Ecological resistance surfaces predict fine‐scale genetic differentiation in a terrestrial woodland salamander

Landscape genetics has seen tremendous advances since its introduction, but parameterization and optimization of resistance surfaces still poses significant challenges. Despite increased availability and resolution of spatial data, few studies have integrated empirical data to directly represent ecological processes as genetic resistance surfaces. In our study, we determine the landscape and ecological factors affecting gene flow in the western slimy salamander (Plethodon albagula). We used field data to derive resistance surfaces representing salamander abundance and rate of water loss through combinations of canopy cover, topographic wetness, topographic position, solar exposure and distance from ravine. These ecologically explicit composite surfaces directly represent an ecological process or physiological limitation of our organism. Using generalized linear mixed‐effects models, we optimized resistance surfaces using a nonlinear optimization algorithm to minimize model AIC. We found clear support for the resistance surface representing the rate of water loss experienced by adult salamanders in the summer. Resistance was lowest at intermediate levels of water loss and higher when the rate of water loss was predicted to be low or high. This pattern may arise from the compensatory movement behaviour of salamanders through suboptimal habitat, but also reflects the physiological limitations of salamanders and their sensitivity to extreme environmental conditions. Our study demonstrates that composite representations of ecologically explicit processes can provide novel insight and can better explain genetic differentiation than ecologically implicit landscape resistance surfaces. Additionally, our study underscores the fact that spatial estimates of habitat suitability or abundance may not serve as adequate proxies for describing gene flow, as predicted abundance was a poor predictor of genetic differentiation.     

Friction ridges in cockroach climbing pads: anisotropy of shear stress measured on transparent,microstructured substrates

The contact of adhesive structures to rough surfaces has been difficult to investigate as rough surfaces are usually irregular and opaque. Here we use transparent, microstructured surfaces to investigate the performance of tarsal euplantulae in cockroaches (Nauphoeta cinerea). These pads are mainly used for generating pushing forces away from the body. Despite this biological function, shear stress (force per unit area) measurements in immobilized pads showed no significant difference between pushing and pulling on smooth surfaces and on 1-μm high microstructured substrates, where pads made full contact. In contrast, on 4-μm high microstructured substrates, where pads made contact only to the top of the microstructures, shear stress was maximal during a push. This specific direction dependence is explained by the interlocking of the microstructures with nanometre-sized “friction ridges” on the euplantulae. Scanning electron microscopy and atomic force microscopy revealed that these ridges are anisotropic, with steep slopes facing distally and shallow slopes proximally. The absence of a significant direction dependence on smooth and 1-μm high microstructured surfaces suggests the effect of interlocking is masked by the stronger influence of adhesion on friction, which acts equally in both directions. Our findings show that cockroach euplantulae generate friction using both interlocking and adhesion.     

Effects of Pendular Waist on Gecko's Climbing: Dynamic Gait,Analytical Model and Bio-inspired Robot

Most quadruped reptiles,such as lizards,salamanders and crocodiles,swing their waists while climbing on horizontal or vertical surfaces.Accompanied by body movement,the centroid trajectory also becomes more of a zigzag path rather than a straight line.Inspired by gecko's gait and posture on a vertical surface,a gecko inspired model with one pendular waist and four active axil legs,which is called GPL model,is proposed.Relationship between the waist position,dynamic gait,and driving forces on supporting feet is analyzed.As for waist trajectory planning,a singular line between the supporting feet is found and its effects on driving forces are discussed.Based on the GPL model,it is found that a sinusoidal waist trajectory,rather than a straight line,makes the driving forces on the supporting legs smaller.Also,a waist close to the pygal can reduce the driving forces compared to the one near middle vertebration,which is in accord with gecko's body bending in the process of climbing.The principles of configuration design and gait planning are proposed based on theoretical analyses.Finally,a bio-inspired robot DracoBot is developed and both of the driving force measurements and climbing experiments reinforce theoretical analysis and the rationality of gecko's dynamic gait.     

