Ambystoma

A Turbo Pascal program for data acquisition and analysis is presented. The program detects incoming data as TTL pulses through the serial port of an IBM-PC and compatible computers and displays the instantaneous frequency plot and the interval histogram on-line. Novel features of this Pascal program are: (1) no special hardware requirements and (2) on-line analysis of more than one source at a time. No hardware additions to the supplied computer and easy operation make this program a valuable tool, directly useable in an IBM-PC and compatible computers.

Dispersal and gene flow within animal populations are influenced by the composition and configuration of the landscape. In this study, we evaluated hypotheses about the impact of natural and anthropogenic factors on genetic differentiation in two amphibian species, the spotted salamander (Ambystoma maculatum) and the wood frog (Lithobates sylvaticus) in a commercial forest in central Maine. We conducted this analysis at two scales: a local level, focused on factors measured at each breeding pond, and a landscape level, focused on factors measured between ponds. We investigated the effects of a number of environmental factors in six categories including Productivity, Physical, Land Composition, Land Configuration, Isolation and Location. Embryos were sampled from 56 spotted salamander breeding ponds and 39 wood frog breeding ponds. We used a hierarchical Bayesian approach in the program GESTE at each breeding pond and a random forest algorithm in conjunction with a network analysis b...

El ajolote es una especie endémica de nuestro país que ha abierto investigaciones que pueden ser aplicables en nivel clínico. Sin embargo desde hace varios años, la disminución de la especie ha estado ligada a la desaparición de su hábitat natural, así como la contaminación del mismo por gente de la misma comunidad y el turismo irresponsable que frecuentan en Xochimilco. Dado a esta problemática se han planteado diversos programas de conservación de la especie, tanto en cautiverio para seguir las investigaciones, como en zonas protegidas dentro de su hábitat de Ambystoma mexicanum. El objetivo de este trabajo es presentar los programas de conservación que se han implementado en el Lago de Xochimilco para evitar la desaparición de la especie.
Palabras clave: Axolote, Ajolote, Ambystoma mexicanum, CIBAC, NOM-059, CITES, conservación, programas.

It is a viable alternative for the management and conservation of the achoque of the Pátzcuaro Lake, whose implementation allows its recovery.  It contains technical and scientific information about its natural history and the state of conservation of the species and its habitat

La dicotomía Arte-Ciencia pareciera obvia y necesaria, y no deja de tener cierto grado de utilidad, de hecho la manera en que se presenta este texto está fuertemente marcada por esa distinción, sin embargo creo que es importante considerar que esto no siempre fue así y no siempre tiene que ser así; en tiempos pasados ésta línea no existía entre las disciplinas y me parece que el reconocimiento de una relación histórica permite comprender la relación actual. He elegido para el caso, y siguiendo la sugerencia de mis mentores, investigar acerca del reconocido pintor mexicano José María Velasco quien también, aunque menos reconocido por ello a juzgar por la información encontrada, fue un naturalista importante; el hecho de que un hombre haya combinado actividades como la pintura y la ciencia aprovechando las habilidades que tenía, da la pauta para comprender el posible, y me parece indiscutible, link que ha habido y conviene que exista entre los pinceles y las colecciones, por decirlo de alguna manera. La elección de este individuo de entre los muchos reconocidos artistas que dedicaron su vida a prácticas tanto artísticas como científicas, es en primera instancia por la impresión que me causó la obra del pintor, pero también ha tenido que ver la relativa facilidad que se ha tenido para conseguir material considerando que es un mexicano que vivió en el siglo XIX y principios del XX. Este trabajo no busca hacer una revisión exhaustiva y detallada de las obras del autor, en principio porque mis conocimientos de pintura han apenas iniciado con este acercamiento, pero además porque el interés que se tiene es más bien el de comprender la posible influencia recíproca de las áreas, examinando algunos elementos de las obras del autor y el contexto en el que fueron realizadas, esto ha pretendido lograrse a través de las opiniones que de él tienen aquellos que han estudiado su labor artística y científica desde una " La representación del mundo que el hombre se forma, sea de origen científico o mítico, apela en buena medida a su imaginación "

