The Season of the Newt

Listen in to Director Emeritus Paul Licht’s fascinating talk about the newts mating cycle in the Japanese Pool, then plan your visit to see them through March.

[Transcript]

PAUL LICHT

This is Paul Licht, Director [Emeritus] of the University California Botanical Garden, and I’d like to tell you about one of the fascinating and cute little denizens of the Garden, because this is the season of the newt. It would be an understatement to say that I like plants, but one of my first research projects in an earlier life as a zoologist at Cal dealt with the newt, and I now find myself immersed in them again.

The Japanese Pool here at the Garden is a major breeding site for local newts. And this is the season when the action really gets going. The California newts Taricha are salamanders, a kind of amphibian, They look like lizards, about 5 to 8 in long, with brown backs and yellowish orange bellies and long tails. But unlike lizards, they have the typical moist skin of amphibians. And they breed and lay eggs in the water, which is what they’re doing now.

The Japanese pool actually houses two species of newt. The two look very much alike. And in fact, it’s almost impossible to tell them apart unless you’re an expert. However, they’re very distinctive when it comes to egg-laying. The most familiar species, Taricha torosa, lays its eggs in masses of several dozen.

The eggs look like little yellowish BB’s encased in a gelatinous, clear, golf ball-sized mass. This egg mass is typically attached to a twig or a stem of a submerged plant. Like the water lilies we have. In contrast, the second species, Taricha granulosa, lays eggs singly, wrapping each one in the small leaf of an aquatic plant. The single eggs are not usually seen by visitors.

The eggs of both species hatch into tiny larvae in about a month. Unlike frog tadpoles, these larvae look like little miniature adult newts with four limbs, but they have external gills and translucent skin, unlike the lungs of the adult. They spend the summer in the water feeding on tiny invertebrates—unlike frog tadpoles, which are mostly vegetarians—and in the fall the newts metamorphose into the adult form and leave the pond.

The tiny little newts, about an inch long, disappear into the Garden and hopefully will return after several years to breed again. And this is when you’ll first see them. Amazingly, during the summer, we rarely see these young ones or even the many thousands of older, larger adults that live in the Garden, and we’re still unsure of what they do most of the time.

We become aware of them again in the fall, when they start emerging from their summer hiding places with the rains. This is when they begin searching for food, worms and small invertebrates. We have to put up caution signs on our roads and drive carefully to avoid hurting them. In nearby Tilden Park, some of the roads are closed starting in November and newt crossing signs are posted to protect them.

Most of the movement occurs at night, especially wet nights, but you’ll often see them wandering around during the day as well. When conditions are right, sufficient rain and perhaps warm enough, the newts begin their migration to the pond. First the males return and they’re transformed into a more aquatic form. Their skins get smoother and shiny. Their tail flattens and looks like a fin, which is enlarged for swimming, and their muscles, especially in the front legs, enlarge to enable them to hold on to females during courtship.

The males may spend weeks or even months in the pond waiting for females, and some can usually be found in the water year-round. In contrast, the females return to the pond slightly later and don’t show the dramatic aquatic transformation, and they leave shortly after laying their eggs. Courtship is what most visitors will often observe. A male tries to hold onto the back of a gravid— that is, a female with eggs—rubbing the top of her head with his chin while he releases chemicals that are designed to stimulate her.

In the meantime, they’re swimming around. Often a large mating ball forms, with several males jockeying for the attention of one female. Sometimes it even looks like they can drown the female. But don’t worry, they can all hold their breath for long periods.

Eventually, one male seems to win. He’ll then release the female and then begin slowly walking along the bottom of the pond, enticing her to follow until he deposits a tiny package of sperm on the pond floor. The female has to pick this up and uses it to fertilize her eggs as they are released.

The female then goes off on her own to lay her eggs. You can often observe a female holding on to vegetation as she lays her eggs, and forms the gelatinous egg ball. Hopefully the cycle will repeat itself and one or more of her offspring will return to breed, perhaps five years later.

Newts may live for a long time, 10 to 20 years, maybe longer, and breed almost every year, but evidently they only rarely successfully produce a surviving young. Reason for the longevity of the adults is their very potent toxin produced in the skin. Few predators can eat a newt and live to tell the tale.

An interesting recent discovery show that in some northern parts of the newt range around Oregon, garter snakes are starting to feed on newts because they have apparently evolved the ability to detoxify them. We see lots of garter snakes in and around our pond in Berkeley during the summer, but never eating newts. It turns out that the Berkeley newts are among the most poisonous of any population, and the snakes haven’t caught up with them. In fact, the newt poison here is one of the most potent of any animal toxin.

One aspect of the story that I worked on when I first came to Cal, concerned what made the newts migrate to the water to start breeding. This behavior is called water drive and can be easily demonstrated in a terrarium. Normally, newts will try to stay out of the water, but when water drive sets in, they want to enter the water and it’s hard to keep them out of it.

And then they start transforming as I described. We found that this behavioral change was induced by a hormone called prolactin that was produced in a tiny gland, the pituitary gland at the base of the brain. This hormone is virtually identical to the one produced by mammals, including humans like ourselves. Where it gets its name from its role in inducing milk formation called lactation in females, you can induce water drive in a newt by injecting it with human prolactin. We don’t know if newt prolactin will induce lactation, however. Our hormones have evidently been around for a long time. We just started using them for new purposes.

I hope you’ll have a chance to visit the Garden and stand in front of the Japanese Pool to enjoy the biological spectacle of the newt season. This is one of the best places to watch them in the Bay Area, because of the crystal-clear water that we have.

They can almost always be seen, just stand quietly and watch for their movement, or look around for the egg masses. The newts know they’re safe with us, and will soon be out to put on a show for you.