Juvenile Salamanders Research Articles

Juvenile Salamanders Do Not Exhibit Compensatory Growth Post-metamorphosis in an Experimental Setting

Compensatory growth, where an organism can grow faster during recovery from low resource periods, is a mechanism used by a wide variety of taxa to mitigate previous deficiencies. Here we present experimental data to test whether pond-breeding salamander juveniles raised in different quality larval habitats can catch up to larger cohort members after metamorphosis. We reared larval Spotted Salamanders (Ambystoma maculatum) in ponds of differing habitat quality resulting in large size differences at metamorphosis. We then kept juveniles in the lab for a year, fed them ad libitum, and measured their growth at three time points post-metamorphosis. We found large differences in size at metamorphosis related to larval habitat, but salamanders that were small at metamorphosis remained smaller a year later and relative growth rates were equal across all metamorphic sizes. Thus, we have little evidence that juveniles can compensate for small size by growing more in the year after metamorphosis, even in conditions of unlimited food. Our data suggest compensatory growth in amphibians may be species-specific, and that poor quality larval environments may be a disadvantage during subsequent life stages.

How does landscape permeability affect the movement of eastern red‐backed salamanders?

AbstractDemographic and genetic connectivity have important implications for population dynamics of wildlife and their ability to adapt to changing environments. Landscape features such as roads and streams can inhibit movement of species with poor dispersal capabilities and exacerbate the effects of habitat fragmentation. Terrestrial plethodontid salamanders are generally thought of as incapable of long‐distance movement and may vary in their motivation to move across a landscape by sex and size classes. To examine landscape permeability to movement, we assessed how distance and natural or man‐made landscape features affect recapture rates after displacement in red‐backed salamanders (Plethodon cinereus). We randomly assigned marked salamanders from 6 plots at Camp Karoondinha in Millmont, Pennsylvania, USA, to a control (placed under the same cover board) or a treatment (displaced 25 m or 50 m through the forest or across a stream or road). Of 290 marked individuals, we recaptured 29.8%. We recaptured more individuals in the control treatment compared to displaced individuals, with recapture rates decreasing with the presence of a road or stream. Landscape feature type and sex did not affect the probability of recapture, but developmental stage did, with adult salamanders more likely to be recaptured than juvenile salamanders. Our results suggest that landscape permeability is reduced for terrestrial salamanders when a landscape feature is present compared to open forest. Narrow, dirt roads present a similar challenge to a natural stream for red‐backed salamanders. Our study should be of value to land managers who are concerned about the negative effects of landscape permeability on terrestrial salamander populations.

Response to conspecific alarm cues by larval and juvenile spotted salamanders (Ambystoma maculatum)

For many species, the highest predation rates are on the earliest life stages, favoring the early development of predator detection mechanisms. Aquatic larvae of Spotted salamanders, Ambystoma maculatum, suffer very high mortality rates and juveniles are vulnerable to a new suite of terrestrial predators after metamorphosis. In some species, adult salamanders assess predation risk via chemical cues released by damaged conspecifics and some heterospecifics (“alarm cues”), but responses of larvae and metamorphs have not been tested. Our first experiment confirmed that field-caught, experienced larvae responded with fright to chemical cues of damaged conspecifics, but not to control cues or alarm cues from toad tadpoles. Responses of sedentary hatchlings in the next experiment indicated that the alarm cue was not present in damaged tissues of hatchlings (1-day-old), but was present by the time the larvae reached the age of 1 month. The third experiment tested responses of naïve lab-reared, free-swimming larvae to alarm cue. In contrast to the other two experiments, these larvae without experience did not distinguish between conspecific alarm cues and control stimuli, suggesting that either embryonic learning or reinforcement learning as larvae may be required to develop or maintain the alarm response. In the fourth experiment, post-metamorphic juveniles raised from field-experienced larvae significantly avoided alarm cues from conspecifics but not control stimuli, indicating that the production and recognition of alarm cues can be retained after metamorphosis. Our study provides the first evidence of chemical alarm cues produced by both larval and juvenile salamanders and indicates that alarm responses may vary according to experience.

