John H. Larsen

The feeding system of terrestrial tiger salamanders (Ambystoma tigrinum melanostictum baird)

High speed cinematography was used to record the feeding activities of terrestrial Ambystoma tigrinum melanostictum. A description of these activities based on films of more than 50 feeding sequences is presented, and the mechanical units involved are defined, described, and functionally analyzed. Evolutionary implications of the feeding system are discussed.

Postembryonic ontogeny of the spadefoot toad, Scaphiopus intermontanus (Anura: Pelobatidae): skeletal morphology.

Postembryonic skeletal ontogeny of the pelobatid frog Scaphiopus intermontanus is described based on a developmental series of cleared‐and‐stained, whole‐mount specimens. The focus is on laboratory‐reared individuals fed a herbivorous diet as larvae. Although there is variation in the timing of ossification of individual skeletal elements relative to developmental stages based on external morphological criteria, the sequence of skeletal development generally is conservative. Compared with its close relative, S. bombifrons, ossifications that occur during prometamorphosis tend to be slightly delayed in S. intermontanus; however, cranial bones that ossify during late metamorphic climax in S. intermontanus are delayed until postmetamorphosis in S. bombifrons. The differences in timing between the two species are consistent, however, with differences observed between two developmental series of S. intermontanus raised at two different temperatures. Noteworthy features of skeletal development in S. intermontanus include: 1) presence of palatine ossifications that form from independent centers of ossification and soon fuse with the postnarial portion of the vomers to form the compound vomeropalatine bones; 2) compound sphenethmoid that may arise from four or more endochondral centers of ossification and one dorsal, dermal center of ossification; and 3) presence of transverse processes and vestigal prezygapophyses on the first postsacral vertebra. The morphology of the larval orbitohyoideus and interhyoideus muscles is compared. The record of skeletal ontogeny and muscle morphology presented herein for the herbivorous larval morph can serve as a baseline for comparisons with the ontogeny of the carnivorous larval morph of Scaphiopus. J. Morphol. 238:179–244, 1998.

Demography and migratory patterns of the eastern long-toed salamander, Ambystoma macrodactylum columbianum

The breeding migration of the eastern long-toed salamander, Ambystoma macrodactylum columbianum, was studied at a small pond in NW Idaho using a drift fence and pitfall traps. During the period of 27 Feb.-25 April 1983, 2030 adult salamanders (1054 males and 976 females) were intercepted at the drift fence. The timing of migratory events was influenced by a combination of environmental and biological factors: 95% of all migration occurred when the minimum air temperature was 0 C or greater and 78% of all migration occurred on days with measurable precipitation. The pattern of migratory movement was either continuous or episodic, depending on the prevailing pattern of air temperatures and precipitation. Female salamanders arrived at the breeding pond later than males and appeared to leave the pond soon after oviposition; male emigration began shortly thereafter. No preferred migration routes with respect to various measures of habitat quality (i.e., habitat type, relative soil moisture, or vegetation type) were evident. Individual salamanders, however, did tend to use the same habitat for immigration and emigration. Based on the computed sampling efficiency of the drift fence, population size was estimated at 3141 adult salamanders (1986 males and 1155 females) in a 1.7:1 male: female sex ratio.

Interspecific, ontogenetic, and life history variation in the tooth morphology of mole salamanders (Amphibia, Urodela, and Ambystomatidae)

As revealed by scanning electron microscopy, three basic cusp shapes are found on the premaxillary teeth of mole salamanders: disc, cone, and club. In fully metamorphosed adults, tooth crowns are subdivided into labial and lingual cusps. Except for species of Linguaelapsus, the labial cusps of all adult bifid teeth are disc shaped; lingual cusp shape is more variable, but the taxonomic distribution of the various configurations is generally consistent within the subgroups Rhycosiredon, Ambystoma, and Linguaelapsus. The club shape appears to be a derived character state, but the cone and disc shapes may be either primitive or derived. Prior to the start of metamorphosis, all larvae have conical, monocuspid teeth. During metamorphosis these salamanders develop incipient bifid teeth that have the same basic adult pattern of cusp shapes but in which the cusps are smaller and more generalized. Crown morphology in paedomorphic ambystomatids is similar to that of older larvae; as such, paedomorphosis seems to interrupt and retard the ontogenetic sequence of development rather than to introduce (or reintroduce) novel morphologies into the developmental program. In larvae the crown is firmly attached to the tooth base along the putative zone of weakness, but in transformed adults the crown is separated from a pedicel by a narrow zone of fibrous connective tissue. This latter structural arrangement allows unidirectional lingual flexing of the crowns relative to the pedicel and appears to facilitate the process of tooth replacement.

