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PubMed2004

Speciation, phylogeography and evolution of life history and morphology in plethodontid salamanders of the Eurycea multiplicata complex.

Understanding the complex interactions among environment, genotype and ontogeny in determining organismal phenotypes is cental to many biological disciplines. The Eurycea multiplicata complex, endemic to the Interior Highlands (Ozark Plateau and Ouachita Mountains) of eastern North America, comprises a diverse radiation of paedomorphic surface-dwelling (E. tynerensis), metamorphic surface-dwelling (E. multiplicata multiplicata and E. m. griseogaster) and metamorphic subterranean (Typhlotriton spelaeus) hemidactyliine plethodontid salamanders. Portions of two mitochondrial genes, cytochrome-b and NADH dehydrogenase-4, totalling 1818 base pairs (bp) were sequenced for 70 ingroup individuals plus numerous outgroup taxa, to examine the biogeography and relationships among these morphologically disparate species. Results show the E. multiplicata complex to be monophyletic, with its two most divergent clades corresponding to geography, not morphology or life history. Transforming surface-dwelling populations from the Ouachitas (E. m. multiplicata) are sister to the Ozark taxa, including paedomorphic surface-dwelling (E. tynerensis), subterranean (T. spelaeus) and transforming surface-dwelling salamanders assigned to the 'subspecies'E. m. griseogaster. Among Ozark taxa T. spelaeus (deeply nested within Eurycea) is sister to a clade that includes E. m. griseogaster and E. tynerensis. Current taxonomy suggests that paedomorphic populations (E. tynerensis) from the western Ozarks are distinct from nearby transforming populations (E. m. griseogaster). However, paedomorphic and transforming salamanders do not form reciprocally monophyletic groups and many populations share almost identical haplotypes. Ancestral state reconstruction of life history traits shows that paedomorphosis arose independently from three to nine times. Most populations are either completely paedomorphic or completely transforming. This suggests that local habitat parameters strongly influence life history mode in this complex, either facultatively or by selection for particular genotypes.

Animals↗
PubMed2007

Fine-scale spatial genetic structure and dispersal among spotted salamander (Ambystoma maculatum) breeding populations.

We examined fine-scale genetic variation among breeding aggregations of the spotted salamander (Ambystoma maculatum) to quantify dispersal, interpopulation connectivity and population genetic structure. Spotted salamanders rely on temporary ponds or wetlands for aggregate breeding. Adequate breeding sites are relatively isolated from one another and field studies suggest considerable adult site fidelity; therefore, we expected to find population structure and differentiation at small spatial scales. We used microsatellites to estimate population structure and dispersal among 29 breeding aggregations in Tompkins County, New York, USA, an area encompassing 1272 km(2). Bayesian and frequency-based analyses revealed fine-scale genetic structure with two genetically defined demes: the North deme included seven breeding ponds, and the South deme included 13 ponds. Nine ponds showed evidence of admixture between these two genetic pools. Bayesian assignment tests for detection of interpopulation dispersal indicate that immigration among ponds is common within demes, and that certain populations serve as sources of immigrants to neighbouring ponds. Likewise, spatial genetic correlation analyses showed that populations < or = 4.8 km distant from each other show significant genetic correlation that is not evident at higher scales. Within-population levels of relatedness are consistently larger than expected if mating were completely random across ponds, and in the case of a few ponds, within-population processes such as inbreeding or reproductive skew contribute significantly to differentiation from neighbouring ponds. Our data underscore the importance of these within-population processes as a source of genetic diversity across the landscape, despite considerable population connectivity. Our data further suggest that spotted salamander breeding groups behave as metapopulations, with population clusters as functional units, but sufficient migration among demes to allow for potential rescue and recolonization. Amphibian habitats are becoming increasingly fragmented and a clear understanding of dispersal and patterns of population connectivity for taxa with different ecologies and life histories is crucial for their conservation.

Ambystoma↗
PubMed2006

Catastrophic reproductive failure, terrestrial survival, and persistence of the marbled salamander.