Spatial distribution and seasonal movement patterns of reintroduced Chinese giant salamanders

BackgroundVery little is known about the temporal or spatial movement patterns of Chinese giant salamanders (Andrias davidianus) due to their rarity, remote habitat and secretive nature. Commercial breeding farms provide a unique opportunity as a source of animals for reintroduction and spatial ecology studies, which will help inform conservation management efforts for this threatened species. We surgically implanted radio transmitters into the body cavity of 31 juvenile giant salamanders, and these salamanders were subsequently released into two small river systems (Donghe and Heihe Rivers) located in the Qinling Mountains of central China and were monitored daily from May 2013 to August 2014.ResultsOnly two salamanders survived through the end of the project at the Heihe River compared with 12 at the Donghe River, thus movement data for salamanders released at the Heihe river are described individually. The overall sedentariness (ratio of no movement to all observations) for the two salamanders at the Heihe River was 0.29 and 0.28 compared to the average sedentariness of 0.26 ± 0.01 for the 12 salamanders at the Donghe River. Mean daily movement was 15.4 m ± 0.7 at the Heihe River compared to 9.3 m ± 0.3 at the Donghe River. Overall linear home range (LHR) was 246 m and 392 m for the two salamanders at the Heihe River, compared with a mean LHR of 227.2 m ± 70.5 at the Donghe River. The Donghe salamanders exhibited different movement patterns across seasons, having higher sedentariness, shorter daily movement, and smaller LHR in winter than in summer. Up-stream dispersal and fidelity to release site were recorded at both rivers. The mean dispersal distance for the Donghe River salamanders was 145.3 m ± 61.9, while the two surviving salamanders at the Heihe River had a dispersal distance of 211 m and 205 m.ConclusionsThis project provides important insights on the movement ecology of a large aquatic salamander species, and in particular, our results may assist with reintroduction efforts by developing best management practices on when and where to release animals as a conservation strategy.

Behavioral syndrome persists over metamorphosis in a pond-breeding amphibian

In recent years, behavioral ecology has shifted from assuming animal behavior is infinitely plastic and situation specific to recognizing that behavior can be limited in its plasticity and correlated across different ecological situations. At the center of this new framework are behavioral syndromes or consistent individual differences in behavioral tendencies. Over the past decade, numerous studies have identified the evolutionary mechanisms and ecological implications of behavioral syndromes. However, the persistence of behavioral syndromes over ontogeny remains an open question. Species with complex life cycles present an interesting system in which to test the persistence of behavioral syndromes, because such life histories are thought to evolve when correlations between life stages are costly. In this study, we tested the hypothesis that behavioral tendencies of species with complex life histories are consistent within a life stage (before or after metamorphosis) but not between life stages. We experimentally assayed the activity, boldness, and exploration of spotted salamanders (Ambystoma maculatum) before and after metamorphosis. We found most behaviors to be at least moderately repeatable. Additionally, there was support for a behavioral syndrome within the larval stage as well as between larval behaviors and juvenile boldness. Our results reject the adaptive decoupling hypothesis and instead suggest that behavioral syndromes in species with complex life cycles can be maintained over metamorphosis. A central prediction of behavioral syndromes is that individual behavioral consistency should be maintained over the life of an organism. However, in species with complex life cycles, evolution is thought to act independently on each stage, leading to the prediction that behavioral syndromes should not persist over metamorphosis. We tested for behavioral correlations over metamorphosis by assaying salamander activity, boldness, and exploration in larval and juvenile salamanders. We found support for behavioral syndromes within and between life stages. These findings contradict the predictions of complex life cycle evolution and instead suggest that behavioral syndromes may span metamorphosis. However, because support for the persistence of syndromes over metamorphosis varies between taxa, we caution researchers against extrapolating inferences from the larval stage to the juvenile stage.

