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PubMed2005

Ontogeny discombobulates phylogeny: paedomorphosis and higher-level salamander relationships.

Evolutionary developmental biology ("evo-devo") has revolutionized evolutionary biology but has had relatively little impact on systematics. We show that similar large-scale developmental changes in distantly related lineages can dramatically mislead phylogenetic analyses based on morphological data. Salamanders are important model systems in many fields of biology and are of special interest in that many species are paedomorphic and thus never complete metamorphosis. A recent study of higher-level salamander phylogeny placed most paedomorphic families in a single clade based on morphological data. Here, we use new molecular and morphological data to show that this result most likely was caused by the misleading effects of paedomorphosis. We also provide a well-supported estimate of higher-level salamander relationships based on combined molecular and morphological data. Many authors have suggested that paedomorphosis may be problematic in studies of salamander phylogeny, but this hypothesis has never been tested with a rigorous phylogenetic analysis. We find that the misleading effects of paedomorphosis on phylogenetic analysis go beyond the sharing of homoplastic larval traits by paedomorphic adults, and the problem therefore is not solved by simply excluding suspected paedomorphic characters. Instead, two additional factors are critically important in causing paedomorphic species to be phylogenetically "misplaced": (1) the absence of clade-specific synapomorphies that develop during metamorphosis in nonpaedomorphic taxa and allow their "correct" placement and (2) parallel adaptive changes associated with the aquatic habitat of the larval stage. Our results suggest that the effects of paedomorphosis on phylogenetic analyses may be complex, difficult to detect, and can lead to results that are both wrong and statistically well supported by parsimony and Bayesian analyses.

Animals↗
PubMedDate not supplied

Exposure to ultraviolet radiation (290-400 nm) causes oxidative stress, DNA damage, and expression of p53/p73 in laboratory experiments on embryos of the spotted salamander, Ambystoma maculatum.

Developing embryos of the spotted salamander, Ambystoma maculatum, exposed to ultraviolet radiation (UVR; 290-400 nm) in the laboratory show a significant sensitivity to UVB (290-320 nm) radiation. Embryos in laboratory experiments exhibited significant DNA damage during exposures to UVR despite a significant increase in the production of the protective pigment melanin in response to UVR exposure. DNA damage occurs as a result of both the direct effects of exposure to UVR, and the indirect effects are mediated by the production of reduced oxygen intermediates. The production of reactive oxygen species initiates the expression of p53/p73 that leads to either DNA repair or apoptosis. When similar experiments are conducted on salamander embryos exposed to solar UVR in vernal pools, the embryos show significantly less sensitivity and higher survivorship. The differences between laboratory and field experiments are a result of the attenuation of UVR caused by the accumulation of dissolved organic carbon within the pools of these wooded areas. These findings suggest that northeastern populations of spotted salamanders are sensitive to UVR but are not significantly affected by present-day irradiances of UVR in the field. These results do suggest that continued decreases in stratospheric ozone over temperate latitudes have the potential to affect spotted salamanders in their natural habitats.

Ambystoma↗
PubMed1997

Rapid classical conditioning of odor response in a physiological model for olfactory research, the tiger salamander.

In recent years there have been a number of important advances in the understanding of cellular mechanisms related to olfactory function. Hypotheses regarding the complex relationships among odorant structure, physiological activity and behavioral outcome generated by these findings, however, remain largely untested due to a paucity of psychophysical data on stimulus discrimination in the same experimental species. Comparisons between behavioral and physiological responses are essential for elucidating the critical aspects of stimulus coding in sensory systems. We have developed a method for generating psychophysical data in one of the primary model species used in olfactory research, the tiger salamander, Ambystoma tigrinum. These psychophysical experiments are carried out under the same conditions as physiological experiments in our laboratory. Using classical conditioning, individual salamanders are trained over a period of 2-3 h to show skin potential responses to odor and not air. Failure to train using backward pairing demonstrates that the response is not due to sensitization or pseudoconditioning. The conditioned response is mediated by the olfactory pathway, as it is blocked by olfactory nerve section. We show that salamanders detect three odorants that are commonly used stimuli in physiological experiments (butyl alcohol, butyl acetate and amyl acetate), but cannot detect a fourth common experimental odorant, camphor. This method should be a powerful tool for studying olfactory information processing by providing data on discriminability of stimuli used in salamander physiological studies.

