Synthesis of Nature's Extravaganza: An Augmented Meta-Meta-Analysis on (Putative) Sexual Signals.

Colourful body parts and bizarre displays that do not seem to contribute to the survival of individuals that express them have puzzled biologists for centuries. Sexual selection theory posits that these traits evolved because more conspicuous individuals attract more mates and experience greater fitness, yet evidence for this remains fragmented. Our augmented meta-meta-analysis of 41 meta-analyses, encompassing 375 animal species and 7428 individual effect sizes, shows that the conspicuousness of (putative) sexual signals is positively related to mate attractiveness, fitness benefits, individual condition, and other characteristics (e.g., body size) of signal bearers. Most of these patterns are consistent across both taxa and sexes, underscoring the generalisability of our results. Furthermore, the strength of pre-copulatory sexual selection on conspicuousness is positively associated with the relationship between (i) conspicuousness and fitness benefits and (ii) conspicuousness and individual condition. This suggests that the relationships we assessed regarding trait conspicuousness would be stronger if we could select only traits that are truly used for mate attraction. Our study unifies several decades of knowledge on conspicuous traits, confirms many predictions made by the theory of sexual selection, and lays a clear path for the future of research on this topic.