Summary of the Results.

Generalised Least-squares (multiple) regression analyses controlling for phylogeny and sample size. Index of Variation in Sperm Size = coefficient of variation (CV) in sperm total length. Index of Variation in Sperm Design = scores of the first principal component (PC1) from a Principal Component Analysis of CVs of three independent sperm components: head, flagellum and midpiece lengths; PC1 explained 85% of the interspecific differences in CVs. All the relationships above were independent of: (a) phylogeny: the fitted models did not differ significantly from equivalent models where the λ estimate was set as 0 (Likelihood Ratio Tests: P>0.99; see Ref. 21 and 76); and (b) sample size (GLS: sample size term, P>0.15). All analyses conducted on transformed variables. See Methods for more details.