Repeated evolution of viviparity in phrynosomatid lizards constrained interspecific diversification in some life-history traits.

In vertebrates, viviparity has evolved independently multiple times, apparently increasing morphological diversification and speciation rates as a consequence. We tested whether the evolution of viviparity has also increased diversification of life-history traits by estimating evolutionary rates of lizards from the North American family Phrynosomatidae. Using modern phylogenetic comparative methods, we compared these rates between oviparous and viviparous species, and found no support for this hypothesis. Instead, we found higher evolutionary rates for oviparous species in some life-history traits. Our results suggest that the evolution of viviparity may have constrained rather than facilitated evolution of life histories.