Amphiuma Means Research Articles

Immunohistochemical Characterization of Langerhans Cells in the Skin of Three Amphibian Species.

The amphibian taxon includes three orders that present different morphological characteristics: Anura, Caudata, and Apoda. Their skin has a crucial role: it acts as an immune organ constituting a physical, chemical, immunological, and microbiological barrier to pathogen insult and conducts essential physiological processes. Amphibians have developed specialized features to protect the vulnerable skin barrier, including a glandular network beneath the skin surface that can produce antimicrobial and toxic substances, thus contributing to the defense against pathogens and predators. This study aims to characterize Langerhans cells in the skin of Lithobates catesbeianus (order: Anura; Shaw, 1802), Amphiuma means (order: Caudata; Garden, 1821), and Typhlonectes natans (order: Apoda; Fischer, 1880) with the following antibodies: Langerin/CD207 (c-type lectin), Major Histocompatibility Complex (MHC)II, and Toll-like receptor (TLR)2 (expressed by different types of DCs). Our results showed Langerhans cells positive for Langerin CD/207 in the epidermis of the three species; moreover, some antigen-presenting cells (APCs) in the connective tissue expressed TLR2 and MHCII. The distribution of the Langerhans cells is very similar in the three amphibians examined, despite their different habitats. A greater knowledge of the amphibian immune system could be useful to better understand the phylogeny of vertebrates and to safeguard amphibians from population declines. Furthermore, the similarities between amphibians' and human skin concerning immunological features may be useful in both biology and translational medicine.

Radiocesium (137Cs) concentrations in the two-toed amphiuma (Amphiuma means) and the lesser siren (Siren intermedia)

This study sought to determine radiocesium (137Cs) concentrations in two species of aquatic salamanders – the two-toed amphiuma (Amphiuma means) and the lesser siren (Siren intermedia) on the Savannah River Site. Concentrations (137Cs Bq/g, dry wt) of the two species were similar at both 137Cs-contaminated (A. means = 0.733 ± 0.242, n = 5; S. intermedia = 0.839 ± 0.722, n = 5) and reference sites (A. means = 0.028 ± 0.020, n = 5; S. intermedia = 0.042 ± 0.027, n = 11). Salamanders captured in areas impacted by 137Cs contamination exhibited significantly higher 137Cs concentrations than individuals captured at reference sites (U = 146, p < 0.001). Salamander size (snout-vent length) was not correlated with whole-body 137Cs. An analysis of our data using the ERICA tool suggests that negative impacts due to 137Cs exposure are unlikely in these species. Overall, these data indicate that A. means and S. intermedia inhabiting contaminated sites bioaccumulate but do not biomagnify 137Cs.

Mercury Concentrations in the Two-Toed Amphiuma (Amphiuma means) and the Lesser Siren (Siren intermedia): Validating Non-lethal Sampling Methods in Southeastern Aquatic Salamanders.

The global decline of amphibians is a major conservation issue. Many stressors are recognized for this decline including exposure to environmental contaminants. Mercury (Hg) is an environmental contaminant that bioaccumulates in wildlife and can cause a variety of negative impacts across taxa, including amphibians. Amphiuma and Siren spp. can comprise a large portion of biomass within their respective ecosystems, and thus, likely serve as important predators or prey in wetland communities. However, due to their cryptic nature, little is known about their ecology, diet, and accumulation potential. We sought to validate a nonlethal sampling method to quantify total mercury (THg) in two enigmatic species of aquatic salamanders: the two-toed amphiuma (Amphiuma means) and the lesser siren (Siren intermedia). We examined relationships between THg content in lethal (whole-body) and nonlethal (tail clip) samples. Tail clips were statistically significant predictors of whole-body THg (all p < 0.001), explaining 84-89% of variation in whole-body THg. Average whole-body THg (mg/kg) did not significantly differ between the two species (p = 0.97), and overall, they had similar whole-body THg content (S. intermedia = 0.330 ± 0.04, n = 18; A. means = 0.333 ± 0.07, n = 11). To our knowledge, these data represent the first reported Hg burdens in A. means and S. intermedia.