Microornamentation of leaf chameleons (Chamaeleonidae: Brookesia,Rhampholeon, and Rieppeleon)—with comments on the evolution of microstructures in the chamaeleonidae

Chameleons (Chamaeleonidae) feature many adaptations to their arboreal lifestyle, including zygodactylous feet, a prehensile tail, and epidermal microstructures. In arboreal tree chameleons, the substrate‐contacting site of the feet and tail is covered by microscopic hair‐like structures (setae) of 6–20 µm length. Their friction enhancing function has been shown in recent studies. Leaf chameleons and one representative of the tree chameleons (Chamaeleo namaquensis) secondarily have become ground‐dwelling. Because leaf chameleons are paraphyletic, one could expect that in the three leaf chameleon genera Brookesia, Rhampholeon, and Rieppeleon and the tree chameleon Ch. namaquensis, epidermis has adapted independently to terrestrial locomotion. Using scanning electron microscopy, we investigated the substrate‐contacting surfaces of the feet (subdigital) of 17 leaf chameleon species and five tree chameleon species that have not yet been examined. Additionally, surfaces not involved in locomotion, the flanks (dorsolateral), and scale interstices, were examined. Although the subdigital microstructures in leaf chameleons are more diverse than in tree chameleons, we found some features across the genera. The subdigital microornamentation of Rhampholeon spinosus consists of long thin setae and spines, comparable to those of tree chameleons. All other Rhampholeon species have spines or short but broad setae. Rh. spectrum had tooth‐like structures instead of setae. Subdigital scales of Brookesia have either thorns or conical scale‐tops in the center and feature honeycomb microstructures. In Rieppeleon, subdigital scales have a thorn. Scale surfaces are covered by honeycombs and short hair‐like structures (spines). As subdigital scales with a thorn in the center and honeycomb microstructures were also found in the terrestrial tree chameleon Ch. namaquensis, one can assume that this geometry is a convergent adaptation to terrestrial locomotion. Despite the great number of genus‐specific traits, the convergent evolution of honey‐comb structures in Brookesia, Rieppeleon, and Ch. namaquensis and the high variability of spines and setae in Rhampholeon suggests a rapid adaptation of subdigital microornamentation in Chamaeleonidae. J. Morphol. 276:167–184, 2015. © 2014 Wiley Periodicals, Inc.     

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

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

Plasmolysis of Pteridium protoplasts: A study using light and scanning-electron microscopy

A study was undertaken using gametophytes of the fern Pteridium aquilinum to examine the effects of plasmolysis on the topography of protoplasts. Methods are described whereby the surfaces of non-isolated protoplasts can be observed in the plasmolysed condition using scanning electron microscopy. Plasmolysed gametophytes were also examined in the light microscope using differential interference contrast and ultra-violet fluorescence microscopy after staining with fluorescein diacetate. With scanning electron microscopy, plasmolysed protoplast surfaces appeared smooth with no evidence of wrinkling or infolding of excess membrane. The formation of irregular-shaped protoplasts, protoplasmic threads, subprotoplasts, and protoplasmic networks covering internal wall surfaces all provided evidence for strong wall adhesion of the protoplasm. The availability of membrane for uptake into folds or vesicles is therefore thought to be minimal. Transmission electron microscopy showed some protoplasmic threads to be plasmodesmata, the remainder being cell-wall contact points. Remnants of these threads were occasionally observed on isolated protoplasts in both the light and electron microscopes.     

The structure of epidermal feet during their development

Epidermal cells in Calpodes and other insects form basal processes or feet that at first extend axially and later shorten at the same time as the larval segment shortens to the pupal shape. The feet grow into spaces at the surfaces of other cells to make a basal interlacing meshwork of cellular extensions that are combined mechanically by their desmosomal attachments to cell bodies above and to the basal lamina below. Microtubules and microfilaments are linked to these junctions by a reticular fibrous matrix. Gap junctions on the feet may couple cells that are several cell bodies removed from one another. The meshwork is also a sieve separating the hemolymph from the spaces between cells to form an intercellular compartment. Entry to the intercellular compartment is through the sieve made by the negatively charged basolateral cell surfaces that can prevent the entry of positively charged molecules such as cationic ferritin. As the cells become columnar, coincident with the metamorphic change in segment shape, the feet shorten and pack more densely together. At this time the basal lamina buckles axially as if responding to contraction of the feet. Segment shape change involves cell rearrangement and relative cell movement, necessitating the transient loss of plasma membrane plaque attachments to the cuticle apically and the loss of junctions laterally. Gap junctions involute in characteristic vacuoles. The metamorphic reduction in cell surface area coincides with the loss of basolateral membrane in smooth tubes and vesicles and the turnover of the apical surface in multivesicular bodies. New apical plasma membrane plaques and new lateral and basal junctions stabilize the cells in their pupal positions.     

Diet diversity and clutch size of aquatic and terrestrial salamanders

Summary Terrestrial species of salamanders generally have a higher diversity of prey in their stomachs and produce smaller and less frequent clutches than do species living in wetter habitats. This may be a consequence of differences in prey availability in the two types of habitats. Prey frequently fluctuate in availability in terrestrial areas as a result of fluctuations in rainfall and the inability of salamanders to forage efficiently during dry periods; the salamanders respond with a generalist diet and relatively K-selected reproductive tactics. In wetter habitats, prey fluctuations are probably dampened due to more constant conditions of moisture; salamanders respond with a more specialized diet and relatively r-selected reproductive tactics.     