Wide variation in reproductive success is common among amphibians that breed in seasonal ponds, but persistence of adults can buffer against these fluctuations, particularly for long-lived species. We hypothesized that the frequent episodes of catastrophic failure of the marbled salamander (Ambystoma opacum) enhance the importance of high terrestrial survival. At Rainbow Bay in South Carolina reproductive success was poor (< 1 metamorph/breeding female) in nearly half of the 22 years that the species bred. Complete failure occurred in 6 of 22 years. To study catastrophic failure, we adapted an age-structured, individual-based model with density-dependent growth and survival of larvae. The model was based on extensive data from local field studies and experiments. With consistently good survival in the pond stages, the simulated population required survival probabilities in the upland stages (juveniles and adults) near 0.5/year to persist and near 0.8/year to achieve the increases observed. Catastrophic failure, occurring randomly with probability 0.5/year created additional fluctuations in the population, raised the thresholds of survival required for persistence, and caused extinction under conditions that were otherwise favorable. The marbled salamander at Rainbow Bay is not at great risk of extinction because of catastrophic failure, but the risk increases dramatically if life span is decreased or frequency of failure is increased. Any reduction in terrestrial survival will have deleterious consequences by reducing the breeding populations at equilibrium, even if it does not jeopardize persistence. Our model provides assessments of risk that can be applied to poorly studied species with similar life histories, such as the endangered flatwoods salamander (A. cingulatum).

Ambystoma↗
PubMed2006

Effects of warming conditions in eastern North American forests on red-backed salamander morphology.

Several studies have reported climate-associated changes in phenotypically plastic traits of amphibians, yet it remains unknown whether amphibians can manifest an evolutionary response to global climate change at the rate and magnitude that it is occurring. To assess this issue, we examined temporal change in the morphology of the red-backed salamander (Plethodon cinereus), a small, abundant woodland salamander distributed widely in eastern North America with two distinct morphotypes: striped individuals associated with cooler microclimates and unstriped individuals associated with warmer microclimates. We compiled morph frequencies for 50,960 individual salamanders from 558 sites as recorded in the published literature and in unpublished field notes of herpetologists between 1908 and 2004. We observed that striping probability increased with increasing latitude, longitude, and elevation and decreased (from 80% to 74% range wide) with time. The combined forces of regional climate warming and, particularly, forest disturbance have evidently been sufficient to cause morphological evolution in this amphibian over the last century.

Animals↗
PubMed1973

The effect of increasing the innervation field sizes of nerves on their reflex response time in salamanders.

1. A simple quantitative measure was sought which could describe the relationship between reflex coupling in the spinal cord of salamanders and the peripheral innervation fields of the nerves from which the reflexes were elicited.2. In decerebrate salamanders reflex responses were recorded between pairs of cut hind limb nerves. The latencies (S/R times) of these reflex responses were bilaterally symmetrical for a given pair of nerves and were shorter when the stimulated nerve of the pair had a large motor and sensory peripheral limb innervation field; this was especially obvious for reflexes between 15th and 17th segmental nerves.3. After cutting or crushing the 16th nerve in adult salamanders, the adjacent 15th and 17th nerves sprouted collaterally to innervate denervated skin and muscle. There was apparently complete recovery of normal tactile reflexes and walking movements within a month.4. The operation did not affect the reflex response (S/R) times for nerve combinations on the unoperated side, which were not significantly different from those of normal animals with similar sized peripheral nerve fields. The unoperated side therefore represented the preoperative condition.5. In animals where one or both the 15th and 17th nerves had increased its innervation field size, the S/R times between them were significantly shorter on the operated side when the nerve with the enlarged field was stimulated. The degree of shortening was greatest for nerves showing the largest increase in peripheral field area.6. The S/R times between the 15th and 17th nerves were similar to those measured in normal animals in which the peripheral fields were of similar size to the enlarged fields in the operated animals. In a few cases where the increase in field size was considerable, the S/R time between the 15th and 17th nerves became as short as that between the 15th and 16th nerves on the control side.7. After removal of the 15th nerve, the 14th nerve sprouted into the trunk skin and muscle previously innervated by the 15th nerve and the 16th nerve into denervated limb skin and muscle. In spite of the increased peripheral fields of both these nerves, there was no change in the S/R times between them, or between any other pair of limb nerves on the operated side.8. The decrease in the S/R times between the 15th and 17th nerves was only observed where the stimulated nerve had increased its peripheral limb innervation field. The possible causes and significance of this shortening reflex response times are discussed in the context of an apparently functionally appropriate adaptation in the spinal cord.