Postembryonic Ontogeny of the Spadefoot Toad, Scaphiopus intermontanus (Anura: Pelobatidae): External Morphology

We provide a detailed description of and a staging table that portrays the ontogeny of the Great Basin spadefoot (Scaphiopus intermontanus Cope) from the just-hatched larva through the adult. We concentrate on the development of external morphological characters as observed in individuals raised under controlled laboratory conditions. We suggest that our staging table, besides providing greater detail, is more appropriate than a generalized staging table for describing the ontogeny of species within Scaphiopus. Also, unlike other staging tables, we delineate stage bound- aries. We recommend the use of stage boundary criteria for the construction of all future staging tables. Our findings indicate that some aspects of Scaphiopus ontogeny may be unique. Unlike other anuran larvae with sinistral spiracles, the operculum in S. intermontanus does not pass through a stage in which there are two separate openings. Other features, such as mouthpart characteristics, may be useful for intrageneric larval identification; however, we show that at least the labial tooth-row formula variation is affected by both rearing temperature and geographic origin of the specimen sample. Finally, rearing conditions possibly affect the timing of certain developmental events in S. intermontanus. Specifically, the timing of hindlimb differentiation seems to be labile relative to when differentiation occurs in other morphological features. table DETAILED DESCRIPTIONS of the ontog- eny of embryonic, larval, metamorphic, and postmetamorphic frogs (Anura) are important for understanding the general pattern(s) of development of representa- tive taxa and, by comparisons of different patterns, for resolving questions about sys- tematic relationships. For anurans, staging tables are a condensed way of describing ontogenetic changes. In a review of the lit- erature, Fox (1984:30) indicated that of the few thousand known species of anu- rans there are complete staging tables- fertilized egg through the completion of metamorphosis-for fewer than 20 spe- cies. Just et al. (1981: their Table 3) com- pared the staging tables of a number of these species. Most of the tables that have been constructed are for species contained in the genera Bufo and Rana. Two of the most detailed tables, for the African

Structure and function of the hyolingual system in Hynobius and its bearing on the evolution of prey capture in terrestrial salamanders

The Hynobiidae is generally regarded as the most phylogenetically basal and least derived extant family of terrestrial salamanders. As in the other families of terrestrial salamanders, prey capture in the Hynobiidae is accomplished by lingual prehension. In Hynobius, the prey capture system appears to be a mosaic of derived and primitive features. This, in conjunction with previous studies, suggests that the hyolingual systems of all families of terrestrial salamanders have evolved various degrees of specialization since the appearance of the common ancestral condition. We propose that the generalized feeding system for the extant terrestrial salamanders includes a hyolingual skeleton comprised of one basibranchial, one pair of radial or radial‐like structures, two pairs of ceratobranchials, two pairs of epibranchials, one pair of ceratohyals, and one urohyal arranged in a configuration similar to that of Hynobius; a simple, sac‐like secondary tongue pad; a lift and thrust system of tongue projection; a four‐part gape cycle; and a forward head and body surge. Modifications to this general plan, previously described for the disparate families, include various changes in the size, shape, and definition of the tongue pad, changes in the specific types of structures and configurations in the anterior hyolingual skeleton, secondary ossification in the posterior hyolingual skeleton, the appearance of various protrusion, projection, and flipping systems for tongue protraction, simplification of the kinematic gape profile, and loss of the forward head and body surge. The evolutionary trends in these modifications have provided a rich data set from which much phylogenetic information has been inferred.

