Ali Waleed

Why do frogs have the ability to jump?

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Frog limbs in deep time: is jumping locomotion at the roots of the anuran Bauplan?

By: Celeste M. Pérez-Ben, Andrés I. Lires, and Raúl O. Gómez

Summarized by: Ali Waleed is a biology major on the pre-med track at Binghamton University. When he isn’t studying, he likes to train in martial arts or go on hikes.

What data were used? They gathered limb data from both fossilized and modern frogs. For the sampling, they used 826 adult specimens. This comprised 48 species which are extinct. and 411 species which are alive today. They had a variety of living species in order to get an idea of the variation today in locomotion between different species of frogs. 

What was the hypothesis being tested? The goal of this paper was to retest a popular hypothesis which stated that the frog’s modern anatomical structure had evolved specifically for the frog to be able to participate in jumping locomotion. In order to test this, they attempted to construct what the original body plan of the ancestral frog species would have looked like, and then see how that body plan adapted to different environments requiring different modes of locomotion. They decided to revisit this hypothesis because of recent studies which have challenged the jumping hypothesis.

Methods: There was one outlier species that had limb proportions which were different enough from the other frogs for them to remove it from the study. For collecting the data, they measured the limb proportions of each frog. Specifically, they collected measurements on the lengths of the bones of the leg (i.e. the humerus, radio ulna, femur, tibia fibula, and proximal tarsals, as well as the metacarpal and metatarsal arches). The limb proportions themselves were relative to the total length of all of the fore and hind limb bones from each frog species. In the cases where they had multiple individuals representing a species, they took the average of the measurements between the individuals from each species. 

The measurements themselves were taken using a digital caliper, as well as digital photographs with a program called Screen Calipers. Using these measurements, they conducted an evolutionary analysis on the frogs by using the different measurements to determine the overall differences between the species used. Scientists produced an evolutionary tree showing how the major groups are related to one another (Fig. 1). The results of this analysis indicated that among modern living species, there are three categories of locomotion: jumpers, swimmers, or walker-hoppers. The researchers explained that these are generalizations of the many varied modes of locomotion found between different frog species and they assigned each species in the analysis to one of these categories. 

Results: They found that walker-hoppers and jumpers were different in terms of the size of their forelimbs and hindlimbs. The swimmers had limbs of an intermediate size. They found a lot of overlap overall with the swimmers in terms of limb size compared to the other two modes of locomotion. Out of the classifications for different modes of locomotion, they didn’t find one mode in particular which the ancestral frog body plan would have had. The statistical analyses the scientists used in the evolutionary analysis indicated that jumping appeared to be the most likely mode of locomotion for frog ancestors.

This image shows the major groups of anurans (Latin name for frogs). It was shared in the article because it shows evolutionary changes and speciation events between different frog species throughout time. This figure depicts an evolutionary tree, with time periods on the x axis and the different species of anurans (Latin name for frogs) on the y axis. The x axis covers the time periods Triassic, Jurassic, Cretaceous, and Paleogene, from 250 million years ago to the present. The tree begins in the Triassic period with Salienta, the common ancestor on this chart. From there it branches off into Triadobatrichus and the “Frog-like Bauplan” mentioned in the article. It also branches off into Anura at this point which are frogs. From Anura, there are further splits in the tree which are represented by Leiopelmatoidea, and Coatata. In the Jurassic period, the ancestral frog body plan branches off into Prosilarus, Nothobranchius, and Viarella. Also in this period, there are further branches within the Anuran tree depicting the species of Rhadinosteus, Rhinophynidae, Pipidae, Anomocoela, and Neobatrachia.
Fig. 1 The evolutionary relationships frog species through different geological periods. It depicts how modern-day frogs are related to the ancestral frog body plan. It shows where different speciation events occur as well, where the branches occur. Most of the speciation shown on this figure depicts it happening during the Jurassic and Triassic periods. It depicts when certain species are thought to have gone extinct by the length of the branches, as well as various species which are known to still exist today.

Why is this study important? This study was important because scientists can learn about how certain limb proportions in animals can help achieve certain tasks. Perhaps having a certain size of hind-leg is indeed greater for jumping: this would help us identify jumpers from the fossil record more easily.

Broader Implications beyond this study: Overall, they found a variety of modes of locomotion within the various species of frogs, and so they couldn’t state that any mode was used by the ancestral frog body plan. The scientists  hypothesized that this was due to repeated homoplasy, meaning independent evolution of traits over time rather than receiving traits from an ancestral species. Because of this, they suspected that there may not have been a particular mode of locomotion such as jumping which set the ancestral frog body plan apart from other organisms. They conclude the article by saying that future studies should start considering other hypotheses on what set the ancestral frog body plan apart from other organisms at the time. 

Citation: Pérez-Ben, C. M., Lires, A. I., & Gómez, R. O. (2024). Frog limbs in deep time: is jumping locomotion at the roots of the anuran Bauplan? Paleobiology, 50(1), 96–107. doi:10.1017/pab.2023.23