Ecology and behavior predict an evolutionary trade-off between song complexity and elaborate plumages in antwrens (Aves, Thamnophilidae).

The environment can impose constraints on signal transmission properties such that signals should evolve in predictable directions (Sensory Drive Hypothesis). However, behavioral and ecological factors can limit investment in more than one sensory modality leading to a trade-off in use of different signals (Transfer Hypothesis). In birds, there is mixed evidence for both sensory drive and transfer hypothesis. Few studies have tested sensory drive while also evaluating the transfer hypothesis, limiting understanding of the relative roles of these processes in signal evolution. Here, we assessed both hypotheses using acoustic and visual signals in male and female antwrens (Thamnophilidae), a species-rich group that inhabits diverse environments and exhibits behaviors, such as mixed-species flocking, that could limit investment in different signal modalities. We uncovered significant effects of habitat (sensory drive) and mixed-species flocking behavior on both sensory modalities, and we revealed evolutionary trade-offs between song and plumage complexity, consistent with the transfer hypothesis. We also showed sex- and trait-specific responses in visual signals that suggest both natural and social selection play an important role in the evolution of sexual dimorphism. Altogether, these results support the idea that environmental (sensory drive) and behavioral pressures (social selection) shape signal evolution in antwrens.

Revisiting the drivers of acoustic similarities in tropical anuran assemblages.

Acoustic signaling is key in mediating mate choice, which directly impacts individual fitness. Because background noise and habitat structure can impair signal transmission, the acoustic space of mixed-species assemblages has long been hypothesized to reflect selective pressures against signal interference and degradation. However, other potential drivers that received far less attention can drive similar outputs on the acoustic space. Phylogenetic niche conservatism and allometric constraints may also modulate species acoustic features, and the acoustic space of communities could be a side-effect of ecological assembly processes involving other traits (e.g., environmental filtering). Additionally, the acoustic space can also reflect the sorting of species relying on public information through extended communication networks. Using an integrative approach, we revisit the potential drivers of the acoustic space by addressing the distribution of acoustic traits, body size, and phylogenetic relatedness in tropical anuran assemblages across gradients of environmental heterogeneity in the Pantanal wetlands. We found the overall acoustic space to be aggregated compared with null expectations, even when accounting for confounding effects of body size. Across assemblages, acoustic and phylogenetic differences were positively related, while acoustic and body size similarities were negatively related, although to a minor extent. We suggest that acoustic partitioning, acoustic adaptation, and allometric constraints play a minor role in shaping the acoustic output of tropical anuran assemblages and that phylogenetic niche conservatism and public information use would influence between-assemblage variation. Our findings highlight an overlooked multivariate nature of the acoustic dimension and underscore the importance of including the ecological context of communities to understand drivers of the acoustic space.

Habitat structure drives the evolution of aerial displays in birds.

John Endler's sensory drive hypothesis posits that physical properties of the environment may shape signalling traits by determining how effective they are in communicating. Evidence abounds of signalling environment driving selection on colours and vocalizations, yet little is known about its influence on visual signals produced via body movements (i.e., gestural displays). Here, we aimed to perform the most taxonomically comprehensive assessment of sensory drive by testing the hypothesis that habitat structure drives the evolution of aerial sexual displays in passerine birds (order Passeriformes). We base this hypothesis on physical properties of habitats that should allow aerial displays to transmit more broadly in open habitats. To test the hypothesis, we performed Bayesian phylogenetic comparative analyses using species-level phylogenetic trees and a dataset of 469 species from across the Americas. We found that evolutionary gain of aerial displays is on average six times more frequent in open-habitat passerines than in forest ones. The influence of habitat structure on the evolution of aerial sexual displays attests to the importance of sensory drive as a deterministic evolutionary force within sexual selection, as opposed to models that assume a purely arbitrary direction of sexual trait evolution.

Resumo A hipótese da condução sensorial de John Endler postula que propriedades físicas do ambiente podem influenciar traços de sinalização ao determinar quão efetivos eles são em comunicar. Enquanto há bastante evidência do ambiente influenciando cores e vocalizações, pouco se sabe de sua influência sobre sinais visuais produzidos por movimentos corporais (i.e., gestos). Nesse estudo, realizamos a avaliação mais taxonomicamente abrangente da condução sensorial ao testar a hipótese de que a estrutura do hábitat influencia a evolução de exibições sexuais aéreas em aves da ordem Passeriformes. Baseamos essa hipótese em propriedades físicas dos hábitats que deveriam permitir uma transmissão mais ampla de exibições aéreas em áreas abertas. Para testar a hipótese, realizamos análises comparativas filogenéticas Bayesianas utilizando árvores filogenéticas ao nível de espécie e um banco de dados de 469 espécies que ocorrem ao longo do continente americano. Encontramos que o ganho evolutivo de exibições aéreas é, em média, seis vezes mais frequente em Passeriformes de áreas abertas do que em florestais. A influência da estrutura do hábitat sobre a evolução de exibições sexuais aéreas evidencia a importância da condução sensorial como uma força evolutiva determinística dentro da seleção sexual, contrastando com modelos que predizem uma direção puramente arbitrária na evolução de traços sexuais.

The influence of developmental environment on courtship song in cactophilic Drosophila.

Closely related species often differ in the signals involved in sexual communication and mate recognition. Determining the factors influencing signal quality (i.e. signal's content and conspicuousness) provides an important insight into the potential pathways by which these interspecific differences evolve. Host specificity could bias the direction of the evolution of sexual communication and the mate recognition system, favouring sensory channels that work best in the different host conditions. In this study, we focus on the cactophilic sibling species Drosophila buzzatii and D. koepferae that have diverged not only in the sensory channel used for sexual communication and mate recognition but also in the cactus species that use as primary hosts. We evaluate the role of the developmental environment in generating courtship song variation using an isofemale line design. Our results show that host environment during development induces changes in the courtship song of D. koepferae males, but not in D. buzzatii males. Moreover, we report for the first time that host rearing environment affects the conspicuousness of courtship song (i.e. song volume). Our results are mainly discussed in the context of the sensory drive hypothesis.

Evolution of male coloration during a post-Pleistocene radiation of Bahamas mosquitofish (Gambusia hubbsi).

Sexual signal evolution can be complex because multiple factors influence the production, transmission, and reception of sexual signals, as well as receivers' responses to them. To grasp the relative importance of these factors in generating signal diversity, we must simultaneously investigate multiple selective agents and signaling traits within a natural system. We use the model system of the radiation of Bahamas mosquitofish (Gambusia hubbsi) inhabiting blue holes to test the effects of resource availability, male body size and other life-history traits, key aspects of the transmission environment, sex ratio, and predation risk on variation in multiple male color traits. Consistent with previous work examining other traits in this system, several color traits have repeatedly diverged between predation regimes, exhibiting greater elaboration in the absence of predators. However, other factors proved influential as well, with variation in resource levels, body size, relative testes size, and background water color being especially important for several color traits. For one prominent signaling trait, orange dorsal fins, we further confirmed a genetic basis underlying population differences using a laboratory common-garden experiment. We illustrate a promising approach for gaining a detailed understanding of the many contributing factors in the evolution of multivariate sexual signals.