Differences between urban and natural populations of dwarf chameleons (Bradypodion damaranum): a case of urban warfare?

Urbanisation creates novel environments, not only through (abiotic) microhabitat alterations, but also due to changes in (biotic) inter- and intraspecific interactions. Where sheltering sites in urban habitats are limited, intra or interspecific interactions may increase, resulting in increased competition and changes in predation risk in urban areas compared to natural habitats. The Knysna Dwarf Chameleon (Bradypodion damaranum) occurs in both urban and natural settings, is extremely ornamented, and individuals have been observed with multiple wounds and scars. We therefore hypothesised that urban populations may have adapted to the physical features of urban habitats, and that this would be detectable through ornament size and bite force, as well as the presence of scarring. We quantified these traits from urban and natural populations from two separate localities (the towns of George and Knysna, South Africa). Our results showed that female and male B. damaranum from urban populations had a higher number of injuries and that urban males were more likely to be injured than males from natural habitats. Bite force was only recorded at one locality (Knysna), but both sexes in urban habitats had higher bite force when accounting for casque height as compared to those from the natural habitats. Urban chameleons also had less developed ornamentation but wider and/or higher heads compared to populations in natural habitats. Urban habitats had significantly lower tree density than natural habitats, and this may be a factor in driving the morphological differences between populations, whereby reduced ornamentation confers an advantage for remaining cryptic to predators in the open habitat but compromises the ability for signalling conspecifics with encounters escalating to physical contests.