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1,047 results for “Salamanders”
Supplementary materials - Taxonomic status of the Neotropical salamanders Bolitoglossa altamazonica and Bolitoglossa peruviana (Amphibia: Caudata: Plethodontidae), with the description of a new species from Northern Peru
<p><strong>Supplementary materials for article</strong></p> <p><strong>Taxonomic status of the Neotropical salamanders Bolitoglossa altamazonica and Bolitoglossa peruviana (Amphibia: Caudata: Plethodontidae), with the description of a new species from Northern Peru</strong></p> <p>JUAN C. CUSI, GIUSSEPE GAGLIARDI-URRUTIA, ISABELA CARVALHO-BRCKO, DAVID B. WAKE, & RUDOLF VON MAY</p> <p>Supplementary FIGURE S1 - S12, Supplementary TABLE S1 - S6</p>
Relaxed predation selection on rare morphs of Ensatina salamanders (Caudata: Plethodontidae) promotes a polymorphic population in a novel dune sand habitat
<p>The Ensatina ring species represents a classic example of locally adapted lineages. The Monterey Ensatina (Ensatina eschscholtzii eschscholtzii) is a cryptic subspecies with brown coloration, however, a recently discovered polymorphic population within a wind-blown sand region also contains leucistic (pink) and xanthistic (orange) morphs. Leucism/xanthism frequency was mapped across the subspecies' range revealing that these morphs are generally rare or absent except within regions containing light-colored substrate. Attack rates were estimated using clay models of the three morphs, deployed only at the crepuscular period and during the night, on both light and dark substrates at a site within the dune sand region. Model selection found that the interaction between morph and substrate color best predicted attack rates. Typical morphs had equal attack rates on both substrates while xanthistic and leucistic morphs incurred significantly fewer attacks on light versus dark substrate, and there was no significant difference in attack rates among morphs on light substrates. These results support the idea that xanthistic and leucistic morphs are poorly adapted for dark substrates compared to typical morphs, but they are more or less equally adapted for light substrates. We suggest that this microgeographic island of relaxed selection on light-colored morphs helps explain the existence of this polymorphic population.</p>
Data from: Genetic data reveal fine-scale ecological segregation between larval plethodontid salamanders in replicate contact zones
<p>Contact zones present unique opportunities to investigate ecological divergence, reproductive barriers, and gene flow between species. The two-lined salamander (<em>Eurycea</em> <em>bislineata</em>) species complex is a group of semiaquatic plethodontid salamanders with a reticulate evolutionary history that reflects the reorganization of river drainage basins. Although evidence for widespread, ancient introgression suggests an absence of reproductive isolating mechanisms in the early evolutionary history of the group, modern contact zones reveal a broader diversity of outcomes—with some putative species pairs occurring in sympatry and others exhibiting narrow hybrid zones. Here, we used RADcap data to investigate gene flow and ecological divergence in replicate contact zones between two species in the Appalachian foothills. Our results demonstrate that gene flow between these species is absent or rare, and larvae show strong, fine-scale ecological segregation among riffles, runs, and pools in streams. These results reinforce the more ambiguous conclusions of previous studies that suggested the evolutionary distinctiveness of these two species and underscore the importance of ecological factors in shaping local distributions.</p>
Data from: Disruption of skin microbiota contributes to salamander disease
Escalating occurrences of emerging infectious diseases underscore the importance of understanding microbiome-pathogen interactions. The amphibian cutaneous microbiome is widely studied for its potential to mitigate disease-mediated amphibian declines. Other microbial interactions in this system, however, have been largely neglected in the context of disease outbreaks. European fire salamanders have suffered dramatic population crashes as a result of the newly emerged Batrachochytrium salamandrivorans(Bsal). We investigate microbial interactions on multiple fronts within this system. We show that wild, healthy fire salamanders maintain a complex skin microbiota containingBsal-inhibitory members, but the community is present at remarkably low abundance. Through experimentation, we show that increasing bacterial densities of Bsal-inhibiting bacteria via daily addition slowed disease progression in fire salamanders. Additionally, we find that experimental-Bsal infection elicited subtle changes in the skin microbiome, with selected opportunistic bacteria increasing in relative abundance resulting in septicemic events that coincide with extensive destruction of the epidermis. These results suggest that fire salamander skin, in natural settings, maintains bacterial communities at numbers too low to confer sufficient protection againstBsal,and in fact the native skin microbiota can constitute a source of opportunistic bacterial pathogens that contribute to pathogenesis.By shedding light on the complex interaction between the microbiome and a lethal pathogen, these data put the interplay between skin microbiomes and a wildlife disease in a new perspective.