Landscape genetics reveals unique and shared effects of urbanization for two sympatric pool‐breeding amphibians

Metapopulation‐structured species can be negatively affected when landscape fragmentation impairs connectivity. We investigated the effects of urbanization on genetic diversity and gene flow for two sympatric amphibian species, spotted salamanders (Ambystoma maculatum) and wood frogs (Lithobates sylvaticus), across a large (>35,000 km²) landscape in Maine, USA, containing numerous natural and anthropogenic gradients. Isolation‐by‐distance (IBD) patterns differed between the species. Spotted salamanders showed a linear and relatively high variance relationship between genetic and geographic distances (r = .057, p < .001), whereas wood frogs exhibited a strongly nonlinear and lower variance relationship (r = 0.429, p < .001). Scale dependence analysis of IBD found gene flow has its most predictable influence (strongest IBD correlations) at distances up to 9 km for spotted salamanders and up to 6 km for wood frogs. Estimated effective migration surfaces revealed contrasting patterns of high and low genetic diversity and gene flow between the two species. Population isolation, quantified as the mean IBD residuals for each population, was associated with local urbanization and less genetic diversity in both species. The influence of geographic proximity and urbanization on population connectivity was further supported by distance‐based redundancy analysis and multiple matrix regression with randomization. Resistance surface modeling found interpopulation connectivity to be influenced by developed land cover, light roads, interstates, and topography for both species, plus secondary roads and rivers for wood frogs. Our results highlight the influence of anthropogenic landscape features within the context of natural features and broad spatial genetic patterns, in turn supporting the premise that while urbanization significantly restricts interpopulation connectivity for wood frogs and spotted salamanders, specific landscape elements have unique effects on these two sympatric species.     

Using stable isotopes to test for trophic niche partitioning: a case study with stream salamanders and fish

1. Stream salamanders and fish often co‐occur even though fish prey on and outcompete salamanders. However, the mechanisms that allow palatable salamanders to coexist with fish are unknown. 2. We tested mechanisms in the field that promote coexistence between Idaho giant salamanders (Dicamptodon aterrimus) and stream salmonid fishes in headwater streams. Previous research in this system indicated that salamander dispersal did not promote coexistence with fish. We tested the hypothesis that D. aterrimus shift their diet when they occur with fish, facilitating coexistence through local niche partitioning. 3. We used nitrogen and carbon stable isotopes to describe the trophic niche of D. aterrimus and fish in three co‐occurring populations of salamanders and fish and three populations of salamanders without fish. We used two approaches to quantify trophic niche partitioning with stable isotopes: 95% kernel density estimators and isotopic mixing models. 4. We found that salamanders and fish were generalists that consumed aquatic invertebrates primarily, but both species were also cannibalistic and predatory on one another. We also found no support for trophic niche partitioning as a coexistence mechanism because there were no differences in the trophic niche metrics among salamander populations with and without fish. 5. Although we did not identify mechanisms that facilitate salamander and fish coexistence, our empirical data and use of novel approaches to describe the trophic niche did yield important insights on the role of predator–prey interactions and cannibalism as alternative coexistence mechanisms. In addition, we found that 95% kernel estimators are a simple and robust method to describe population‐level measure of trophic structure.     

Effects of Timber Management on Pond-Breeding Salamanders

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

Trout affect the density, activity and feeding of a larval plethodontid salamander

1. Ecologists have struggled to describe general patterns in the impacts of predators on stream prey, particularly at large, realistic spatial and temporal scales. Among the confounding variables in many systems is the presence of multiple predators whose interactions can be complex and unpredictable. 2. We studied the interactions between brook trout (Salvelinus fontinalis) and larval two‐lined salamanders (Eurycea bislineata), two dominant vertebrate predators in New England stream systems, by examining patterns of two‐lined salamander abundance in stream reaches above and below waterfalls that are barriers to fish dispersal, by measuring the effects of trout on salamander density and activity using a large‐scale manipulation of brook trout presence, and by conducting a small‐scale laboratory experiment to study how brook trout and larval two‐lined salamanders affect each other's prey consumption. 3. We captured more salamanders above waterfalls, in the absence of trout, than below waterfalls where trout were present. Salamander density and daytime activity decreased following trout addition to streams, and salamander activity shifted from aperiodic to more nocturnal with fish. Analysis of stomach contents from our laboratory experiment revealed that salamanders eat fewer prey with trout, but trout eat more prey in the presence of salamanders. 4. We suggest that as predators in streams, salamanders can influence invertebrate prey communities both directly and through density‐ and trait‐mediated interactions with other predators.     