Acetates↗
PubMed2004

Phylogenetic evidence for a major reversal of life-history evolution in plethodontid salamanders.

The transition from aquatic to terrestrial eggs is a key evolutionary change that has allowed vertebrates to successfully colonize and exploit the land. Although most amphibians retain the primitive biphasic life cycle (eggs deposited in water that hatch into free-living aquatic larvae), direct development of terrestrial eggs has evolved repeatedly and may have been critical to the evolutionary success of several amphibian groups. We provide the first conclusive evidence for evolutionary reversal of direct development in vertebrates. The family Plethodontidae (lungless salamanders) contains the majority of salamander species, including major radiations of direct developers. We reconstruct the higher level phylogenetic relationships of plethodontid salamanders using molecular and morphological data and use this phylogeny to examine the evolution of direct development. We show that the predominantly biphasic desmognathines, previously considered the sister group of other plethodontids, are nested inside a group of direct-developing species (Plethodontini) and have re-evolved the aquatic larval stage. Rather than being an evolutionary dead end, the reversal from direct developing to biphasic life history may have helped communities in eastern North America to achieve the highest local diversity of salamander species in the world.

Adaptation, Physiological↗
PubMed2006

Insights into the mating habits of the tiger salamander (Ambystoma tigrinum tigrinum) as revealed by genetic parentage analyses.

Among urodeles, ambystomatid salamanders are particularly amenable to genetic parentage analyses because they are explosive aggregate breeders that typically have large progeny arrays. Such analyses can lead to direct inferences about otherwise cryptic aspects of salamander natural history, including the rate of multiple mating, individual reproductive success, and the spatial distribution of clutches. In 2002, we collected eastern tiger salamander (Ambystoma tigrinum tigrinum) egg masses (> 1000 embryos) from a approximately 80 m linear transect in Indiana, USA. Embryos were genotyped at four variable microsatellite loci and the resulting progeny array data were used to reconstruct multilocus genotypes of the parental dams and sires for each egg mass. UPGMA analysis of genetic distances among embryos resolved four instances of egg mass admixture, where two or more females had oviposited at exactly the same site resulting in the mixing of independent cohorts. In total, 41 discrete egg masses were available for parentage analyses. Twenty-three egg masses (56%) consisted exclusively of full-siblings (i.e. were singly sired) and 18 (44%) were multiply sired (mean 2.6 males/clutch). Parentage could be genetically assigned to one of 17 distinct parent pairs involving at least 15 females and 14 different males. Reproductive skew was evident among males who sired multiply sired clutches. Additional evidence of the effects of sexual selection on male reproductive success was apparent via significant positive correlations between male mating and reproductive success. Females frequently partitioned their clutches into multiple discrete egg masses that were separated from one another by as many as 43 m. Collectively, these data provide the first direct evidence for polygynandry in a wild population of tiger salamanders.

Ambystoma↗
PubMed2007

Phylogeographic concordance in the southeastern United States: the flatwoods salamander, Ambystoma cingulatum, as a test case.

