Detection of the Sexual Identity of Conspecifics through Volatile Chemical Signals in a Territorial Salamander

Territorial red‐backed salamanders (Plethodon cinereus) have been shown to use nonvolatile chemical signals in both territorial defense and to convey a variety of information to conspecifics. We investigated whether or not red‐backed salamanders could determine the sexual identity of conspecifics through volatile chemical signals, and we explored their use in the context of territorial defense. We exposed male and female red‐backed salamanders to four experimental treatments (i.e. filter papers that had been scent marked by male or female conspecifics for 1 and 5 d) and two control treatments (i.e. unscented filter papers for 1 and 5 d tests). The focal salamanders were prevented from physically accessing the scent marked filter papers and, presumably, some of the substrate scent marks had volatile components that were detected and interpreted by the focal salamanders. Both male and female red‐backed salamanders spent significantly more time in threat displays when they were exposed to volatile chemical signals from same‐sex conspecifics than they did toward similar signals from opposite‐sex conspecifics. A similar statistical pattern was observed for the amount of chemosensory sampling exhibited by focal red‐backed salamanders. From these results, we infer that red‐backed salamanders can determine the sexual identity of conspecifics through volatile chemical signals, some of which may be used in territorial defense. Further, such airborne pheromones may influence the spatial organization of salamander territories on the forest floor.     

Effects of Timber Management on Pond-Breeding Salamanders

Abstract: Pond-breeding salamanders spend most of their lives in forested habitat surrounding the vernal pools where they breed. Timber harvesting has been demonstrated to have negative impacts on salamander populations due to changes in soil temperature, soil compaction, and general degradation of habitat. However, little is known about how long it takes for harvested forest habitat to once again become suitable for salamanders. Questions also remain as to whether salamanders will use an area that has been harvested in recent years if an older intact forest area is available. We used drift fences and pitfall traps to capture adult spotted salamanders (Ambystoma maculatum) and marbled salamanders (A. opacum) migrating to 3 vernal ponds during their breeding seasons. The study area contained tracts of forest that were clear-cut 11–12 years prior to the study. All 3 ponds were surrounded by areas of clear-cut and intact forest and drift fences were placed in both habitat types. Similar numbers of spotted salamanders entered the ponds from clear-cut and intact forest areas. The number of marbled salamanders migrating to the ponds did not differ between areas of clear-cut and intact forest. These results suggest that clear-cut habitats may become suitable for adult pond-breeding salamanders after a relatively short regeneration period.     

Genetic Variation among <Emphasis Type="Italic">Ambystoma</Emphasis> Breeding Populations on the Savannah River Site

We surveyed 16 Carolina bay breeding ponds for Ambystoma salamanders. Tail tissue samples were collected from adult and juvenile mole salamanders (A. talpoideum), marbled salamanders (A. opacum), and spotted salamanders (A. maculatum) captured leaving the Carolina bays. We used amplified fragment length polymorphisms (AFLP) to determine the genetic variation associated with the breeding populations. The Carolina bays could be considered as individual populations, metapopulation groups, or as one big metapopulation depending on gene flow between these bays. Bays range from less than 100 m apart to more than 24 km apart, much further than any reported movement for these species. Animals were marked in the field. We documented little movement of salamanders between breeding locations. Using 392 polymorphic bands produced with the AFLP technique, we were able to separate the samples into the correct species from which the tissues were collected. However, within species analyses failed to find structure associated with populations of salamanders. We failed to document a correlation between geographic and genetic distance (Mantel r = 0.05235, P=0.6800 for mole salamanders; r = 0.46077, P=0.9547 for marbled salamanders). Only 27.8% of mole salamanders and 60.9% of marbled salamanders were assigned back to the population of capture. The majority of the genetic variation was attributable to the individual as opposed to the population. The results of this study suggest that while the majority of these salamanders may be philopatric, some mixing maybe occurring or alternatively, that these populations have not been genetically isolated for sufficient time to develop unique genotypes through drift.     

