Aerial maneuvering by plethodontid salamanders spanning an arboreality gradient.

Wandering salamanders (Aneides vagrans) inhabit the crowns of the world's tallest trees, taking refuge in epiphytic fern mats within these complex arboreal environments. These salamanders readily jump from the canopy when disturbed and maintain stable postures while falling via fine adjustments of the limbs and tail in lieu of dedicated aerodynamic control surfaces, thus reliably carrying out non-vertical descent. Here, we examined the aerial behavior and performance of A. vagrans and three other species of plethodontid salamander across a habitat gradient of arboreality by recording salamanders falling from short heights and moving within the jet of a vertical wind tunnel. Kinematic performance of aerial behavior in plethodontid salamanders was correlated with a gradient of arboreal habitats; moreover, salamanders from arboreal niches were more effective in slowing and redirecting descent compared with other salamanders. Aneides vagrans and the closely related Aneides lugubris consistently engaged in parachuting and gliding when falling; their trajectories were very steep, but were sufficiently angled to enable contact with either the home trunk or nearby branches during falls or jumps from great heights. Aerial maneuvering in arboreal salamanders is similar to that seen in other vertebrates capable of non-vertical and controlled descent, suggesting that the long limbs and active tail of these arboreal plethodontids (often cited as adaptations for climbing) may also contribute to parachuting and gliding when falling from trees. These aerial behaviors within the redwood canopy warrant further investigations into other canopy residents that lack conspicuous surfaces for aerodynamic control.

Characterizing lift, drag, and pressure differences across wandering salamanders (Aneides vagrans) with computational fluid dynamics to investigate aerodynamics.

Wandering salamanders (Aneides vagrans), known to occupy the crowns of old growth coast redwood trees, have recently been found to decelerate and engage in controlled, nonvertical descent while falling. Closely related, nonarboreal species with seemingly minor morphological differences exhibit far less behavioral control while falling; however, the influence of salamander morphology on aerodynamics remains to be tested. Here, we examine differences in morphology and aerodynamics of two salamander species, A. vagrans and the nonarboreal ensatina salamander (Ensatina eschscholtzii), using a combination of traditional and contemporary techniques. Specifically, we compare morphometrics statistically, then use computational fluid dynamics (CFD) to characterize predicted airflow and pressure over digitally reconstructed models of the salamanders. While similar in body and tail lengths, A. vagrans are more dorsoventrally flattened with longer limbs and greater surface area of the foot relative to body size than the nonarboreal E. eschscholtzii. CFD results show dorsoventral pressure gradients differ between the two digitally reconstructed salamanders resulting in lift coefficients of approximately 0.02 and 0.00, and lift:drag ratios of approximately 0.40 and 0.00 for A. vagrans and E. eschscholtzii, respectively. We conclude that the morphology of A. vagrans is better suited for controlled descent than that of the closely related E. eschscholtzii and highlight the importance of subtle morphological features, such as dorsoventral flatness, foot size, and limb length, for aerial control. That our simulation reports align with real-world performance data underscores the benefits of CFD for studying the link between morphology and aerodynamics in other taxa.

Air-to-land transitions: from wingless animals and plant seeds to shuttlecocks and bio-inspired robots.

Recent observations of wingless animals, including jumping nematodes, springtails, insects, and wingless vertebrates like geckos, snakes, and salamanders, have shown that their adaptations and body morphing are essential for rapid self-righting and controlled landing. These skills can reduce the risk of physical damage during collision, minimize recoil during landing, and allow for a quick escape response to minimize predation risk. The size, mass distribution, and speed of an animal determine its self-righting method, with larger animals depending on the conservation of angular momentum and smaller animals primarily using aerodynamic forces. Many animals falling through the air, from nematodes to salamanders, adopt a skydiving posture while descending. Similarly, plant seeds such as dandelions and samaras are able to turn upright in mid-air using aerodynamic forces and produce high decelerations. These aerial capabilities allow for a wide dispersal range, low-impact collisions, and effective landing and settling. Recently, small robots that can right themselves for controlled landings have been designed based on principles of aerial maneuvering in animals. Further research into the effects of unsteady flows on self-righting and landing in small arthropods, particularly those exhibiting explosive catapulting, could reveal how morphological features, flow dynamics, and physical mechanisms contribute to effective mid-air control. More broadly, studying apterygote (wingless insects) landing could also provide insight into the origin of insect flight. These research efforts have the potential to lead to the bio-inspired design of aerial micro-vehicles, sports projectiles, parachutes, and impulsive robots that can land upright in unsteady flow conditions.

Gliding and parachuting by arboreal salamanders.

Wandering salamanders (Aneides vagrans) reside in the crowns of the world's tallest trees and have been observed to readily jump from the canopy when disturbed1,2. Here, we describe the aerial performance of falling A. vagrans, which maintain stable gliding postures via adjustments of the limbs and tail in lieu of specialized control surfaces. In wind tunnel trials, A. vagrans parachuted consistently and slowed their vertical speed by up to 10% while falling. Furthermore, A. vagrans coupled parachuting with parasagittal undulations of the tail and torso to effect gliding at non-vertical angles (minimum of ∼84°) in 58% of trials. Selection pressures imposed on falling from heights can be substantial, and have resulted in the evolution of diverse aerial behaviors among arboreal taxa; nonetheless, aerial behavior occurring in arboreal salamanders is surprising, and calls for further work on the natural occurrence of falling, gliding, and directed aerial descent in canopy-dwelling tetrapods.

Jumping in arboreal salamanders: A possible tradeoff between takeoff velocity and in-air posture.

Jumping performance can have important implications for an animal's fitness by expanding its ability to evade predators and move between microhabitats. Jumping in terrestrial plethodontid salamanders is achieved through lateral bending and rapid unbending of the trunk, an action powered by axial musculature. Arboreal plethodontids, some of which are known to occupy tree crowns, tend to have more robust limbs and longer digits, which may affect their jumping kinematics and performance. We examined jumping kinematics in ten species of plethodontid salamanders, including four arboreal species of the genus Aneides, using high speed imaging and kinematic analysis. Salamanders of the genus Aneides exhibit lower takeoff velocities when compared with the terrestrial plethodontids Eurycea, Desmognathus, and Plethodon, possibly due to reduced trunk bending. Aneides also exhibit higher frequencies of two-footed takeoffs, and often orient their feet to launch from vertical surfaces when presented with the option. This suggests an alternative jumping behavior in salamanders that may reflect an arboreal lifestyle. All plethodontid species examined displayed distinctive in-air parachute postures after 45-100% of descending jumps, with Aneides showing the highest frequency of this behavior.