Well-supported, congruent phylogeographic and biogeographic patterns permit the development of a priori phylogeographic and distributional predictions. In the southeastern Coastal Plain of the United States, the common discovery of east-west disjunctions (phylogeographic breaks and species' distributional boundaries) suggests that similar disjunctions should occur in codistributed taxa. Despite the near ubiquity of these disjunctions, the most recent morphological analyses of the flatwoods salamander, Ambystoma cingulatum, indicate that none occur in this low-vagility, Coastal Plain endemic. We conducted molecular and morphological analyses to test whether the flatwoods salamander is an exception to this common biogeographic pattern. Assessing geographic variation in this species is also an important management tool for this threatened, declining amphibian. We demonstrate that flatwoods salamanders, as predicted by comparisons to codistributed taxa, are polytypic with a major disjunction at the Apalachicola River. This drainage is a common site for east-west phylogeographic breaks, probably because repeated marine embayments during the Pliocene and Pleistocene interglacials generated barriers to gene flow. Based on mitochondrial DNA, morphology, and allozymes, we recognize two species of flatwoods salamanders -- Ambystoma cingulatum to the east of the Apalachicola drainage and Ambystoma bishopi to the west. Given this increased diversity, the conservation status of these two taxa may warrant re-evaluation. More generally, these results emphasize that in the absence of taxon-specific data, established comparative patterns can provide strong expectations for designing management units for unstudied species of conservation concern.

Ambystoma↗
PubMed1995

Salamander olfactory bulb neuronal activity observed by video rate, voltage-sensitive dye imaging. I. Characterization of the recording system.

1. In this paper we describe properties of a video imaging system used to acquire voltage-sensitive dye fluorescence signals from the salamander olfactory bulb. Sources of noise in these signals were evaluated in preparations stained with the potentiometric probe RH-414. These were compared with noise levels in signals obtained from a light-emitting diode array designed to stimulate the experimental conditions with light levels similar to those seen in the salamander bulb recordings. These experiments define a number of determinants of video image quality to standardize optical voltage measurements in the salamander olfactory bulb. 2. Images were acquired at video rates using a Newvicon camera in a standard upright microscope and digitized with an eight-bit video frame grabber. 3. Sources of noise related to camera sensitivity, stability of illumination, and mechanical vibration were characterized. Camera dark noise was less than the pixel variability due to photon noise at the camera faceplate. This pixel noise was the limiting factor for discriminating the spatial and temporal properties of the optical responses. 4. No significant noise was found to be related to image digitization, transmission, or readout by the eight-bit frame grabber. Mechanical vibration, light stability, and other sources of noise could be controlled in vitro. In this condition, voltage-sensitive dye signal noise was similar to that in stimulated experiments using the light-emitting diode array. Higher levels of noise were found in vivo; some of this was reduced by sychronizing frame acquisition to the heartbeat. 5. On the basis of photodiode and video measurements, voltage-sensitive dye responses in the salamander olfactory bulb typically fell between 0.75% and 2.5% fractional change of background fluorescence. By appropriately adjusting the video signals before analog-to-digital conversion, we could detect fractional changes of < 0.5%. 6. Both response averaging and low-bandpass spatial filtering improved the signal-to-noise ratios of the images. For small numbers of averaged runs, the best improvement was obtained by low-bandpass spatial filtering. 7. Acquisition of high-spatial resolution video images permitted the use of low-bandpass spatial filters to suppress pixel noise. The degree of spatial enhancement depended on the relationship between the size of the structures of interest, pixel density, and the properties of the convolution filter kernel. This method avoided exposure of the preparation to prolonged illumination and the necessity of applying the large numbers of repeated stimuli required for averaging.

Animals↗
PubMedDate not supplied

Effects of 2,4,6-trinitrotoluene in a holistic environmental exposure regime on a terrestrial salamander, Ambystoma tigrinum.

2,4,6-Trinitrotoluene (TNT) is a defense-related environmental contaminant present at high concentrations in soil at some military installations. Tiger salamanders (Ambystoma tigrinum, family Ambystomatidae) were exposed to TNT in a soil matrix and fed earthworms that had also been exposed to TNT via contaminated soil. Such exposure was previously shown to result in significant accumulation of both TNT and TNT metabolites by salamanders. Following 14 days of combined oral and dermal exposures, salamanders were evaluated for signs of toxicity. Control and TNT-exposed salamanders gained weight (p < 0.025). In addition, organ to body weight ratios (kidney, liver, and spleen) were not affected by treatment. The function of splenic phagocytic cells was evaluated because these cells are sensitive to certain environmental chemical exposures. Neither the chemiluminescence response (H2O2 production) nor the phagocytic capacity of such cells were different between controls and treatment groups. In like manner, no changes were seen in the peripheral hematologic parameters investigated. Histopathologic evaluations were inconclusive, yet the liver revealed the presence of heavily pigmented iron-rich phagocytes (melanomacrophages). This investigation presents a realistic approach and preliminary data for investigating the effects of xenobiotic exposure in a soil matrix on a terrestrial vertebrate.

