On weapons allometry and the form of sexual selection.

The study of trait scaling with body size (allometry) has a long history, and it has been argued that positive static allometry is an indicator of directional sexual selection. However, a range of allometries exists for sexually selected traits, and modelling shows this variation can be generated by altering the form of selection (fitness functions) on the trait and/or body size. Interestingly, in all models, positive allometry appears to emerge only when there is directional selection on trait size. Here, we report on a sexually selected trait that shows strong positive static allometry and yet appears to be under stabilizing selection. This surprising finding suggests the evolution of trait scaling is even more nuanced than currently appreciated.