Animals↗
PubMed1987

Voltage gain of signal transfer from retinal rods to bipolar cells in the tiger salamander.

1. Intracellular recordings of the voltage responses of rods and both functional classes of bipolar cell were made in the isolated, perfused retina of the tiger salamander, Ambystoma tigrinum. 2. Brief, dim flashes of 519 nm light delivered to the receptive-field centres were used to measure the flash sensitivities of twenty-one on-centre bipolar cells and thirty-six off-centre cells. In each experiment the flash sensitivity of a rod was also measured using diffuse illumination of the same duration and wave-length. 3. The mean flash sensitivity of the rods (fifty-nine cells) was 4.47 mV photon-1 micron 2 flash. The mean flash sensitivity of the off-centre bipolar cells was 35.4 mV photon-1 micron 2 flash (thirty-six cells). The mean flash sensitivity of the on-centre bipolar cells was 12.5 mV photon-1 micron 2 flash. 4. The ratio of the flash sensitivity of the bipolar cell to that of a rod recorded in the same retina defined the gain of voltage transfer from rod to bipolar cell. For signal transfer to on-centre bipolar cells the mean value of the voltage gain was 5.05 +/- 1.34 (S.E. of mean). For signal transfer to the off-centre bipolar cells, the mean value of the gain was 10.4 +/- 1.29. 5. The on-centre cell gain in the salamander was smaller by a factor of 27 than that of the on-centre cells in the dogfish retina (Ashmore & Falk, 1980 a), while the off-centre cell gain was comparable in the two species. Possible reasons for the large difference between the voltage gains of on-centre cells in the dogfish and salamander are considered.

Action Potentials↗
PubMed1989

Temperature and sperm incorporation in polyploid salamanders.

Although most animals reproduce sexually, a number of all-female groups exist. Triploid hybrid salamanders appear to maintain themselves by using a male's sperm to activate their eggs, after which the sperm nucleus is eliminated (gynogenesis). The incidence of sperm nuclear incorporation in eggs of these salamanders depends on temperature. Triploid offspring derived gynogenetically are more frequent at lower temperature, whereas tetraploid offspring derived sexually are far more frequent at higher temperatures. Temperature-dependent variability in sperm nuclear incorporation helps explain the variability in reproductive modes reported for hybrid salamanders.

Ambystoma↗
PubMed1985

Banding differences between tiger salamander and axolotl chromosomes.

The Hoechst 33258 - Giemsa banding patterns were compared on axolotl (Ambystoma mexicanum Shaw) and axolotl - tiger salamander (Ambystoma tigrinum Green) species hybrid prophase chromosomes. Approximately 369 bands per haploid chromosome set were seen in the axolotl and about 344 bands in the tiger salamander. In the haploid set of 14 chromosomes, chromosome 3 has a constant short or q-arm terminal constriction at the location of the nucleolar organizer. Chromosomes 14 Z and W carry the sex determinants, the female being the heterogametic sex (ZW). The banding patterns of chromosomes 1, 6, 11, and 14 Z of the two species are apparently indistinguishable by our banding method. In the axolotl, chromosome 9 has a small long or p-arm terminal deletion. In the tiger salamander, the remaining 10 chromosomes have terminal or internal deletions. No translocations or inversions seem to have occurred since the gene pool separation of the two closely related species.

Ambystoma↗
PubMed1993

Effects of temperature on muscle pHi and phosphate metabolites in newts and lungless salamanders.

