Chemical access to the vomeronasal organs of a plethodontid salamander

Plethodontid salamanders have unique nasolabial grooves that may function as “capillary tubes” to convey chemicals to the vomeronasal organ when these animals nose-tap. ³H-proline was placed at the base of these grooves in Plethodon cinereus, and autoradiography revealed large concentrations of radioactive material in the vomeronasal organs. There was no significant accumulation of radioactive material in the main olfactory epithelium. Salamanders with blocked nasolabial grooves lacked significant accumulation of material in their nasolabial grooves or vomeronasal epithelia, although some salamanders had radioactive material in the posterior portion of their vomeronasal organ that had entered through the internal nares. Anteriorly placed vomeronasal organs situated adjacent to the posterior limits of the nasolabial grooves may insure that nose-tapping primarily stimulates the vomeronasal sensory epithelium.     

Cytogenetic evolution in the plethodontid salamander genus Aneides

Chromosomal variation in the plethodontid salamander genus Aneides was analyzed using C-banding, to visualize heterochromatin distribution, as well as silver and fluorochrome banding, to reveal nucleolus organizer regions. Evidence is presented that Aneides has undergone pronounced karyological divergence from a Plethodon-like ancestor. It is concluded that this divergence reflects accelerated rates of chromosomal rearrangements in Aneides relative to Plethodon. These rearrangements have involved mainly pericentric inversions that have occurred in one or more of the three smallest pairs of chromosomes in the karyotype. Karyological variation within and between species of Aneides was used to analyze phylogenetic relationships within the genus. This analysis revealed at least two karyologically distinct species that had not been previously recognized by morphological criteria.     

On the environmental control of oocyte maturation in a plethodontid salamander

Summary The relationship between condition and oocyte maturation was experimentally studied in Plethodon cinereus. Gravid females with immature oocytes were collected in September and maintained on different feeding regimes for 180 days. An index of salamander condition was derived. There was no significant relationship between the number of maturing oocytes and condition of the salamander at the end of the experiment, but oocyte size was signifiantly related to condition. A significant regression relationship was found for oocyte number and initial body weight, suggesting that condition may affect oocyte number early in the reproductive cycle. The implications of environmental induction of oocyte number for affecting clutch size and fitness are discussed.     

Chromosome variation in the plethodontid salamander,Aneides ferreus

Karyotype variation in the plethodontid salamander, Aneides ferreus, has been analysed. 358 individuals from 14 populations, representing the major portion of the range of this salamander, have been karyologically examined. In A. ferreus, n=14. When the chromosomes are arranged in a decreasing relative length series, the karyotype is heteromorphic with respect to chromosome number 13, which may be either telocentric (T) or subtelocentric (ST). Variation in the heteromorphism over the range of the species is sex related, and probably also reflects relative population sizes. The heteromorphism in the isolated populations of A. ferreus on Vancouver Island, British Columbia, Canada, resembles a WZfemale/ZZmale sex chromosome dimorphism, suggesting the possibility that chromosome number 13 may be involved in sex determination in this population. The possibility that chromosome number 13 is involved in sex determination in all populations of A. ferreus is discussed. Our data suggest that the ancestral A. ferreus karyotype was homomorphic for T (T/T), and that the ST was derived from the T by a pericentric inversion. In peripheral populations, only the W homologue has been affected, whereas in central populations both the W and the Z chromosomes have been rearranged. Comparisons are made with other species of Aneides for which karyological information is available, and it is concluded that chromosome rearrangements have played an important role in the evolution of the genus. In C-banded chromosomes of A. ferreus, staining is most intense at the centromere regions of the larger chromosomes and is absent only in some of the smaller chromosomes. Implications of this C-banding pattern are discussed.     

Responses of a plethodontid salamander to conspecific and congeneric intruders

After inhabiting their home sites for a few days, both males and females of the salamander Desmognathus monticola directed agonistic behaviour toward intruding salamanders. Resident D. monticola were significantly more aggressive toward D. fuscus intruders than toward conspecific ones, although both conspecific and congeneric intruders were frequently attacked. Responses of D. monticola residents were independent of sex, and no difference was found in the behaviour of residents toward conspecific male and female intruders. Small D. fuscus intruders were attacked and injured more frequently than similar-sized D. monticola intruders and, in general, smaller-sized salamanders were the victims of aggressive attacks more frequently than larger ones. The proportions of bites on the head and tail of intruders were similar, although injuries were much more frequent to the tail than to the head. This species-related and size-related agonistic behaviour may be functional in maintaining the spatial distribution of species in communities of Desmognathus salamanders.     

