Evolutionary origins of viviparity in Chamaeleonidae
© 2019 Blackwell Verlag GmbH Historically, an understanding of viviparity and its evolution in Old World chameleons (Chamaeleonidae) has lagged behind that of other squamate families. Not only is reproductive information scarce or entirely absent for most chameleon species, but the literature reveals no consensus as to the frequency and ecological circumstances under which chameleon viviparity evolved. We integrated information on reproductive modes for nearly all chameleon species with recently published family-scale phylogenetic and ecological analyses to clarify aspects of reproductive evolution in chameleons. Ancestral-trait reconstructions, after accounting for phylogenetic uncertainty, indicated that viviparity has arisen a minimum of three times in Chamaeleonidae, with each origin of live birth in closed-canopy forests. Our maximum-likelihood optimization therefore did not support the previous hypotheses of one, two or four origins of viviparity in the family. Past claims that arboreality would not allow for evolution of viviparity were also not supported, nor was a recent suggestion that viviparity has reverted to oviparity. However, cold climates of high latitudes and elevations may have selected for viviparity in arboreal chameleons. While peritoneal pigmentation may facilitate viviparity, its role as an exaptation rather than an adaptation remains equivocal without data from a wider range of chameleon species. Based on a comprehensive review of reproductive modes throughout the family, our study has resolved the number of origins of viviparity in Chamaeleonidae and provided evidence that live birth evolved under arboreal conditions on three separate occasions in this enigmatic squamate group. This study also reveals the value of using phylogenetic analysis in a manner that is robust to uncertainty (rather than simple correlational approaches) when the goal is to reconstruct evolutionary sequences and selective pressures.