Microstructure of the tarsal attachment devices in the earwig Timomenus komarovi

The biological attachment device on the tarsal appendage of the earwig, Timomenus komarovi (Insecta: Dermaptera: Forficulidae) was investigated using field emission scanning electron microscopy to reveal the fine structural characteristics of its biological attachment devices to move on smooth and rough surfaces. They attach to rough substrates using their pretarsal claws; however, attachment to smooth surfaces is achieved by means of two groups of hairy tarsal pads. This biological attachment device consists of fine hairy setae with various contact sizes. Three different groups of tenent setae were distinguished depending on the cuticular substructure of the endplates. Two groups of setae commonly had flattened surfaces, and they were covered with either spoon‐shaped or spatula‐shaped endplates, respectively. While the flattened tip setae were distributed at the central region, the pointed tip setae were characteristically found along the marginal region. There were no obvious gender‐specific differences between fibrillar adhesive pads in this insect mainly because the forceps‐like pincers are used during copulation to grasp the partner.     

The development of epidermal feet in preparation for metamorphosis in an insect

Insect epidermal cell surfaces can be seen by scanning electron microscopy after removal of the basal lamina. This let us study surface changes in the 5th larval stage of Calpodes ethlius (Lepidoptera, Hesperiidae) in preparation for metamorphosis at the end of the stadium, in particular changes in the basal cell processes or feet, intercellular lymph spaces, filopodia and hemidesmosomes. The feet develop in three phases, initiation, elongation and contraction. Initial growth begins immediately after ecdysis and continues until commitment to pupation 66 hr later. During this phase the feet are randomly oriented. Elongation and orientation begin after commitment to pupation. Orientation is probably achieved by selective survival and growth of those feet that are axially oriented rather than by reorientation. As the larva shortens to the pupal form late in the stadium, contraction of the feet occurs and the cells become columnar. The feet finally disappear as the cells rearrange themselves into new positions in the pupal epidermis. The lateral margins of the feet are united by adhesions even when their interdigitations are most complex. The adhesions separate an intercellular lymph space from the haemolymph. The lymph space remains small through most of the stadium, but enlarges with the loss of lateral junctions as the feet contract and eventually extends along most of the length of the columnar cells. Filopodia then form and span the gaps between the cells as though they have been induced by the separation and loss of lateral cell to cell contact. Scanning electron microscopy also shows that hemidesmosomes reflect the axial alignment of the cells even before the orientation of the feet. The hemidesmosome plaques are linear structures having a constant width of 0.15 - 0.2 mum and variable length. They arise in short sections and lengthen by the linear addition of more sections with the same width. Late in the stadium they lose their axial alignment and may become branched.     

Chemical Alarm Signalling in Terrestrial Salamanders: Intra- and Interspecific Responses

Chemical alarm cues are known to be important in mediating predator avoidance in a variety of taxonomic groups. The purpose of this study was to test whether three species of salamanders that co-occur in the coastal mountains of Oregon utilize chemical alarm cues in predator avoidance. In laboratory experiments, Western redback salamanders, Plethodon vehiculum, and Southern torrent salamanders, Rhyacotriton variegatus, exhibited an avoidance response to stimuli from injured conspecifics, while Dunn's salamanders, Plethodon dunni did not. Additional experiments demonstrated interspecific alarm responses. P. vehiculum and R. variegatus responded to each other's alarm cues but did not respond to the alarm cues of allotopic long-toed salamanders, Ambystoma macrodactylum. For R. variegatus, this is despite the fact that they are more closely related to the allotopic species (A. macrodactylum) than to the syntopic species (P. vehiculum). Thus phylogeny alone may not explain patterns of cross-species alarm responses. Instead, interspecific alarm responses may occur between syntopic species that belong to the same prey guild (i.e. those species that co-occur spatially and temporally and are exposed to the same suite of predators).     