A recombinant courtship pheromone affects sexual receptivity in a plethodontid salamander

Pheromones are important chemical signals for many vertebrates, particularly during reproductive interactions. In the terrestrial salamander Plethodon shermani, a male delivers proteinaceous pheromones to the female as part of their ritualistic courtship behavior. These pheromones increase the female's receptivity to mating, as shown by a reduction in courtship duration. One pheromone component in particular is plethodontid receptivity factor (PRF), a 22-kDa protein with multiple isoforms. This protein alone can act as a courtship pheromone that causes the female to be more receptive. We used a bacterial expression system to synthesize a single recombinant isoform of PRF. The recombinant protein was identical to the native PRF, based on mass spectrometry, circular dichroism spectra, and a behavioral bioassay that tested the effects of recombinant PRF (rPRF) on female receptivity (21% reduction in courtship duration). The rPRF appears to mimic the activity of a mixture of PRF isoforms, as well as a mixture of multiple different proteins that comprise the male courtship gland extract. Pheromones that are peptides have been characterized for some vertebrates; to date, however, rPRF is one of only 2 synthesized vertebrate proteins to retain full biological activity.     

Territorial defence of space and feeding sites by a plethodontid salamander

Two series of experiments were conducted, one in field enclosures and another in the laboratory, to test the hypothesis that the salamander Desmognathus monticola (family Plethodontidae) defends its refuges and feeding sites against conspecific intruders. When two identical cover sites were provided as refuges in the laboratory, residents and intruders occupied separate cover sites significantly more often than the same sites. Residents did not, however, show strong preference for the same site, nor did they consistently defend a specific site. When food supplements were provided consistently at the same cover sites in field enclosures, resident D. monticola occupied and defended the feeding sites significantly more frequently against intruders than the non-feeding cover sites. Individuals not receiving food supplements also excluded intruders from the occupied cover sites but did not defend a specific cover site. Residents in enclosures where no food supplements were provided were significantly more active at night, outside cover sites, than residents receiving food supplements. Individual D. monticola exhibit territoriality by excluding intruders from the refuges they occupy. Providing food supplements increases the site specificity of individuals and decreases the amount of time spent in nocturnal activity.     

Trout affect the density, activity and feeding of a larval plethodontid salamander

1. Ecologists have struggled to describe general patterns in the impacts of predators on stream prey, particularly at large, realistic spatial and temporal scales. Among the confounding variables in many systems is the presence of multiple predators whose interactions can be complex and unpredictable. 2. We studied the interactions between brook trout (Salvelinus fontinalis) and larval two‐lined salamanders (Eurycea bislineata), two dominant vertebrate predators in New England stream systems, by examining patterns of two‐lined salamander abundance in stream reaches above and below waterfalls that are barriers to fish dispersal, by measuring the effects of trout on salamander density and activity using a large‐scale manipulation of brook trout presence, and by conducting a small‐scale laboratory experiment to study how brook trout and larval two‐lined salamanders affect each other's prey consumption. 3. We captured more salamanders above waterfalls, in the absence of trout, than below waterfalls where trout were present. Salamander density and daytime activity decreased following trout addition to streams, and salamander activity shifted from aperiodic to more nocturnal with fish. Analysis of stomach contents from our laboratory experiment revealed that salamanders eat fewer prey with trout, but trout eat more prey in the presence of salamanders. 4. We suggest that as predators in streams, salamanders can influence invertebrate prey communities both directly and through density‐ and trait‐mediated interactions with other predators.     

Influence of intraspecific density and cover on home range of a plethodontid salamander

Summary Hypotheses about the influence of intraspecific density and available cover on home range size (=mean activity radius) of a plethodontid salamander (Desmognathus monticola) were tested by field experimentation from June 1980 to October 1981. A second order mountain stream in southwestern North Carolina was marked into five sections (two control and three experimental) and three replicated treatments were performed: Treatment I, low and high density additions of D. monticola; Treatment II, addition of cover objects (rocks); Treatment III, addition of cover and D. monticola.In Treatment I, home ranges of D. monticola on high density addition plots increased significantly relative to those on control and low density addition plots. Mean stomach content biomass and number of prey items of salamanders from high density plots were less than controls in all comparisons throughout the experiment but only one comparison revealed a statistically significant difference. Mean stomach contents of salamanders from low density plots were less than controls in 60% of all comparisons and only one statistically significant difference was found. Home range size was not affected significantly by Treatments II and III.Results of these experiments suggest that home range size of D. monticola may vary as a function of the number of conspecifics and cover objects; i.e., when the number of D. monticola increases where cover is limited, home range size increases.     

Magnetic resonance imaging of the vomeronasal organ

The vomeronasal organ of mice and frogs was studied by highspatial resolution magnetic resonance imaging. By this techniquethe presence of material in the vomeronasal lumen can be evidencedin vivo.     

