Fly Away Little Salamander

Humans have long been fascinated by flight. As a dominant terrestrial species, the notion of sustained suspension in the air has created a wonder that transcends both cultures and generations (Alexander, 2002). While the flight of birds has created an entire industry, from bird watching to backyard feeders (Tobalske, 2006), many other species have mastered aerial locomotion through other means: Gliding and controlled descent, not just a trait of flying squirrels, but also… flying salamanders. 

Aneides vagrans, the wandering salamander, has an unusual habitat for an amphibian: it lives among the tallest trees on Earth in California’s Redwood Forest (Spickler et al., 2006). This habitat may seem odd, however, the fog that rolls in from the Pacific Ocean has created a moisture-rich haven that is ideal for the species. To quickly maneuver through this arboreal habitat, controlled descent has given the salamander a competitive advantage (Brown et al., 2022). While it was demonstrated that the species was reluctant to jump, it was nonetheless an efficient approach to descent in response to predatory cues. If the species began jumping to evade predation, there was likely a selection pressure towards those who could survive the fall by slowing down their descent and directing themselves to a lower branch (Brown et al., 2022). 

So how does this phenomenon occur? It all comes down to physics and anatomy. By analyzing the salamanders in a wind tunnel, Brown et al. (2022) discovered that the species was able to control its pitch (side-to-side rotation), roll (front-to-back rotation), and yaw (rotation around the vertical axis). This allows them to right themselves while falling by creating a skydiving posture (Figure 1): a body angle of up to 39° and repeated movements of the tail and torso. This posture maximizes the frontal area and therefore increases drag, which reduces their falling velocity by up to 10% (Brown et al., 2022). Furthermore, by changing their body posture the salamander can create a descent angle of 5-6° (Figure 2) (Lentink, 2022). 

Figure 1: The wandering salamander, Aneides vagrans, in a wind tunnel. The salamander rights ifself by maneuvering its tail and then assuming a skydiving posture. This reduces vertical velocity by increasing drag and lift (Brown et al., 2022).

Figure 2: A free body diagram demonstrating the forces acting on a wandering salamander during free-fall. The salamander’s position allows it to control its lift-to-drag ratio which ultimately allows it to direct its motion forward by 5-6° (Lentink, 2022). 

Other anatomical features that help the salamander are their long digits and large feet. These form a concave surface that further helps with drag and lift control (Holden et al., 2014; Brown et al., 2022). Their long limbs may also help increase torque as the feet are farther away from the center of their body. 

Finally, it is important to analyze the salamander’s takeoff. There are two factors that make this species of salamander unique: they have two-footed takeoffs, and they have less lateral bending before their jump than other salamanders (Brown and Deban, 2020). It was reported that the two-footed takeoff allows the salamander to enter the skydiving posture more quickly and lower lateral bending reduces the amphibian’s takeoff velocity (Figure 2). 

Figure 3: The wandering salamander’s jump. Sections A and B demonstrate a “toe-off” where the animal uses the vertical portion of the platform to push off from one front toe. Sections C and D demonstrate the final push-off from the back two legs, which allows for a quick transition to the skydiving posture. Finally, all sections of the figure demonstrate a lack of lateral trunk bending, which contributes to a reduced takeoff velocity (Brown and Deban, 2020).

This leaves us wondering if the wandering salamander will ever be able to truly fly away. As evolution has no means to plan ahead, we will likely never have a clear answer. However, by studying different species and populations we can better understand why they have evolved to their current morphology. Furthermore, we must analyze the selection pressures that they are currently facing in their habitat to better understand what could possibly improve their evolutionary fitness.

References

Alexander, D.E., 2002. Nature’s Flyers: Birds, Insects, and the Biomechanics of Flight. JHU Press.

Brown, C.E. and Deban, S.M., 2020. Jumping in arboreal salamanders: A possible tradeoff between takeoff velocity and in-air posture. Zoology, 138, p.125724. https://doi.org/10.1016/j.zool.2019.125724.

Brown, C.E., Sathe, E.A., Dudley, R. and Deban, S.M., 2022. Gliding and parachuting by arboreal salamanders. Current Biology, 32(10), pp.R453–R454. https://doi.org/10.1016/j.cub.2022.04.033.

Holden, D., Socha, J.J., Cardwell, N.D. and Vlachos, P.P., 2014. Aerodynamics of the flying snake Chrysopelea paradisi: how a bluff body cross-sectional shape contributes to gliding performance. Journal of Experimental Biology, 217(3), pp.382–394. https://doi.org/10.1242/jeb.090902.

Lentink, D., 2022. How wingless salamanders fly. Nature, 606(7913), pp.251–252. https://doi.org/10.1038/d41586-022-01375-x.

Spickler, J.C., Sillett, S.C., Marks, S.B. and Jr, H.H.W., 2006. Evidence of a new niche for a North American salamander: Aneides vagrans residing in the canopy of old-growth redwood forest. Herpetological Conservation and Biology, Vol. 1(1): 16-27. [online] Available at: <http://www.fs.usda.gov/treesearch/pubs/25045> [Accessed 26 September 2022].

Tobalske, B.W., 2006. FLIGHT OF FASCINATION: Avian Flight. Journal of Experimental Biology, 209(11), pp.2005–2006. https://doi.org/10.1242/jeb.02229.


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