Siren Lacertina Research Articles

PILOT STUDY OF INTRACOELOMIC TERBINAFINE IMPLANTS IN GREATER SIRENS (SIREN LACERTINA).

Chytridiomycosis caused by Batrachochytrium dendrobatidis (Bd) has been documented in greater sirens (Siren lacertina) in the wild and in the pet trade. This study evaluated the use of terbinafine-impregnated implants for chytridiomycosis prophylaxis in greater sirens exposed to Bd. Implants were placed intracoelomically in both control (blank implant, n = 4) and treatment (24.5 mg of terbinafine implant, n = 4) groups. Sirens were exposed to Bd zoospores via 24-h immersion bath at 1 and 2 mon postimplant placement. Blood was collected monthly for plasma terbinafine levels, and skin swabs were collected weekly for Bd quantitative PCR. Animals with terbinafine implants had detectable concentrations of plasma terbinafine ranging from 17 to 102 ng/ml. Only one terbinafine-implanted animal had a peak concentration above the published minimum inhibitory concentration for terbinafine against Bd zoospores (63 ng/ml); however, it is unknown how plasma terbinafine concentrations relate to concentrations in the skin. There was no difference between the two treatment groups in clinical signs or Bd clearance rate, and no adverse effects from implants were observed. These findings indicate using intracoelomic drug implants for drug delivery in amphibians is safe; however, terbinafine efficacy in preventing Bd chytridiomycosis in sirens remains unclear. Further investigation of the use of intracoelomic implants and identification of effective drugs and doses in other amphibian species against Bd and other infectious diseases is warranted, as this may provide a practical method for long-term drug delivery in wildlife.

A Pilot Study Investigating Plasma Protein Electrophoresis in One Anuran and Six Urodelan Species.

As threats to amphibian health increase, there is a growing need for diagnostic tools to assess and monitor their health status. Plasma protein electrophoresis has proven to be useful in other nonmammalian species. It enables quantification of protein fractions in plasma that may be altered in various disease processes, and is therefore useful in narrowing down differential diagnoses and detecting inflammation, in combination with other modalities such as biochemical and hematologic testing. The amphibian electrophoretogram must be defined before baseline reference intervals are obtained across species. Agarose gel electrophoresis was performed on plasma samples collected from presumed clinically normal individuals of one anuran and six urodelans: Osteopilus septentrionalis (n=2), Gyrinophilus porphyriticus (n=1), Notophthalmus viridescens (n=1), Eurycea guttolineata (n=2), Amphiuma tridactylum (n=2), Cryptobranchus alleganiensis (n=5), and Siren lacertina (n=6). The electrophoretograms varied in number of fractions between each species; however, the number of fractions was consistent within a species. An albumin migrating fraction was consistently observed in all species. A prealbumin migrating fraction was identified in species that primarily use organs other than skin for respiration. This study provides preliminary examples of a normal plasma protein electrophoretogram for seven amphibian species. Further studies quantifying reference intervals and identification of protein fractions will help establish protein electrophoresis as a useful tool in amphibian health investigations.

Unraveling Siren (Caudata: Sirenidae) systematics and description of a small, seepage specialist.

For approximately four decades, scientists have known of the existence of several undescribed species of Siren in the southeastern United States Coastal Plain. One of these species, S. reticulata, was recently described, but a small, seepage-dwelling species has remained undescribed until now. To resolve outstanding questions concerning the phylogeny of Siren, we collected sequence and morphometric data from specimens across the range of Siren. We found S. lacertina and S. reticulata to represent strongly supported monophyletic groups, with S. reticulata having a sister relationship to all other Siren. Additionally, we found five distinct mtDNA lineages within what has been recognized as S. intermedia. Siren lacertina and type-locality S. intermedia (lineage A) are sister mtDNA lineages, whereas S. intermedia lineages B and C show a high level of mitogenomic divergence from type-locality S. intermedia. Analyses of two scnDNA loci revealed that S. lacertina is monophyletic but nested with low positional support in a clade including the three S. intermedia mtDNA lineages. Further study is needed to determine whether S. intermedia lineages A, B, and C represent distinct species or incompletely sorted lineages. We restrict the range of S. intermedia to the region from the Escambia and Perdido river drainages of Florida and Alabama eastward through Virginia (the combined ranges of lineages A, B, and C). We also elevate S. i. nettingi (lineage E) to species status and include the larger S. i. texana form in that taxon, generating a species that occurs from the Mobile Bay drainages westward through the Mississippi Basin and southwest into northeastern Mexico. Lastly, we describe a new miniature species, S. sphagnicola, that ranges from the Florida Parishes of Louisiana eastward to the westernmost tributary creeks of Choctawhatchee Bay in the western Florida panhandle.

