Functional evolution of jumping in frogs: Interspecific differences in take‐off and landing

Abstract

Ancestral frogs underwent anatomical shifts including elongation of the hindlimbs and pelvis and reduction of the tail and vertebral column that heralded the transition to jumping as a primary mode of locomotion. Jumping has been hypothesized to have evolved in a step-wise fashion with basal frogs taking-off with synchronous hindlimb extension and crash-landing on their bodies, and then their limbs move forward. Subsequently, frogs began to recycle the forelimbs forward earlier in the jump to control landing. Frogs with forelimb landing radiated into many forms, locomotor modes, habitats, and niches with controlled landing thought to improve escape behavior. While the biology of take-off behavior has seen considerable study, interspecific comparisons of take-off and landing behavior are limited. In order to understand the evolution of jumping and controlled landing in frogs, data are needed on the movements of the limbs and body across an array of taxa. Here, we present the first description and comparison of kinematics of the hindlimbs, forelimbs and body during take-off and landing in relation to ground reaction forces in four frog species spanning the frog phylogeny. The goal of this study is to understand what interspecific differences reveal about the evolution of take-off and controlled landing in frogs. We provide the first comparative description of the entire process of jumping in frogs. Statistical comparisons identify both homologous behaviors and significant differences among species that are used to map patterns of trait evolution and generate hypotheses regarding the functional evolution of take-off and landing in frogs.

Pelvic function in anuran jumping: Interspecific differences in the kinematics and motor control of the iliosacral articulation during take‐off and landing

“…Figure presents sample traces for AP translation and angular excursion during take‐off and landing. Patterns in these variables are compared to mean force data and mean timings of kinematic events from Reilly et al ().…”

“…During landing in Rhinella , the CI motor pattern is characterized by two bursts (as are the LD and PF). This is likely related to their two‐phase landing behavior – i.e., hand landing first followed by the body‐feet landing (Reilly et al, ). However, the first CI landing burst is noticeable in only about half of the trials recorded for two individuals, and totally absent in the third individual.…”

“…Student's t ‐tests were used to investigate the temporal correspondence between key kinematic and EMG events within species. Moreover, because the trials of Lithobates and Rhinella used in this study are exactly the same trials as those for which force patterns were recorded, we were able to test the temporal correspondence between key kinematic and EMG events with the behavioral and force events presented previously (Reilly et al, ). In these comparisons, significance ( P < 0.05, adjusted after Bonferroni's correction) indicates that the two events occurred at different times.…”

“…Key behavioral and force events from the analysis of these species by Reilly et al (: Fig. ) are applied to this study.…”

“…For each trial we extracted AP excursion at the onset of the jump (start of leg extension), at the instant of take‐off, at the onset of landing (body hit or hands hit) and at any maxima and minima observed in each profile. In addition, we measured AP excursion at the time of peak take‐off forces (averaging time to peak vertical force and time to peak fore‐aft force; from Reilly et al, ). This is the time when maximum take‐off forces have been imparted to pelvic movements.…”