Data from: Macroecological patterns of sexual size dimorphism in turtles of the world

Sexual size dimorphism (SSD) is a well-documented phenomenon in both
plants and animals; however, the ecological and evolutionary mechanisms
that drive and maintain SSD patterns across geographic space at regional
and global scales are understudied, especially for reptiles. Our goal was
to examine geographic variation of turtle SSD and to explore ecological
and environmental correlates using phylogenetic comparative methods. We
use published body size data on 135 species from nine turtle families to
examine how geographic patterns and the evolution of SSD are influenced by
habitat specialization, climate (annual mean temperature and annual
precipitation) and climate variability, latitude, or a combination of
these predictor variables. We also found that geographic variation,
magnitude, and direction of turtle SSD are best explained by habitat
association, annual temperature variance, and annual precipitation. Use of
semi-aquatic and terrestrial habitats was associated with male-biased SSD,
whereas use of aquatic habitat was associated with female-biased SSD. Our
results also suggest that greater temperature variability is associated
with female-biased SSD. In contrast, wetter climates are associated with
male-biased SSD compared with arid climates that are associated with
female-biased SSD. We also show support for a global latitudinal trend in
SSD, with females being larger than males towards the poles, especially in
the families Emydidae and Geoemydidae. Estimates of phylogenetic signal
for both SSD and habitat type indicate that closely related species occupy
similar habitats and exhibit similar direction and magnitude of SSD. These
global patterns of SSD may arise from sex-specific reproductive behavior,
fecundity, and sex-specific responses to environmental factors that differ
among habitats and vary systematically across latitude. Thus, this study
adds to our current understanding that while SSD can vary dramatically
across and within turtle species under phylogenetic constraints, it may be
driven, maintained, and exaggerated by habitat type, climate, and
geographic location.