Using data gathered over a 4-year period from a large population of the A. laterale-jeffersonianum complex from Haliburton, Ontario, I examined four areas of reproductive ecology that may contribute to ecological partitioning: (1) fluctuating sex, hybrid, and ploidy ratios; (2) differential migratory response by triploid and tetraploid genomotypes; (3) ontogenetic differences among triploid and tetraploid genomotypes; and (4) genotypic differences within unisexual genomotypes. For each case I was able to reject a null hypothesis ascribing ecological equivalency to those biotypes involved. The most germane ecological differences among unisexuals were imbedded in the broad syndrome of delays in larval development, metamorphosis, and sexual maturity displayed by tetraploids. These findings parallel those reported in a large body of literature generated from laboratory studies of polyploid salamanders. Using these corresponding data, I conducted a broad review of potential developmental, physiological, and biotypic causes and consequences of the observed delays. The results indicated that several effects of polyploidy and hybridity directly influence community ecology and contribute to stable coexistence of bisexuals and unisexuals. Based on these findings, a strategic model summarizing interaction in these communities was constructed, from which testable hypotheses may be derived for future research. The findings of this study confirmed the ontological status of the biotypic distinctions (genomotype versus genotype) advanced here.

Studies of habitat selection are crucial for the conservation of threatened amphibians. Wild salamanders are often distributed near rocks or vegetation, which provide shelter. However, nothing is known about habitat selection of the Mexican axolotl (Ambystoma mexicanum), an endangered salamander of great cultural and ecological value. This study aims to test the relationship between vegetation presence and the distribution of captive-raised axolotls in two systems: a closed canal in their native ecosystem (n = 10) and an artificial canal within a zoological park (n = 6). We used radio-telemetry to analyse the hourly distribution and movement patterns of axolotls in each study site during 72-h observational periods. We found that movement patterns and microhabitat selection were related to vegetation coverage and diurnal and nocturnal periods. Sex and age had no effect in habitat selection. Axolotls in both study sites preferred vegetated microhabitats, but in Xochimilco this preference was only significant during daytime when they were less active. These habitat-specific patterns of spatial distribution may represent behavioural strategies for reducing predation. The first approach of behavioural insights from this study will inform the construction of refuges to reduce the alarming depletion of axolotls in the wild.

Major histocompatibility complex (MHC) class II genes, which play a major role in the immune system response, are some of the most polymorphic genes in vertebrates. We developed polymerase chain reaction primers for part of the second exon of an expressed MHC class II gene in the common frog, Rana temporaria. We genotyped this locus in five frog populations in southeast England and detected eight alleles in 215 individuals. Five or six alleles were detected in each population with a maximum of two alleles per individual, indicating that only a single locus was amplified. We also inferred the possible existence of a null allele. There were 23 variable nucleotide sites (out of 136) and 13 variable amino acid sites (out of 44), many of which corresponded to amino acids involved in antigen recognition. We detected a significant excess of nonsynonymous substitutions at antigen binding sites, indicating that this gene is under positive selection. The level of variation we found was similar to that in other amphibian MHC class II loci, such as those in Bombina bombina, Xenopus laevis and Ambystoma tigrinum.