Patterns of habitat and invertebrate diet overlap between tiger salamanders and ducks in prairie potholes

During the breeding season, migratory waterfowl are attracted to wetlands characterized by high macroinvertebrate availability. Many of these prairie potholes are fishless and this apparent void is filled, at least partially, by tiger salamanders. Based on gut contents from 98 tiger salamanders and published diet data from over 1500 ducks, we show that there is general overlap in diet between both larval and adult tiger salamanders and 10 duck species. Furthermore, when the ducks were split into foraging guilds and compared with tiger salamanders, prey type overlap was 1.7 times higher and prey size was 1.8 times higher with dabbling ducks than diving ducks. Field surveys show that tiger salamander density is more highly correlated with diving duck density across potholes than dabbling duck density. Tiger salamanders have higher diet overlap with dabbling ducks than diving ducks whereas tiger salamanders have higher spatial overlap with diving ducks than dabbling ducks suggesting that these consumers coarsely partition diet and habitat resources. It has been reported that tiger salamanders have specialized diets that are associated with foraging preferences for benthic habitats. This view is too narrow: in southwestern Manitoba, Canada, tiger salamanders are more general consumers with diets more like dabbling ducks that forage mostly in planktonic and littoral habitats. Our results suggest that dabbling and diving ducks are, to different extents, liable to the effects of indirect interactions, specifically competition for common prey, with tiger salamanders.     

In search of critically endangered species: the current situation of two tiny salamander species in the Neotropical mountains of Mexico

Worldwide, one in every three species of amphibian is endangered, 39 species have gone extinct in the last 500 years and another 130 species are suspected to have gone extinct in recent decades. Of the amphibians, salamanders have the highest portion of their species in one of the risk categories, even higher than the frogs. To date there have been few studies that have used recent field data to examine the status of populations of endangered salamanders. In this study we evaluate the current situation of two tiny salamanders, Parvimolge townsendi and Thorius pennatulus, both of which are distributed at intermediate elevations in the mountains of the northern Neotropics and are considered to be critically endangered; the first has been proposed as possibly extinct. By carrying out exhaustive surveys in both historical and potentially suitable sites for these two species, we evaluated their abundance and the characteristics of their habitats, and we estimated their potential geographic distribution. We visited 22 sites, investing 672 person-hours of sampling effort in the surveys, and found 201 P. townsendi salamanders in 11 sites and only 13 T. pennatulus salamanders in 5 sites. Both species were preferentially found in cloud forest fragments that were well conserved or only moderately transformed, and some of the salamanders were found in shade coffee plantations. The potential distribution area of both species is markedly fragmented and we estimate that it has decreased by more than 48%. The results of this study highlight the importance of carrying out exhaustive, systematic field surveys to obtain accurate information about the current situation of critically endangered species, and help us better understand the crisis that amphibians are facing worldwide.     

Perceived predation risk as a function of predator dietary cues in terrestrial salamanders

Prey often avoid predator chemical cues, and in aquatic systems, prey may even appraise predation risk via cues associated with the predator's diet. However, this relationship has not been shown for terrestrial predator-prey systems, where the proximity of predators and prey, and the intensity of predator chemical cues in the environment, may be less than in aquatic systems. In the laboratory, we tested behavioural responses (avoidance, habituation and activity) of terrestrial red-backed salamanders, Plethodon cinereus, to chemical cues from garter snakes, Thamnophis sirtalis, fed either red-backed salamanders or earthworms (Lumbricus spp.). We placed salamanders in arenas lined with paper towels pretreated with snake chemicals, and monitored salamander movements during 120 min. Salamanders avoided substrates preconditioned by earthworm-fed (avoidanceX+/-SE=91.1+/-2.5%, N=25) and salamander-fed (95.2+/-2.5%, N=25) snakes, when tested against untreated substrate (control). Salamanders avoided cues from salamander-fed snakes more strongly (75.2+/-5.5%, N=25) than earthworm-fed snakes when subjected to both treatments simultaneously, implying that salamanders were sensitive to predator diet. Salamanders tended to avoid snake substrate more strongly during the last 60 min of a trial, but activity patterns were similar between salamanders exposed exclusively to control substrate versus those subject to snake cues. In another experiment, salamanders failed to avoid cues from dead conspecifics, suggesting that the stronger avoidance of salamander-fed snakes in the previous experiment was not directly due to chemical cues emitted by predator-killed salamanders. Salamanders also did not discriminate between cues from a salamander-fed snake versus a salamander-fed snake that was recently switched (i.e. <14 days) to an earthworm diet. Our results imply that terrestrial salamanders are sensitive to perceived predation risk via by-products of predator diet, and that snake predators rather than dead salamanders may be largely responsible for the release of such chemicals. Copyright 1999 The Association for the Study of Animal Behaviour.     