Natural history of the critically endangered salamander Ambystoma leorae (Caudata: Ambystomatidae) from the Río Tonatzin, Mexico

In Mexico, many species of Ambystoma are endangered, but unfortunately little is known about their natural history and ecology. We report on aspects of the natural history of A. leorae, a critically endangered endemic salamander, from the Río Tonatzin, State of México, Mexico. We observed egg masses, which were attached to vegetation, from April to June, with a mean of 7.28 eggs per egg mass. Larval A. leorae were found in sections of the Río Tonatzin with muddy bottoms and submerged aquatic vegetation. We observed adult and juvenile salamanders throughout the year except September, but with a peak from May to July. The use of sites along the Río Tonatzin by adult and juvenile A. leorae was driven primarily by vegetation type and substrate type of the site, with mud or sand substrate with grass roots and submerged aquatic vegetation being the most used site types. We found no evidence of sexual dimorphism in A. leorae. Our results suggest that adult and juvenile A. leorae use a variety of stream sites, although larvae appear to be more limited in their use of stream sites. These observations indicate that to maintain this population of A. leorae, the general conditions existing in the Río Tonatzin should be protected, especially the sections with muddy bottoms and aquatic vegetation where larvae, juveniles, and adults are found

Moving beyond the plane: measuring 3D home ranges of juvenile salamanders with passive integrated transponder (PIT) tags

An individual’s home range, or how much space it requires to obtain resources and meet its needs for survival and reproduction, affects the scale of many fundamental processes in ecology and can inform the management of species. Although home range size has been described for many taxa in two dimensions (2D), for species that also have a strong vertical component to their movement, such representations can miss core components of their ecology, including the size of their home ranges and the amount of overlap, and thus competition, between individuals. Measuring three-dimensional (3D) home ranges for small-bodied life history stages and species can be particularly difficult, as they cannot tolerate high resolution tracking technologies like GPS collars. In this study, we used Passive Integrated Transponder (PIT) tags to measure the 2D and 3D home ranges of two species of fossorial juvenile salamander: the ringed salamander (Ambystoma annulatum) and the spotted salamander (A. maculatum). We also tested whether individuals modified their habitat selection or movement behavior in response to environmental variation. Salamanders in our study frequently used subterranean habitats. However, we rarely detected them more than 5 cm below ground. Additionally, the overlap among 2D and 3D home ranges, respectively, were similar. These findings indicate that these salamanders may move vertically through their habitat less than previously thought. Alternatively, salamanders may have moved into soil strata beyond the detection range of PIT telemetry. We conclude that PIT telemetry can be a suitable technique for determining the 3D home range of fossorial life-stages or species for which other tracking technologies are unsuitable. When animal behavior includes movements with a vertical component, simplifying assumptions of 2D home ranges can affect ecological inferences by overestimating competition between individuals and underestimating home range size. We used Passive Integrated Transponder (PIT) tags to describe the home range of fossorial juvenile salamanders in 3D. The juvenile salamanders in this study modulated their habitat selection in response to weather, but in general remained close to the soil surface. As a result, juveniles may be more susceptible than previously thought to habitat management practices that alter the local microclimate. Because individuals moved vertically less than predicted, 2D and 3D home ranges had similar patterns. We demonstrate that PIT telemetry can facilitate subterranean tracking of a cryptic life stage. However, this technology is limited in its subterranean detection depth, and until antenna strength is improved, the resolution of 3D home ranges may be limited.

The effects of conspecifics on burrow selection in juvenile spotted salamanders (Ambystoma maculatum)

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.

Better than fish on land? Hearing across metamorphosis in salamanders.