Ontogenetic alterations in the gross tooth morphology of Dicamptodon and Rhyacotriton (amphibia, urodela, and dicamptodontidae)

During ontogeny, the apical and basal components of dicamptodontid teeth exhibit three major developmental stages: nonpedicellate, subpedicellate, and pedicellate. Premetamorphic larvae tend to have nonpedicellate teeth, incompletely or recently metamorphosed individuals tend to have subpedicellate teeth, and fully transformed adults usually have pedicellate teeth. In concert with this transition, cusp morphology is modified from a larval monocuspid, to an incipiently bicuspid, to definitive adult bicuspid, and finally to an adult monocuspid condition. Thus, the larval and adult monocuspid conditions are ontogenetically distinct. The morphology of the larval monocuspid, adult bicuspid, and adult monocuspid conditions differs between Dicamptodon and Rhyacotriton. However, the incipient bicuspid condition in these two genera is very similar in appearance, suggesting that Dicamptodon and Rhyacotriton may be more closely related to each other than to the family Ambystomatidae in which they both sometimes are placed. The method of establishing ontogenetic trajectories seems to be preferable to comparisons based on adult structure, since similarities in the morphology of adults often is owing to convergent or parallel evolution.

Reproductive Biology of the Larch Mountain Salamander (Plethodon larselli

ABSTRAcr. - The Larch Mountain salamander Plethodon larselli Burns, is a potentially threatened species endemic to a narrow corridor along the Columbia River in the states of Washington and Oregon (Herrington and Larsen, 1985). Its reproductive biology is poorly understood. Males are 39-42 mm SVL and 3-31/2 years of age when they reach sexual maturity; females mature a year later, and are >44 mm SVL. At the onset of markedly increased precipitation in the fall, courtship is inferred from the presence of sperm masses in female cloacae. The number of eggs in a clutch ranges from 2-12 (x = 7.33) and is not significantly correlated with the size of the female. Large females may exhibit biennial ovarian cycles; however, many females above the minimum size for sexual maturity are non-reproductive and either become reproductive after reaching age 4 or have ovarian cycles >2 years.

Current status, habitat requirements and management of the Larch Mountain salamander Plethodon larselli burns

The Larch Mountain salamander Plethodon larselli is endemic to a narrow corridor along the Columbia River gorge where it occurs within talus slopes in the states of Washington and Oregon. While very little new information has been published on this species since its first description by Burns (1954), its limited range and data indicating that most populations are small and isolated suggest that it is a relict species on the decline. Space analysis of the microhabitat requirements indicates that this plethodon is restricted to steep, wooded talus slopes where the rocks are of small size (1 to 6 cm in length) and there are relatively large amounts of decaying plant material and small quantities of soil. Recently identified additional populations are being or have been severely impacted by a variety of human activities, including extensive removal of gravel from the slopes for road building and maintenance and clear cutting of the overstorey. These environmental alterations appear to damage significantly the salamanders habitat. Therefore, if this species is to survive, appropriate action must be undertaken immediately to protect the remaining habitat.

Discrimination of Kin- and Diet-based Cues by Larval Spadefoot Toads, Scaphiopus intermontanus (Anura: Pelobatidae), under Laboratory Conditions

We conducted laboratory choice tests with larval Great Basin spadefoot toads, Scaphiopus intermontanus Cope, to evaluate their ability to discriminate kin- and diet-based cues. When offered a choice between stimulus groups composed of familiar siblings and unfamiliar nonsiblings (both stimulus groups, as well as test individuals, raised on the same diet), larvae did not associate preferentially with either stimulus group. In diet-based cue experiments, larvae raised on Tubifex worms associated prefer- entially with unfamiliar nonsiblings raised on the same diet over unfamiliar siblings raised on rabbit chow. In the complementary experiment, however, larvae raised on rabbit chow did not associate pref- erentially with either stimulus group. These results do not support a role for kin discrimination and kin selection in S. intermontanus larvae. If discrimination does occur, the results suggest that environmentally derived cues may be the predominant means by which kin are discriminated. Moreover, the different results of the diet-based cue experiments suggest that larvae are not restricted to prefer only cues repre- sentative of their natal environment. Although familiarity is involved, larvae also may be capable of reacting preferentially to a novel stimulus based on some type of quality assessment.