Recognition by Population and Genetic Similarity in the Mountain Dusky Salamander,Desmognathus ochrophaeus (Amphibia: Plethodontidae)

Adult males and females of Desmognathus ochrophaeus were tested in two-choice substrate discrimination trials in which salamanders were given a choice of the marked substrates of opposite-sex individuals from their own population and from a geographically distinct population. Females exhibited a significant preference for the marked substrates of extrapopulation males, whereas there was no evidence that males made any such discrimination of the marked substrates of females. We suggest that females may utilize substrate cues to make initial assessments of potential mates. We compared data from substrate discrimination trials to random amplified polymorphic DNA (RAPD) profiles generated for each individual. There was no evidence that females made any distinction of substrate odours based on our assessment of genetic similarity. The estimated genetic differences between the two populations were minimal.     

The courtship behaviour of the spotted dusky salamander, Desmognathus fuscus conanti (Amphibia: Caudata: Plethodontidae)

The courtship behaviour of the North American southern dusky salamander, Desmognathus fuscus conanti (Plethodontidae), is described for the first time. The male is the most active participant, as is typical for caudate amphibians, and much of his behaviour can be understood in terms of orientation to and stimulation (or persuasion) of the female. The latter is largely accomplished by the transfer of courtship pheromones from the male's mental (chin) gland. The orientation and persuasion phases of courtship appear necessary if sperm transfer by means of a spermatophore deposited upon the substratum is to be successful. The courtship of D. fuscus conanti is qualitatively identical to that of D. santeetlah , with which it is sexually compatible in the laboratory and with which it may hybridize in nature. However, a broader comparison of species in the genus Desmognathus reveals that the greatest interspecific differences occur during the orientation and persuasion phases of courtship. A complete understanding of the evolution of courtship behaviour in desmognathine salamanders awaits availability of ethograms for all other taxa and a robust, independent phytogeny for the entire subfamily.     

Osseous pathologies in the lungless salamander Desmognathus fuscus (Plethodontidae)

The majority of reported pathologies in lissamphibians (salamanders, caecilians and frogs) include limb deformities such as missing limbs, multiple extra limbs and digits, or incomplete limb formation. However, comparatively little is known about congenital vertebral malformations or posttraumatic pathologies (e.g. injuries, infections) in the vertebral column of salamanders. In the present study, we describe eight vertebral deformities in three cleared and stained specimens of Desmognathus fuscus. Two specimens display developmental deformities which range from a potential non-segmented wedge vertebra to fully segmented hemivertebrae. The vertebral pathology in the third specimens possibly results from a parasitic infection. Apparently, these osseous deformities were not severe enough to prohibit survival of the specimens.     

Divergence of mate recognition systems among conspecific populations of the plethodontid salamander Desmognathus santeetlah (Amphibia: Plethodontidae)

The disjunct geographic distribution of plethodontid salamanders of the genus Desmognathus provides excellent opportunities to test whether populations diverge in mate recognition systems so as to result in sexual incompatibility. Previous work has shown that sexual incompatibility may exist both among conspecific populations and between different species in this genus. Populations of the Santeetlah dusky salamander, Desmognathus santeetlah , are found at higher elevations in three mountain ranges in the southern Appalachian Mountains of eastern North America, where they are sympatric with congeneric species of similar body size. We report that statistically significant levels of sexual incompatibility exist among populations of D. santeetlah collected from across the species' range. Contrary to popular belief, but in accord with a growing body of empirical literature, aspects of mate recognition systems can diverge among conspecific populations of salamanders, resulting in incidental sexual incompatibility.     

Male—male aggression in the plethodontid salamander Desmognathus ochrophaeus

Aggressive encounters between pairs of male mountain dusky salamanders (Desmognathus ochrophaeus) were staged in the laboratory in the absence of any obvious limited resource. We observed aggressive interactions which sometimes escalated to biting. Physical injuries were inflicted during some aggressive encounters; however, the consequences of injury for future fitness are uncertain. Several behaviour patterns used in contests apparently functioned as threat displays, and these sometimes ended contests before they escalated to biting. We could detect no significant influences of three types of asymmetries among males in determining the winners and losers of contests (body size, recent mating experience and familiarity with the testing arena). Three cases of 'homosexual' courtship were observed. Both intermale aggression and intermale courtship may be interpreted as forms of competition for mates.     

