Adaptive tails? Parallel evolution of expanded tails in monsoonal tropics lineages of an Australian gecko radiation (Oedura)

Abstract

Abstract Ecological drivers of variation in the morphology of the lizard tail are understudied despite its important and varied functions in defence, locomotion, balance, climbing, and resource storage. We quantified variation in original tail shape and surface area-to-volume ratio (SA : V) in an Australian gecko clade (Oedura) and tested whether environmental variables are predictors of this variation. To use museum specimens, we developed an approach to straighten deformed preserved tails for accurate shape analysis. Tail shape varied from a relatively ‘typical lizard’ tail—long, tapered, and circular in cross-section—to a distinctive expanded, wide, and flat shape. Extreme versions of the latter shape seem to have evolved in parallel in two distantly related lineages. Wide tails and low SA : V ratio values occur in the Australian Monsoonal Tropics, while arid zone species all had a narrow, tapered tail with high SA : V. These data suggest expanded or bulbous tails may be analogous to succulence in plants and an adaptation for resource storage in environments with predictable peaks (wet season) and dearths (dry season) of resource availability. However, limited replicated evolution of bulbous tails precludes statistical significance in this case, and more analyses of tail anatomy in Oedura and other lizard clades are required to test this hypothesis further.