Improvement of the vomeronasal organ ablation in the rat

The vomeronasal organ (VNO) in most mammalian species consists of a bilaterally paired tubular structure lying on either side at the base of the nasal septum. Functionally, the VNO receives chemosensory informations and conveys it to its parts of the hypothalamus thought to be important in the regulation of reproductive physiology and behavioral functions. Here the authors report an improvement of the VNO ablation in the rat. With the exception of restraint of a rat, this operation method is fundamentally similar to those reported by Saito and Mennella (1986). The rat was anesthetized and placed supine on a home-made operating board with some accessories, and its extremities and head were fixed. It should be emphasized that the restraint of its lower incisor and tongue to keep the mouth open was performed with home-made restraint devices. The above method enabled us to remove the VNO easily. In addition, it could be useful in this field of oral surgery in small animals.     

The vomeronasal organ of the male ferret.

The vomeronasal organ (VNO) is known to play a major role in sexual behavior in many mammals. This study is the first report that the adult male ferret has a VNO, which is considerably smaller and morphologically different from the usually crescent-shaped epithelium in several mammalian species, particularly rodents. There were no differences in the size or structure of the ferret VNO between the mating season in spring and the sexually quiescent season in autumn, although plasma testosterone, testis size and brain size are dramatically increased in spring and behavior changes significantly. The histological data suggest that the VNO might be not as important a structure in male ferret sexual behavior as in rodents.     

Effect of temperature,photoperiod, and feeding on the rate of tail regeneration in a semiaquatic plethodontid salamander

Salamander tail autotomy improves survival, but loss of the tail can subsequently be costly. For example, burst swimming speed is significantly slower after autotomy in desmognathan salamanders, which may increase predation risk in aquatic habitats. However, any long-term cost of tail loss is contingent on the rate of tail regeneration. To examine variation among seasons and environments in the cost of tail autotomy, we tested the effect of temperature, photoperiod, and feeding on tail-length re-growth in the semiaquatic plethodontid salamander Desmognathus conanti. Eight experimental groups (n=15 each, equivalent in body size) were tested. After acclimation for four weeks at one of two temperatures (either 10 °C or 20 °C) and one of two photoperiods (either L:D 9.5:14.5 h or 14.5:9.5 h), 60% of the tail length was autotomized for each individual. After autotomy, each experimental group was maintained under unique conditions of temperature (either 10 °C or 20 °C), photoperiod (either L:D 9.5:14.5 h or 14.5:9.5 h), and feeding (either fasting or weekly feeding). The length of the regenerated tail portion for each individual was measured each week until the group with the fastest re-growth had regenerated 50% of the lost tail length. Low temperature had a large, negative effect, fasting had a small, negative effect, but photoperiod had no significant effect on tail re-growth. The large thermal effect resulted from a combination of delayed initiation of tail-length re-growth and reduced regeneration rate thereafter at low temperature. We conclude that the cost of salamander tail autotomy differs among seasons and environments based on variation in temperature and food availability.     

A classification schema for the vomeronasal organ in humans

The vomeronasal organ is a chemoreceptive structure located at the base of the nasal septum with direct axonal connections to the accessory olfactory bulb in many terrestrial vertebrates. Pheromones presumably bind to the vomeronasal organ and exert behavioral or physiologic responses, thereby allowing chemical communication between animals of the same species. The presence and function of the vomeronasal organ in humans is debated. A phenotypic classification schema for the human vomeronasal organ is described and applied to 253 human subjects who underwent nasal examination. Of these subjects, only 6 percent possessed a vomeronasal organ with 64 percent unilateral and 36 percent bilateral in appearance. No difference existed in gender, age, or race between those subjects with or without a vomeronasal organ. There is no evidence supporting involutional senescence of this structure. Future investigations should use this phenotypic schema for the vomeronasal organ to allow accurate comparisons of study populations.     

Nursing behavior in lactating rats--the role of the vomeronasal organ

The vomeronasal organ (VNO) of female Wistar-Imamichi rats was removed completely. The females were impregnated and gave birth to young. The question addressed was whether such dams would show deficits in nursing behavior. The data indicated that removal of the VNO severely depressed nursing behavior. We conclude that the VNO contributes to the nursing behavior of lactating rats.     

Streambed microstructure predicts evolution of development and life history mode in the plethodontid salamander Eurycea tynerensis

Background

Habitat variation strongly influences the evolution of developmentally flexible traits, and may drive speciation and diversification. The plethodontid salamander Eurycea tynerensis is endemic to the geologically diverse Ozark Plateau of south-central North America, and comprises both strictly aquatic paedomorphic populations (achieving reproductive maturity while remaining in the larval form) and more terrestrial metamorphic populations. The switch between developmental modes has occurred many times, but populations typically exhibit a single life history mode. This unique system offers an opportunity to study the specific ecological circumstances under which alternate developmental and life history modes evolve. We use phylogenetic independent contrasts to test for relationships between a key microhabitat feature (streambed sediment) and this major life history polymorphism.

