The effect of miniaturization on the evolution of sexual size dimorphism in geckos

The evolution of miniaturization can result in dramatic alterations of morphology, physiology and behavior; however the effects of miniaturization on sexual dimorphism remain largely unknown. Here we investigate how miniaturization influences patterns of sexual size dimorphism (SSD) in geckos. Measuring 1,875 individuals from 131 species, we characterized patterns of SSD relative to body size across two families. We found that miniaturized species were more female-biased than nonminiaturized species. Additionally, one family, Phyllodactylidae, contained few miniaturized species and displayed an isometric trend in SSD with body size, where changes in female body size were accompanied by similar changes in male body size. By contrast, Sphaerodactylidae, which contained many miniaturized species, displayed strongly allometric patterns, where larger species were male-biased and smaller species were more female biased. Smaller species in this lineage also produced proportionally larger eggs. Together, these observations are consistent with the hypothesis that selection for increased reproductive success in small species drives the positive SSD allometry observed in the lineage, and that selection for increased miniaturization in the clade may be offset by selection on maintaining a female size in smaller taxa that ensures reproductive success.

Methods
We measured body size (snout-to-vent length: SVL) from a total of 1,875 adult specimens using digital calipers, with a minimum 124 of 3 males and 3 females per species. Measurements were log-transformed and the mean of the of each species by sex combination was calculated.