Holaspis, a lizard that glided by accident: mosaics of cooption and adaptation in a tropical forest lacertid (Reptilia, Lacertidae)

Abstract

Holaspis is the most morphologically apomorphic lacertid taxon with 42 or more derived morphological features arising on its exclusive lineage. Nearly all of these confer advantages in three specialised activities, or ameliorate problems resulting from them. The activities are: climbing on the often vertical open surfaces on tree boles and branches, utilising very narrow crevices in wood and beneath bark, and the ability, unique among lacertids, to glide from tree to tree. Although many of the features related to these activities are likely to result from direct adaptation to the situations concerned, exaptation has been critical in the development of gliding. Two behaviours present in the earliest lacertids have been coopted to this activity: rib spreading associated with basking contributes to an effective aerofoil, and balance control associated with running helps maintain appropriate posture in the air. Features originally developed in the context of crevice use also contribute to the aerofoil and a high surface: weight ratio. So, while natural selection has moulded Holaspis for its present activities, multiple accidents of history have also been important, as they also have in the evolution of bird flight.