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Socially induced plasticity in mating signals and mate preferences is widespread in animals. The timing of plasticity induction is key for mating and evolutionary consequences: plasticity induced before and after dispersal often results in different patterns of mate choices. Here we discuss two additional factors that may be of importance: the nature of social interactions that are involved at different stages, and the direction and strength of the effects. We review a case study with the Enchenopa binotata species complex of treehoppers. In spite of a wide scope for social plasticity in E. binotata across life stages, effects of the juvenile social environment were stronger and more common, especially those influencing the signalepreference relationship. These results emphasize the importance of studying variation in plasticity induced along various life stages and of considering all the mating traits that may be socially plastic. We suggest that systematic investigation of these patterns across taxa will help better understand the origin of diversity in animal communication systems. 

Abstract Animals often mimic the behaviours or signals of conspecifics of the opposite sex while courting. We explored the potential functions of a novel female-like signal type in the courtship displays of male Enchenopa treehoppers. In these plant-feeding insects, males produce plant-borne vibrational advertisement signals, to which females respond with their own duetting signals. Males also produce a signal type that resembles the female duetting responses. We experimentally tested whether this signal modifies the behaviour of receivers. First, we tested whether the female-like signal would increase the likelihood of a female response. However, females were as likely to respond to playbacks with or without them. Second, we tested whether the female-like signal would inhibit competing males, but males were as likely to produce displays after playbacks with or without them. Hence, we found no evidence that this signal has an adaptive function, despite its presence in the courtship display, where sexual selection affects signal features. Given these findings, we also explored whether the behavioural and morphological factors of the males were associated with the production of the female-like signal. Males that produced this signal had higher signalling effort (longer and more frequent signals) than males that did not produce it, despite being in worse body condition. Lastly, most males were consistent over time in producing the female-like signal or not. These findings suggest that condition-dependent or motivational factors explain the presence of the female-like signal. Alternatively, this signal might not bear an adaptive function, and it could be a way for males to warm up or practice signalling, or even be a by-product of how signals are transmitted through the plant. We suggest further work that might explain our puzzling finding that a signal in the reproductive context might not have an adaptive function. 

The social environment is often the most dynamicandfitness-relevant environment animals experience. Here we testedwhether plasticity arising from variation in social environments canpromote signal-preference divergence—a key prediction of recentspeciation theory but one that has proven difficult to test in natural sys-tems. Interactions in mixed social aggregations could reduce, create,or enhance signal-preference differences. In the latter case, social plas-ticity could establish or increase assortative mating. We tested this byrearing two recently diverged species ofEnchenopatreehoppers—sap-feeding insects that communicate with plant-borne vibrationalsignals—in treatments consisting of mixed-species versus own-speciesaggregations. Social experience with heterospecifics (in the mixed-species treatment) resulted in enhanced signal-preference species dif-ferences. For one of the two species, we tested but found no differencesin the plastic response between sympatric and allopatric sites, sug-gesting the absence of reinforcement in the signals and preferencesand their plastic response. Our results support the hypothesis that so-cial plasticity can create or enhance signal-preference differences andthat this might occur in the absence of long-term selection against hy-bridization on plastic responses themselves. Such social plasticity mayfacilitate rapid bursts of diversification. 

Abstract The interaction effect coefficient ψ has been a much-discussed, fundamental parameter of indirect genetic effect (IGE) models since its formal mathematical description in 1997. The coefficient simultaneously describes the form of changes in trait expression caused by genes in the social environment and predicts the evolutionary consequences of those IGEs. Here, we report a striking mismatch between theoretical emphasis on ψ and its usage in empirical studies. Surveying all IGE research, we find that the coefficient ψ has not been equivalently conceptualized across studies. Several issues related to its proper empirical measurement have recently been raised, and these may severely distort interpretations about the evolutionary consequences of IGEs. We provide practical advice on avoiding such pitfalls. The majority of empirical IGE studies use an alternative variance-partitioning approach rooted in well-established statistical quantitative genetics, but several hundred estimates of ψ (from 15 studies) have been published. A significant majority are positive. In addition, IGEs with feedback, that is, involving the same trait in both interacting partners, are far more likely to be positive and of greater magnitude. Although potentially challenging to measure without bias, ψ has critically-developed theoretical underpinnings that provide unique advantages for empirical work. We advocate for a shift in perspective for empirical work, from ψ as a description of IGEs, to ψ as a robust predictor of evolutionary change. Approaches that “run evolution forward” can take advantage of ψ to provide falsifiable predictions about specific trait interactions, providing much-needed insight into the evolutionary consequences of IGEs. 

The urgency for remote, reliable and scalable biodiversity monitoring amidst mounting human pressures on ecosystems has sparked worldwide interest in Passive Acoustic Monitoring (PAM), which can track life underwater and on land. However, we lack a unified methodology to report this sampling effort and a comprehensive overview of PAM coverage to gauge its potential as a global research and monitoring tool. To address this gap, we created the Worldwide Soundscapes project, a collaborative network and growing database comprising metadata from 416 datasets across all realms (terrestrial, marine, freshwater and subterranean).