Data from: LTR retrotransposons contribute to genomic gigantism in plethodontid salamanders
Among vertebrates, most of the largest genomes are found within the salamanders, a clade of amphibians that includes 613 species. Salamander genome sizes range from ∼14 Gb to ∼120 Gb. Because genome size is correlated with nucleus and cell sizes, as well as other traits, morphological evolution in salamanders has been profoundly affected by genomic gigantism. However, the molecular mechanisms driving genomic expansion in this clade remain largely unknown. Here, we present the first comparative analysis of transposable element (TE) content in salamanders. Using high-throughput sequencing, we generated genomic shotgun data for six species from the Plethodontidae, the largest family of salamanders. We then developed a pipeline to mine TE sequences from shotgun data in taxa with limited genomic resources, such as salamanders. Our summaries of overall TE abundance and diversity for each species demonstrate that TEs make up a substantial portion of salamander genomes, and that all of the major known types of TEs are represented in salamanders. The most abundant TE superfamilies found in the genomes of our six focal species are similar, despite substantial variation in genome size. However, our results demonstrate a major difference between salamanders and other vertebrates: salamander genomes contain much larger amounts of LTR retrotransposons, primarily Ty3/gypsy elements. Thus, the extreme increase in genome size that occurred in salamanders was likely accompanied by a shift in TE landscape. These results suggest that increased proliferation of LTR retrotransposons was a major molecular mechanism contributing to genomic expansion in salamanders.
Data from: When are phylogenetic analyses misled by convergence? A case study in Texas cave salamanders
Convergence, i.e., similarity between organisms that is not the direct result of shared phylogenetic history (and that may instead result from independent adaptations to similar environments), is a fundamental issue that lies at the interface of systematics and evolutionary biology. Although convergence is often cited as an important problem in morphological phylogenetics, there have been few well-documented examples of strongly supported and misleading phylogenetic estimates that result from adaptive convergence in morphology. In this article, we propose criteria that can be used to infer whether or not a phylogenetic analysis has been misled by convergence. We then apply these criteria in a study of central Texas cave salamanders (genus Eurycea). Morphological characters (apparently related to cave-dwelling habitat use) support a clade uniting the species E. rathbuni and E. tridentifera, whereas mitochondrial DNA sequences and allozyme data show that these two species are not closely related. We suggest that a likely explanation for the paucity of examples of strongly misleading morphological convergence is that the conditions under which adaptive convergence is most likely to produce strongly misleading results are limited. Specifically, convergence is most likely to be problematic in groups (such as the central Texas Eurycea) in which most species are morphologically very similar and some of the species have invaded and adapted to a novel selective environment.
Data from: Genetic drift and rapid evolution of viviparity in insular fire salamanders (Salamandra salamandra)
Continental islands offer an excellent opportunity to investigate adaptive processes and to time microevolutionary changes that precede macroevolutionary events. We performed a population genetic study of the fire salamander (Salamandra salamandra), a species that displays unique intraspecific diversity of reproductive strategies, to address the microevolutionary processes leading to phenotypic and genetic differentiation of island, coastal and interior populations. We used eight microsatellite markers to estimate genetic diversity, population structure, and demographic parameters in viviparous insular populations and ovoviviparous coastal and interior populations. Our results show considerable genetic differentiation (FST range: 0.06 - 0.27), and no clear signs of gene flow among populations, except between the large and admixed interior populations. We find no support for island colonization by rafting or intentional/accidental anthropogenic introductions, indicating that rising sea levels were responsible for isolation of the island populations approximately 9,000 years ago. Our study provides evidence of rapid genetic differentiation among island and coastal populations, and rapid evolution of viviparity driven by climatic selective pressures on island populations, geographic isolation with genetic drift, or a combination of these factors. Studies of these viviparous island populations in early stages of divergence help us better understand the microevolutionary processes involved in rapid phenotypic shifts.
Data from: Correlations of life-history and distributional-range variation with salamander diversification rates: evidence for species selection
Evolutionary biologists have long debated the relative influence of species selection on evolutionary patterns. As a test, we apply a statistical phylogenetic approach to evaluate the influence of traits related to species distribution and life-history characteristics on patterns of diversification in salamanders. We use independent contrasts to test trait-mediated diversification while accommodating phylogenetic uncertainty in relationships among all salamander families. Using a neontological data set, we find several species-level traits to be variable, heritable, and associated with differential success (i.e., higher diversification rates) at higher taxonomic categories. Specifically, the macroecological trait of small geographic-range size is strongly correlated with a higher rate of net diversification. We further consider the role that plasticity in life-history traits appears to fulfill in macroevolutionary processes of lineage divergence and durability. We find that pedotypy—wherein some, but not all, organisms of a species mature in the gilled form without metamorphosing—is also associated with higher net diversification rate than is the absence of developmental plasticity. Often dismissed as an insignificant process in evolution, we provide direct evidence for the role of species selection in lineage diversification of salamanders.
