Data from: Sexual dimorphism and sex-biased sampling influence analyses of trait evolution and diversity in a major songbird clade

Avian functional traits are widely studied in ecology and evolutionary
biology, and these traits are often quantified from museum study skins.
Across such studies, the sex ratio of specimens is highly variable or
often unreported, despite knowledge that many species are sexually
dimorphic in size and shape and that museum collections are sex-biased
toward male specimens. Our study explicitly quantified whether sex-biased
specimen sampling influences the answers to primary research questions
about avian functional trait diversity and evolution. We focused on the
songbird clade Emberizoidea, using an existing phylogenetic tree for this
clade and a large male-specific dataset for 10 functional traits. After
inter-measurer calibration, we collected a matching female-specific
dataset for 408 species to assess the degree of size and shape dimorphism
across the clade. We found that emberizoids are significantly dimorphic in
both size and shape. We then quantified three metrics of functional trait
diversity and found that estimated diversity differed significantly
between male, female, and pooled datasets for all metrics. We found that
all traits have strong significant phylogenetic signal that was of
comparable magnitude despite differing significantly between sex-biased
samples. We also modeled branch-specific rates of trait evolution and
found these inferences to be more nuanced. Estimated rate shifts were
largely congruent between sex-biased datasets, but branch-specific rates
of size evolution were strongly impacted by both the sex ratio of the
dataset and the choice of tool that quantified them. Thus, we found that
sex-biased sampling can influence the answers to primary research
questions in ecology and evolutionary biology. These issues may be avoided
by sampling sex ratios consistently across taxa in these studies. Further,
we recommend that these ratios should be clearly reported, and that
researchers sample specimens in a way that makes sense given their
questions and the biology of the organisms being studied.