Early tetrapods faced an auditory challenge from the impedance mismatch between air and tissue in the transition from aquatic to terrestrial lifestyles during the Early Carboniferous (350 Ma). Consequently, tetrapods may have been deaf to airborne sounds for up to 100 Myr until tympanic middle ears evolved during the Triassic. The middle ear morphology of recent urodeles is similar to that of early 'lepospondyl' microsaur tetrapods, and experimental studies on their hearing capabilities are therefore useful to understand the evolutionary and functional drivers behind the shift from aquatic to aerial hearing in early tetrapods. Here, we combine imaging techniques with neurophysiological measurements to resolve how the change from aquatic larvae to terrestrial adult affects the ear morphology and sensory capabilities of salamanders. We show that air-induced pressure detection enhances underwater hearing sensitivity of salamanders at frequencies above 120 Hz, and that both terrestrial adults and fully aquatic juvenile salamanders can detect airborne sound. Collectively, these findings suggest that early atympanic tetrapods may have been pre-equipped to aerial hearing and are able to hear airborne sound better than fish on land. When selected for, this rudimentary hearing could have led to the evolution of tympanic middle ears.

Spatial variation in water loss predicts terrestrial salamander distribution and population dynamics.

Many patterns observed in ecology, such as species richness, life history variation, habitat use, and distribution, have physiological underpinnings. For many ectothermic organisms, temperature relationships shape these patterns, but for terrestrial amphibians, water balance may supersede temperature as the most critical physiologically limiting factor. Many amphibian species have little resistance to water loss, which restricts them to moist microhabitats, and may significantly affect foraging, dispersal, and courtship. Using plaster models as surrogates for terrestrial plethodontid salamanders (Plethodon albagula), we measured water loss under ecologically relevant field conditions to estimate the duration of surface activity time across the landscape. Surface activity time was significantly affected by topography, solar exposure, canopy cover, maximum air temperature, and time since rain. Spatially, surface activity times were highest in ravine habitats and lowest on ridges. Surface activity time was a significant predictor of salamander abundance, as well as a predictor of successful recruitment; the probability of a juvenile salamander occupying an area with high surface activity time was two times greater than an area with limited predicted surface activity. Our results suggest that survival, recruitment, or both are demographic processes that are affected by water loss and the ability of salamanders to be surface-active. Results from our study extend our understanding of plethodontid salamander ecology, emphasize the limitations imposed by their unique physiology, and highlight the importance of water loss to spatial population dynamics. These findings are timely for understanding the effects that fluctuating temperature and moisture conditions predicted for future climates will have on plethodontid salamanders.

The Influence of Social Environment: Behavior of Unrelated Adults Affects Future Juvenile Behaviors

AbstractJuveniles' behaviors are often influenced by the behaviors of conspecifics. Most experimental studies of the influence of conspecific behavior vary the social environment by the presence or absence of conspecifics or investigate the impact of the outcome of social encounters (winner/loser effects) but less frequently expose individuals to variation in behavioral phenotypes present in the social environment. Based on previous work showing that juveniles of the salamander Plethodon cinereus are likely to interact frequently with non‐parental adults, I hypothesized that territorial adults in the social environment alter the future behaviors of juveniles. I measured the intracohort social behaviors of juvenile salamanders collected from two geographic areas, Michigan (MI) and Virginia (VA), before and after housing with ostensibly territorial (VA) or non‐territorial (MI) adults. There were overall effects of adult territoriality and aggression on the behavior of juveniles. However, juveniles from populations in MI were especially susceptible to behavioral modification. Compared with behaviors prior to being housed with adults, MI juveniles increased investigatory and escape behaviors in juvenile–juvenile interactions after being housed with adults that displayed territorial behaviors and decreased investigatory and escape behaviors after being housed with non‐territorial adults. This study shows that not only is a specific behavior, territoriality of adult salamanders, a social environment that modifies future juvenile behaviors, but the effects of social environment may differ between populations.

