Rhyacotritonidae

Relationships among the four recognized species of the family Rhyacotritonidae are based upon the allozymic study of Good et al. (1987). No fossils have been reported for this family (Estes, 1981).

Introduction

The salamander family Rhyacotritonidae contains four extant, geographically distinct species placed in the single genus, Rhyacotriton (Good and Wake, 1992). All species inhabit well aerated springs and streams in the humid coniferous forests of northwestern California, and the coastal and cascade regions of Oregon and Washington (Good and Wake, 1992).

Rhyacotriton has a biphasic life cycle with gilled, aquatic larvae and metamorphosed adults that generally live under rocks in streams, although adults also utilize moist terrestrial habitats on the forest floor. Good and Wake (1992) note that Rhyacotriton populations are closely tied to old-growth forest and do not tolerate logging, making Rhyacotriton a useful biological indicator of the recovery of degraded habitats.

Prior to the work of Good et al. (1987), Rhyacotriton was considered a single species, Rhyacotriton olympicus. This species was placed in the salamander family Ambystomatidae and later moved with Dicamptodon to the family Dicamptodontidae. Molecular phylogenetic studies (Larson, 1991; Larson and Dimmick, 1993) showed that Rhyacotriton is only a distant relative to the genera Ambystoma and Dicamptodon, which are closer phylogenetically to salamandrid and proteid genera than they are to Rhyacotriton. Rhyacotriton represents an ancient lineage within the clade of internally fertilizing salamanders and it has no close relatives. Good and Wake (1992) formally recognized the family Rhyacotritonidae to acknowledge the evolutionary distinctness of this taxon.

Characteristics

Diagnosis

Rhyacotritonids are relatively small salamanders (body length under 5 inches) having short tails and small heads with eyes proportionally large and prominent. Dorsal coloration is brown, sometimes mottled with grey, and the ventral coloration is yellow-orange, sometimes with black spotting. Costal grooves usually number 14-15 and are clearly demarcated.

Detailed Characteristics of the Rhyacotritonidae

The morphological characters given below are the ones standardly used to diagnose the salamander family Rhyacotritonidae and to assess its phylogenetic relationships to other salamanders. The individual characteristics are in most cases shared with other salamanders and should not be interpreted as synapomorphies of the Rhyacotritonidae. Absence of characteristics found in other salamanders is noted where it is important for distinguishing Rhyacotriton from other salamanders and/or determining its relationships to other salamanders. These characteristics were assembled from a large number of original sources by Duellman and Trueb (1986), Larson (1991), Good and Wake (1992) and Larson and Dimmick (1993).

Morphology of the Skull

The premaxilla consists of separated, paired bones. Nasal bones are absent or reduced in size. Premaxillary processes have long posterior extensions. Maxillary bones are present and well developed. Bilaterally paired septomaxillary bones are present. Lacrimal bone is present. Quadratojugal bone is absent. Pterygoid bones are present but small. Internal carotid foramina are present in the parasphenoid bone. The angular bone is fused to the mandible. Ear bones include a detached columella but no operculum. Replacement of vomerine teeth proceeds from the posterior of the vomer. Teeth have a distinct crown and pedicel. Origin of the levator mandibulae anterior superficialis muscle includes the exoccipital.

Inner Ear

A basilaris complex is present in the inner ear. Recessus amphibiorum is oriented horizontally in the inner ear. The otic sac is bulbar and unvascularized. The amphibian periotic canal lacks fibrous connective tissue. The periotic cistern is small and does not protrude into the fenestra.

Hyobranchial Structures

The first hypobranchial and first ceratobranchial (alternatively homologized as the first ceratobranchial and first epibranchial, respectively) exist as separate structures. The second ceratobranchial (alternatively homologized as the second epibranchial) comprises a single element. The otoglossal cartilage is present as a semicircular ring in the hyoid apparatus of adults. Lungs are present but reduced in size. An ypsiloid cartilage is present. Larvae have four pairs of gill slits. Presence of three larval gill rakers is unique to Rhyacotriton.

Characteristics of the Trunk and Vertebral Column

The scapula and coracoid bones of the pectoral girdle are fused to form the scapulocoracoid. Vertebral centra are amphicoelous. Ribs are bicapitate. Only the sacral and postsacral vertebrae have spinal-nerve foramina in their neural arches (foramen is partial in sacral vertebra). The pubotibialis and puboischiotibialis exist as separate muscles. Anterior glomeruli of the kidney are reduced or absent.

Reproductive Characters

Fertilization is internal. Ciliated epithelium is absent from the cloacal tube and anterior cloacal chamber of females. Epidermal lining is present in the anterior cloacal chamber of females. Evaginations are present in dorsolateral walls of the cloacal tube in males. Anterior ventral glands are absent from the cloacae of females. Spermathecae are present in the female cloacal chamber. Glands secreting into the dorsal walls of the female cloaca are absent. Anterior ventral glands are present in male cloacae. Kingsbury's glands are present in male cloacae. Dorsal pelvic glands are present in males. Lateral pelvic glands are present in males. Glands secreting into the male cloacal orifice are present. A tail-wagging display during courtship appears unique to Rhyacotriton. Parental care of eggs is absent.

The diploid number of chromosomes is 26.

Classification

The family Rhyacotritonidae was recognized by Good and Wake (1992) as containing the single genus Rhyacotriton. This genus formerly was placed in the families Ambystomatidae and Dicamptodontidae, but the phylogenetic analyses of Larson (1991) and Larson and Dimmick (1993) indicate that Rhyacotriton is only a distant relative of the other salamanders placed in these families.

Discussion of Phylogenetic Relationships

Knowledge of phylogenetic relationships among the four species of Rhyacotriton comes from the allozymic studies of Good et al. (1987). The phylogenetic relationships shown are revealed by analysis of Nei's genetic distances using UPGMA clustering, analysis of Rogers's genetic distances using the Fitch-Margoliash procedure, and analysis of presence/absence of protein variants using the Wagner phylogenetic method (Good et al., 1987). Outgroups were not used in these analyses, so the position of the root corresponds to the midpoint of the tree and should be considered tentative.

Other Names for Rhyacotritonidae

• Torrent Salamanders

References

Duellman, W. E. and L. Trueb. 1986. Biology of Amphibians. McGraw-Hill, New York.

Estes, R. 1981. Gymnophiona, Caudata. Handbuch der Paläoherpetologie 2:1-115.

Good, D. A. and D. B. Wake. 1992. Geographic variation and speciation in the torrent salamanders of the genus Rhyacotriton (Caudata: Rhyacotritonidae). University of California Publications in Zoology 126:1-91.

Good, D. A., G. Z. Wurst and D. B. Wake. 1987. Patterns of geographic variation in allozymes of the olympic salamander, Rhyacotriton olympicus (Caudata: Dicamptodontidae). Fieldiana Zoology New Series 32:1-15.

Larson, A. 1991. A molecular perspective on the evolutionary relationships of the salamander families. Evolutionary Biology 25:211-277.

Larson, A. and W. W. Dimmick. 1993. Phylogenetic relationships of the salamander families: A analysis of congruence among morphological and molecular characters. Herpetological Monographs 7:77-93.