Administration, Cutaneous↗
PubMed2005

Sal-Site: integrating new and existing ambystomatid salamander research and informational resources.

Salamanders of the genus Ambystoma are a unique model organism system because they enable natural history and biomedical research in the laboratory or field. We developed Sal-Site to integrate new and existing ambystomatid salamander research resources in support of this model system. Sal-Site hosts six important resources: 1) Salamander Genome Project: an information-based web-site describing progress in genome resource development, 2) Ambystoma EST Database: a database of manually edited and analyzed contigs assembled from ESTs that were collected from A. tigrinum tigrinum and A. mexicanum, 3) Ambystoma Gene Collection: a database containing full-length protein-coding sequences, 4) Ambystoma Map and Marker Collection: an image and database resource that shows the location of mapped markers on linkage groups, provides information about markers, and provides integrating links to Ambystoma EST Database and Ambystoma Gene Collection databases, 5) Ambystoma Genetic Stock Center: a website and collection of databases that describe an NSF funded salamander rearing facility that generates and distributes biological materials to researchers and educators throughout the world, and 6) Ambystoma Research Coordination Network: a web-site detailing current research projects and activities involving an international group of researchers. Sal-Site is accessible at http://www.ambystoma.org.

Animals↗
PubMed2000

The effect of graded hypoxia on the metabolic rate and buccal activity of a lungless salamander (Desmognathus fuscus).

The hypothesis that the lungless salamander Desmognathus fuscus responds actively to hypoxia was tested. Patterns of buccal movements [apneic period duration, the duration (min h(-)(1)) of buccal pumping and buccal pumping frequency], heart rate and metabolic rate (rates of oxygen uptake and carbon dioxide output) were determined during a control period (21 % oxygen), a hypoxic period (2, 5, 6.5, 8 or 10 % oxygen) and a recovery period (21 % oxygen). Hypoxic salamanders maintained their rate of oxygen uptake at control levels until a critical oxygen level between 10 and 8 % oxygen was reached. The rate of carbon dioxide output remained constant across all oxygen levels, except for a significant increase during exposure to 5 % oxygen. The buccal activity of lungless salamanders was responsive to environmental hypoxia, with a significant stimulation during exposure to 6.5 % and 5 % oxygen. Buccal pumping frequency was inhibited at 2 % oxygen. Heart rate was stimulated at all hypoxic levels except 2 % O(2). During recovery, metabolic rate and heart rate returned to control levels within 20 min after all hypoxic exposures. The durations of apneic periods increased significantly compared with the hypoxic value during recovery from exposure to 10 %, 6.5 % and 5 % oxygen. Overall, the animals responded actively to hypoxia by increasing the duration of buccal activity as oxygen levels decreased. The ability of these changes to facilitate oxygen uptake is not known. However, the response of the dusky salamander to low levels of oxygen is analogous to the hypoxic ventilatory response observed in lunged vertebrates.

Animals↗
PubMed2001

Twisting and bending: the functional role of salamander lateral hypaxial musculature during locomotion.

