display of Courting Drosophila persimilis Flies Produces Substrate-Borne Vibratory Signals

Sexual selection has led to the evolution of extraordinary and elaborate male courtship behaviors across taxa, including mammals and birds, as well as some species of flies. Drosophila persimilis flies perform complex courtship behaviors found in most Drosophila species, which consist of visual, air-borne, gustatory and olfactory cues. In addition, Drosophila persimilis courting males also perform an elaborate postural display that is not found in most other Drosophila species. This postural display includes an upwards contortion of their abdomen, specialized movements of the head and forelegs, raising both wings into a "wing-posture" and, most remarkably, the males proffer the female a regurgitated droplet. Here, we use high-resolution imaging, laser vibrometry and air-borne acoustic recordings to analyse this postural display to ask which signals may promote copulation. Surprisingly, we find that no air-borne signals are generated during the display. We show, however, that the abdomen tremulates to generate substrate-borne vibratory signals, which correlate with the female's immobility before she feeds onto the droplet and accepts copulation.