ENHS Nature Trails April 2001 Article 3

Space Monsters
by Tom Titus

Brown and slimy with protruding eyes and bulging glands on the sides of their heads that secrete an gooey white toxin. They come out only at night during the warm rains of a dying Pacific Northwest winter, appearing as if from nowhere to dance in underwater ritualized courtship. They are gone by morning, the only evidence of their presence a baseball-sized, slimy glob of jelly that gradually turns green over time, eventually rupturing to release the young into the water.

Something right out of the X Files, right? Not a bad guess. At least my wife thinks they look like space monsters. They are Northwestern Salamanders (Ambystoma gracile), one of my favorite local salamander species, and that's saying something because I like salamanders a lot. If the Pacific Giant Salamander is the Mac truck of Oregon salamanders, then the Northwestern Salamander is at least a Cadillac, and a good-sized adult can be 8 inches in total length. They are chocolate brown with large parotid glands on either side of the head. The Pacific Giant Salamander is the only species that a Northwestern Salamander might be mistaken for, but Giant Salamanders lack the parotid glands and exhibit a beige-on-brown marbled coloration.

You can find Northwestern Salamanders from the crest of the Cascades west to the Sitka spruce belt along the coast. By day they are subterranean, but they may come out at night to forage when conditions are moist. If you like searching for things, metamorphosed adults can occasionally be found under pieces of wood or other debris on the forest floor, having taken refuge there after a night spent searching for forest floor invertebrates. The most predictable method for observing adults is to drive a road on a rainy night in late winter, especially one that parallels a slow moving stream or pond, and watch for adults crossing the road to breed.

One of the things I find most fascinating about Northwestern Salamanders is their life cycle. Typically, adults breed in later winter and the eggs hatch in the spring. The egg masses turn green as a result of a species of alga that grows within the egg capsules. This alga increases the amount of dissolved oxygen available to the developing embryos, in return receiving nitrogen-containing compounds excreted from the embryos. The eggs hatch in the spring, and the larval salamanders spend their entire first year and the following summer in the natal pond, metamorphosing in the fall of their second year. This life history pattern requires permanent water, at least on an annual basis. There is a population of Northwestern Salamanders that breed in a farm pond at Mom and Dad's place east of Springfield, and last year the pond dried, eliminating one entire cohort (same age individuals) of salamanders in that population. It is likely that this year's drought conditions will adversely affect a large number of Northwestern Salamander populations that utilize such marginal breeding habitats. On the bright side, Northwestern Salamanders are apparently good at dispersal and will rapidly colonize a new breeding pond. Even if populations in these marginal ponds go extinct in the face of a long drought, even one lasting for years, they are likely to be recolonized soon after conditions improve.

Individuals in some populations may actually forgo metamorphosis, continuing to grow and eventually becoming sexually mature as gill-breathing larvae. This phenomenon is referred to generally as paedomorphosis, the presence of juvenile features in sexually mature animals, but this terminology opens a rhetorical can of worms, and I prefer the more generic and more easily understood term larval reproduction.

The frequency with which larval reproduction occurs in Northwestern Salamanders depends on several factors related to both aquatic and terrestrial habitats. To support a population of larval reproducers, the aquatic habitat must be stable over a long period of time (no larval reproducers in Mom and Dad's pond!) and must be relatively free of large predators. Larval salamanders are like candy to trout and bass because the salamanders did not evolve in the presence of these predators and thus have a limited bag of tricks available to avoid being eaten.. It would be interesting to know how many Northwestern Salamander populations in the High Cascade lakes are now extinct as a result of Eastern Brook Trout introductions. The frequency of larval reproduction is often higher in areas where terrestrial conditions are harsh, such as aridity, heavy snow pack, and/or cold temperatures throughout much of the year. One of my graduate school buddies referred to these sexually mature larvae as "snot monsters." A snot monster can be thought of as being like a space monster except that it has gills. This terminology has the advantage of allowing us to restrict our use of the term space monster to the metamorphosed adults.

Two populations inhabiting Scout Lake and Dark Lake east of the Cascade crest off Highway 126 appear to be composed entirely of larval adults. These lakes have all of the attributes associated with a high frequency of larval reproduction: a stable, fish-free aquatic habitat, surrounded by a dry, cold terrestrial environment not well suited to life as a metamorphosed salamander. Natural selection has eliminated all metamorphosing individuals, and by extension the genes that they carry, from these two lakes. Find Dark Lake on a map, go there in the summer after dark, and shine a flashlight into the shallows at the lake's edge. You'll be astounded at the number of salamanders resting on the bottom, having apparently come up from the depths of the lake to forage in the more productive shallows under cover of darkness.

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