Washington, July 22 (ANI Frogs became proficient at jumping before they perfected landing. according to a new study.
Dr. Richard Essner from Southern Illinois University Edwardsville in the US and colleagues believe this evolutionary split, characterized by an inability to rapidly rotate the limbs forward during flight in order to land front legs first, might also explain why primitive frogs' back legs are out-of-phase with one another when they swim.
Essner's research appears in Springer's journal Naturwissenschaften.
Prior to this study, it had generally been assumed that all frogs jumped in a similar manner by rapidly extending their back legs during the propulsive phase and rotating the limbs forward during flight so that they could land front legs first. However, no studies had looked at the jumping behaviour of the most primitive living frogs of the family Leiopelmatidae, which uniquely among frogs use a trot-like rather than a frog-kick swimming gait.
Essner and team compared the jumping behaviour of leiopelmatids with that of more advanced frogs. They analysed video footage from 5 species - 3 primitive (Ascaphus montanus, Leiopelma pakeka, and L. hochstetteri) and advanced (Bombina orientalis and Lithobates pipiens).
They found that although launch movements were similar among the species, primitive frogs maintained extended back legs throughout their flight and landing phases and did not land on their front legs. These belly flop landings limited their ability to jump again quickly.
According to Essner, this unique behaviour of leiopelmatids shows that the evolution of jumping in frogs was a two-step process with symmetrical back leg extension jumping appearing first and mid-flight back leg recovery and landing on forelimbs appearing later. The frogs' inability to rapidly cycle the limbs may also provide a functional explanation for the absence of synchronous swimming in leiopelmatids. It is also plausible that the reason these primitive frogs have unusual anatomical features such as large, shield-shaped pelvic cartilage and abdominal ribs is to prevent damage to their internal soft tissues and organs during uncontrolled landing.
The authors conclude: "The simple shift to early hind limb recovery may have been a key feature in the evolutionary history of frogs, facilitating controlled terrestrial landings and enabling rapid repetition of jumping and swimming cycles. These changes may have offered advantages for longer distance locomotion, better landing postures and improved predator avoidance and foraging." (ANI)