Droughts Reduce Growth Rates and Increase Vulnerability to Increasingly Frequent and Severe Drying Events in an Aquatic Ectotherm

Many aquatic organisms are experiencing increasingly severe and frequent droughts and drying events. Simultaneously, drought effects are carrying over to nondrought years as ecosystems remain in incomplete states of recovery. Aquatic organisms are thus faced with fewer sequential years under degraded environmental conditions to prepare for increasingly severe droughts and potential drying events. We assessed the effect of droughts and sex on the growth, mass, and mass-dependent estivation potential of long-lived aquatic salamanders (Greater Sirens, Siren lacertina) that estivate during drying events brought on by severe droughts. We calculated growth rates of S. lacertina based on mark–recapture data spanning 11 yr of a severe drought local minimum (of past 50 yr) in the southeastern United States. Sirens showed a distinct seasonal gain in body length and mass from March through September and little growth for the rest of the year. Gains during the growth season were strongly reduced by drought conditions. Although male and female sirens were predicted to reach a similar maximum body size, females grew much slower. Recruitment into drying event “size refugia” is constrained by drying event severity (determines minimum size required), frequency (determines available time between events to grow), and environmental conditions between drying events (determines the rate of growth). Thus, increases in drying event severity and frequency will require faster growth to a larger body size for successful recruitment into a size class that is resistant to drying events. The slower growth of females and reduction of growth during suboptimal years (mild to moderate droughts) suggest that the life history strategy of Greater Sirens for persisting through drying events potentially increases their demographic susceptibility to the predicted effects of climate change.

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.

Trade-offs between growth and maturation: the cost of reproduction for surviving environmental extremes.

Life-history trade-offs and the costs of reproduction are central concepts in evolution and ecology. Episodic climatic events such as drought and extreme temperatures provide strong selective pressures that can change the balance of these costs and trade-offs. We used size-structured matrix models parameterized from field and laboratory studies to examine the effect of periodic drought on two species of aquatic salamanders (greater siren, Siren lacertina; lesser siren, Siren intermedia) that differ in size at reproduction and maximum body size. Post-drought body size distributions of the larger species (S. lacertina) are consistent with size-dependent mortality. Smaller individuals were extirpated from the population during each drought while large animals persisted, a pattern that contrasted with that seen in several ectotherms. This appears to be largely explained by estivation proficiency and a positive relationship between body size and estivation potential. Increased body size, however, may come at the cost of fecundity and maturation rate compared to a closely related congener. The cost of somatic allocation in this case may manifest itself via reduced per-capita competitive ability, which (at least in simulation studies) allows the smaller, fast-maturing species to outcompete the larger, slow-maturing species when drought is minimal or nonexistent.

Effects of hypoxia on oxygen uptake and surfacing behavior in the giant aquatic salamander Siren lacertina

The greater siren (Siren lacertina) can acquire oxygen from both air and water (bimodal breathing). Currently, only physiological measurements have been made on bimodal breathing, with little work being done on the unique surfacing behaviors associated with this process. Flow-through respirometry was used to measure O2 uptake in increasingly hypoxic water. In addition, video recordings were made to capture and quantify the surfacing behavior of greater sirens in response to progressive hypoxia. Greater sirens showed an increase in aerial O2 uptake, a decrease in aquatic O2 uptake, and no change in total O2 uptake as the aquatic O2 tension decreased. Also, greater sirens shifted only the number of surfacing trips they made as the aquatic O2 tension decreased; all other surfacing behaviors remained unchanged. Greater sirens appear to maintain their metabolic rate despite the aquatic O2 tension solely by modifying the number of trips they take to the surface.