Data from: Do genetic structure and landscape heterogeneity impact color morph frequency in a polymorphic salamander?
Landscape heterogeneity plays an important role in population structure and divergence, particularly for species with limited vagility. Here, we used a landscape genetic approach to identify how landscape and environmental variables affect genetic structure and color morph frequency in a polymorphic salamander. The Eastern Red-backed Salamander, Plethodon cinereus, is widely distributed in northeastern North America and contains two common color morphs, striped and unstriped, that are divergent in ecology, behavior, and physiology. To quantify population structure, rates of gene flow, and genetic drift, we amplified 10 microsatellite loci from 648 individuals across 28 sampling localities. This study was conducted in northern Ohio, where populations of P. cinereus exhibit an unusually wide range of morph frequency variation. To test whether genetic distance was more correlated with morph frequency, elevation, canopy cover, waterways, ecological niche, or geographic distance, we used resistance distance and least cost path analyses. We then examined whether landscape and environmental variables, genetic distance, or geographic distance were correlated with variation in morph frequency. Tests for population structure revealed three genetic clusters across our sampling range, with one cluster monomorphic for the striped morph. Rates of gene flow and genetic drift were low to moderate across sites. Genetic distance was most correlated with ecological niche, elevation, and a combination of landscape and environmental variables. In contrast, morph frequency variation was correlated with waterways and geographic distance. Thus, our results suggest that selection is also an important evolutionary force across our sites, and a balance between gene flow, genetic drift, and selection interact to maintain the two color morphs.
Data from: Strong selection barriers explain microgeographic adaptation in wild salamander populations
Microgeographic adaptation occurs when populations evolve divergent fitness advantages across the spatial scales at which focal organisms regularly disperse. Although an increasing number of studies find evidence for microgeographic adaptation, the underlying causes often remain unknown. Adaptive divergence requires some combination of limited gene flow and strong divergent natural selection among populations. In this study, we estimated the relative influence of selection, gene flow and the spatial arrangement of populations in shaping patterns of adaptive divergence in natural populations of the spotted salamander (Ambystoma maculatum). Within the study region, A. maculatum co-occur with the predatory marbled salamander (A. opacum) in some ponds, and past studies have established a link between predation risk and adaptive trait variation in A. maculatum. Using 14 microsatellite loci, we found a significant pattern of genetic divergence among A. maculatum populations corresponding to levels of A. opacum predation risk. Additionally, A. maculatum foraging rate was strongly associated with predation risk, genetic divergence and the spatial relationship of ponds on the landscape. Our results indicate the sorting of adaptive genotypes by selection regime and strongly suggest that substantial selective barriers operate against gene flow. This outcome suggests that microgeographic adaptation in A. maculatum is possible because strong antagonistic selection quickly eliminates maladapted phenotypes despite ongoing and substantial immigration. Increasing evidence for microgeographic adaptation suggests a strong role for selective barriers in counteracting the homogenizing influence of gene flow.
Data from: The effects of contig length and depth on the estimation of SNP frequencies, and the relative abundance of SNPs in protein-coding and non-coding transcripts of tiger salamanders (Ambystoma tigrinum)
BACKGROUND: Next-generation sequencing methods have contributed to rapid progress in the fields of genomics and population genetics. Using this high-throughput and cost-effective technology, a number of studies have estimated single nucleotide polymorphism (SNP) frequency by calculating the mean number of SNPs per unit sequence length (e.g., mean SNPs/kb). However, both read length and contig depth are highly variable and thus raise doubt about simple methods of SNP frequency estimation. RESULTS: We used 454 pyrosequencing to identify 2,980 putative SNPs in the eastern tiger salamander (Ambystoma tigrinum tigrinum) transcriptome, then constructed analytical models to estimate SNP frequency. The model which considered only contig length (i.e., the method employed in most published papers) was evaluated with very poor likelihood. Our most robust model considered read depth as well as contig length, and was 7.5 × 1055 times more likely than the length-only model. Using this novel modeling approach, we estimated SNP frequency in protein-coding (mRNA) and non-coding transcripts (e.g., small RNAs). We found little difference in SNP frequency in the contigs, but we found a trend of a higher frequency of SNPs in long contigs representing non-coding transcripts relative to protein-coding transcripts. These results support the hypothesis that long non-coding transcripts are less conserved than long protein-coding transcripts. CONCLUSIONS: A modeling approach (i.e., using multiple model construction and model selection approaches) can be a powerful tool for identifying selection on specific functional sequence groups by comparing the frequency and distribution of polymorphisms.
