Data from: Phylogeny suggests non-directional and isometric evolution of sexual size dimorphism in argiopine spiders

Sexual dimorphism describes substantial differences between male and
female phenotypes. In spiders, sexual dimorphism research almost
exclusively focuses on size, and recent studies have recovered steady
evolutionary size increases in females, and independent evolutionary size
changes in males. Their discordance is due to negative allometric size
patterns caused by different selection pressures on male and female size
(converse Rensch's rule). Here, we investigated macroevolutionary
patterns of sexual size dimorphism (SSD) in Argiopinae, a global lineage
of orb weaving spiders with varying degrees of SSD. We devised a Bayesian
and maximum likelihood molecular species level phylogeny, then used it to
reconstruct sex specific size evolution, to examine general hypotheses and
different models of size evolution, to test for sexual size coevolution,
and to examine allometric patterns of SSD. Our results, revealing
ancestral moderate sizes and SSD, failed to reject the Brownian motion
model, which suggests a non-directional size evolution. Contrary to
predictions, male and female sizes were phylogenetically correlated, and
SSD evolution was isometric. We interpret these results to question the
classical explanations of female-biased SSD via fecundity, gravity, and
differential mortality. In argiopines, SSD evolution may be driven by
these or additional selection mechanisms, but perhaps at different
phylogenetic scales.