Sperm storage in the spermatheca of the red-back salamander,Plethodon cinereus (Amphibia: Plethodontidae)

In northern Indiana, the mating season of Plethodon cinereus occurs after hibernation from March until June, when oviposition begins. During the mating season, a female stores sperm in its spermatheca, a compound tubular gland in the roof of the cloaca. The apical cytoplasm of the spermathecal epithelium is filled with large secretory vacuoles whose product is released while sperm are stored. Females induced to oviposit in June and July by injections of human chorionic gonadotropin (hCG) still retain much sperm 1 month after oviposition, but secretory vacuoles are absent in all specimens sacrificed in July and August. Instead, some sperm are embedded in the spermathecal epithelium with resultant spermiophagy involving lysosomes. A female sacrificed in September 2 months after oviposition possesses scant sperm, but spermiophagy alone does not seem extensive enough to account for the decrease in sperm numbers. Females sacrificed in October prior to hibernation lack sperm in their spermathecae; some secretory vacuoles are present, but they are not as numerous or as enlarged as in specimens collected in March and May. Inter- and intrafamilial differences in the cytology of sperm storage may not be phyletically informative at the family level but related to species-specific reproductive adaptations. J. Morphol. 234:131–146, 1997. © 1997 Wiley-Liss, Inc.     

Heterochronic mechanisms of morphological diversification and evolutionary change in the neotropical salamander,Bolitoglossa occidentalis (Amphibia: Plethodontidae)

Bolitoglossa occidentalis, a lowland salamander of Mexico and Guatemala, has a highly derived morphology. The features that are derived with respect to the condition in generalized members of the genus include the following: (1) small body size; (2) short tail; (3) fully webbed hands and feet; (4) reduction and loss of certain phalangeal elements; (5) fusion of carpals and tarsals; (6) absence of prefrontal bones; and (7) reduced skull ossification. The ontogeny of this species was analyzed quantitatively and compared with the patterns of growth and differentiation encountered in two morphologically generalized members of the genus, B. rostrata and B. subpalmata. Most of the derived features can be explained by invoking a single heterochronic process: truncation of development at a small size (most likely the product of early maturation). Therefore, B. occidentalis is a paedomorphic species whose morphology has been attained through the process of progenesis. This result supports Alberch's ('80a) prediction, based on functional analysis, that the principle adaptation to arboreality in B. occidentalis is small size; other derived morphological features are associated with the organism's truncated development and may have no adaptive significance. However, patterns of dissociation are found within this overall progenetic process. Some of these include the following: (1) accelerated growth rates of the metatarsals and first phalanges, and retarded growth rates of the second and third phalangeal elements; (2) dissociation between rates of ossification of the skull and the autopodial elements; and (3) dissociation between the timing of termination of the process of shape change during the ontogeny of the foot (the product of differential growth between digital and interdigital areas) and termination of growth in overall foot size (foot surface area). This later result illustrates the independence of morphogenetic phenomena (shape change) from processes of growth (size increase).     

Population differentiation in plethodontid salamanders: divergence of allozymes and sexual compatibility among populations of Desmognathus imitator and D. ochrophaeus (Gaudata: Plethodontidae)

Plethodontid salamanders of the genus Desmognathus exhibit varying levels of genetic differentiation among and within both allopatric and sympatric taxa. This provides excellent opportunities to study population differentiation and speciation. Two morphologically similar species in this genus, D. imitator and D. ochrophaeus, are genetically well-differentiated from one another and occur in sympatry with no evidence of hybridization and introgression. We report that the degree of sexual isolation between these two species is very high, regardless of whether the populations under comparison are allopatric or sympatric with one another. Neither reinforcement nor reproductive character displacement are required to explain the evolution of sexual incompatibility in sympatry. Sexual behaviour apparently diverges while populations are allopatric with one another. Preliminary study indicates that D. imitator consists of populations among which there may be significant sexual isolation in the absence of detectable genetic differentiation.     