Results

We find streambed microstructure (sediment particle size, type and degree of sorting) to be highly correlated with life-history mode. Eurycea tynerensis is paedomorphic in streams containing large chert gravel, but metamorphoses in nearby streams containing poorly sorted, clastic material such as sandstone or siltstone.

Conclusion

Deposits of large chert gravel create loosely associated streambeds, which provide access to subsurface water during dry summer months. Conversely, streambeds composed of more densely packed sandstone and siltstone sediments leave no subterranean refuge when surface water dries, presumably necessitating metamorphosis and use of terrestrial habitats. This represents a clear example of the relationship between microhabitat structure and evolution of a major developmental and life history trait, and has broad implications for the role of localized ecological conditions on larger-scale evolutionary processes.     

Complex secretory products in the oviduct of the plethodontid salamander Bolitoglossa dofleini (Amphibia, Urodela)

The ultrastructure of the secretory granules in the cells of the subdivisions of the oviduct in the neotropical plethodontid salamander Bolitoglossa dofleini was studied by transmission electron microscopy. In addition, we applied the cationic dye Cuprolinic Blue (CB) at different electrolyte concentrations to demonstrate proteoglycans, and the pyrogallol red-copper (PR-C) method to stain proteins at the ultrastructural level. The entire oviduct is lined by a simple epithelium that contains ciliated and microvillous cells in the first subdivision, the aglandular pars recta; microvillous cells show a moderate secretory activity. The following pars convoluta is differentiated into five glandular subdivisions and the aglandular “uterine portion”. Especially in the glandular parts, the epithelium is arranged in longitudinal folds. At their crests ciliated and microvillous cells similar to those in the pars recta occur. Gland cells are crowded with secretory granules that differ in their structural complexity (with and without electron-dense spheres or masses; elaborated, homogeneous or granular matrix; spherical; distorted) along the various subdivisions. Further, as suggested by the CB-technique, the cranial subdivisions contain large amounts of sulphated proteoglycans that decrease in the caudal direction. Carboxylated proteglycans appear to be present in all subdivisions examined. Electron-dense spheres of secretory granules are largely free of CB-precipitates, but stain more or less intensely with PR-C. The ultrastructure of the pars recta, and especially the “uterine portion” indicates transporting capability. The epithelial cells of the “uterus” have coated pits and a considerable amount of lysosome-like bodies.     

High-resolution magnetic resonance spectroscopy of the mouse vomeronasal organ

The chemical composition of the vomeronasal organ (VNO) was investigated by means of in vitro proton magnetic resonance spectroscopy (MRS) in prepubertal and adult mice of both sexes. Results demonstrate that MRS detects several chemical constituents in the VNO, showing their age- and sex-associated changes in concentration. Preliminary experiments also suggest the ability of MRS to show compositional changes in the VNO after pheromonal stimulation. MRS can serve as a useful technique to investigate vomeronasal chemoreception.     

Morphology of the pineal organ in the salamander Ensatina eschscholtzi

The pineal organ of Ensatina eschscholtzi, a terrestrial and secretive species of salamander of the family Plethodontidae, is a photoreceptive structure lying on the dorsal surface of the diencephalon. The pineal is flattened with a broad lumen and consists of three cell types: photoreceptors, supportive cells, and neurons. Pineal photoreceptors are typical vertebrate photoreceptors and possess outer segment formations which, however, are frequently contorted and disorganized. Sloughing of apical portions of outer segments and vesiculation along the lateral edges of outer segment membrane disks are consistently observed and presumed to represent mechanisms of outer segment membrane recycling. Photoreceptors have basal processes which synapse with neural dendrites. Synapses between photoreceptor basal processes are occasionally observed. All synapses are characterized by synaptic ribbon structures of variable number, size, and configuration. Dense-core vesicles are occasionally observed mingled with clear synaptic vesicles within photoreceptor basal processes. Supportive cells within the pineal function in phagocytosis and recycling of shed outer segment membrane material, and neurons are localized at the lateral margins of the organ. The latter send axons into the ipsilateral side of the dorsal diencephalon. The pineal organ of Ensatina shows marked variation in overall size (cell total), cell type proportions, absolute neuron number, and ratio of photoreceptor number to neuron number for individual pineals. None of these morphological parameters is correlated with body size, sex, or season, and it is assumed that such variability represents significant variation in photosensory capabilities. It is suggested that the pineal organ of Ensatina is a partially degenerate photoreceptive structure.