The effect of acute alterations in body temperature (BT) on intracellular pH (pHi) and phosphate metabolites was assessed in white skeletal muscle of intact newts and lungless red-backed salamanders using 31P-nuclear magnetic resonance spectroscopy. pHi decreased with increasing BT in the tail muscle of both newts and lungless red-backed salamanders. The change in pH with change in temperature from 10 to 30 degrees C was -0.018 U/degrees C in newts and -0.041 U/degrees C in red backs. The calculated alpha-imidazole for skeletal muscle cytosol did not change (0.56) in newts from 10 to 30 degrees C but fell from 0.69 to 0.43 in red-backed salamanders. Phosphocreatine (PCr)/Pi fell and Pi/beta-ATP rose with increasing temperature in both newts and red backs; however, the change was much greater in red backs. Providing the red backs with O2 at 30 degrees C led to higher pH and alpha-imidazole, comparable to that of newts, along with increased PCr/Pi and lower Pi/beta-ATP. Thus newts maintain white skeletal muscle cell cytosol alpha-imidazole constant with changes in BT, whereas red backs apparently do not. However, at the BT of preference, red backs and newts maintain similar muscle pHi and alpha-imidazole. The method of gas exchange appears to strongly influence the ability of an animal to maintain its acid-base status over a range of temperatures, and our results suggest that behavioral regulation of BT may involve alpha-imidazole regulation as well.

Acclimatization↗
PubMed2003

Cannabinoid receptor activation differentially modulates ion channels in photoreceptors of the tiger salamander.

Cannabinoid CB1 receptors have been detected in retinas of numerous species, with prominent labeling in photoreceptor terminals of the chick and monkey. CB1 labeling is well-conserved across species, suggesting that CB1 receptors might also be present in photoreceptors of the tiger salamander. Synaptic transmission in vertebrate photoreceptors is mediated by L-type calcium currents-currents that are modulated by CB1 receptors in bipolar cells of the tiger salamander. Presence of CB1 receptors in photoreceptor terminals would therefore be consistent with presynaptic modulation of synaptic transmission, a role seen for cannabinoids in other parts of the brain. Here we report immunohistochemical and electrophysiological evidence for the presence of functional CB1 receptors in rod and cone photoreceptors of the tiger salamander. The cannabinoid receptor agonist WIN 55212-2 enhances calcium currents of rod photoreceptors by 39% but decreases calcium currents of large single cones by 50%. In addition, WIN 55212-2 suppresses potassium currents of rods and large single cones by 44 and 48%, respectively. Thus functional CB1 receptors, present in the terminals of rod and cone photoreceptors, differentially modulate calcium and potassium currents in rods and large single cones. CB1 receptors are therefore well positioned to modulate neurotransmitter release at the first synapse of the visual system.

Ambystoma↗
PubMed1997

Response sensitivity and voltage gain of the rod- and cone-bipolar cell synapses in dark-adapted tiger salamander retina.