The function of the lateral hypaxial muscles during locomotion in tetrapods is controversial. Currently, there are two hypotheses of lateral hypaxial muscle function. The first, supported by electromyographic (EMG) data from a lizard (Iguana iguana) and a salamander (Dicamptodon ensatus), suggests that hypaxial muscles function to bend the body during swimming and to resist long-axis torsion during walking. The second, supported by EMG data from lizards during relatively high-speed locomotion, suggests that these muscles function primarily to bend the body during locomotion, not to resist torsional forces. To determine whether the results from D. ensatus hold for another salamander, we recorded lateral hypaxial muscle EMGs synchronized with body and limb kinematics in the tiger salamander Ambystoma tigrinum. In agreement with results from aquatic locomotion in D. ensatus, all four layers of lateral hypaxial musculature were found to show synchronous EMG activity during swimming in A. tigrinum. Our findings for terrestrial locomotion also agree with previous results from D. ensatus and support the torsion resistance hypothesis for terrestrial locomotion. We observed asynchronous EMG bursts of relatively high intensity in the lateral and medial pairs of hypaxial muscles during walking in tiger salamanders (we call these 'alpha-bursts'). We infer from this pattern that the more lateral two layers of oblique hypaxial musculature, Mm. obliquus externus superficialis (OES) and obliquus externus profundus (OEP), are active on the side towards which the trunk is bending, while the more medial two layers, Mm. obliquus internus (OI) and transversus abdominis (TA), are active on the opposite side. This result is consistent with the hypothesis proposed for D. ensatus that the OES and OEP generate torsional moments to counteract ground reaction forces generated by forelimb support, while the OI and TA generate torsional moments to counteract ground reaction forces from hindlimb support. However, unlike the EMG pattern reported for D. ensatus, a second, lower-intensity burst of EMG activity ('beta-burst') was sometimes recorded from the lateral hypaxial muscles in A. tigrinum. As seen in other muscle systems, these beta-bursts of hypaxial muscle coactivation may function to provide fine motor control during locomotion. The presence of asynchronous, relatively high-intensity alpha-bursts indicates that the lateral hypaxial muscles generate torsional moments during terrestrial locomotion, but it is possible that the balance of forces from both alpha- and beta-bursts may allow the lateral hypaxial muscles to contribute to lateral bending of the body as well.

Ambystoma↗
PubMed2005

Simulation and robotics studies of salamander locomotion: applying neurobiological principles to the control of locomotion in robots.

This article presents a project that aims at understanding the neural circuitry controlling salamander locomotion, and developing an amphibious salamander-like robot capable of replicating its bimodal locomotion, namely swimming and terrestrial walking. The controllers of the robot are central pattern generator models inspired by the salamander's locomotion control network. The goal of the project is twofold: (1) to use robots as tools for gaining a better understanding of locomotion control in vertebrates and (2) to develop new robot and control technologies for developing agile and adaptive outdoor robots. The article has four parts. We first describe the motivations behind the project. We then present neuromechanical simulation studies of locomotion control in salamanders. This is followed by a description of the current stage of the robotic developments. We conclude the article with a discussion on the usefulness of robots in neuroscience research with a special focus on locomotion control.

Animals↗
PubMed2003

Evidence for multiple Pleistocene refugia in the postglacial expansion of the eastern tiger salamander, Ambystoma tigrinum tigrinum.

Pleistocene glaciations were important determinants of historical migration and, hence, current levels of genetic diversity within and among populations. In many cases, these historical migrations led to the existence of disjunct populations of plants and animals. However, the origin and timing of arrival of these disjunct populations is often debated. In the current study, we identify potential refugia and estimate the timing of vicariance events of the eastern tiger salamander, Ambystoma tigrinum tigrinum, using mitochondrial sequence data. The results suggest a vicariant event 0.75-2 million years ago, separating the tiger salamanders to the east and west of the Apalachicola River Basin. East of the Appalachians, there appear to be multiple independent refugia with little migration among the remaining populations. In particular, populations along the Atlantic Coastal Plain were likely isolated in a coastal plain refugium in the Carolinas. Migrants from this refugium were the likely source of colonists for populations occupying previously glaciated areas along the northeastern Atlantic Coast. A second potential refugium occurs in the Blue Ridge Mountains of western Virginia. This refugium contains a disjunct population of the eastern tiger salamander, as well as a community of nearly 70 other disjunct plant and animal species. The tiger salamanders here have been isolated from other populations for 200,000-500,000 years. These results suggest that disjunct mountain populations of Coastal Plain species may have existed in situ throughout the Pleistocene in Appalachian refugia. Therefore, these disjunct populations are not of recent origin, but rather exist as relicts of a warmer, more widespread fauna and flora that is now restricted to the Coastal Plain.