Hearing and Sound Production in the Aquatic Salamander, Amphiuma means

Abstract: In contrast to anurans, acoustic communication and hearing within Order Urodela is poorly understood. Several studies have documented sound production in a few salamander species; however, these studies did not examine auditory ranges of these salamanders simultaneously. Two-Toed Amphiumas (Amphiuma means) were used as a model to examine the ecological significance of sound production in salamanders. We conducted a series of behavioral trials to validate sound production in this species, and auditory-evoked potentials (AEPs) were measured to assess hearing abilities. Amphiuma means produced three unique broadband acoustic signals: low-, mid-, and high-frequency clicks. All acoustic signals were produced when A. means were placed in groups, but not when housed individually. The audiogram was relatively flat at 100–700 Hz; above this range, sensitivity declined with increasing frequency. No auditory responses were detected between 1.5 and 10 kHz. The dominant frequencies of the acoustic signals (...

Trap characteristics and species morphology explain size-biased sampling of two salamander species

Demographic studies often depend on sampling techniques providing representative samples from populations. However, the sequence of events leading up to a successful capture or detection is susceptible to biases introduced through individual-level behaviour or physiology. Passive sampling techniques may be especially prone to sampling bias caused by size-related phenomena (e.g., physical limitations on trap entrance). We tested for size-biased sampling among five types of passive traps using a 9-year data set for two species of aquatic salamanders that have a 20 and 61 fold change in length over their ontogeny (Amphiuma means, Siren lacertina). Size-biased trapping was evident for both species, with body size distributions (body length mean and SD) of captured individuals differing among sampling techniques. Because our two species differed in girth at similar lengths, we were able to show that size biases (in length) were most likely caused by girth limitations on trap entry rates, and potentially by differences in retention rates. Accounting for the biases of sampling techniques may be critical when assessing current population status and demographic change.

Body Size and Diet of Amphiuma Means (Caudata: Amphiumidae) From Southeastern Virginia

Abstract Body size relationships and diet was obtained largely from a sample of Two-toed Amphiuma (Amphiuma means) from the Great Dismal Swamp in southeastern Virginia. Maximum body size (842 mm total length) was similar to that reported for other locations farther south in the species' range but less than the maximum known size. Adult males (x̄ SVL = 489 mm) were significantly larger than adult females (x̄ SVL = 424 mm). Tail length was linearly related to total length and was not sexually dimorphic. Log transformed body size explains 93.7% of log-body weight; the relationship did not differ between sexes. Prey consisted of several insect taxa (including bees), crayfish (Procambarus), tadpoles (Lithobates), and small fish (Umbra), further confirming that amphiumas have catholic diets.

The role of size preference in prey selection ofAmphiuma means

Abstract. The two-toed amphiuma, Amphiuma means, is a large aquatic salamander and a potentially important predator of crayfish. However, little is known about the effects of predation by A. means on crayfish communities. This study was carried out to determine if there is a size preference in A. means predation on crayfish. A. means was expected to prefer medium sized crayfish in accordance with the optimal foraging theory because they were more energetically rewarding than smaller crayfish but easier to capture than larger crayfish. Seven similarly-sized A. means were placed in individual aquatic mesocosms. Six crayfish of the subgenus Scapulicambarus, two from each of three size categories, were also placed in each tub. The percent mortality and location of the crayfish in the tub were observed for 11 days. A. means had a significant preference for medium-sized crayfish on day four, but there were no significant differences among predation rates by the final day. Small crayfish had the lowest predation...

