Anti-Predator Mechanisms in Salamanders

Kari Yoshida

"...While removing the skin from a T. granulosa, the senior author jabbed a sharp forceps into his left index finger. Efforts were made to remove as much blood as possible from the injury. Despite these efforts there was an intense burning sensation at the point of injury followed within a few minutes by numbness. This loss of feeling progressed up the arm, eventually involving the entire left arm and shoulder. This sensation persisted for about 30 minutes and was accompanied by light-headedness and dizziness." (Brodie Jr., 510)
     Various salamanders are known for their extensive anti-predator mechanisms such as this example of the Taricha granulosa (Rough-skinned Newt). There exists today 450 good species of salamanders. Of this 450 salamanders, approximately 19 live here in Oregon. These species are derived from a total of five families including; Ambystomtidae, Dicamptodontidae, Rhyacotritonidae, Salamandridae, and Plethodontidae. Of these, nine species are found to display at least one type of anti-predator mechanism.
 
     Anti-predator mechanisms come in an array of flavors. Those prevalent in Oregon salamanders include distasteful/toxic skin secretions, warning color patterns, immobility, biting, tail autotomy, flipping, warning postures, tail lashing, and vocalization. (Some others that aren't found in Oregon salamanders include mimicked color warning and projected ribs through the side of its body).
 
     Noxious and/or toxic skin secretions irritate and repel predators and is probably the most important technique. The fluid can irritate the lining of the mouth and/or eyes and act as a deterrent when disturbed while others have the potential to kill certain predators. When approached by a predator, the fluid is secreted by the paratoid glands of the salamander which are enlarged areas at the backside of its head. Secretion can also be sprayed onto its predator by its granular glands.
 
     Warning coloration is another mechanism for an anti-predator response, which are usually correlated with the secretions of toxins and acts as an avoidance cue (Brodie, Jr. 533). Coloration can be present on either the dorsum or venter (back or frontside of salamander, respectively). Suggested aposematic colors include orange, red, yellow, or white with contrasting black. Most effective designs are suggested to be alternating rings, longitudinal stripes, or spots (Poulton, 1890). Pseudoaposematic coloration is when a non-secreting salamander poses as one that does by secrete mimicking its warning colorations. This will only work, however, when the predator has learned to avoid the colors that are associated with the noxious/toxic secretions.
 
     Displaying of colors lead us to the topic of warning postures. There are many postures salamanders contort themselves into as a defense mechanism. One example is the coiled body, where its snout is positioned under its vent region. Another is where its venter (underside) is exposed by either lifting its tail, chin, or both depending how intense the reflex is. Its body, in this case, can be coiled or uncoiled. This position is relatively prevalent in the Salamandridae family, commonly known as the "unken reflex". A head butted position is when its head is flexed in a vertically downward fashion, swinging the parotoid region toward predator. Most species vocalize while butting (Brodie Jr., 115).
 
     Immobility is a basic response, where the salamander attempts to decrease the chances of the predator actually distinguishing it from its environment. The predator sometimes only attack prey that move. They do not recognize the salamander as potential prey when limbs are tucked in, and body contorted since they appear resemble twigs or straw. Immobile salamanders are also ignored by avian predators while moving ones are attacked (Dodd and Brodie, 1976). However, if the immobile salamander has been spotted and attacked, intensity of the attack itself is lessened, reducing potential of injury (Brodie Jr., 533).
 
     The salamander can also flip its body back and forth (also known as flashing) by coiling and uncoiling with rapid movements, propelling itself with its tail, or by laterally writhing its body, resembling a small snake. This flip-flop movement usually precedes immobility, and can startle and confuse the predator causing its attack to be misled (Brodie Jr., 533).
 
     Tail lashing is the most active anti-predator mechanism since it entails forceful swinging of the usually elevated tail and also lashing of its granular glands into the predator, exposing its noxious/toxic secretions.
 
     Other mechanisms include biting, which can inflict painful wounds, tail autotomizing, which is the breaking off of its tail when attacked to confuse predator, and also vocalization. Some salamanders give off a low pitched yelp when approached by predators (Brown, et al., 36).
 
     Ambystoma gracile can be found from the coast of Oregon to the crests of the Cascades. It shows a defensive posture by closing its eyes and head butting. It elevates its tail and also secretes sticky, white poison from its paratoid glands which can kill small animals. A. gracile has concentrations of granular glands along its tail dorsum, making it unpalatable to predators. It also lashes its tail when encountered by a predator. Ambystoma tigrinum is not very common in Oregon, however a few have been cited along the Columbia River and south of Klamath Falls. Its anti-predator mechanisms are similar to that of the A. gracile where it elevates the rear portion of its body on its hind limbs and arches its long tail into the air, lashing its tail forcibly toward stimulus. This lashing often emits secretion (Brown, et al 20).
 
     Batrachoseps attenuatus can be found in the extreme southwest of Oregon. This salamander coils its body and tail in a spiral manner when approached by predator, and may result in violent flipping. When utilizing its immobility technique, its dorsal stripe enables it to mimic millipedes, which are unpalatable to most predators but has no distasteful skin secretions (Brodie Jr., 532) It also autotomizes its tail as a second mechanism. Batrachoseps wrighti can be found only in the west slopes of the Oregon Cascades and has anti-predator mechanisms very similar to that of the B. attenuatus (Brown, et al 94, 98).
 
     Dicamptodon copei can be found in northwestern Oregon. Its best defense mechanism is biting which can be quite formidable. Dicamptodon tenebrosus can be found from the coast to the Cascades of Oregon. Its anti-predator mechanisms are similar to that of the D. copei. It also bites, inflicting painful cuts, and also produce vocalizations, something which is uncommon among salamanders. When preyed on, they produce a very low-pitched yelp (Brown, et al 30, 34).
 
     The Ensatina eschscholtzii is found west of the Cascades in forest regions where it is humid. This species has various anti-predator mechanisms, and is probably the most effective defensively compared to other Oregon salamanders. When attacked, it assumes a warning posture by arching its back, keeping body high off the ground and swinging its heavy tail side to side. It also can secrete milky poison more noxious than that of Plethodon (Brodie Jr., 532), autotomize and lash its tail, and vocalize (Brown, et al 84).
 
     Plethodon larselli's method of defense is by remaining immobile, taking advantage of its dorsal stripe. It too, may use its stripe to resemble a millipede during an immobilized state.
 
     Taricha granulosa lives predominantly on the western side of the Cascades. Its venter being bright orange serves as an aposematic color pattern. It secretes a poison called tetrodotoxin which is also identical to the toxins of puffer fishes. There are known human deaths from this salamander (Brown, et al 56). However, there exists snakes such as the Thamnophis fulvus, which are immune to the toxins of T. granulosa, probably due to an evolved resistance to its skin secretions (Baness, 61).

A bibliography was not included with this paper.