Digits lost or gained? Evidence for pedal evolution in the dwarf salamander complex (Eurycea, Plethodontidae)

Change in digit number, particularly digit loss, has occurred repeatedly over the evolutionary history of tetrapods. Although digit loss has been documented among distantly related species of salamanders, it is relatively uncommon in this amphibian order. For example, reduction from five to four toes appears to have evolved just three times in the morphologically and ecologically diverse family Plethodontidae. Here we report a molecular phylogenetic analysis for one of these four-toed lineages--the Eurycea quadridigitata complex (dwarf salamanders)--emphasizing relationships to other species in the genus. A multilocus phylogeny reveals that dwarf salamanders are paraphyletic with respect to a complex of five-toed, paedomorphic Eurycea from the Edwards Plateau in Texas. We use this phylogeny to examine evolution of digit number within the dwarf-Edwards Plateau clade, testing contrasting hypotheses of digit loss (parallelism among dwarf salamanders) versus digit gain (re-evolution in the Edwards Plateau complex). Bayes factors analysis provides statistical support for a five-toed common ancestor at the dwarf-Edwards node, favoring, slightly, the parallelism hypothesis for digit loss. More importantly, our phylogenetic results pinpoint a rare event in the pedal evolution of plethodontid salamanders.     

Avoidance of Chemical Alarm Cues Released from Autotomized Tails of Ravine Salamanders (Plethodon richmondi)

The ability of animals to detect and avoid areas containing chemical alarm cues from conspecifics is well documented in aquatic species. The ability to detect chemical alarm cues in terrestrial organisms has not been tested until recently. In this study, we tested the ability of the ravine salamander ( Plethodon richmondi ) to detect and avoid areas containing chemicals released from the autotomized tails of conspecifics and sympatric zigzag salamanders ( P. dorsalis ). We also ascertained whether any avoidance response could be attributed to the size or sex of the animal. Our results suggest that ravine salamanders avoid substrates containing odors released from the autotomized tails of conspecifics, but not of heterospecific salamanders and that this response occurs independent of the size and/or sex of the animal. By avoiding areas where a conspecific has recently been injured, an organism could reduce its chances of encountering a predator and thus increase its chances of survival.     

Ontogenetic evidence for the Paleozoic ancestry of salamanders

The phylogenetic positions of frogs, salamanders, and caecilians have been difficult to establish. Data matrices based primarily on Paleozoic taxa support a monophyletic origin of all Lissamphibia but have resulted in widely divergent hypotheses of the nature of their common ancestor. Analysis that concentrates on the character states of the stem taxa of the extant orders, in contrast, suggests a polyphyletic origin from divergent Paleozoic clades. Comparison of patterns of larval development in Paleozoic and modern amphibians provides a means to test previous phylogenies based primarily on adult characteristics. This proves to be highly informative in the case of the origin of salamanders. Putative ancestors of salamanders are recognized from the Permo-Carboniferous boundary of Germany on the basis of ontogenetic changes observed in fossil remains of larval growth series. The entire developmental sequence from hatching to metamorphosis is revealed in an assemblage of over 600 specimens from a single locality, all belonging to the genus Apateon. Apateon forms the most speciose genus of the neotenic temnospondyl family Branchiosauridae. The sequence of ossification of individual bones and the changing configuration of the skull closely parallel those observed in the development of primitive living salamanders. These fossils provide a model of how derived features of the salamander skull may have evolved in the context of feeding specializations that appeared in early larval stages of members of the Branchiosauridae. Larvae of Apateon share many unique derived characters with salamanders of the families Hynobiidae, Salamandridae, and Ambystomatidae, which have not been recognized in any other group of Paleozoic amphibians.     