Effects of timber harvesting on terrestrial survival of pond-breeding amphibians

Successful forest management for multiple uses requires balancing extractive practices with maintaining biodiversity, among other important goals. Amphibians comprise an important and abundant part of the biodiversity of many forests. Previous studies have documented declines in the abundance and diversity of amphibians in harvested forests. However, only recently have studies begun to elucidate the mechanisms that underlie such declines. Here, we studied the effects of timber harvesting on survival of geographically widespread ambystomatid salamanders in three forest regions of North America. We used terrestrial enclosures in the Northeast, Midwest, and Southeast to compare amphibian survival in unharvested controls, partially harvested stands (∼25% canopy reduction), and clearcuts with coarse woody debris either retained or removed. In all regions, patterns of amphibian survival were similar, with both juvenile and adult salamanders generally having significantly lower survival in clearcuts compared with unharvested controls. Survival of juvenile salamanders in partially harvested stands was also low, but adult salamanders survived as well or better in partially harvested stands as in controls. Larger body size in juveniles was significantly correlated with recapture, irrespective of treatment, in both the Northeast and Southeast, but not in the Midwest or for adults in any region. Relatively heavier adults were more likely to be captured again in the Southeast, but relative mass was not correlated with recapture in any other regions or for juveniles. Our results suggest that increased amphibian mortality may contribute to declines of amphibian abundance and richness after forest clearcutting for the regions evaluated here. Although our results indicate that partial harvesting is compatible with survival of adult salamanders, retention of intact forest around breeding ponds would benefit all terrestrial stages of pond-breeding salamanders and represents a best management practice for the maintenance of amphibian biodiversity.

Habitat type and distance to edge affect movement behavior of juvenile pond‐breeding salamanders

AbstractBehavioral strategies of natal dispersers in response to human‐altered habitat have far‐reaching implications for functional connectivity and local population dynamics. Spotted salamanders Ambystoma maculatum are forest‐dependent, pond‐breeding amphibians which metamorphose and disperse out of aquatic habitat with limited knowledge of the terrestrial habitat. We quantified the fine‐scale movement behavior and search strategies of recently metamorphosed spotted salamanders in three different habitat types (field, early successional forest and forest) and at varying distances from both hard (field and forest) and soft (early successional forest and forest) edges using fluorescent powder tracking. We found that salamanders moved straighter and with fewer turns through field habitat compared with both forest and early successional habitat. Salamanders significantly oriented movement toward forest when released in the field and when released on the edge between the forest and field. We found that salamander movement in the forest and early successional forest was approximated by a correlated random walk. Based on these results, dispersing spotted salamanders exhibit strong edge‐mediated behavior when differences between habitats are stark (forest and field) and can perceive forest habitat from distances of at least 10 m. These results indicate that dispersing juvenile salamanders exhibit reasonable behavioral rules when moving through habitat types of differing quality. Knowledge of these behavioral rules will improve predictions of the effects of habitat type and configuration on amphibian survival and dispersion in altered landscapes.

Sensory determinants of agonistic interactions in the red-backed salamander, Plethodon cinereus

Many animals use and react to multimodal signals — signals that occur in more than one sensory modality. This study focused on the respective roles of vision, chemoreception, and their possible interaction in determining agonistic responses of the red-backed salamander, Plethodon cinereus. The use of a computer display allowed separate or combined presentation of visual and chemical cues. A cue isolation experiment using adult male and juvenile salamanders showed that both visual and chemical cues from unfamiliar male conspecifics could increase aggressive displays. Submissive displays were only increased in juveniles, and specifically by the visual cue. The rate of chemoinvestigation of the substrate was increased only by chemical cues in adults, whereas both chemical and visual cues increased this behaviour in juveniles. Chemoinvestigation appears, thus, more dependent on sensory input in juvenile salamanders. A follow-up experiment comparing responses to visual cues of different animals (conspecific salamander, heterospecific salamander and earthworm) or an inanimate object (wood stick) showed that exploratory behaviour was higher in the presence of the inanimate object stimulus. The heterospecific salamander stimulus produced strong submissive and escape responses, while the conspecific salamander stimulus promoted aggressive displays. Finally, the earthworm stimulus increased both aggressive and submissive behaviours at intermediate levels when compared to salamander cues. These specific combinations of agonistic and exploratory responses to each stimulus suggest that salamanders could discriminate the cues visually. This study sheds some light on how information from different sensory modalities guides social behaviour at different life stages in a salamander.