Response sensitivity and voltage gain of the rod- and cone-bipolar cell synapses in dark-adapted tiger salamander retina. J. Neurophysiol. 78: 2662-2673, 1997. Rods, cones, and bipolar cells were recorded in superfused, flat-mounted isolated retinas of the larval tiger salamander, Ambystoma tigrinum, under dark-adapted conditions. Voltage responses of 24 rods, 15 cones, and 41 bipolar cells in dark-adapted retinas to 500 nm light steps of various intensities were listed and fitted with hyperbolic functions, and their step sensitivities and relative sensitivities (log sigma) were estimated. In the linear response-intensity ranges, the step sensitivity of rods, SS(rod), is -1.0 mV photon-1 micron2 s or 0.034 mV Rh*-1 s rod and that of the cones, SS(cone), is approximately 0. 00146 mV photon-1 micron2 s or 0.000048 mV Rh*-1 s rod. The rod and cone responses were relatively homogenous with little variations in response amplitude and sensitivity. In contrast, bipolar cell responses were heterogenous with large variations in response amplitude and sensitivity. The maximum response amplitude of bipolar cells varied from 5 to 25 mV, and the relative response sensitivity (log sigma) varied >6 log units (-8.11 to -2.32). The step sensitivity of bipolar cells in the linear response-intensity range varied from 0.0000438 to 51.82 mV photon-1 micron2 s. Bipolar cells in dark-adapted tiger salamander retinas fell into two groups according to their relative sensitivities with very few cells falling in the intermediate light intensity region. The mixed bipolar cells (DBCM and HBCM) exhibited relative response sensitivity ranged from -8.11 to -5.54, and step sensitivity ranged from 1.22 to 51.82 mV photon-1 micron2 s. The cone-driven bipolar cells (DBCC and HBCC) exhibited relative response sensitivity ranged from -3.45 to -2.32, and step sensitivity ranged from 0.0000438 to 0. 00201 mV photon-1 micron2 sec. The chord voltage gain of the rod-DBCM or rod-HBCM synapses near the rod dark membrane potential ranged from 1.14 to 48.43 and that of the cone-DBCC or cone-HBCC synaptic gain near the cone dark membrane potential ranged from 0.03 to 1.38. The highest voltage gains were found near the rod or cone dark membrane potentials. By the use of linear subtraction method, we studied the synaptic inputs from cones to five mixed bipolar cells, and the voltage gains of the cone synapses in each of the bipolar cells were very close to the voltage gain of the rod synapses. This result suggests that although the responses of mixed bipolar cells are mediated mainly by rods when lights of short and medium wavelengths are used, their responses to long wavelength lights (>650 nm) are mediated by both rods and cones with comparable synaptic gains. Functional roles of the mixed and cone-driven bipolar cells in information processing in dark-adapted retinas are discussed.

Adaptation, Ocular↗
PubMed2000

Seasonal cell proliferation in the chemosensory epithelium and brain of red-backed salamanders, Plethodon cinereus.

The chemosensory epithelium of vertebrates retains the ability to produce new receptor neurons throughout life, presumably as a mechanism to replace aging or damaged receptors. We examined cell division in the main olfactory and vomeronasal epithelia of red-backed salamanders (Plethodon cinereus) because previous studies had shown that the volume of sensory epithelia changes seasonally. Cell division was compared throughout the year by injecting salamanders once with 5-bromo-2'-deoxyuridine (BrdU), which is incorporated into the DNA of cells during DNA synthesis, and sacrificing them one hour after injection. We used immunocytochemistry to locate cells that had arisen from cell division since BrdU injection and compared the number of labeled cells per area among animals. Animals collected in May had significantly more labeled nuclei than animals collected in any other month. However, proliferation rates among the other months were not significantly different and were quite low. Labeled nuclei also were found around the cerebral ventricles of salamanders collected in May, but rarely in any other month, although other tissues in the head often were heavily labeled. Cell proliferation appears to be up-regulated in the chemosensory epithelia and in the telencephalon during May, and we hypothesize that new receptors, and perhaps their interneurons in the telencephalon, are being generated in anticipation of seasonal events that are mediated by chemoreception.

Animals↗
PubMed2006

Cell birth and survival following seasonal periods of cell proliferation in the chemosensory epithelia of red-backed salamanders, Plethodon cinereus.

