Variation of outbreeding responses with explanatory variables (effect modifiers). Outbreeding responses are given as proportion changes in phenotype relative to the mid-parent phenotype. An outbreeding response of zero means hybrid offspring have phenotype equivalent to the mid-parent value. Positive values represent phenotypic benefit relative to parent lineages. (a) Overall pooled outbreeding response (for a model fitting only an intercept). (b) – (l) Variation of outbreeding responses with individual explanatory variables. Points give posterior means for the pooled effect sizes (on the relative phenotypic scale). Error bars bracket the corresponding 95% credible interval. n
give respectively the number of studies and the number of effect sizes underpinning each estimate. See Methods and Additional file 1: Text S2 for a description of the explanatory variables.