The permeability of red blood cells to chloride, urea, and water

This study extends permeability (P) data on chloride, urea and water in red blood cells (RBC), and concludes that the urea transporter (UT-B) does not transport water. P of chick, duck, Amphiuma means, dog and human RBC to (36)Cl(-), (14)C-urea and (3)H2O was determined under self-exchange conditions. At 25°C and pH 7.2-7.5, PCl is 0.94 × 10(-4)-2.15 × 10(-4) cm s(-1) for all RBC species at [Cl]=127-150 mmol l(-1). In chick and duck RBC, P(urea) is 0.84 × 10(-6) and 1.65 × 10(-6) cm s(-1), respectively, at [urea]=1-500 mmol l(-1). In Amphiuma, dog and human RBC, P(urea) is concentration dependent (1-1000 mmol l(-1), Michaelis-Menten-like kinetics; K1/2;=127, 173 and 345 mmol l(-1)), and values at [urea]=1 mmol l(-1) are 29.5 × 10(-6), 467 × 10(-6) and 260 × 10(-6) cm s(-1), respectively. Diffusional water permeability, Pd, was 0.84 × 10(-3) (chick), 5.95 × 10(-3) (duck), 0.39 × 10(-3) (Amphiuma), 3.13 × 10(-3) (dog) and 2.35 × 10(-3) cm s(-1) (human). DIDS, DNDS and phloretin inhibit PCl by >99% in all RBC species. PCMBS, PCMB and phloretin inhibit P(urea) by >99% in Amphiuma, dog and human RBC, but not in chick and duck RBC. PCMBS and PCMB inhibit Pd in duck, dog and human RBC, but not in chick and Amphiuma RBC. Temperature dependence, as measured by apparent activation energy, EA, of PCl is 117.8 (duck), 74.9 (Amphiuma) and 89.6 kJ mol(-1) (dog). The EA of P(urea) is 69.6 (duck) and 53.3 kJ mol(-1) (Amphiuma), and that of Pd is 34.9 (duck) and 32.1 kJ mol(-1) (Amphiuma). The present and previous RBC studies indicate that anion (AE1), urea (UT-B) and water (AQP1) transporters only transport chloride (all species), water (duck, dog, human) and urea (Amphiuma, dog, human), respectively. Water does not share UT-B with urea, and the solute transport is not coupled under physiological conditions.

DORSAL LAMINECTOMY IN A TWO-TOED AMPHIUMA (AMPHIUMA MEANS)

An adult male two-toed amphiuma (Amphiuma means) was evaluated for kyphosis and a self-inflicted ulcerative dermal lesion at the site of a midbody spinal deformity. Radiology revealed a proliferative bony lesion at the 39th vertebra. A dorsal laminectomy was performed to alleviate pressure on the spinal cord believed to be secondary to bone remodeling. Resolution of the scoliosis occurred at the surgical site, and the ulcerative lesion of the body wall healed. Three weeks postoperatively, the amphiuma resumed self-mutilation caudal to the surgery site. Euthanasia was elected. Necropsy revealed focal osteonecrosis and vertebral fractures at the laminectomy site with regionally extensive fibrosis, fibrin deposition, and focal spinal cord compression. Resolution of clinical signs suggests that surgical decompression of the spine was clinically successful short term, but the patient deteriorated for reasons possibly related, although not directly attributable, to the surgery.

Vagility of Aquatic Salamanders: Implications for Wetland Connectivity

Research on landscape connectivity for amphibians that use isolated wetlands has focused on terrestrial and semiterrestrial species. Although aquatic species are commonly encountered in isolated wetlands, their dispersal capability and mode of dispersal has yet to be conclusively determined. For these salamander species, temporary waterways formed during heavy rains may provide transient dispersal opportunities among otherwise terrestrially isolated wetland patches and large contiguous sources (e.g., river swamps, lake systems). We assessed the vagility of two aquatic salamanders, the Greater Siren (Siren lacertina) and Two-Toed Amphiuma (Amphiuma means), under three simulated environmental conditions: terrestrial (damp but no standing water); shallow standing water (1 cm of water); and complete submergence (approximately 5 cm of water). Salamanders were placed inside a modified Living Stream container and stimulated into moving through each treatment. Both species demonstrated a trend toward exhaustion for all treatments and failed to move more than 8 m in the terrestrial or shallow water treatments. As expected, animals in the fully submerged treatment were able to disperse the farthest. Physical characteristics of salamanders did not affect vagility. To disperse, these species likely rely on the formation of aquatic corridors during flooding events. Therefore, successful dispersal among isolated wetlands depends on the ability of the surrounding landscape either to be periodically inundated with water or to form temporary waterways during heavy rains. Human activities that alter flooding events and watershed connectivity, such as flood control regimes and roads, may have important implications for wetland connectivity and, thus, metapopulation viability of aquatic salamanders.