Effects of even-aged timber harvest on stream salamanders: Support for the evacuation hypothesis

Habitats worldwide are increasingly threatened by degradation and conversion. Critical to the process of habitat loss is the organismal response, which can have effects on immediate conservation measures or future restoration. Among the most threatened and underappreciated habitats are headwater streams, which are small but abundant features of montane forests. These habitats comprise a significant proportion of the total stream length, can harbor remarkable biodiversity, and are critical for numerous ecosystem processes. One of the most abundant organisms in montane headwater ecosystems are salamanders, and therefore what happens to salamanders when the forest habitats surrounding headwater streams are altered? Three main hypotheses exist: (1) mortality hypothesis; (2) retreat hypothesis; and (3) evacuation hypothesis. To examine these hypotheses we evaluated the impacts of even-aged riparian timber harvest on stream-breeding salamanders. Riparian forests along headwater streams were logged, leaving riparian buffers of 0 m, 9 m, and 30 m. Responses to each riparian alteration were measured in terms of salamander terrestrial habitat use and growth in the riparian habitat, as well as changes in population density within headwater streams. Adult and juvenile salamander densities measured in headwater streams were significantly greater in logged riparian treatments than in unaltered riparian treatments. In addition, salamanders significantly reduced their terrestrial habitat use following riparian logging with both the average distance from the stream and the relative abundance of salamanders decreasing. It is unlikely that salamanders will persist in highly modified riparian habitats, as we measured significantly reduced body conditions over short periods of time at these sites. We present corroborative evidence that salamanders evacuate the riparian habitat following intensive riparian logging, emigrating to adjacent headwater streams. Our results underscore the sensitivity of stream salamanders to riparian habitat alteration as well as the importance of riparian buffers in preserving amphibian assemblages.

Muscarinic control of the excitability of hindlimb motoneurons in chronic spinal-transected salamanders

The excitability of spinal motoneurons (MNs) is regulated by acetylcholine via the activation of muscarinic receptors. The objective of the present study was to determine whether this cholinergic modulation of MN excitability is altered following a chronic spinal cord transection. Juvenile salamanders (Pleurodeles waltlii) were spinally transected at the mid-trunk level, and patch-clamp recordings from hindlimb MNs in spinal cord slices were performed 9-30 days after transection, with and without bath application of muscarine (20 mum). Our results showed that the input-output relationship was larger in MNs recorded 2 weeks after spinal transection than in MNs recorded 3-4 weeks after spinal transection. They further revealed that muscarine increased both the gain of MNs and the proportion of MNs that could exhibit plateau potentials and afterdischarges, whereas it decreased the amplitude of the medium afterhypolarizing potential. Moreover, muscarine had no effect on the hyperpolarization-activated cation current (I(h)), whereas it increased the inward rectifying K(+) current (I(Kir)) in MNs recorded > or = 2 weeks after spinal transection. We conclude that following chronic spinal cord injury, the muscarinic modulation of some intrinsic properties of MNs previously reported in acute spinal-transected animals [S. Chevallier et al. (2006)The Journal of Physiology, 570, 525-540] was preserved, whereas that of other intrinsic properties of MNs was suppressed, either transiently (I(Kir)) or definitively (I(h)). These alterations in muscarinic modulation of MN excitability may contribute to the spontaneous recovery of locomotion displayed in long-term chronic spinal-transected salamanders.

