Aerial maneuvering by plethodontid salamanders spanning an arboreality gradient

Abstract

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

“…Performance data from the vertical wind tunnel confirms that only A. vagrans can glide and can do so at steep angles (Brown et al, 2022a(Brown et al, , 2022b. We also discerned from CFD simulations that the lift:drag ratio changes with angle of attack (Table 4).…”

“…From the fluid-preserved specimens measured above, we selected one of each species to be scanned and reconstructed for CFD analyses. We formalin-fixed salamanders into a skydiving posture (Figure 1) with the limbs extended laterally and dorsally and the tail elevated dorsally to form the classic U-shape body of a falling salamander (see Brown et al, 2022aBrown et al, , 2022b for detailed descriptions of posture). Formalin fixing maximized rigidity during the 3D scanning process, allowing for multiple scan positions without deformation.…”

“…When the simulations reached 100 iterations or converged, we then computed static pressure contours, velocity magnitude vectors, static pressure pathlines, and velocity magnitude pathlines for each mesh. Aerial performance data from a vertical wind tunnel (Brown et al, 2022a(Brown et al, , 2022b were used both to inform and interpret our CFD predictions; moreover, because A. vagrans has been observed gliding at steep angles while pivoting in body angle, we varied the simulated angle of attack for that species from 0°, 5°, and 10°in CFD.…”

“…We used the Ansys Student 2022 (Ansys, Inc.) R2 Workbench bundle to create a digital wind tunnel to visualize airflow patterns around the meshes. The digital wind tunnel was rectangular and built with dimensions based on the physical wind tunnel used to test live performance (Brown et al, 2022a(Brown et al, , 2022b: 30 x 25 x 30 cm. We imported the.obj files into ANSYS SpaceClaim (Ansys, Inc.) and built a fluid domain enclosure around the geometry.…”

“…Body shape is more flattened in A. vagrans, perhaps accounting for the increased disruption to airflow and greater dorsoventral pressure gradient discussed above. Finally, both salamanders have functionally identical Reynolds numbers (Brown et al, 2022a(Brown et al, , 2022b due to being so close in length, mass, and general shape, and thus Reynolds number is likely not contributing to differences in aerodynamics or aerial performance.…”