Sexual Selection and Life History Allocation

Abstract

Abstract A comprehensive explanation for sexual trait diversity depends on integrating life history theory and sexual selection to compare costs and benefits of sexual traits. A universal cost for all sexual traits involves the resources required to create and maintain them, which are consequently unavailable to other life history characters. This resource trade‐off typically causes covariance between an organism's resource budget and its level of sexual trait expression, which is known as condition‐dependence. Condition‐dependence has several implications. It may be particularly important for ornaments signalling genetic quality, by helping to maintain the genetic variation that favours mate choice. It may also reduce extinction risk in sexually selected populations. Further life history studies of sexually selected traits are required, mindful of the inherent difficulties in quantifying resource acquisition and allocation, not least of which is that these processes are not independent of one another. Key Concepts: Trait evolution is restricted by trade‐offs, where the benefit of increased investment in a trait is opposed by the cost of investment. The acquisition and allocation of resources is central to life history theory, but these processes are extremely difficult to quantify. Phenotypic correlations are not necessarily good metrics for the strength or importance of a trade‐off between traits. Condition‐dependence in mating systems featuring choice for indirect genetic benefits can help to maintain genetic variation for ornamental traits. Sex‐role reversed systems have life history features that may clarify some of the outstanding questions in sexual selection.