It has been suggested that streptomycin might be an antagonist of the glutamate receptors, and that it selectively blocks quisqualic acid receptors. We studied whether streptomycin blocks the responses to excitatory amino acid agonists on the vestibular system primary afferents, and if it allows us to differentiate between kainate (KA) and quisqualate (QA) receptor mediated responses. The experiments were performed in the axolotl (Ambystoma tigrinum). Intra- and extracellular records of the electrical activity of semicircular canal afferent fibers were obtained. Drugs were applied by pressure ejection in volumes of 20 μl in a 10 ml bath. Streptomycin (0.01–10 mM), induced a dose dependent reversible inhibition of the basal spike discharge of the afferent fibers. This coincided with a reduction in the amplitude of excitatory postsynaptic potentials (EPSP) recorded recorded intracellularly in the afferent fibers. Streptomycin also blocked the excitatory action produced by KA and QA; increasing concentrations of streptomycin produced a rightward shift in the concentration-response curves for both KA and QA. This action persisted even in a high Mg2+ (10 mM), low Ca2+ (0.09 mM) Ringer solution, indicating its postsynapsic nature. These results show that streptomycin might be a non-selective excitatory amino acid (EAA) receptor antagonist.

Autopentaploidy is a death sentence for vertebrate animals, which explains why none has ever been found outside of experimental laboratory settings. Allopentaplody appears to be somewhat better tolerated, with at least a few individuals able to make it past the embryonic stage and some to adulthood. Here, flow cytometry allows for documentation of the first known naturally occurring pentaploid vertebrate—a salamander with four sets of chromosomes from one species, and a single set from a related species.

It is hypothesized that coexistence of bisexual and unisexual salamanders depends upon various forms of ecological partitioning, as in analogous complexes of fishes. The mixture of clonal and nonclonal, obligately sperm-dependent reproduction occurring in unisexual mole salamanders of the genus Ambystoma suggests that some of this partitioning may be manifest in the variable reproductive attributes of different biotypes and in community structure. Within biotypes, ecological differences related to genomic composition (genomotype) and specific origin (genotype) of individuals are also expected. Using data gathered over a 4-year period from a large population of the A. laterale–jeffersonianum complex from Haliburton, Ontario, I examined four areas of reproductive ecology that may contribute to ecological partitioning: (1) fluctuating sex, hybrid, and ploidy ratios; (2) differential migratory response by triploid and tetraploid genomotypes; (3) ontogenetic differences among triploid an...

At the first synapse in the vertebrate visual pathway, light-evoked changes in photoreceptor membrane potential alter the rate of glutamate release onto second-order retinal neurons. This process depends on the synaptic ribbon, a specialized structure found at various sensory synapses, to provide a supply of primed vesicles for release. Calcium (Ca(2+)) accelerates the replenishment of vesicles at cone ribbon synapses, but the mechanisms underlying this acceleration and its functional implications for vision are unknown. We studied vesicle replenishment using paired whole-cell recordings of cones and postsynaptic neurons in tiger salamander retinas and found that it involves two kinetic mechanisms, the faster of which was diminished by calmodulin (CaM) inhibitors. We developed an analytical model that can be applied to both conventional and ribbon synapses and showed that vesicle resupply is limited by a simple time constant, τ = 1/(Dρδs), where D is the vesicle diffusion coefficien...

Retinal cones are depolarized in darkness, keeping voltage-gated Ca2+ channels open and sustaining exocytosis of synaptic vesicles. Light hyperpolarizes the membrane potential, closing Ca2+ channels and suppressing exocytosis. Here, we quantify the Ca2+ concentration in cone terminals, with Ca2+ indicator dyes. Two-photon ratiometric imaging of fura-2 shows that global Ca2+ averages ~360 nM in darkness and falls to ~190 nM in bright light. Depolarizing cones from their light to their dark membrane potential reveals hot spots of Ca2+ that co-label with a fluorescent probe for the synaptic ribbon protein ribeye, consistent with tight localization of Ca2+ channels near ribbons. Measurements with a low-affinity Ca2+ indicator show that the local Ca2+ concentration near the ribbon exceeds 4 μM in darkness. The high level of Ca2+ near the ribbon combined with previous estimates of the Ca2+ sensitivity of release leads to a predicted dark release rate that is much faster than observed, sug...