Behavioral interactions between salamanders and centipedes: competition in divergent taxa

Red-backed salamanders, Plethodon cinereus, use territorialadvertisement in the form of agonistic displays and pheromonalscent marking as a mechanism for intraspecific interferencecompetition. Although ecological and behavioral interactionsamong species of salamanders have been well studied, littleis known about the interactions between territorial P. cinereusand other ecologically similar species, such as large predatoryinvertebrates. Our field data indicate that P. cinereus anda large syntopic centipede, Scolopocryptops sexspinosus, exhibitnegative spatial associations in natural habitats, possiblyindicating interspecific territoriality. Only seven instancesof salamander/centipede co-occurrence were recorded from a fieldsample of 247 occupied cover objects. Cover object size waspositively correlated with salamander SVL (tip of the snoutto the anterior end of the cloaca), but there was no correlationof cover object size to centipede length. Data on the abilityof P. cinereus to differentiate among chemicals on the substratesuggest that visual cues are not necessary to elicit a territorialresponse from intruding salamanders. Although in laboratorytrials salamanders behaved similarly toward intruders of bothspecies, biting was directed only toward centipedes. Salamandersspent significantly more time approaching centipedes than theydid approaching other salamanders. Approach behavior was oftenassociated with nose tapping and may be an investigative, ratherthan aggressive, behavior. We suggest that territorial P. cinereusrespond similarly to intruding salamanders and centipedes, butthat they escalate more readily to biting centipedes becauseS. sexspinosus is sightless and thus unable to respond to visualsignals.     

Salamander drift

SUMMARY. Interpretation of data collected from a spring-fed stream suggests the existence of a phenomenon in running water that has not been previously described — salamander drift. Stream substrate and drift collections indicated that pre-metamorphic salamanders ( Eurycea bislineata ) entered the water train and drifted during the months of April, May and June. Post-metamorphic salamanders, and individuals about to undergo metamorphosis, did not appear in the stream drift.     

Detection of Batrachochytrium dendrobatidis in Mexican Bolitoglossine Salamanders Using an Optimal Sampling Protocol

The role of the chytrid fungus Batrachochytrium dendrobatidis (Bd), which is the causal agent of chytridiomycosis, in the declines of Central American bolitoglossine salamanders is unknown. Here we establish a swabbing protocol to maximize the detection probability of Bd in salamanders. We then used this protocol to examine captive and wild Mexican bolitoglossine salamanders of 14 different species for the presence of Bd. Of the seven body parts sampled, the pelvic region, hindlimbs, forelimbs, and the ventral side of the tail had the most Bd per surface area and thus might provide the best sampling regions of salamanders to detect Bd infections. Sixteen out of 33 (48%) of the dead captive salamanders had Bd infections and epidermal hyperkeratosis, whereas none of the 28 clinically healthy captive animals were infected. Nine out of 17 (53%) of the wild salamanders carried low zoospore loads of Bd but had no clinical signs of disease. The high prevalence of Bd in dead captive salamanders, its absence in clinically healthy living ones and its presence in wild salamanders is consistent with Bd being involved in recent bolitoglossine population declines, but further studies would be required to draw a causal link.     

A New Species of Eimeria (Apicomplexa: Eimeriidae) from the marbled salamander, Ambystoma opacum (Caudata: Ambystomatidae), from northern Louisiana

Between December 2002 and June 2004, 10 marbled salamanders, Ambystoma opacum, were examined for coccidian parasites. Salamanders were collected in Bradley (n = 2), Little River (n = 1), Miller (n = 1), and Sevier (n = 1) Counties, Arkansas; Webster Parish, Louisiana (n = 2); and Bowie (n = 1) and Nacogdoches (n = 2) Counties, Texas. Two of 10 (20%) A. opacum from Louisiana harbored an undescribed species of Eimeria. Oocysts of Eimeria trauthi n. sp. were ellipsoidal, 36.6 x 33.1 (33-40 x 29-37) microm, with a thin, single-layered wall; shape index 1.1. Polar granule(s) and micropyle were absent. Oocyst residuum was composed of hundreds of loosely packed homogenous granules of various sizes enclosing a vacuole. Sporocysts were elongate-ellipsoidal, 20.8 x 8.1 (19-22 x 7-9) microm; shape index 2.6. Sporocyst residuum was spherical and composed of a cluster of granules often membrane-bound. This is the first time a coccidium has been reported from an amphibian species in Louisiana and the second time a coccidium has been described from this salamander host. In addition, the following 26 salamanders from various counties in Arkansas, Oklahoma, and Texas were surveyed during the study period and were negative for coccidia: Ambystomatidae, 4 spotted salamanders (Ambystoma maculatum) and 7 mole salamanders (Ambystoma talpoideum); Cryptobranchidae, 4 Ozark hellbenders (Cryptobranchus alleganiensis bishopi); Plethodontidae, 6 spotted dusky salamanders (Desmognathus conanti) and 3 many-ribbed salamanders (Eurycea multiplicata multiplicata); and Salamandridae, 2 central newts (Notophthalmus viridescens louisianensis).     

