Abstract
Many sexually selected traits exhibit phenotypic plasticity. Despite a growing appreciation for the ecological context in which sexual selection occurs, and for the role of plasticity in shaping traits associated with local adaptation and divergence, there is an important gap in knowledge about the onset and duration of plasticity in sexual trait expression. Integrating this temporal dimension of plasticity into models of sexual selection informs our understanding of the information conveyed by sexual traits and our predictions related to trait evolution, and is critical in this time of unprecedented and rapid environmental change. We conducted a systematic review of 869 studies to ask how trait modalities (e.g., visual and chemical) relate to the onset and duration of plasticity in vertebrate sexual signals. We show that this literature is dominated by studies of coloration in birds and fish, and most studies take place during the breeding season. Where possible, we integrate results across studies to link physiology of specific trait modalities with the life stage (e.g., juvenile, breeding, or nonbreeding) during which plasticity occurs in well‐studied traits. Limitations of our review included a lack of replication in our dataset, which precluded formal analysis. We argue that the timing of trait plasticity, in addition to environmental context, is critical for determining whether and how various communication signals are associated with ecological context, because plasticity may be ongoing or occur at only one point in an individual's lifetime, and determining a fixed trajectory of trait expression. We advocate for careful consideration of the onset and duration of plasticity when analyzing how environmental variation affects sexual trait expression and associated evolutionary outcomes.
Highlights
Selected phenotypes are some of the most notable features of wild animals and have fascinated biologists since Darwin proposed their function in reproductive behavior (Darwin, 1896).A key question in sexual selection research is why certain traits, but not others, become the targets of sexual selection
To answer our driving questions about the state of the literature in the context of the timing of sexual trait plasticity, we summarized the distribution of papers among years, taxa, traits, environmental variables, experimental designs, and life stages
In reality, traits may have differential sensitivity to their environment over time. These trait syntheses show how patterns of plasticity may differ among trait modalities, but we were unable to conduct a formal analysis due to the limitations of our dataset—namely, that most trait–environment associations were only tested in one life stage
Summary
Selected phenotypes are some of the most notable features of wild animals and have fascinated biologists since Darwin proposed their function in reproductive behavior (Darwin, 1896).A key question in sexual selection research is why certain traits, but not others, become the targets of sexual selection. Decades of research has identified (1) specific examples of plasticity in sexual traits, and (2) the types of environmental factors that influence expression of sexual traits. Research on sexually selected traits has shown that the degree of trait exaggeration is associated with environmental context (Martín & López, 2015; Scheuber et al, 2003a; Thompson et al, 1997). Behavioral ecologists recognize how moment-to-moment changes in the environment alter an animal's behavior, that is, continuous or contextual plasticity (Stamps, 2016). These types of plasticity differ in onset and duration of a sensitive period in trait expression (Table 2)
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