Familiarity with adults, but not relatedness, affects the growth of juvenile red-backed salamanders (Plethodon cinereus)

The relative roles of kinship and familiarity in affecting an individual’s growth and fitness are not easy to disentangle. Not only is an individual more likely to have prior behavioral interactions with conspecifics in close proximity, it may also be related (in terms of kinship) to those nearby conspecifics. While some studies have inferred that kin discrimination affects fitness correlates, other studies found that familiarity alone can reduce aggressive interactions, thus increasing fitness. These studies have all focused on intra-age class pairs or groups. However, many animals interact with conspecifics from different cohorts. In many populations, adults of Plethodon cinereus territorially defend rocks and logs that retain moisture and food resources. We investigated whether juveniles of P. cinereus grew more in the presence of adults that were relatives or familiar. We collected pairs of juveniles and adults found under the same cover objects in the forest (familiar) and pairs of juveniles and adults found under different cover objects, approximately 10 m apart (unfamiliar). We determined parentage and relatedness of the adult–juvenile pairs and then placed these pairs in semi-natural mesocosms for 17 days. We found that juveniles housed with familiar adults had significantly greater increases in mass and snout–vent length than juveniles housed with unfamiliar adults in 2006 but not in 2007. Relatedness had no effect on growth. In addition, juveniles cohabitating with adults were not more likely to be their offspring. At least under certain environmental conditions, familiarity with adults, independent of relatedness or parentage, increased the growth of juvenile salamanders.

The importance of understanding spatial population structure when evaluating the effects of silviculture on spotted salamanders (Ambystoma maculatum)

Current silvicultural practices in the northeastern United States create diverse vegetation patterns and microclimates that provide a mosaic of terrestrial habitats for amphibian species. We inferred patterns of habitat use by the spotted salamander, Ambystoma maculatum, by studying colonization of four newly created breeding pools each surrounded by four different forest treatments: a control, partial cut, clearcut with coarse woody debris (CWD) removed, and clearcut with CWD retained. Created pools were rapidly colonized, indicating that breeding salamanders readily bred in new pools they encountered. This suggests that in our study area pool-specific philopatry and site fidelity may not be high and that particular pools may not define local breeding populations. In the experimental silvicultural treatments, juvenile salamanders preferred the control forest to the clearcuts, whereas adult salamanders showed no significant preferences among the treatments. Although silvicultural practices such as clearcutting may reduce juvenile movement between pools, inter-pool movement by adults that are more tolerant of habitat change may ameliorate this effect in our study area. If juveniles are the primary life-history stage dispersing between local populations (i.e., moving between more isolated groups of pools), however, there is potential for clearcutting to reduce the connectivity between local populations.

Responses of juvenile terrestrial salamanders to introduced (Lithobius forficatus) and native centipedes (Scolopocryptops sexspinosus)

AbstractWhen introduced species invade ecosystems, alterations in community structure can emerge from the competitive and predatory interactions that occur between introduced and native guild members. Because a number of recent studies have shown that large predatory invertebrates can both compete with and prey on small vertebrates and because introductions of non‐native species may play a role in amphibian declines, the effects of introduced centipedes Lithobius forficatus and native centipedes Scolopocryptops sexspinosus on juveniles of the red‐backed salamander Plethodon cinereus were examined. In laboratory arenas, juvenile salamanders exhibited submissive behaviour in response to the odours of both species of centipede. There were no significant differences in salamander response to the two centipede odour treatments, but compared to controls, juveniles of P. cinereus spent significantly more time in escape and in a flattened submissive posture when presented with native centipede odours. Despite significant size differences between centipedes and juvenile salamanders, no predation of salamanders by either species of centipede occurred in any pairings. Juveniles exhibited more chemosensory behaviour towards native centipedes and towards their odours and exhibited marked reductions in aggressive posturing when centipedes were present. Field and laboratory data suggest that juveniles of P. cinereus and centipedes were negatively associated. In laboratory trials, the native centipede excluded juvenile salamanders from cover objects and we found fewer instances of co‐occurrence in the field than expected. These studies are the first to examine the behavioural interactions between juveniles of P. cinereus and invertebrate predators, one introduced and one native, of eastern deciduous forest‐floor food webs.

Genetic Variation among Ambystoma 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.