Summer microhabitat use of the Greater Siren (Siren lacertina) and Two-toed Amphiuma (Amphiuma means) in an isolated wetland

AbstractAlthough the habitats of the Greater Siren (Siren lacertina) and Two-toed Amphiuma (Amphiuma means) have been described on a coarse scale; the microhabitat(s) of these species has not been examined. We trapped from 12 June 2008 to 1 July 2008 in an isolated wetland on the Savannah River Site in South Carolina where these two salamander species occur in sympatry. Traps were set in three different microhabitats; the water's surface and benthic zone in deep water, and in a littoral zone. Siren lacertina captures were highest in the benthic zone, while A. means were captured more in the littoral zone. This differentiation in microhabitat usage may reflect a difference in prey availability or habitat structure; alternatively, it may be a response to interspecific interactions between species.

Evolution of Gigantism in Amphiumid Salamanders

The Amphiumidae contains three species of elongate, permanently aquatic salamanders with four diminutive limbs that append one, two, or three toes. Two of the species, Amphiuma means and A. tridactylum, are among the largest salamanders in the world, reaching lengths of more than one meter, whereas the third species (A. pholeter), extinct amphiumids, and closely related salamander families are relatively small. Amphiuma means and A. tridactylum are widespread species and live in a wide range of lowland aquatic habitats on the Coastal Plain of the southeastern United States, whereas A. pholeter is restricted to very specialized organic muck habitats and is syntopic with A. means. Here we present analyses of sequences of mitochondrial and nuclear loci from across the distribution of the three taxa to assess lineage diversity, relationships, and relative timing of divergence in amphiumid salamanders. In addition we analyze the evolution of gigantism in the clade. Our analyses indicate three lineages that have diverged since the late Miocene, that correspond to the three currently recognized species, but the two gigantic species are not each other's closest relatives. Given that the most closely related salamander families and fossil amphiumids from the Upper Cretaceous and Paleocene are relatively small, our results suggest at least two extreme changes in body size within the Amphuimidae. Gigantic body size either evolved once as the ancestral condition of modern amphiumas, with a subsequent strong size reduction in A. pholeter, or gigantism independently evolved twice in the modern species, A. means and A. tridactylum. These patterns are concordant with differences in habitat breadth and range size among lineages, and have implications for reproductive isolation and diversification of amphiumid salamanders.