Ambystoma↗
PubMed2001

Cloning and characterization of three salamander retinal G-protein beta subunits.

PURPOSE: Recent evidence has shown that the beta-gamma dimers (beta gamma) of activated heterotrimeric G-proteins are important in many cellular signaling pathways. Since two distinct transducin alpha subunits have been cloned from the salamander retina, we aimed to identify and characterize the G-protein beta (Gbeta) subunits that are involved in visual signal transduction in the salamander. METHODS: A salamander retina cDNA library was screened using degenerate oligonucleotide primers designed from a compilation of known Gbeta sequences. Tissue specific expression was determined by reverse transcriptase PCR (RT-PCR). RESULTS: The library screening resulted in the cloning of three full-length sequences, two of which encode proteins of 340 residues and the third being an iniation variant of 353 and 395 residues. No identical matches were found in GenBank but each shows highest homology to G-beta-1 (beta1), G-beta-3 (beta3), and G-beta-5 (beta5 and beta5L) subunits of other species, respectively. The beta1 and beta3 subunits are 84.7% identical to each other but both show only 52% identity to beta5 at the protein level. RT-PCR analysis showed that all the subunits are expressed in multiple tissues, including the retina. However, the beta5L splice variant was found only in the retina. CONCLUSIONS: Three distinct Gbeta subunit transcripts are expressed in the salamander retina. These subunits have proven to be important in the visual system of mammalian models.

Amino Acid Sequence↗
PubMed2001

Adaptation to temporal contrast in primate and salamander retina.

Visual adaptation to temporal contrast (intensity modulation of a spatially uniform, randomly flickering stimulus) was examined in simultaneously recorded ensembles of retinal ganglion cells (RGCs) in tiger salamander and macaque monkey retina. Slow contrast adaptation similar to that recently discovered in salamander and rabbit retina was observed in monkey retina. A novel method was developed to quantify the effect of temporal contrast on steady-state sensitivity and kinetics of light responses, separately from nonlinearities that would otherwise significantly contaminate estimates of sensitivity. Increases in stimulus contrast progressively and reversibly attenuated and sped light responses in both salamander and monkey RGCs, indicating that a portion of the contrast adaptation observed in visual cortex originates in the retina. The effect of adaptation on sensitivity and kinetics differed in simultaneously recorded populations of ON and OFF cells. In salamander, adaptation affected the sensitivity of OFF cells more than ON cells. In monkey, adaptation affected the sensitivity of ON cells more than OFF cells. In both species, adaptation sped the light responses of OFF cells more than ON cells. Functionally defined subclasses of ON and OFF cells also exhibited asymmetric adaptation. These findings indicate that contrast adaptation differs in parallel retinal circuits that convey distinct visual signals to the brain.

Action Potentials↗
PubMed2003

Bimodal locomotion elicited by electrical stimulation of the midbrain in the salamander Notophthalmus viridescens.

The present experiments were designed to identify the mesencephalic locomotor region (MLR) in the salamander. An in vitro semi-intact preparation from a decerebrate adult salamander (Notophthalmus viridescens) was developed in which the locomotor activities were monitored from electromyographic and video recordings. The results show that the two locomotor modes exhibited by salamanders (i.e., stepping and swimming) were evoked by electrical microstimulation (5-15 Hz; 0.1-10 microA; 2 msec pulses) of a circumscribed region in the caudal mesencephalon. At threshold current strength (0.5-3.5 microA at 15 Hz), rhythmic limb movements and intersegmental coordination, such as during stepping, were induced. As the stimulation strength was subsequently increased, the frequency of stepping became more rapid, and, at 2.0-5.5 microA, the limbs were held back against the body wall and swimming movements of the trunk were induced. An additional increase of the stimulation strength induced an increase of the frequency and amplitude of the swimming movements. Anatomical studies conducted in parallel revealed the presence of choline acetyltransferase immunoreactive cells in the functionally identified MLR region. Together, the present results indicate that the MLR is present in salamanders and that its level of activation determines the mode of locomotion. Walking is induced at low activation levels, and swimming, which constitutes a faster mode of locomotion, requires stronger stimulation of the MLR. Furthermore, as in other vertebrates, the MLR contains cholinergic cells.