Testing the Threat-Sensitive Hypothesis with Predator Familiarity and Dietary Specificity

In a system with multiple predators, the threat-sensitive predator avoidance hypothesis predicts that prey respond differently to predators relative to the risks each poses (e.g., degree of dietary specialization). Aquatic animals often rely heavily on detecting predators via chemical cues (kairomones) and respond with a suite of behaviors including detection and avoidance. However, little is known about how animals respond to kairomones of specialist versus generalist predators. In laboratory experiments, we compared behavioral responses of a poorly studied aquatic salamander, the greater siren (Siren lacertina), to cues from specialist and generalist predator snakes to evaluate threat-sensitive responses. Sirens exhibited a novel behavior (gill-flushing) most often in the presence of specialist predator cues. Avoidance behavior (reversing direction following cue detection) was higher in response to specialist predator and novel animal control cues and lowest in response to generalist predator cues. An intermediate response to the animal control, an unfamiliar amphibian predator, indicated that sirens respond cautiously to a novel cue. The gradient of observed responses to different snake cues indicates that sirens may be evaluating predation potential of animals based on their foraging specificity and familiarity.

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.

Architectural gear ratio and muscle fiber strain homogeneity in segmented musculature

In the segmented axial musculature of fishes and amphibians, the patterns of muscle fiber shortening depend on both the orientation of muscle fibers relative to the long axis of the body as well as the distance of fibers from the neutral axis of bending (vertebral column). In this study we use the relatively simple architecture of salamander hypaxial muscles to explore the separate and combined effects of these morphological features on muscle fiber strains during swimming. In Siren lacertina the external oblique (EO) muscle has more obliquely oriented muscle fibers and is located further from the neutral axis of bending than the internal oblique (IO) muscle. To examine the effect of muscle fiber angle on strain patterns during swimming, we used sonomicrometry to quantify architectural gear ratio (AGR=longitudinal strain/fiber strain) in these two hypaxial muscles. By comparing the muscle fiber strains and shortening velocities of the EO and IO during swimming, we test whether variation in mediolateral position of the muscle layers is counteracted by their differences in AGR. We find that despite substantial differences in mediolateral position, the EO and IO undergo similar fiber strains and shortening velocities for a given amount of axial bending. Our results show that variation in muscle fiber angle acts to counteract differences in mediolateral position, thereby minimizing variation in muscle fiber strain and shortening velocity during swimming. These results highlight the significance of both muscle architecture and muscle moment arms in determining the fiber strains required for a given movement.

Red blood cell size and the Fåhraeus–Lindqvist effect

The reason for the large interspecies variation in vertebrate red blood cell (RBC) size is poorly understood. To test the effect of RBC size on blood viscosity, blood samples from two vertebrates, the dog (Canis familiaris L., 1758) and the greater siren (Siren lacertina L., 1766), with extremely different RBC sizes were examined. In this study, we examined whether RBC size altered the relationship of viscosity and viscometer tube diameter, the well-known Fåhraeus–Lindqvist effect (FLE). We used a glass capillary viscometer that incorporates tubes with a diameter narrow enough to evoke the FLE. At similar RBC concentrations, viscosity of suspensions with the larger siren RBCs were greater than the viscosity of suspensions with the smaller dog RBCs. However, the relationship between viscosity and tube diameter is independent of RBC size. The results of this study allow us to conclude that the FLE is not related to RBC size. While packaging hemoglobin in RBCs appears adaptive by reducing blood viscosity through the FLE, RBC size does not contribute to the reductions in tube-relative viscosity.

