Sexual selection and sexual size dimorphism in animals

Sexual selection is often considered as a critical evolutionary force
promoting sexual size dimorphism (SSD) in animals. However, empirical
evidence for a positive relationship between sexual selection on males and
male-biased SSD received mixed support depending on the studied taxonomic
group and on the method used to quantify sexual selection. Here, we
present a meta-analytic approach accounting for phylogenetic
non-independence to test how standardized metrics of the opportunity and
strength of pre-copulatory sexual selection relate to SSD across a broad
range of animal taxa comprising up to 95 effect sizes from 59 species. We
found that SSD based on length measurements was correlated with the sex
difference in the opportunity for sexual selection but showed a weak and
statistically non-significant relationship with the sex difference in the
Bateman gradient. These findings suggest that pre-copulatory sexual
selection plays a limited role for the evolution of sexual size dimorphism
in a broad phylogenetic context.