Inconsistency between different measures of sexual selection

Measuring the intensity of sexual selection is of fundamental importance in the study of sexual dimorphism, population dynamics, and speciation. Several indices, pools of individuals, and fitness proxies are used in the literature, yet their relative performances are strongly debated. Using twelve independent common lizard populations, we manipulated the adult sex ratio (ASR), a potentially important determinant of the intensity of sexual selection at a particular time and place. We investigated differences in the intensity of sexual selection, as estimated using three standard indices of sexual selection: selection gradients (β′), opportunity of selection (I), and Bateman gradients (βss), calculated for different pools of individuals and different fitness proxies. We show that results based on estimates of I were opposite to those derived from the other indices, while those based on estimates of β′ were consistent with predictions derived from knowledge about the species' mating system...