Diversity: Arboreal

Introduction

Arboreal species tend to have relatively large heads and eyes, with long legs and slim waists. As well as leaping they are just as likely to move by quadrupedal walking and climbing. In fact many hylids, hyperoliids and rhacophonids (treefrogs) are incredibly proficient climbers and possess enlarged toe disks to aid sticking to trees and leaves, often capable of moving on leaves upside down. (Pough 1996).

The enlarged toe pads have an epidermal layer made up of peg like projections that are separated by canals, with mucus glands opening into these canals that secrete a viscous solution. Sticking is by means of wet adhesion, with the mucus establishing a meniscus at the interface between air and fluid. (Emerson 1980).

The efficiency of sticking ability varies between species and families, but the treefrogs tend to perform better. Some non-arboreal anurans are also particularly good at sticking, having varying forms of toe pad to help move across slippery surfaces, although they will often rely also on using the abdomen as another adhesive surface. The toe pads are removed by peeling, from the rear forwards during forward movement, with no detachment forces involved. This method of detachment is particularly effective, as it does not waste any energy in overcoming the sticking forces of the toe pads. Instead, the peeling is a natural consequence of the way in which the toes are lifted from the rear. This method means that the toe pads can never be placed facing down a slope, or it will automatically peel off. (Emerson 1980). (Hanna 1991).

Many arboreal species contain an extra set of extensor muscles in their fingers as an adaptation to arboreality, although some non-arboreal species also contain this extra set of muscles, but they probably had an arboreal ancestor and retained the hand muscles as a conserved feature. Arboreal species that lack this muscle would most likely, therefore, have had non-arboreal ancestors. (Burton 1998).