Tracking the evolution of the proenkephalin gene in tetrapods

In gnathostomes there is remarkable consistency in the organization of the proenkephalin gene. This opioid precursor encodes seven opioid (YGGF) sequences: five pentapeptide sequences, a met-enkephalin-7 sequence and a met-enkephalin-8 sequence. Yet, within vertebrate lineages there can be distinct sets of pentapeptide opioids (YGGFM or YGGFL). In the Sarcopterygii, the sixth opioid position in lungfishes and anuran amphibian proenkephalin genes encodes a met-enkephalin (YGGFM) sequence. However, in mammalian proenkephalin there is a leu-enkephalin (YGGFL) sequence at this position. This study was done to test the hypothesis that the presence of the leu-enkephalin sequence in mammals is a feature common to amniote vertebrates, but not present in anamniote vertebrates. To resolve this issue, proenkephalin cDNAs were cloned from the urodele amphibians, Amphiuma means and Necturus maculosus, and two amniote vertebrates, the turtle, Chrysemys scripta, and the brown snake, Storeria dekayi. As predicted, a met-enkephalin sequence is present at the sixth opioid position in urodele amphibians; whereas, a leu-enkephalin sequence is present at this opioid site in the reptile proenkephalin sequences. These data are consistent with the conclusion that the transition from a met-enkephalin sequence to a leu-enkephalin sequence at the sixth opioid position in tetrapod proenkephalins occurred in the ancestral proto-reptiles. Phylogenetic analyses, using the Maximum Parsimony and Neighbor-Joining algorithms, of the amphibian proenkephalin sequences supported the position that anuran and urodele amphibians are a monophyletic assemblage. The same analysis of reptile-related proenkephalin sequences, including the deduced amino acid sequence of a partially characterized alligator proenkephalin cDNA, could not conclusively resolve the phylogeny of the major reptilian orders.

Analyzing the radiation of the melanocortins in amphibians: Cloning of POMC cDNAs from the pituitary of the urodele amphibians, Amphiuma means and Necturus maculosus

Proopiomelanocortin (POMC) cDNAs were cloned and sequenced from brain extracts of two species of urodele amphibians: Amphiuma means and Necturus maculosus. Although the two species of urodele amphibians belong to separate families, and do not share a direct common ancestor, the level of primary sequence identity for the open reading of the POMC cDNAs was 90% at the amino acid level and 79% at the nucleotide level. It appears that the POMC gene in these urodele amphibians has been accumulating mutations at the amino acid level at a slower rate than the POMC gene in other sarcopterygian orders.

Unveiling Escape and Capture Rates of Aquatic Snakes and Salamanders (Siren spp. and Amphiuma means) in Commercial Funnel Traps

ABSTRACT Aquatic funnel trapping with commercially available minnow traps has proven effective for sampling several aquatic snake species. However, the efficacy of this technique for sampling snakes has received little controlled evaluation. We investigated the ability of aquatic snakes to escape from three funnel trap varieties (cylindrical steel, cylindrical plastic, and rectangular collapsible nylon mesh). We found that when intentionally released into traps, the majority (74%) of snakes escaped within 24 hours. Snakes escaped most frequently from collapsible traps, and of the species tested, Seminatrix pygaea escaped most frequently. We found significant differences in capture rates among trap types for S. pygaea, Farancia abacura (both captured most in plastic traps), and Nerodia fasciata (captured most in steel traps). Additionally, as we captured many large aquatic salamanders (Siren spp. and Amphiuma means), we also report trapping efficacies of the funnel traps for these amphibians.

Population Characteristics of Siren lacertina and Amphiuma means in North Florida

Abstract I conducted a mark-recapture study of Siren lacertina and Amphiuma means for one year at a lake in north Florida and documented average individual movement, size class distribution, seasonal activity patterns, survival rates, and density estimates. I captured Siren lacertina more frequently in winter and A. means more frequently in spring. Recapture probabilities of both species were low, whereas survival rates and density estimates (1.3 salamanders/m2 for S. lacertina, 0.28 salamanders/m2 for A. means) were high. I recorded no individual movement of over 10 m for either species. Sirens and amphiumas are large, predatory generalists that can have substantial biomass in wetlands (233 g/m2 and 44 g/m2, respectively, at this study site), and therefore can impact many other wetland species. Thus, more attention must be focused on evaluating and monitoring their populations.