Animals↗
PubMed1992

Emergent properties of odor information coding in a representational model of the salamander olfactory bulb.

In the salamander olfactory bulb, mitral output cells exhibit a variety of responses to electrical and odor stimulation, but the cellular interactions within the bulb that give rise to these responses are not completely understood. We have developed a computer model to investigate whether available data are sufficient for formulating a simulated bulb circuit that can generate realistic mitral cell output. A set of coupled difference equations incorporating mathematical descriptions of anatomical and physiological data was used to calculate changes in membrane potentials of olfactory bulb neurons over time. Model mitral cells showed responses to simple orthodromic and antidromic electrical stimuli that were similar to salamander intracellular responses. Without changing the parameters of the equations, simulated odor stimuli were applied that elicited complex patterns of mitral depolarization, spike activation, and hyperpolarization that emerged from the interactions among the numerous elements in the model. As with the electrical stimuli, model mitral responses to odor were also strikingly similar to those of real mitral cells. As an initial test of how different circuit components contribute to the responses, the lateral interactions between mitral cells and bulbar interneurons were manipulated. Tests with reduced lateral interactions and other tests with no inhibitory synaptic connections both produced mitral cell outputs that were uncharacteristic of salamander recordings. The similarity of the model's output to the complex properties of salamander single-cell recordings suggests that several critical features of the bulb circuit responsible for shaping mitral cell responsivity have been captured.(ABSTRACT TRUNCATED AT 250 WORDS)

Ambystoma↗
PubMed2005

Phylogenetic analysis of ecomorphological divergence, community structure, and diversification rates in dusky salamanders (Plethodontidae: Desmognathus).

An important dimension of adaptive radiation is the degree to which diversification rates fluctuate or remain constant through time. Focusing on plethodontid salamanders of the genus Desmognathus, we present a novel synthetic analysis of phylogeographic history, rates of ecomorphological evolution and species accumulation, and community assembly in an adaptive radiation. Dusky salamanders are highly variable in life history, body size, and ecology, with many endemic lineages in the southern Appalachian Highlands of eastern North America. Our results show that life-history evolution had important consequences for the buildup of plethodontid-salamander species richness and phenotypic disparity in eastern North America, a global hot spot of salamander biodiversity. The origin of Desmognathus species with aquatic larvae was followed by a high rate of lineage accumulation, which then gradually decreased toward the present time. The peak period of lineage accumulation in the group coincides with evolutionary partitioning of lineages with aquatic larvae into seepage, stream-edge, and stream microhabitats. Phylogenetic simulations demonstrate a strong correlation between morphology and microhabitat ecology independent of phylogenetic effects and suggest that ecomorphological changes are concentrated early in the radiation of Desmognathus. Deep phylogeographic fragmentation within many codistributed ecomorph clades suggests long-term persistence of ecomorphological features and stability of endemic lineages and communities through multiple climatic cycles. Phylogenetic analyses of community structure show that ecomorphological divergence promotes the coexistence of lineages and that repeated, independent evolution of microhabitat-associated ecomorphs has a limited role in the evolutionary assembly of Desmognathus communities. Comparing and contrasting our results to other adaptive radiations having different biogeographic histories, our results suggest that rates of diversification during adaptive radiation are intimately linked to the degree to which community structure persists over evolutionary time.

Adaptation, Biological↗