Data from: Rates of morphological evolution are correlated with species richness in salamanders
The tempo and mode of species diversification and phenotypic evolution vary widely across the tree of life, yet the relationship between these processes is poorly known. Previous tests of the relationship between rates of phenotypic evolution and rates of species diversification have assumed that species richness increases continuously through time. If this assumption is violated, simple phylogenetic estimates of net diversification rate may bear no relationship to processes that influence the distribution of species richness among clades. Here we demonstrate that the variation in species richness among plethodontid salamander clades is unlikely to have resulted from simple time-dependent processes, leading to fundamentally different conclusions about the relationship between rates of phenotypic evolution and species diversification. Morphological evolutionary rates of both size and shape evolution are correlated with clade species richness, but are uncorrelated with simple estimators of net diversification that assume constancy of rates through time. This coupling between species diversification and phenotypic evolution is consistent with the hypothesis that clades with high rates of morphological trait evolution may diversify more than clades with low rates. Our results indicate that assumptions about underlying processes of diversity regulation have important consequences for interpreting macroevolutionary patterns.
Data from: Preservation-induced morphological change in salamanders and failed DNA extraction from a decades-old museum specimen: implications for Plethodon ainsworthi
<p>Natural history collections are important data repositories, but different chemical treatments of specimens can influence morphological measurements and DNA extraction, complicating taxonomic and conservation decisions dependent upon these data. One such example is the Bay Springs Salamander (<i>Plethodon ainsworthi</i>), the only United States amphibian categorized as Extinct by the IUCN.<i> </i>Recent research has proposed that <i>P. ainsworthi </i>is an invalid taxon, arguing that the 55-year-old type specimens' morphological distinctiveness from syntopic <i>P. mississippi</i> is a preservation artifact. To address this controversy, we tested for morphological changes across five experimental treatments in proxy <i>P. shermani</i> specimens, and we re-examined the datasets used to support the invalidity of <i>P. ainsworthi</i>. We also tested recently developed DNA extraction techniques on the putatively formalin-fixed <i>P. ainsworthi</i> holotype. We used Bayesian models to demonstrate that preservation method can differentially bias morphological measurements, with most methods causing lower estimates of mass and modestly higher estimates of snout-vent-length:head width ratio. These results are broadly consistent with previous studies of other vertebrates, but inconsistent with the hypothesis that <i>P. ainsworthi </i>type specimens are actually poorly preserved <i>P. mississippi</i>. Attempts to extract DNA from the <i>P. ainsworthi</i> holotype unfortunately proved unsuccessful, preventing conclusive resolution of its status and emphasizing the limitations of promising new methods. Nonetheless, we tentatively recommend continued recognition of <i>P. ainsworthi</i> as a valid but possibly extinct taxon. More generally, we invite all authors who study preserved specimens to recognize and report how certain chemical treatments might impact their results.</p>
Data from: Defensive posture in a terrestrial salamander deflects predatory strikes irrespective of body size
A wide variety of prey use defensive postures as a means of protection from predators. Many salamanders engage in broadly similar defensive postures, which may function as a warning signal and reduce the probability of attack, or may deflect predator attacks away from vital body parts. The extent to which these strategies (i.e. aposematism and deflection) act exclusively or synergistically, however, remains unknown. We deployed clay salamanders in the field, manipulating size (small, large) and posture (resting, defensive), and documented attack rates across three predator types. Competing risks analysis revealed that attack rates were affected by model size, deployment period, and leaf litter depth at the site of deployment, whereas model posture had no significant effect. Model size and posture did not interact, indicating that defensive posture was ineffective in deterring attack irrespective of prey size. Model prey in the defensive posture received significantly more attacks on the tail irrespective of size, and the defensive posture was more effective at deflecting avian attacks compared to mammal predation. We conclude that defensive posture increases tail conspicuousness without increasing predation risk, and primarily functions to deflect attacks away from vital body parts. The efficacy of defection may be further increased by tail undulation, however our use of static models means that we cannot exclude aposematic or deimatic functions for such movements. Our results provide important support for the deflection hypothesis in explaining antipredator behavior, and thereby set the stage for additional research targeting the functionality of attack deflection in natural predator-prey encounters.