Structural heterogeneity in the basal regions of the teeth of the red-backed salamander,Plethodon cinereus (Amphibia,Plethodontidae)

Ultrastructural and histochemical features of marginal (monostichous) teeth associated with the jawbones are compared with those of palatal (polystichous) teeth that compose two patches in the roof of the mouth. The apices and uncalcified regions are similar in both kinds of teeth, but the basal regions display distinctive differences. While bases (pedestals) of marginal teeth are essentially hollow cylinders that attach to the jawbones by their labial faces, bases of teeth in palatal patches are fused to form two horizontal plates which lack direct attachment to underlying bone. The plates are separated from each other by a pulp-filled space containing fibroblasts, blood vessels, and vertically oriented elements resembling bony spicules. Cylindrical pedestals like those of marginal teeth project from the ventral plate. While the identity of the material composing the basal regions remains controversial, the following evidence suggests that it is similar to “bone of attachment” (Tomes, '23): most of it, unlike dentin, does not develop in direct association with an enamel organ; alcian blue stains the bases of developing teeth but stains dentin, developing dentin, enamel, or mature bone very weakly (if at all); bases of teeth in palatal patches develop in isolation from the parasphenoid bone and thus cannot be considered extensions of it; and marginal teeth attach directly to the jawbones, but the material composing their bases does not blend with the bone. Structural heterogeneity of the basal regions appears to be linked to functional differences exhibited by these two types of teeth.     

Histology and ultrastructure of the caudal courtship glands of the red‐backed salamander,Plethodon cinereus (Amphibia: Plethodontidae)

Caudal courtship glands (CCGs) are sexually dimorphic glands described in the skin of the dorsal tail base of some male salamanders in the genera Desmognathus, Eurycea, and Plethodon in the family Plethodontidae. These glands are believed to deliver pheromones to females during courtship, when the female rests her chin on the dorsal tail base during the stereotypic tail straddling walk unique to plethodontids. Although CCGs have been studied histologically, no investigations of their ultrastructure have been made. This article presents the first study on the fine structure and seasonal variation of CCGs, using the plethodontid Plethodon cinereus. The CCGs vary seasonally in height and secretory activity. The mature secretory granules observed in males collected in October and April consist of oval, biphasic granules that are eosinophilic and give positive reactions to periodic acid‐Schiff for neutral carbohydrates but do not stain for acidic mucosusbtances or proteins with alcian blue and bromphenol blue, respectively. Granular glands, some of which contain mucous demilunes, are twice as large as CCGs, are syncytial (unlike CCGs), and stain for proteins. Mucous glands are similar in size to CCGs, but are basophilic, show no seasonal variation in secretory activity, and stain positive for acidic mucosubstances. CCGs do not resemble cytologically the sexually dimorphic mental glands of some plethodontids, which contain round or oval granules filled with an electron‐dense amorphous substance. The CCGs are similar histologically to sexually dimorphic skin glands described in some anurans, but more comparative work is needed. J. Morphol. 276:319–330, 2015. © 2014 Wiley Periodicals, Inc.     

Structure of the radially asymmetrical uncalcified region of the teeth of the red-backed salamander,Plethodon cinereus (Amphibia,Plethodontidae)

The teeth of the adult plethodontid salamander, Plethodon cinereus, were examined by light and electron microscopy with emphasis on the ringlike zone of uncalcified dentin that divides the calcified portion of each tooth into a proximal pedestal and a distal apex. The uncalcified region displays radial asymmetry, forming an integral part of the posterior wall of the tooth but bulging into the pulp cavity anteriorly, thus forming a hingelike structure. All portions of the dentin, including the uncalcified region, are composed predominantly of collagenous fibers but lack elastin. In scanning electron micrographs of teeth from which the oral mucosa has been removed, the location of the anterior uncalcified hinge is marked externally by a notch-like articulation of the apex and pedestal. Sites of transition between calcified and uncalcified areas of the dentin show no special modifications in transmission electron micrographs, but collagenous fibers in calcified portions are associated with more electron-dense amorphous material than are those in the uncalcified region. Odontoblasts associated with the uncalcified region possess ultrastructural features closely resembling those of odontoblasts found in calcified areas. The uncalcified region seems to afford the teeth a certain degree of flexibility, and the asymmetry of the region appears to allow the teeth to flex only in a posterior direction, thus facilitating the entry of living prey but hindering its escape. The uncalcified region also seems to permit the apex of a tooth to break away from its pedestal without damage to underlying bone.     

