Evolutionary innovations of squamate reproductive and developmental biology in the family Chamaeleonidae

Abstract

The availability of molecular phylogenies has greatly accelerated our understanding of evolutionary innovations in the context of their origin and rate of evolution. Here, we assess the evolution of reproductive mode, developmental rate and body size in a group of squamate reptiles: the chameleons. Oviparity is ancestral and viviparity has evolved at least twice: Bradypodion and members of the Trioceros bitaeniatus clade are viviparous. Viviparous species are medium-sized as a result of convergence from either small-sized ancestors or large-sized ancestors, respectively, but do not differ from oviparous species in clutch size, hatchling size or the trade-off between clutch and hatchling size. Basal chameleons (Brookesia, Rhampholeon and Rieppeleon) are small-sized and have developmental rates comparable with those of other lizards. Derived chameleons (Calumma, Chamaeleo, Trioceros and Furcifer) are mostly large-sized and all have relatively slow developmental rates. Several clades of derived chameleons also exhibit developmental arrest (embryonic diapause or embryonic diapause plus cold torpor) and incubation periods extend to 6-10 months or more. Developmental arrest is associated with dry, highly seasonal climates in which the period favourable for oviposition and hatching is short. Long incubation periods thus ensure that hatching occurs during the favourable season following egg laying. © 2010 The Linnean Society of London.