Influence of temperature on Ranavirus infection in larval salamanders Ambystoma tigrinum

Temperature strongly influenced percent mortality and time to death of salamanders exposed to the Ambystoma tigrinum virus (iridovirus) (ATV). Most salamanders survived when exposed at 26 degrees C, whereas all died at 18 degrees C and nearly all died at 10 degrees C. Some asymptomatic salamanders that survived 60 d at 10 or 26 degrees C were found to be carrying virus. Polymerase chain reaction (PCR) confirmed the presence of virus in ATV-exposed salamanders but was found to be less sensitive than cell culture in detecting ATV at low concentrations. PCR products were 100% identical to ATV in the major capsid protein sequence. Virus titer was higher in salamanders held at 10 degrees C than at 18 degrees C but little virus, if any, was present in the small number of salamanders that died at 26 degrees C. These results may help explain periodic viral epizootics in field populations of A. tigrinum where water temperatures fluctuate widely.     

The effects of conspecifics on burrow selection in juvenile spotted salamanders (<Emphasis Type="Italic">Ambystoma maculatum)</Emphasis>

Spotted salamanders (Ambystoma maculatum) are pond-breeding amphibians that disperse into terrestrial habitat from natal wetlands after undergoing metamorphosis, relying on small-mammal burrows and coarse woody debris for refugia. The effect of conspecifics on burrow use in juvenile salamanders is poorly understood. Determining how the presence of conspecifics influences the settlement decisions of juvenile salamanders can increase our understanding of amphibian dispersal and our ability to predict population dynamics. We conducted behavioral laboratory trials using 58 recently metamorphosed salamanders to examine how salamanders selected burrows in the presence of conspecifics. Salamanders were more likely to settle in a burrow that was occupied by a conspecific versus an unoccupied burrow. Our results indicate that juvenile salamanders may show conspecific attraction and/or trailing behavior during the dispersal phase.     

Effects of Timber Harvests and Silvicultural Edges on Terrestrial Salamanders

Balancing timber production and conservation in forest management requires an understanding of how timber harvests affect wildlife species. Terrestrial salamanders are useful indicators of mature forest ecosystem health due to their importance to ecosystem processes and sensitivity to environmental change. However, the effects of timber harvests on salamanders, though often researched, are still not well understood. To further this understanding, we used artificial cover objects to monitor the relative abundance of terrestrial salamanders for two seasons (fall and spring) pre-harvest and five seasons post-harvest in six forest management treatments, and for three seasons post-harvest across the edge gradients of six recent clearcuts. In total, we recorded 19,048 encounters representing nine species of salamanders. We observed declines in mean encounters of eastern red-backed salamanders (Plethodon cinereus) and northern slimy salamanders (P. glutinosus) from pre- to post-harvest in group selection cuts and in clearcuts. However, we found no evidence of salamander declines at shelterwoods and forested sites adjacent to harvests. Edge effects induced by recent clearcuts influenced salamanders for approximately 20 m into the forest, but edge influence varied by slope orientation. Temperature, soil moisture, and canopy cover were all correlated with salamander counts. Our results suggest silvicultural techniques that remove the forest canopy negatively affect salamander relative abundance on the local scale during the years immediately following harvest, and that the depth of edge influence of clearcuts on terrestrial salamanders is relatively shallow (<20 m). Small harvests (<4 ha) and techniques that leave the forest canopy intact may be compatible with maintaining terrestrial salamander populations across a forested landscape. Our results demonstrate the importance of examining species-specific responses and monitoring salamanders across multiple seasons and years. Long-term monitoring will be necessary to understand the full impacts of forest management on terrestrial salamanders.     

