The salamanders that live their entire lives in the crowns of the world’s tallest trees, California’s coastal redwoods, have evolved behaviors well suited to the dangers of falling from heights: the ability to parachute, glide, and maneuver in tunes.
Flying squirrels, not to mention many species of gliding frogs, geckos, ants, and other insects, are known to use similar aerial maneuvers when leaping from tree to tree or when falling, in order to stay in the trees and avoid landing on the ground. .
Likewise, researchers suspect that this salamander’s parachute jumping skills are a way to navigate itself to a tree it fell or jumped from, to better avoid terrestrial predators.
“While they’re skydiving, they have an exquisite amount of maneuverable control,” said Christian Brown, a doctoral student at the University of South Florida (USF) in Tampa and first author of a paper on these behaviors. “They are able to turn. They are able to turn around if they get upside down. They are able to maintain this skydiving posture and pump their tail up and down to perform horizontal maneuvers. The level of control is just awesome.”
The aerial dexterity of the so-called wandering salamander (Vagrans aneids) was revealed by high-speed video footage taken in a wind tunnel at the University of California, Berkeley, where the salamanders were pushed from a perch into an upward-moving column of air simulating free fall.
“What struck me when I first saw the videos is that they (the salamanders) are so gentle – there is no discontinuity or noise in their movements, they surf just totally up in the air,” said Robert Dudley, a professor of integrative biology at UC Berkeley and a specialist in animal flight. “That, to me, implies that this behavior is something deeply embedded in their motor response, that it (the fall) must occur at reasonably high frequencies in order to select on this behavior. isn’t just passive skydiving, they’re not just parachuting down, they’re also clearly doing the lateral movement, what we would call gliding.
The behavior is all the more surprising since salamanders, in addition to having slightly larger foot pads, are no different from other salamanders which are unwieldy in flight. They don’t have skin flaps, for example, which would tell you about their skydiving ability.
“Wandering salamanders have big feet, they have long legs, they have active tails. All of these things lend themselves to aerial behaviors. them,” Brown said. “So it’s not really a dedicated aerodynamic control surface, but it works like both. It helps them climb, and it also seems to help them parachute and glide.”
Among the questions the researchers hope to answer in future research are how salamanders manage to parachute and maneuver without obvious anatomical adaptations to gliding and whether many other animals with similar aerial skills have never been noticed before.
“Salamanders are slow, you wouldn’t think they have particularly quick reflexes. That’s life in the slow lane. And flight control is about reacting quickly to dynamic visual cues and being able to target, orient and change your body position,” Dudley said. “So it’s just a little weird. How often can this happen, anyway, and how would we know?”
An article describing the behavior will be published on May 23 in the journal Current biology.
life in the canopy
Using the wind tunnel, Brown and UC Berkeley graduate student Erik Sathe compared the gliding and skydiving behavior of A.vagrans – adults measure about 4 inches (10 centimeters) from snout to tip of tail – with the abilities of three other salamander species native to Northern California, each with varying degrees of treeiness – i.e. the propensity to climb or live in trees. The wandering salamander, which probably spends its entire life in a single tree, moving up and down but never touching the ground, was the most capable skydiver. A related species, the so-called arboreal salamander, A. lugubriswhich lives in shorter trees, such as oaks, was almost equally effective for parachuting and gliding.
Two of the least arboreal salamanders — Ensatina eschscholtziia forest floor salamander, and A. flavipunctatus, the occasional tree-climbing black spotted salamander – essentially fluttered about inefficiently for the few seconds it was airborne in the wind tunnel. All four species are plethodontid or lungless salamanders, the largest family of salamanders and are found primarily in the Western Hemisphere.
“The two less arboreal species wiggle a lot. We call it inefficient, undulating motion because they don’t slide, they don’t move horizontally, they just hover in the wind tunnel in a panic,” Brown said. . “The two most arboreal species never actually fought.”