Data from: Genomic data detect corresponding signatures of population size change on an ecological time scale in two salamander species
Understanding the demography of species over recent history (e.g., < 100 years) is critical in studies of ecology and evolution, but records of population history are rarely available. Surveying genetic variation is a potential alternative to census-based estimates of population size, and can yield insight into the demography of a population. However, to assess the performance of genetic methods it is important to compare their estimates of population history to known demography. Here, we leveraged the exceptional resources from a wetland with 37 years of amphibian mark-recapture data to study the utility of genetically-based demographic inference on salamander species with documented population declines (Ambystoma talpoideum) and expansions (A. opacum); patterns that have been shown to be correlated with changes in wetland hydroperiod. We generated ddRAD data from two temporally sampled populations of A. opacum (1993, 2013) and A. talpoideum (1984, 2011) and used coalescent-based demographic inference to compare alternate evolutionary models. For both species, demographic model inference supported population size changes that corroborated mark-recapture data. Parameter estimation in A. talpoideum was robust to our variations in analytical approach, while estimates for A. opacum were highly inconsistent, tempering our confidence in detecting a demographic trend in this species. Overall, our robust results in A. talpoideum suggest that genome-based demographic inference has utility on an ecological scale, but researchers should also be cognizant that these methods may not work in all systems and evolutionary scenarios. Demographic inference may be an important tool for population monitoring and conservation management planning.
Data from: Evolutionary basis of mitonuclear discordance between sister species of mole salamanders (Ambystoma sp.)
Distinct genetic markers should show similar patterns of differentiation between species reflecting their common evolutionary histories yet there are increasing examples of differences in the biogeographic distribution of species-specific nuclear (nuDNA) and mitochondrial DNA (mtDNA) variants within and between species. Identifying the evolutionary processes that underlie these anomalous patterns of genetic differentiation is an important goal. Here we analyze the putative mitonuclear discordance observed between sister species of mole salamanders (Ambystoma barbouri and A. texanum) in which A. barbouri-specific mtDNA is found in animals located in the range of A. texanum. We test three hypotheses for this discordance (undetected range expansion, mtDNA introgression and hybridization) using nuDNA and mtDNA data analyzed with methods that varied in the parameters estimated and the timescales measured. Results from a Bayesian clustering technique (structure), bi-directional estimates of gene flow (migrate-n and IMa2), and phylogeny-based methods (*beast, bucky) all support the conclusion that the discordance is due to geographically restricted mtDNA introgression from A. barbouri into A. texanum. Limited data on species-specific tooth morphology match this conclusion. Significant differences in environmental conditions exist between sites where A. texanum with and without A. barbouri-like mtDNA occur, suggesting a possible role for selection in the process of introgression. Overall, our study provides a general example of the value of using complimentary analyses to make inferences of the directionality, time scale, and source of mtDNA introgression in animals.
Data from: COI is better than 16S rRNA for DNA barcoding Asiatic salamanders (Amphibia: Caudata: Hynobiidae)
The 5' region of the mitochondrial DNA (mtDNA) gene cytochrome c oxidase I (COI) is the standard marker for DNA barcoding. However, because COI tends to be highly variable in amphibians, sequencing is often challenging. Consequently, another mtDNA gene, 16S rRNA gene, is often advocated for amphibian barcoding. Herein, we directly compare the usefulness of COI and 16S in discriminating species of hynobiid salamanders using 130 individuals. Species identification and classification of these animals, which are endemic to Asia, is often based on morphology only. Analysis of Kimura 2-parameter genetic distances (K2P) documents the mean intraspecific variation for COI and 16S rRNA genes to be 1.4% and 0.3%, respectively. Whereas COI can always identify species, sometimes 16S cannot. Intra- and interspecific genetic divergences occasionally overlap in both markers thus reducing the value of a barcoding gap to identify genera. Regardless, COI is the better DNA barcoding marker for hynobiids. In addition to the comparison of two potential markers, high levels of intraspecific divergence in COI (>5%) suggest that both Onychodactylus fischeri and Salamandrella keyserlingii might be composites of cryptic species.
FIGURE 3 in A beautiful new yellow salamander, genus Bolitoglossa (Caudata: Plethodontidae), from the northeastern slopes of the Cordillera de Talamanca, Costa Rica
FIGURE 3. Bolitoglossa aurae sp. nov. Photograph taken by BK.
FIGURE 5 in Description of a new divergent lineage and three new species of Honduran salamanders of the genus Oedipina (Caudata, Plethodontidae)
FIGURE 5. Adult male paratype of Oedipina kasios (USNM 343456). Photograph by J. R. McCranie.
FIGURE 2 in Description of a new divergent lineage and three new species of Honduran salamanders of the genus Oedipina (Caudata, Plethodontidae)
FIGURE 2. Adult female paratype of Oedipina quadra (USNM 343452). Photograph by J. R. McCranie.
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