Functional design of the feeding mechanism in lower vertebrates: unidirectional and bidirectional flow systems in the tiger salamander

There are two basic designs of the aquatic feeding mechanism in lower vertebrates: unidirectional and bidirectional flow systems. Larval salamanders and most fishes posses a unidirectional flow design in which water drawn into the mouth with the prey passes over the gills and exits posteriorly. Metamorphosed salamanders and all other aquatic vertebrates possess a bidirectional system in which water flows into and out of the mouth during a single feeding cycle. We investigated the functional consequences of these two feeding designs in larval and metamorphosed tiger salamanders ( Ambystoma tigrinum ) feeding in the water. Buccal cavity pressures were measured during feeding and 11 variables measured from the pressure traces. Significant differences were found between the larval and metamorphosed salamanders in eight variables. Larval salamanders generate significantly greater negative pressures than do metamorphosed individuals and a principal components analysis of the 11 pressure variables completely separates larval from metamorphosed salamanders. Larval individuals are significantly better at capturing elusive prey than are metamorphosed salamanders, apparently because of changes in the structure of the feeding mechanism and the concomitant functional modifications.     

Modelling reproductive allocation of dusky salamanders using optimal control theory: Pros,cons and caveats

Summary Optimal control theory has been used to examine the evolution of life history characters in a variety of plant and animal species. In this paper, I examine control theoretic models of reproductive allocation in female dusky salamanders and consider some practical aspects of modelling, including the appropriateness of nonlinear formulations, methods for describing semelparous reproduction, and data needed to parameterize models. The model analysed includes state variables for somatic and reproductive tissue, energy intake and requirements for physiological maintenance, and iteroparous reproduction. It predicts that female salamanders should spend the first part of their lives growing. After reaching sexual maturity, females should either spend the remainder of their lives reproducing at the expense of decreasing body size, possibly resulting in death by starvation, or maintain approximately constant body size at the expense of low reproductive output. This lack of correspondence to the observed biology of dusky salamanders suggests that not all the appropriate biology has been described. In particular, inclusion of a storage variable may be necessary in future modelling efforts.     

Competition at the range boundary in the slimy salamander: using reciprocal transplants for studies on the role of biotic interactions in spatial distributions

1. Determining the factors that influence the distribution of species has been a longstanding goal in the field of ecology. New techniques such as ecological niche modelling have the potential to aid in addressing many broad questions in ecology, evolutionary biology, and behavioural ecology. 2. This study combines broad-scale ecological niche models with fine-scaled studies of biotic interactions to examine how abiotic and biotic interactions affect the spatial distribution of the terrestrial salamander species Plethodon glutinosus (northern slimy salamander), in a potential contact zone shared with Plethodon mississippi (Mississippi slimy salamander). 3. The core habitat in the interior portion of the range of P. glutinosus and the contact zone are distributed in unique environmental niche space. 4. The form of competition, inter- or intraspecific, significantly affected mass loss of adult salamanders. Salamanders lost more mass when interacting with a heterospecific. 5. Abiotic conditions strongly influenced the impact of competition on salamanders. Under stressful environmental conditions at the field site located in the contact zone, salamanders lost more mass than at the field site located in the interior of the range. 6. Furthermore, adult salamanders from range-edge populations and core populations (from the interior of the range) differed in their respective abilities to compete under the abiotic conditions in the contact zone.     

人工养殖大鲵全长与体重关系的回归分析

大鲵(Andrias davidianus)隶属两栖纲,有尾目,隐鳃鲵科,大鲵属,为我国特有的珍稀濒危两栖动物。目前在我国一些主要历史分布区掀起了一股大鲵养殖高潮,但是对当前养殖效果缺乏成熟的评价手段,因此本研究通过对陕西省汉中市和安康市两大鲵养殖场养殖的1530尾大鲵的体重和全长进行实际测量,利用SPSS分析软件对数据进行了回归分析。结果表明,体重与全长之间存在极显著的相关关系,体重与全长之间的关系主要表现为幂函数关系,其关系式为:Y=0.010X2.867。本研究的顺利完成,为今后评价大鲵的人工养殖效果提供了科学的方法。