Understanding the impacts of landscape-level processes on the population biology of amphibians is critical, especially for species inhabiting anthropogenically modified landscapes. Many pond-breeding amphibians are presumed to exist as metapopulations, but few studies demonstrate the extent and consequences of this metapopulation structure. Gene flow measures may facilitate the construction of more realistic models of population structure than direct measures of migration. This is especially true for species that are cryptic, such as many amphibians. We used eight polymorphic microsatellite loci to determine the genetic population structure of spotted salamanders (Ambystoma maculatum) breeding at 17 ponds in northeastern Ohio, a landscape fragmented by roads, agriculture, urban areas and the Cuyahoga River. Using a variety of analyses (Bayesian clustering, F-statistics, AMOVA) we generated a model of salamander population genetic structure. Our data revealed patterns of genetic connectivity that were not predicted by geographical distances between ponds (no isolation by distance). We also tested for a relationship between population structure and several indices of landscape resistance, but found no effect of potential barriers to dispersal on genetic connectivity. Strong overall connectivity among ponds, despite the hostile habitat matrix, may be facilitated by a network of riparian corridors associated with the Cuyahoga River; however, high gene flow in this system may
indicate a general ability to disperse and colonize beyond particular corridors.

Facilitated by the ability to screen large numbers of individuals via flow cytometry, this paper documents the results of the first large-scale ecological investigation of a bisexual-unisexual salamander community. Bisexual breeding dynamics largely conformed to the typical breeding dynamic within the genus, but our interesting findings with respect to hybrid migration timing had clear implications for breeding success, outcomes and ecological partitioning.

Establishing genomic resources for closely related species will provide comparative insights that are crucial for understanding diversity and variability at multiple levels of biological organization. We developed ESTs for Mexican axolotl (Ambystoma mexicanum) and Eastern tiger salamander (A. tigrinum tigrinum), species with deep and diverse research histories. Approximately 40,000 quality cDNA sequences were isolated for these species from various tissues, including regenerating limb and tail. These sequences and an existing set of 16,030 cDNA sequences for A. mexicanum were processed to yield 35,413 and 20,599 high quality ESTs for A. mexicanum and A. t. tigrinum, respectively. Because the A. t. tigrinum ESTs were obtained primarily from a normalized library, an approximately equal number of contigs were obtained for each species, with 21,091 unique contigs identified overall. The 10,592 contigs that showed significant similarity to sequences from the human RefSeq database reflect...

The aquatic form of the tiger salamander Ambystoma tigrinum lives in high-altitude ponds and is exposed to a hypoxic environment that may be either chronic or intermittent. In many animal species, exposure to hypoxia stimulates cardiac output and is followed by an increase in cardiac mass. The working hypothesis of the present study was that the hearts of these aquatic salamanders exposed to 10-14 days of 5 % oxygen in a laboratory setting would become larger and would differentially express proteins that would help confer tolerance to hypoxia. During exposure to hypoxia, cardiac output increased, as did hematocrit. Cardiac mass also increased, but mitotic figures were not detected in the cardiac myocytes of colchicine-injected animals. The mass increase was probably due to hypertrophy, although a very slow rate of hyperplasia cannot be ruled out. Representational difference analysis indicated that at least 14 mRNAs were expressed in hearts from the hypoxic animals that were not exp...

Mexico is a hotspot of salamander diversity and harbours 18 species of the genus Ambystoma (Amphibia: Urodela) widely distributed from the Sierra Madre Occidental to the Trans-Mexican Volcanic Belt. These species are highly threatened by various factors and some of them are considered nearly extinct in the wild. The Michoacán stream salamander, Ambystoma ordinarium and the yellow-peppered salamander, A. flavipiperatum are two endemic and scarce species from Mexico living in isolated and declining populations. Few observations have been made on them in their natural habitat since their original description. Here we report new data regarding the biology and habitats of A. ordinarium observed at Rio Bello, 2,120 m a.s.l., Morelia city, Michoacán state, and for A. flavipiperatum at Sierra de Quila, 2,165 m a.s.l., 100 km south from Guadalajara city, Jalisco state. For A. ordinarium we found one neotenic adult male and two dead adult females in a small shallow stream located within a fra...