RhyacotritonidaeTorrent Salamanders

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Four species in a single genus are recognized in this small family of brook-dwelling salamanders. Geographic distribution is limited to the northwestern coastal United States, from Northern California through Washington, especially in the Cascade mountains.

Torrent salamanders are characterized by unique squared-off glands behind the vent in adult males. Other morphological traits that distinguish this family include the absence of an operculum and opercularis muscle (otherwise absent only in a few species of hynobiids), and greatly reduced lungs (also observed in all plethodontids and a few species of hynobiids). Torrent salamanders have several adaptations for their life in fast-moving streams, including reduced gill rami, short fimbriae, and restriction of tail fins posterior to the vent. Maximum adult snout-vent length is 6 cm, but body size varies widely among populations. Torrent salamanders exhibit complete metamorphosis, although some paedomorphic characters have been identified in adults, including the presence of conical teeth, reduced or absent nasal bones, and cartilaginous carpal and tarsal bones.

Both adult and larval torrent salamanders inhabit cold, fast-moving, well-shaded seepages and streams in old-growth forests. They have very low heat tolerance, and may die in a state of heat rigor at temperatures as low as 83° F (28° C). Buccopharyngeal movements have been demonstrated to play a significant role in the respiration of torrent salamanders. They are particularly susceptible to the effects of logging, so may make for appropriate biological indicators in the study of degraded habitats. Male Rhyacotriton are extremely aggressive to one another, chasing and biting at intruders, especially during courtship with a female. Courtship involves a unique tail-wagging display just before the deposition of a spermatophore. Eggs are deposited singly in water beneath stony rubble. Fertilization is internal, as in all members of the suborder Salamandroidea. There is no parental care. Larval development is slow (three to five years), due in part to the low temperature of the water. Age of first reproduction is thus later than in most salamanders. Predator defense behaviors include undulation of the tail, the assumption of a coiled or immobile body, or the exposure of the often brightly colored venter.

There has been much disagreement over the phylogenetic relationship of the rhyacotritonids to other salamanders. The type genus, Rhyacotriton, was believed to be monotypic until recently. Rhyacotritonids were originally believed to be mole salamanders, united with Dicamptodontinae in the Ambystomatidae. They were later moved to the new family Dicamptodontidae, and have only recently achieved family status themselves. Current analyses suggest that they do not form a monophyletic group with the ambystomatids and dicamptodontids. Some researchers have suggested a relationship with the lungless plethodontids instead. By comparison, several analyses suggest that Rhyacotritonidae is the basal taxon in the Salamandroidea, the so-called "advanced salamanders."

No fossil rhyacotritonids are known.

Cogger, H. G., and R. G. Zweifel, editors. 1998. Encyclopedia of Reptiles and Amphibians, 2nd edition. Academic Press, San Diego.

Duellman, W. E., and L. Trueb. 1986. Biology of Amphibians. Johns Hopkins University Press, Baltimore, MD.

Larson, A., K. d. Queiroz, D. Heyse, and T. Jackman. 1996. Rhyacotritonidae: Tree of Life. in.

Pough, F. H., R. M. Andrews, J. E. Cadle, M. L. Crump, A. H. Savitzky, and K. D. Wells. 1998. Herpetology. Prentice-Hall, Inc., Upper Saddle River, NJ.

Stebbins, R. C., and N. W. Cohen. 1995. A natural history of amphibians. Princeton University Press, Princeton.

Zug, G. R. 1993. Herpetology: an introductory biology of amphibians and reptiles. Academic Press, San

Contributors

Heather Heying (author).

Glossary

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.