In addition to the continuous low levels of neurogenesis typical of adult vertebrates to replace damaged chemoreceptor cells, red-backed salamanders (Plethodon cinereus) experience an up-regulation of chemoreceptor epithelial cell proliferation on a seasonal basis. Significantly more cell division occurs in late spring than at any other time of the year, and we investigated the fate and life span of these newly generated cells. We used 5-bromo-2'-deoxyuridine (BrdU) immunocytochemical cell birth dating to examine cell proliferation and cell migration in the main olfactory and vomeronasal epithelia of red-backed salamanders collected in late spring who were allowed to survive for one hour or three, four, 25, 28, 42, 49 and 100 days post-injection. We examined new neuron growth in the vomeronasal and olfactory epithelia using antibodies against Growth Associated Protein-43 (GAP-43), a protein whose synthesis is up-regulated during axon growth. We also tracked apoptosis within both types of chemosensory epithelia using terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL). BrdU-immunoreactive cells were located extensively throughout the vomeronasal epithelia, particularly in the area posterior to the entrance of the nasolacrimal duct, not only after three days of survival, but also all of the longer experimental survival periods as well; BrdU-ir cells within the olfactory epithelia were rarely located after longer survival periods. Salamanders collected in late spring displayed extensive GAP-43 labeling in the vomeronasal epithelia posterior to the entrance of the nasolacrimal duct, indicating a large population of young vomeronasal receptor neurons. Finally, apoptotic cells were evident in this same post-nasolacrimal-duct-area of the vomeronasal organ and in the olfactory epithelium. We suggest that vomeronasal receptor neurons born in late spring function throughout the summer and may be associated with the animals' extensive territoriality during that period.

Analysis of Variance↗
PubMed1995

Brain size and morphology in miniaturized plethodontid salamanders.

In six miniaturized salamanders of the family Plethodontidae, including one of the smallest tetrapod vertebrates. Thorius pennatulus, the anatomical consequences of miniaturization for the brain were investigated. We determined (1) absolute and relative size of the brain, major parts of the brain, the tectum and tectal gray matter, (2) nerve cell size and density, and (3) the number of cells within the visual and visuomotor centers (thalamus, tectum/praetectum and tegmentum). No common compensatory strategy for the brain among the miniaturized salamanders was found. Except for the smallest species, T. pennatulus, only some of the expected compensatory processes (increase in relative size of the brain, relative size of visual centers, relative amount of gray matter or relative density of cell packing density) are found in any species, and these occur in different combinations and degrees. The most decisive factor for maximizing cell number was cell size. Miniaturized species with small cells also have many visual cells, regardless of the other factors. In contrast, the minimum number of visual neurons is found in miniaturized salamanders with large cells. It is concluded that the neuroanatomical traits investigated exert different degrees of resistance to adaptive compensatory processes. Cell size seems to be the most resistant parameter and is strictly dependent on genome size.

Animals↗
PubMed1992

Morphology, behavior, and evolution: comparative kinematics of aquatic feeding in salamanders.

The kinematics of aquatic prey capture were studied in species representing six salamander families (Ambystomatidae, Amphiumidae, Cryptobranchidae, Dicamptodontidae, Proteidae, and Sirenidae) to test the hypothesis that the process of aquatic prey capture is similar in these families. Seven variables were digitized from high-speed video records of prey capture, and a nested analysis of variance was performed to test for both significant individual within taxon and among taxa effects. The time-to-peak head angle and gape variables showed no taxon effect, while the other five variables exhibited highly significant differences among taxa. Cryptobranchus and Siren showed the most divergent kinematic pattern from the other taxa in a multivariate analysis of all variables, while Ambystoma, Dicamptodon, and Amphiuma tended to have similar overall patterns of head movement. These results show that kinematic patterns during aquatic feeding are not conserved across salamander taxa, and that phylogenetic differentiation in head morphology has been accompanied by novelties in feeding function. The feeding mechanisms of Cryptobranchus and Amphiuma have a bidirectional hydrodynamic design with kinematic correlates that are similar to kinematic characteristics of aquatic feeding in turtles and transformed ambystomatid salamanders. A general framework is presented as an aid to understanding the interrelationships among muscle activity patterns, morphology, and behavior (kinematic patterns). By considering the distribution of taxa in three multivariate spaces, corresponding to three of the levels at which one might analyze a behavior (kinematics, morphology, and motor pattern), it is possible to identify patterns of correspondence among the levels, which aid in understanding the evolution of behavior.

Animals↗
PubMed1986

Effect of thermal acclimation on locomotor energetics and locomotor performance in a lungless salamander, Desmognathus ochrophaeus.

