Synthesis of nature’s extravaganza: an augmented meta-meta-analysis on (putative) sexual signals

Pietro Pollo, Malgorzata Lagisz , Renato Chaves Macedo-Rego, Ayumi Mizuno , Yefeng Yang, Shinichi Nakagawa

Conspicuous traits that do not seem to contribute to the survival of their bearers, such as colourful body parts and bizarre behaviours, 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 7,428 individual effect sizes, shows that the conspicuousness of (putative) sexual signals is positively related to attractiveness and benefits to mates, as well as to the fitness, condition, and other characteristics (e.g. body size) of signal bearers. Importantly, most of these patterns are consistent across both taxa and sexes once within-study variation is considered, underscoring the generalisability of our results. However, we found evidence of publication bias for some of these relationships, meaning some of our results need to be taken with caution. Furthermore, the strength of 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 identify and select only traits that are truly used for mate attraction. Our study unifies several decades of knowledge on conspicuous traits, provides new insights about them, and lays a clear path for the future of this topic.