Gastrointestinal Fermentation in Greater Sirens (Siren lacertina)

The nutritional ecology and digestive physiology of salamanders in the Family Sirenidae remain poorly understood. Although the intestinal contents of these salamanders include herbivorous dietary items, the nutritional significance of such ingested matter is unknown. In this study, we examined gut contents, gastrointestinal structure, and microbial fermentation in wild-caught Greater Sirens (Siren lacertina). Ingested items included aquatic invertebrates, vascular plants, and algae. The guts of these amphibians were not as voluminous or morphologically specialized as in many herbivores, but the posterior intestine was enlarged and exhibited a distinct folding pattern and an ileocolonic valve that may help maintain a symbiotic microbial population. An active microbial fermentation was indicated by relatively high levels of short-chain fatty acids in the medial-posterior and posterior gut regions. This is the first account of gastrointestinal fermentation in the Family Sirenidae and only the second account in the Class Amphibia.

Muscle fiber angle, segment bulging and architectural gear ratio in segmented musculature

The anatomical complexity of myomeres and myosepta has made it difficult to develop a comprehensive understanding of the relationship between muscle fiber architecture, connective tissue mechanics, and locomotor function of segmented axial musculature in fishes. The lateral hypaxial musculature (LHM) of salamanders is less anatomically complex and therefore a good system for exploring the basic mechanics of segmented musculature. Here, we derive a mathematical model of the LHM and test our model using sonomicrometry and electromyography during steady swimming in an aquatic salamander, Siren lacertina. The model predicts longitudinal segment strain well, with predicted and measured values differing by less than 5% strain over most of the range. Deviations between predicted and measured results are unbiased and probably result from the salamanders performing slight turns with associated body torsion in our unconstrained trackway swimming experiments. Model simulations of muscle fiber contraction and segment shortening indicate that longitudinal segment strain, for a given amount of muscle fiber strain, increases with increasing initial fiber angle. This increase in architectural gear ratio (AGR = longitudinal strain/fiber strain) is mediated by muscle fiber rotation; the higher the initial fiber angle, the more the fibers rotate during contraction and the higher the AGR. Muscle fiber rotation is additionally impacted by bulging in the dorsoventral (DV) and/or mediolateral (ML) dimensions during longitudinal segment shortening. In segments with obliquely oriented muscle fibers, DV bulging increases muscle fiber rotation, thereby increasing the AGR. Extending the model to include force and work indicates that force decreases with increasing initial muscle fiber angle and increasing DV bulging and that both longitudinal shortening and DV bulging must be included for accurate calculation of segment work.

Patterns of axial and appendicular movements during aquatic walking in the salamander Siren lacertina

Most studies of salamander locomotion have focused either on swimming or terrestrial walking, but some salamanders also use limb-based locomotion while submerged under water (aquatic walking). In this study we used video motion analysis to describe the aquatic walking gait of Siren lacertina, an elongate salamander with reduced forelimbs and no hindlimbs. We found that S. lacertina uses a bipedal-undulatory gait, which combines alternating use of the forelimbs with a traveling undulatory wave. Each forelimb is in contact with the substrate for about 50% of the stride cycle and forelimbs have little temporal overlap in contact intervals. We quantified the relative timing and frequency of limb and tail movements and found that, unlike the terrestrial gaits of most salamanders, axial and appendicular movements are decoupled during aquatic walking. We found no significant relationship between stride frequency and aquatic walking velocity, but we did find a statistically significant relationship between tailbeat frequency and aquatic walking velocity, which suggests that aquatic walking speed is mainly modulated by axial movements. By comparing axial wavespeed and distance traveled per tailbeat during swimming (forelimbs not used) and aquatic walking (forelimbs used), we found lower wavespeed and greater distance traveled per tailbeat during aquatic walking. These findings suggest that the reduced forelimbs of S. lacertina contribute to forward propulsion during aquatic walking.

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.

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.