To determine the effects of thermal acclimation upon locomotor performance and the rate of oxygen consumption (MO2) during activity, small (less than 3 g), lungless salamanders, Desmognathus ochrophaeus Cope, were acclimated to three temperatures (5, 13 and 21 degrees C) and exercised at various controlled speeds within an exercise wheel while their MO2 was measured. MO2 increased with speed at low speeds (less than 14 cm min-1). Although animals could sustain greater speeds, MO2 did not increase further. These small, exclusively skin-breathing salamanders could increase their MO2 9-11 times during exercise and could sustain nearly half of the oxygen flux expected across a similar surface area of the mammalian lung. However, their maximum aerobic speed was remarkably slow (14 cm min-1) and their net cost of transport remarkably large (15-17 ml O2 g-1 km-1). Thermal acclimation affected MO2 during activity, the maximum sustainable speed and locomotor stamina in different ways. During exercise at 13 degrees C, cold-acclimated animals had a significantly greater MO2 than warm-acclimated animals, but did not differ in stamina or the maximum sustainable speed. During exercise at 21 degrees C, cold acclimation did not affect the MO2 significantly, but it decreased the stamina and increased the rate of lactate accumulation. Thus, these results suggest that thermal acclimation of the MO2 is not tightly coupled to thermal acclimation of locomotor performance in salamanders.

Acclimatization↗
PubMed1997

Modulation of prey-capture behavior in the plethodontid salamander Ensatina eschscholtzii

The hypothesis that salamander prey-capture behavior is highly stereotyped was tested in the plethodontid salamander Ensatina eschscholtzii using high-speed videography and kinematic analysis of feedings on two types of prey (waxworms and termites). The results show that E. eschscholtzii is capable of modulating the timing and magnitude of tongue and jaw movements in response to prey type. Feedings on waxworms, the larger prey, were characterized by shorter durations and higher velocities of tongue and jaw movements compared with feedings on termites, particularly in the latter portion of the feeding sequence (i.e. after prey contact). To test the hypothesis that sensory feedback through the tongue pad plays a role in modulating feeding movements in response to prey type, the ramus lingualis of the glossopharyngeal nerve (cranial nerve IX), which is known to carry sensory information from the tongue pad in salamanders, was transected bilaterally. This experimental deafferentation of the tongue pad had no effect on the degree or direction of differences in feeding kinematics across prey type. These results refute the glossopharyngeal feedback hypothesis, but are consistent with the hypothesis that E. eschscholtzii responds more vigorously to larger prey by assessing prey size visually.

Journal Article↗
PubMed1998

Mechanics of lung ventilation in a large aquatic salamander, siren lacertina

Lung ventilation in Siren lacertina was studied using X-ray video, measurements of body cavity pressure and electromyography of hypaxial muscles. S. lacertina utilizes a two-stroke buccal pump in which mixing of expired and inspired gas is minimized by partial expansion of the buccal cavity during exhalation and then full expansion after exhalation is complete. Mixing is further reduced by the use of one or two accessory inspirations after the first, mixed-gas cycle. Exhalation occurs in two phases: a passive phase in which hydrostatic pressure and possibly lung elasticity force air out of the lungs, and an active phase in which contraction of the transverse abdominis (TA) muscle increases body cavity pressure and forces most of the remaining air out. In electromyograms of the lateral hypaxial musculature, the TA became active 200-400 ms before the rise in body cavity pressure, and activity ceased at peak pressure. The TA was not active during inspiration, and no consistent activity during breathing was noted in the external oblique, internal oblique and rectus abdominis muscles. The finding that the TA is the primary expiratory muscle in S. lacertina agrees with findings in a previous study of another salamander, Necturus maculosus. Together, these results indicate that the use of the TA for exhalation is a primitive character for salamanders and support the hypothesis that the breathing mechanism of salamanders represents an intermediate step in evolution between a buccal pump, in which only head muscles are used for ventilation, and an aspiration pump, in which axial muscles are used for both exhalation and inhalation.

Journal Article↗