Article Review: "Skydiving" behavior observed in the Wandering Salamander (Aneides vagrans)

    In May of 2022, Christian E. Brown first described novel aerial behaviors among an arboreal salamander species, the Wandering Salamanders (Aneides vagrans), in an article titled "Gliding and parachuting by arboreal salamanders" that was published to Current Biology. Get ready- I hope you like physics! Prior to Brown's discovery, it was already well-known that Wandering Salamanders are found as disjunct populations in heavily wooded temperate forests. On the canopies of some of the Earth's tallest trees, they jump from canopy to canopy.

 

The Wandering Salamander, Aneides vagrans

    Several taxa, such as green anoles, ants, and spiders lack obvious aerodynamic control morphology yet control the fall through behaviors that manipulate force and momentum. These behaviors include gliding and "parachuting"- that is, redirecting their posture and falling at an angle greater than 45° from the horizontal, potentially with adaptations to increase drag. As an arboreal species, who's to say that the Wandering Salamanders weren't adapted to do this, too? They hypothesized that they likely had some adaptation to combat the dangers of falling from their arboreal habitats. So, Brown et. al used a wind tunnel to simulate a drop. They tested four Plethodontid species which ranged (in order) from highly arboreal to non-arboreal: Aneides vagrans, A. lugubris, A. flavipunctatus, and Ensatina eschscholtzii. In this wind tunnel, they dropped 5 individuals per species directly into the vertical airflow at constant speeds, which were predetermined based on the individual’s mass. They obtained 45 trials per species. They categorized each aerial behavior displayed into one of six categories: inert falling, laterally undulating, aerial righting, controlling for postural stability, parachuting with no lateral displacement, or gliding. Their results showed that I=in all 45 trials, Wandering Salamanders exhibited a controlled pitch, roll, and yaw (as in, the three dimensions an aircraft in flight may rotate) characteristic of a skydiving posture (Figure 1,E). Wandering Salamanders sustained their skydiving positions to reach a nominally constant vertical velocity (i.e. parachuting). They maintained this posture for a longer period than all other species tested (P<0.001).

 

Fig. 1, A-F: A-D is a bar plot comparison of the frequency of A. vagrans' aerial behaviors vs. three other species; E is a stereotypical skydiving posture, and F is an image of A. vagrans gliding in the wind tunnel.

    Gliding in Wandering Salamanders was defined as repeated tail and torso parasagittal undulations. In essence, they also exhibited behavior that allows slow-falling directed horizontal movement to decrease drag force. Brown et. al likened this controlled descent of Wandering Salamanders to very similar behaviors in small, arboreal squamates. Lastly, Brown et. al mentions the lack of aerodynamic features of Wandering Salamanders, but notes distinctive morphology that may assist in arboreal life. Firstly, Wandering Salamanders have flattened bodies, long limbs and toes, and large feet relative to body size- which is consistent with a highly arboreal lifestyle. When they parachute, their large feet and long toes form ventrally concave surfaces (Video S1), which they theorize may be useful in enhancing lift and drag. Lastly, their long limbs position the feet further from the center of body mass, which suggests that there is a possibility for enhanced aerodynamic torque and a potential adaptation for aerial maneuvering.

   

     These behaviors are very exciting, as salamanders already have quite a bit of uniqueness in comparison with other organisms. It adds to our understanding of amphibians as it reiterates their vast ecological diversity- especially for that of caudates, as we typically don't think of them as arboreal or aerial creatures! This study truly corroborates that ectotherms are found in nearly every ecological niche on Earth. The study and link are cited down below. 

 Brown, Christian E., et al. “Gliding and Parachuting by Arboreal Salamanders.” Current Biology, vol. 32, no. 10, 23 May 2022, pp. R453–R454., https://doi.org/10.1016/j.cub.2022.04.033.