A hitherto overlooked type of colour change in frogs and its significance for the identification of species in the Australian genus Neobatrachus

Colour change is a well-known phenomenon in many amphibians. Most of these changes involve transient darkening, lightening, or attainment of breeding colours. Nuptial calosities may become lighter outside the main breeding season. Depigmentation as an extreme form of lightening has been documented also for keratinized structures of tadpole mouths. Here I report a hitherto overlooked type of colour change: darkening of metatarsal tubercles from white to almost black. At Kinchega National Park in New South Wales, individuals of the Australian borrowing frog Neobatrachus pictus emerging from their aestivation burrows after rains had white outer metatarsal tubercles. Within a few hours to two days the metatarsal tubercles had turned completely black. This indicates that the extent of black colouration of the outer metatarsal tubercle hitherto used to discriminate the species N. centralis from N. pictus and N. sudelli is unreliable.