Effects of Large-Scale Sediment Removal on Herpetofauna in Florida Wetlands

Removal of organic sediment from lakes and ponds is an established management technique that is intended to enhance sport fisheries, improve boater access, and increase stormwater capacity. Data on the effects of this management technique on lake ecosystems are limited. Our objective was to determine the effect of mechanical sediment removal on herpetofauna at five sites in northern Florida. We collected a total of 883 individuals of 31 species of herpetofauna excavated by machinery during sediment removal. Across the five sites, the average number of individuals collected was 177 per site (SD = 119, range = 71–310). The most abundant herpetofauna we encountered were aquatic turtles (Trachemys scripta, Chelydra serpentina) and large aquatic salamanders (Amphiuma means, Siren spp.). Mortality from sediment removal operations may have a detrimental effect on herpetofauna populations, especially species that depend on dried lake sediments for aestivation or with limited dispersal abilities.

A Simple Technique for Trapping Siren Iacertina, Amphiuma means, and Other Aquatic Vertebrates

ABSTRACT We describe a commercially-available funnel trap for sampling aquatic vertebrates. The traps can be used in heavily vegetated wetlands and can be set in water up to 60 cm deep without concern for drowning the animals. They were especially useful for capturing the aquatic salamanders Siren lacertina and Amphiuma means, which have been difficult to capture with traditional sampling methods. They also were effective for sampling small fishes, particularly centrarchids, and larval anurans. In total, 14 species of amphibians, nine species of aquatic reptiles, and at least 32 fish species were captured. The trap we describe differs significantly from traditional funnel traps (e.g., minnow traps) and holds great promise for studies of small, aquatic vertebrates, in particular Siren and Amphiuma species.

EVALUATION OF THE HATCHING TRIGGER AND LARVAL ECOLOGY OF THE SALAMANDER AMPHIUMA MEANS

I investigated the early life history of the salamander Amphiuma means. Although adult A. means are entirely aquatic, eggs are often found above water levels in areas from which water has receded. A series of experiments was performed using three egg clutches of A. means collected from organic sediment at the bottom of a dried lake in northern Florida. The first experiment demonstrated that eggs of A. means hatch in response to inundation with water, and aquatic larvae completely resorbed their gills in about 2 wk. Eggs that hatched at later dates produced larger hatchlings in all three clutches and larger juveniles at metamorphosis in two clutches. A second experiment indicated that hatchlings can survive, on average, over 125 d without feeding by using resources from their yolk reserves. The third experiment showed that eggs are capable of surviving an average of 110 d (SD = 47.2 d) on moist substrate without hatching. Some eggs hatched onto the substrate without inundation, and resulting hatchlings could survive on this substrate without inundation for an average of 21 d (SD = 26.1 d). Five eggs produced hatchlings without gills during this experiment, suggesting that this species may bypass the larval period completely if eggs are not inundated. My experiments suggest that the eggs of A. means may be specialized for development in terrestrial nest chambers. Information on development and larval ecology of A. means from my study can be applied to future evaluations of the evolutionary relationships of salamander families.

Ion transport proteins and aquaporin water channels in the kidney of amphibians from different habitats

Amphibians are known to spend part of their life on land and return to water to reproduce. However, some urodeles spend their entire life in water, while others succeed in completely avoiding water even during reproduction. Osmoregulatory mechanisms must therefore be different in the diverse environmental conditions of their respective life histories. The architecture of the kidney is similar in all amphibians; as a consequence the ion–water equilibrium must be regulated in the different environmental conditions. We investigated the immunolocalisation of Na +/K +/Cl − cotransport proteins, sodium pump and water-channel proteins (aquaporins) in aquatic Amphiuma means means, Rana dalmatina, a species that returns to water to reproduce, and Speleomantes genei, a completely terrestrial species. The investigation was carried out with immunohistochemical methods using antibodies to Na +/K +/Cl − cotransport protein NKCC1 T4, Na +/K +ATPase α-subunit, water-channel aquaporin 3 and the inner mitochondrial membrane (AMA). Cotransport proteins and sodium pump, involved in ion reabsorption, are widely distributed in A. means and R. dalmatina and confined to the distal segment in S. genei; conversely water channels, involved in water reabsorption, are limited to the collecting duct in A. means and R. dalmatina and distributed in the proximal and collecting ducts in S. genei.