Juneau has four resident amphibians that breed in fresh water: wood frogs and western (boreal) toads, which have geographic ranges extending way up north, Columbia spotted frogs, which range to about the northern border of Southeast Alaska, and rough-skinned newts, which are at their northern limit in the Juneau area.
These newts (Taricha granulosa) are a west-coast species, from California northward. As the glaciers of the great ice ages retreated, newts apparently expanded their range into coastal British Columbia and then the island archipelago of southern Southeast; not too long ago, in geological time, they reached Admiralty and Shelter Islands. The move to Juneau, probably a few decades ago, is thought to have happened with human assistance.
How did they move north from one coastal island to another? There are several non-exclusive suggestions, but apparently nobody really knows. Perhaps not all of the present-day islands were separated by seawater when the big glaciers prevailed and more dry-land connections might have existed; then terrestrial dispersal may have been feasible in some areas, although land in front of the retreating glaciers would be perhaps too cold and barren. As the glaciers melted and sea levels rose, however, this potential pathway would disappear (unless the land, gradually released from the weight of ice, rose enough). But freshwater drainage from melting glacial ice would make a lens of fresh water on top of the sea water. Could that have helped dispersal? Or did they come down the big river drainages from the interior? But there is no known population source in British Columbia. Or did they get carried around by Native kids as pets, and eventually released on various islands? Or can adult newts tolerate seawater, at least for short periods? Exposure to salty water is known to have deleterious effects on newt embryos (and those of other amphibians), the degree of damage depending on the salt concentration and temperature, and very salty runoff from ice-melting roadway salts is bad for adults too. However, apparently the newts in some populations can tolerate brackish water. It might be surprising for an amphibian to tolerate salt water, although toads can, to some degree. But I have, so far, not found a study of salt tolerance in adult newts. The questions remain unanswered!
Adult rough-skinned newts are small, less than about eight inches long and have a pebbly texture on the back that gives them their name. (Courtesy Photo / Bob Armstrong)
Rough-skinned newts (and a variety of other critters) are well-known for a powerful neurotoxin (TTX for short) in the skin, which causes paralysis and is usually lethal to a consumer. However, toxicity varies among populations; for example, newts that live above 500 meters elevation are much less toxic and can be eaten by mammals and other predators. Toxicity also varies among individuals within many populations.
Various species of garter snakes are known to be resistant to this neurotoxin even in large doses (and egg-eating caddisflies are resistant to the toxin in newt eggs too). Most other predators are reported to be killed when the toxin is ingested (although they survive when eating newts from nontoxic populations). Garter snakes in areas with the most toxic newts tend to be the most resistant. The snakes are reported to be able to judge the toxicity of a newt by grabbing and partially swallowing it, rejecting the newt if it is too toxic. In turn, a newt can smell if a snake has recently eaten another newt and try to avoid it.
The initial, and appealing, story was of a co-evolutionary arms race between predator and prey. The arms race means that the more toxic prey escape more often, so more resistant predators then become more successful; they eat more newts and there then is natural selection for more toxic prey, which in turn favors more resistant predators, and so on. But the initial story was tested by exceptions: populations with no correspondence between newt toxicity and snake resistance, and now researchers suggest that various other factors are probably involved too. (Note: specimens from a particular lake on Wrangell Island and from Juneau were very toxic, but there are no garter snakes there; garter snakes are extremely rare in Southeast). Research continues.
Adult newts have dark backs and orange ventral surfaces. Toxic and venomous organisms often advertise their dangerousness to would-be predators, commonly with bright color contrasts. The combination of blackish and orange or yellow is one of these warning colorations, as in bumblebees and wasps. When an adult newt is threatened, it typically adopts a distinctive posture: arching the back, bending the head back over the shoulders and arching the tail over the body, thus displaying the warning colors. This color display deters at least some predators (and the presentation of a peculiar posture might look difficult to grab).
Newts are carnivores, eating a variety of worms, snails, crustacea, insects, spiders and such, as well as the eggs and tadpoles of other amphibians (and sometimes those of their own species), and occasionally small frogs. Adults are semi-terrestrial, often occurring under logs and other damp places on land.
They mate in fresh water in spring (at low elevations; later at high altitudes), sometimes migrating overland to suitable pools. A courting male becomes smoother-skinned and slimy. He climbs onto a female’s back, hugging her behind her forelimbs and wrapping his hind legs around her abdomen. He rubs his chin on her nose, releasing chemical signals from his chin gland. If she is receptive, she lifts her head, and the pair stays clasped together for an hour or more. They change their positions, and he releases a spermatophore, which she picks up with her cloacal vent. Then the male usually mounts the female again for a while (sometimes many hours), which prevents other males from interfering while the sperm are entering her reproductive tract. Competition among males is said to be intense, and the mate-guarding behavior protects a male’s investment.
Two or three weeks after fertilization of the eggs, a female lays them, singly, attached to vegetation. The eggs are toxic, like their mothers, and hatch in three or four weeks. Tadpoles have frilly, external gills and forage on protozoans and other tiny organisms on the vegetation, sometimes eating smaller tadpoles. Tadpoles metamorphose into adult form the following summer or the next summer, depending on the weather. Newts don’t mature until they are four or five years old, and mature females do not mate every year.