Time courses of thermal acclimation for critical thermal minima in the salamanders Desmognathus quadramaculatus, Desmognathus monticola, Desmognathus ochrophaeus, and Plethodon jordani

1. We examined the time courses of thermal acclimation for critical thermal minima (CTMin) in the salamanders Desmognathus quadramaculatus, D. monticola, D. ochrophaeus, and Plethodon jordani. 2. D. quadramaculatus showed no annual differences in their time courses, but we noted seasonal differences in the CTMin with these salamanders having lower CTMin in the spring. 3. Gain in CTMin (25 degrees C to 5 degrees C transfer) was faster than its corresponding loss (5 degrees C to 25 degrees C transfer) in D. quadramaculatus. 4. Comparison of all three Desmognathus species revealed no differences in the CTMin for the 5 degrees C to 25 degrees C time courses, but P. jordani had lower CTMin than corresponding D. quadramaculatus. 5. Our results indicate that the pattern of CTMin acclimation correlates with the constraints acting on salamanders in their natural environment.     

Limb chondrogenesis of the seepage salamander, Desmognathus aeneus (amphibia: plethodontidae)

Salamanders are infrequently mentioned in analyses of tetrapod limb formation, as their development varies considerably from that of amniotes. However, urodeles provide an opportunity to study how limb ontogeny varies with major differences in life history. Here we assess limb development in Desmognathus aeneus, a direct-developing salamander, and compare it to patterns seen in salamanders with larval stages (e.g., Ambystoma mexicanum). Both modes of development result in a limb that is morphologically indistinct from an amniote limb. Developmental series of A. mexicanum and D. aeneus were investigated using Type II collagen immunochemistry, Alcian Blue staining, and whole-mount TUNEL staining. In A. mexicanum, as each digit bud extends from the limb palette Type II collagen and proteoglycan secretion occur almost simultaneously with mesenchyme condensation. Conversely, collagen and proteoglycan secretion in digits of D. aeneus occur only after the formation of an amniote-like paddle. Within each species, Type II collagen expression patterns resemble those of proteoglycans. In both, distal structures form before more proximal structures. This observation is contrary to the proximodistal developmental pattern of other tetrapods and may be unique to urodeles. In support of previous findings, no cell death was observed during limb development in A. mexicanum. However, apoptotic cells that may play a role in digit ontogeny occur in the limbs of D. aeneus, thereby suggesting that programmed cell death has evolved as a developmental mechanism at least twice in tetrapod limb evolution.     

Comparative skull osteology of Karsenia koreana (Amphibia,Caudata, Plethodontidae)

The recent discovery of a plethodontid salamander, Karsenia koreana, in Korea challenged our understanding of the biogeographic history of the family Plethodontidae, by far the largest family of salamanders, which otherwise is distributed in the New World with a few European species. Molecular studies suggest that Karsenia forms a clade with Hydromantes (sensu lato), which includes among its species the only other Old World plethodontids. We studied the skull of K. koreana and compared it with that of other plethodontid genera, especially members of the subfamily Plethodontinae, which it resembles most closely in general anatomy. The anatomy of its skull corresponds to the most generalized and apparently ancestral condition for plethodontids. No clearly autapomorphic states were detected, and no synapomorphies can be found that would link it to other genera. The Karsenia skull is cylindrical and well ossified, giving an impression of strength. In contrast, the skull of Hydromantes is highly derived; the skull is flattened and the bones are weakly ossified and articulated. Hydromantes and Karsenia share no unique anatomical features; differences between them are especially evident in the hyobranchial skeleton, which is generalized in Karsenia but highly modified in Hydromantes, which is well known for its highly projectile tongue. Plethodon and Plethodon‐like species, including Karsenia and to a lesser degree Ensatina, represent the more generalized and apparently ancestral plethodontid morphology. Specialized morphologies have evolved along only a few morphological axes within the Plethodontidae, resulting in a pattern of rampant homoplasy. Our analysis of the anatomy of the new Asiatic lineage illuminates some potential mechanisms underlying adaptive morphological evolution within the Plethodontidae. J. Morphol. 2010. © 2009 Wiley‐Liss, Inc.