The role of hand, feet, and digits during landing in anurans

Abstract

Jumping consists of a series of complex movements with more variability in landing than in take-off. Different modes have been described concerning the landing phase, which seems to be linked to the general phylogenetic relationships of anuran groups. For example, the belly hit has been recorded in the basal-most living frog family Leiopelmatidae. Here we used high-speed videography to observe the role of hand and foot digits in landing behavior in ten species of neotropical anurans exhibiting different locomotor modes. We also calculated the time-lapse of each jump. We hypothesize that the role of digits can be pivotal to many anuran species during terrestrial landing. We also present data on the comparative anatomy of digits and those parts of the hands and feet involved in landing. Our video records show that landing through hand hit among anurans is performed with the distal curved phalanges of the hand digits. The morphological results show that all species surveyed, even the walker ones, exhibit distally curved phalanges, in lateral view. Movements of the distal phalanges of the hand are a key to understanding landing in anurans. All digits must be resistant to compression, since all the weight of the body falls on them. Digit hit seems to be action-driven by an elastic mechanism, which could indicate the activation, for example, of the flexor digitorum communis muscle. Landing in terrestrial frogs like Rhinella arenarum and Leptodactylus chaquensis follows a highly coordinated and synchronic pattern, with a longer time-lapse to complete each jump. Arboreal jumping frogs like Scinax fuscovarius and Boana riojana and semiaquatic hoppers like Pleurodema borellii and Physalaemus biligonigerus tend to be asynchronic and uncoordinated, but with a shorter time-lapse to complete each jump.