Brown encountered these salamanders while working in Humboldt and Del Norte counties in California with nonprofit and university conservation groups that mark and track animals that live in the canopy of redwood trees, mostly in old-growth forest. about 150 feet above the ground. Using ropes and ascenders, biologists routinely scale the redwoods — the tallest of which rises to 380 feet — to capture and tag wandering salamanders. Over the past 20 years, in a project led by James Campbell-Spickler, now director of the Sequoia Park Zoo in Eureka, researchers found that most of their tagged salamanders could be found in the same tree. year after year, although at different heights. They live mainly in mats of ferns growing in humus, the decaying plant matter that accumulates at the junctions of large branches. Brown said few marked wandering redwood canopy salamanders have been found on the ground, and most of them have been found dead.
Brown noticed, while picking them up to mark them, that the salamanders quickly jumped out of his hands. Even a light tap on a branch or a passing shadow was enough to make them jump out of the redwood canopy. Given their location above the forest floor, their nonchalant leaps through the air were surprising.
“They jump, and before they’re even done jumping, they have their forelimbs spread out and they’re ready to go,” he said. “So the jump and the parachute are very closely linked. They take the position immediately.”
When he approached Dudley, who has studied such behavior in other animals, he invited Brown to bring some of the salamanders into his wind tunnel to record their behavior. Using a high-speed video camera shooting at 400 frames per second, Brown and Sathe filmed the salamanders for as long as they floated in the air column, sometimes for up to 10 seconds.
They then analyzed the frames to determine the animals’ posture in the air and infer how they used their legs, body and tail to maneuver. They usually fell at a steep angle, only 5 degrees from the vertical, but depending on the distances between the branches in the treetops of the redwoods, that would usually be enough for them to reach a branch or trunk before hitting the ground. Skydiving reduced their free fall speed by about 10%.
Brown suspects that their aerial skills have evolved to deal with falls, but are now part of their behavioral repertoire and perhaps their default method of descent. He and USF undergraduate student Jessalyn Aretz found, for example, that walking downhill was much more difficult for the salamander than walking on a horizontal branch or trunk.
“This suggests that when they roam, they’re probably walking on flat surfaces, or they’re walking uphill. And when they run out of habitat, as the upper canopy gets drier and drier, and there’s no nothing else for them. there they might just go back down to those better habitats,” he said. “Why go back down? You’re probably already exhausted. You’ve burned all your energy, you’re a little salamander 5 grams and you’ve just climbed the tallest tree on Earth. You’re not going to turn around and go down – you’re going to take the gravity lift.”
Brown sees A.vagrans as another poster child for old growth forests that is akin to the spotted owl as it is found primarily in the tops of the tallest and oldest redwoods, but also in Douglas fir and Sitka spruce .
“This salamander is a poster child for the part of the redwoods that has been almost completely lost to logging – the canopy world. There are none in these new forests being created by the corporations. logging,” he said. “Maybe it would help not only redwood conservation efforts, but also redwood restoration efforts, so we can actually get canopy ecosystems. Restore the redwoods to the point of carpet ferns, to the point of salamanders in the canopy – that would be a new bar for conservation.
In the meantime, this ancient forest dweller has a lot to tell us about evolution and possibly the origin of flight, Dudley said.
“It’s (gliding) a novelty, something unexpected in an otherwise well-studied group of animals, but it illustrates the urgency with which tree-dwelling animals need to develop their aerial ability, even if they don’t have wings,” Dudley said. mentioned. “Flight, in the sense of controlled aerial behavior, is very common. They control their body posture and move laterally. This predisposes many, many things that live in trees to eventually evolve into flapping flight, which is probably difficult to evolve and why he’s only appeared three times on the planet today.”
The paper’s co-authors with Brown and Dudley are Sathe and Stephen Deban, a professor of integrative biology at the University of South Florida.
The title of the article
Gliding and skydiving by arboreal salamanders (genus: aneids)
Publication date of articles
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