Morphology and mechanics of myosepta in a swimming salamander ( Siren lacertina)

In contrast to the complex, three-dimensional shape of myomeres in teleost fishes, the lateral hypaxial muscles of salamanders are nearly planar and their myosepta run in a roughly straight line from mid-lateral to mid-ventral. We used this relatively simple system as the basis for a mathematical model of segmented musculature. Model results highlight the importance of the mechanics of myosepta in determining the shortening characteristics of a muscle segment. We used sonomicrometry to measure the longitudinal deformation of myomeres and the dorsoventral deformation of myosepta in a swimming salamander ( Siren lacertina). Sonomicrometry results show that the myosepta allow some dorsoventral lengthening, indicating an amplification of myomere shortening that is greater than that produced by muscle fiber angle alone (10% muscle fiber shortening produces 28.7% myomere shortening). Polarized light and DIC microscopy of isolated hypaxial myosepta revealed that the collagen fiber orientation in hypaxial myomeres is primarily mediolateral. The mediolateral collagen fiber orientation, combined with our finding that the hypaxial myosepta lengthen dorsoventrally during swimming, suggests that one possible function of hypaxial myosepta in S. lacertina is to increase the strain amplification of the muscle fibers by reducing the mediolateral bulging of the myomeres and redirecting the bulging toward the dorsoventral direction.

Weak trophic interactions between large predatory fishes and herpetofauna in the channelized Kissimmee River, Florida, USA

We tested the hypothesis that large predatory fishes are major predators of amphibians and reptiles along littoral ecotones by examining the diets of 70 bowfin (Amia calva), 22 chain pickerel (Esox niger), 235 Florida gar (Lepisosteus platyrinchus), 258 largemouth bass (Micropterus salmoides), and 46 warmouth (Lepomis gulosus) collected from enhanced and non-enhanced portions of the channelized Kissimmee River, Florida, USA. Only six bowfin (9%) and four bass (2%) preyed upon herpetofauna. The diet of bowfin included peninsula newts (Notopthalmus viridescens piaropicola), greater sirens (Siren lacertina), and striped crayfish snakes (Regina alleni), whereas the diet of largemouth bass included peninsula newts, striped crayfish snakes, and stinkpot turtles (Kinosternum odoratus). No individual predator consumed more than one type of herpetofauna. The higher percentage of herpetofauna consumed by bowfin reflects this species catholic feeding habits. Prey size was positively correlated with predator size. Eighty percent of fishes that preyed upon herpetofauna were collected from non-enhanced portions of the river, which may reflect lower abundance of preferred prey in these disturbed habitats. Overall, it does not appear that amphibians and reptiles are an important part of the piscine food web in the channelized Kissimmee River.

Morphological variation of hypaxial musculature in salamanders (Lissamphibia: Caudata)

Despite the acknowledged importance of the locomotory and respiratory functions associated with hypaxial musculature in salamanders, variation in gross morphology of this musculature has not been documented or evaluated within a phylogenetic or ecological context. In this study, we characterize and quantify the morphological variation of lateral hypaxial muscles using phylogenetically and ecologically diverse salamander species from eight families: Ambystomatidae (Ambystoma tigrinum), Amphiumidae (Amphiuma tridactylum), Cryptobranchidae (Cryptobranchus alleganiensis), Dicamptodontidae (Dicamptodon sp.), Plethodontidae (Gyrinophilus porphyriticus), Proteidae (Necturus maculosus), Salamandridae (Pachytriton sp.), and Sirenidae (Siren lacertina). For the lateral hypaxial musculature, we document 1) the presence or absence of muscle layers, 2) the muscle fiber angles of layers at mid-trunk, and 3) the relative dorsoventral positions and cross-sectional areas of muscle layers. Combinations of two, three, or four layers are observed. However, all species retain at least two layers with opposing fiber angles. The number of layers and the presence or absence of layers vary within species (Necturus maculosus and Siren lacertina), within genera (e.g., Triturus), and within families. No phylogenetic pattern in the number of layers can be detected with a family-level phylogeny. Fiber angle variation of hypaxial muscles is considerable: fiber angles of the M. obliquus externus range from 20–80°; M. obliquus internus, 14–34°; M. transversus abdominis, 58–80° (acute angles measured relative to the horizontal septum). Hypaxial musculature comprises 17–37% of total trunk cross-sectional area. Aquatic salamanders show relatively larger total cross-sectional hypaxial area than salamanders that are primarily terrestrial. J. Morphol. 241:153–164, 1999. © 1999 Wiley-Liss, Inc.