Are evolutionary transitions in sexual size dimorphism related to sex determination in reptiles? - Electronic supplementary material

Sex determination systems are highly variable in vertebrates, although neither the causes nor the implications of this diversity are fully understood. Theory suggests that sex determination is expected to relate to sexual size dimorphism, because environmental sex determination promotes sex-specific developmental bias in embryonic growth rates. Furthermore, selection for larger size in one sex or the other has been proposed to drive the evolution of different genetic sex determination systems. Here we investigate whether sex determination systems relate to adult sexual size dimorphism, using 250 species of reptiles (Squamata, Testudines, Crocodylia) representing 26 families. Using phylogenetically informed analyses, we find that sexual size dimorphism is associated with sex determination: species with TSDIa sex determination (i.e. in which the proportion of female offspring increases with incubation temperature), have more female-biased size dimorphism than species with TSDII (i.e., spe...