Experimental studies on direct and indirect interactions in a three trophic-level stream system

Summary We used a complete block design to experimentally study direct and indirect interactions in a three trophic-level freshwater system consisting of a top predator, the green sunfish, Lepomis cyanellus, an intermediate predator, small-mouthed salamander larvae, Ambystoma barbouri, and prey, hatchling isopods, Lirceus fontinalis. This system occurs naturally in small stream pools in central Kentucky; experiments were done in laboratory pools. Salamander larvae ate isopods and thus had a direct, negative effect on isopod survival. Accordingly, isopods responded to the presence of salamander larvae by increasing their tendency to bury themselves in the sand substrate. Fish ate salamanders and thus had a direct, negative effect on salamander survival. Salamanders responded to fish presence by increasing their time spent under plexiglass plates that simulate refuge rocks. The overall effect of fish on isopods depended on the presence of salamanders. In the absence of salamanders, fish predation on isopods had a direct, negative effect on isopod survival; isopods thus responded to the presence of fish by burying themselves in the sand. With salamanders present, fish had a positive overall effect on isopod survival; i.e., direct, negative effects of fish on isopods were outweighed by indirect, positive effects. Indirect positive effects of fish on isopods came through a reduction in salamander predation rates on isopods in the presence of fish. The mechanism involved both a decrease in the number of salamanders (a trophic-linkage indirect effect; cf. Miller and Kerfoot 1987) and a reduction in the feeding rate of individual salamanders on isopods (a behavioral indirect effect). The decrease in individual salamander feeding rates on isopods was due to reductions in both salamander activity and in spatial overlap between salamanders and isopods in the presence of fish. The latter effect reflected the fact that salamanders and isopods used different refuges from fish; salamanders went under refuge plates, whereas isopods primarily buried themselves in sand. Estimates of the relative importance of various direct and indirect effects of sunfish on isopods suggested that positive, behavioral indirect effects were of roughly the same magnitude as direct, negative effects, both of which were more important than were trophic-linkage indirect effects. Contrary to expectations, the presence of isopods did not affect the refuge use or survival of salamanders in the presence of fish.     

Electron microscopy of the K2 killer effect of Saccharomyces cerevisiae T206 on a mesophilic wine yeast

A mesophilic wine yeast, Saccharomyces cerevisiae CSIR Y217 K ^– R ^– was subjected to the K₂ killer effect of Saccharomyces cerevisiae T206 K ⁺ R ⁺ in a liquid grape medium. The lethal effect of the K₂ mycoviral toxin was confirmed by methylene blue staining. Scanning electron microscopy of cells from challenge experiments revealed rippled cell surfaces, accompanied by cracks and pores, while those unaffected by the toxin, as in the control experiments, showed a smooth surface. Transmission electron microscopy revealed that the toxin damaged the cell wall structure and perturbed cytoplasmic membranes to a limited extent.     

Do Experience and Body Size Play a Role in Responses of Larval Ringed Salamanders,Ambystoma annulatum,to Predator Kairomones? Laboratory and Field Assays

Prey may experience ontogenetic changes in vulnerability to some predators, either because of changes in morphology or experience. If prey match their level of antipredator behavior to the level of predatory threat, prey responses to predators should reflect the appropriate level of threat for their stage of development. For larval salamanders, responses to predators may change with body size because larger larvae are less vulnerable to predation by gape‐limited predators or because fleeing responses by large salamanders may be more effective than for smaller salamanders. In a field experiment, small larval ringed salamanders, Ambystoma annulatum, responded to chemical stimuli (‘kairomones’) from predatory newts, Notophthalmus viridescens, with an antipredator response (decreased activity). Laboratory‐reared larvae decreased their activity following exposure to newt kairomones, indicating that larval ringed salamanders do not require experience with newts to recognize them as predators. In both experiments, larvae distinguished between chemical stimuli from newts and stimuli from tadpoles (non‐predators) and a blank control. In a third experiment, field‐caught (experienced) larvae showed a graded response to newt kairomones based on their body size: small larvae tended to decrease their activity while larger larvae showed no change or an increase in activity. This graded response was not observed for neutral stimuli, indicating that it is predator‐specific. Therefore, ringed salamander larvae exhibit threat‐sensitive ontogenetic changes in their response to chemical stimuli from predatory newts.     

Development of the tectum in Gymnophiones,with comparison to other amphibians

Tectal development in a number of caecilian (Gymnophiona: Amphibia) species was examined and compared with that in frogs and salamanders. The caecilian optic tectum develops along the same rostrocaudal and lateromedial gradients as those of frogs and salamanders. However, differences exist in the time course of development. Our data suggest that, as in salamanders, simplification of morphological complexity in caecilians is due to a retardation or loss of late developmental stages. Differences in the time course of development (heterochrony) among different caecilian species are correlated with phylogenetic history as well as with variation in life histories. The most pronounced differences in development occur between the directly developing Hypogeophis rostratus and all other species examined. In this species, the increase in the degree of morphological complexity is greatly accelerated. J. Morphol. 236:233–246, 1998. © 1998 Wiley-Liss, Inc.