Terrestrial Passive Integrated Transponder Antennae for Tracking Small Animal Movements

ABSTRACT Measuring terrestrial movements of small animals poses a substantial technological challenge. We developed very long (up to 130 m) passive integrated transponder (PIT) detectors with which we tracked salamanders (Caudata) migrating from breeding ponds to their upland habitat >200 m away. In all 60 trials, salamanders were detected when released near the antennae. In a second test, we tracked 7 of 14 tagged marbled salamanders (Ambystoma opacum) migrating >65 m, well beyond the area protected by existing wetland buffer regulations in Massachusetts, USA. The mean rate of movement for these salamanders (x̄ = 0.9 m/min; SE = 0.1 m/min) was substantially higher than rates of movement reported for related salamanders with radio-implants. These PIT antennae offer researchers a means to study small animal movements with less disruption of the animals’ natural movement patterns than is caused by other available techniques.     

Ultrastructure of lateral line organs in aneurogenic amphibian larvae (Ambystoma)

Summary An ultrastructural study was performed to determine the ability of presumptive lateral line tissue in A. maculatum embryos to migrate and differentiate in the absence of all sensory innervation. In experimental animals, all presumptive neural tissue was surgically removed at Harrison's stage 24, leaving only the posterior portion of the post-auditory placode. At later stages, completely differentiated aneural lateral line organs were found in the midbody region of the larvae. These were morphologically similar to those of control larvae. No signs of atrophy or degeneration of the neurqmasts were seen even after several weeks of nerve-free conditions.The use of the electron microscope of the College of Osteopathic Medicine is gratefully acknowledged. Thanks are due I.M. Korr and G.S.L. Appeltauer for comments and R. Meyers and R. Herbold for technical assistance     

Dobzhansky-Muller model of hybrid dysfunction supported by poor burst-speed performance in hybrid tiger salamanders

Speciation may result from 'complementary' genetic differences that cause dysfunction when brought together in hybrids despite having no deleterious effects within pure species genomes. The theory of complementary genes, independently proposed by Dobzhansky and Muller, yields specific predictions about the genetics of hybrid fitness. Here, I show how alternative models of hybrid dysfunction can be compared using a simple multivariate analysis of hybrid indices calculated from molecular markers. I use the approach to fit models of hybrid dysfunction to swimming performance in hybrid tiger salamander larvae. Poor burst-speed performance is a dysfunction suggesting low vigour and could translate directly into low survival. My analyses show that the Dobzhansky-Muller model fits these data better than heterozygote disadvantage. The approach demonstrated here can be applied to a broad array of nonmodel species, potentially leading to important generalizations about the genetics of hybrid dysfunction.     

The influence of altitude and topography on genetic structure in the long-toed salamander (Ambystoma macrodactulym)

A primary goal of molecular ecology is to understand the influence of abiotic factors on the spatial distribution of genetic variation. Features including altitudinal clines, topography and landscape characteristics affect the proportion of suitable habitat, influence dispersal patterns, and ultimately structure genetic differentiation among populations. We studied the effects of altitude and topography on genetic variation of long-toed salamanders (Ambystoma macrodactylum), a geographically widespread amphibian species throughout northwestern North America. We focused on 10 low altitude sites (< 1200 m) and 11 high-altitude sites in northwestern Montana and determined multilocus genotypes for 549 individuals using seven microsatellite loci. We tested four hypotheses: (1) gene flow is limited between high- and low-altitude sites; and, (2) gene flow is limited among high-altitude sites due to harsh habitat and extreme topographical relief between sites; (3) low-altitude sites exhibit higher among-site gene flow due to frequent flooding events and low altitudinal relief; and (4) there is a negative correlation between altitude and genetic variation. Overall F(ST) values were moderate (0.08611; P < 0.001). Pairwise F(ST) estimates between high and low populations and a population graphing method supported the hypothesis that low-altitude and high-altitude sites, taken together, are genetically differentiated from each other. Also as predicted, gene flow is more prominent among low-altitude sites than high-altitude sites; low-altitude sites had a significantly lower F(ST) (0.03995; P < 0.001) than high altitude sites (F(ST) = 0.10271; P < 0.001). Use of Bayesian analysis of population structure (BAPS) resulted in delineation of 10 genetic groups, two among low-altitude populations and eight among high-altitude populations. In addition, within high altitude populations, basin-level genetic structuring was apparent. A nonequilibrium algorithm for detecting current migration rates supported these population distinctions. Finally, we also found a significant negative correlation between genetic diversity and altitude. These results are consistent with the hypothesis that topography and altitudinal gradients shape the spatial distribution of genetic variation in a species with a broad geographical range and diverse life history. Our study sheds light on which key factors limit dispersal and ultimately species' distributions.     

Phylogenetic concordance analysis shows an emerging pathogen is novel and endemic

Distinguishing whether pathogens are novel or endemic is critical for controlling emerging infectious diseases, an increasing threat to wildlife and human health. To test the endemic vs. novel pathogen hypothesis, we present a unique analysis of intraspecific host-pathogen phylogenetic concordance of tiger salamanders and an emerging Ranavirus throughout Western North America. There is significant non-concordance of host and virus gene trees, suggesting pathogen novelty. However, non-concordance has likely resulted from virus introductions by human movement of infected salamanders. When human-associated viral introductions are excluded, host and virus gene trees are identical, strongly supporting coevolution and endemism. A laboratory experiment showed an introduced virus strain is significantly more virulent than endemic strains, likely due to artificial selection for high virulence. Thus, our analysis of intraspecific phylogenetic concordance revealed that human introduction of viruses is the mechanism underlying tree non-concordance and possibly disease emergence via artificial selection.     

Environment-dependent admixture dynamics in a tiger salamander hybrid zone

After an estimated five million years of independent evolution, the barred tiger salamander (Ambystoma tigrinum mavortium) was introduced by bait dealers into the native range of the California tiger salamander (A. californiense). Hybridization and backcrossing have been occurring in central California for 50-60 years, or an estimated 15-30 generations. We studied genetic and ecological factors influencing admixture of these two divergent gene pools by analyzing frequencies of hybrid genotypes in three kinds of breeding habitats: natural vernal pools, ephemeral man-made cattle ponds, and perennial man-made ponds. Perennial ponds tended to have higher frequencies of nonnative alleles than either type of seasonal pond, even in cases where perennial and seasonal ponds are within a few hundred meters. Thus, the hybrid zone has a mosaic structure that depends on pond hydrology or ecology. The presence of some broadly acting constraints on admixture is suggested by linkage disequilibria between physically unlinked molecular markers within ponds. In addition, we found several marker-specific deviations from Hardy-Weinberg equilibrium. One marker showed a consistent deficit of heterozygotes across pond types. Another showed heterozygote deficits only in vernal pools. A third was more likely to have heterozygote excess in ephemeral cattle ponds. These patterns indicate that admixture is influenced by complex genotype-by-environment interactions.     

Genome‐specific histories of divergence and introgression between an allopolyploid unisexual salamander lineage and two ancestral sexual species

Quantifying introgression between sexual species and polyploid lineages traditionally thought to be asexual is an important step in understanding what drives the longevity of putatively asexual groups. Here, we capitalize on three recent innovations—ultraconserved element (UCE) sequencing, bioinformatic techniques for identifying genome‐specific variation in polyploids, and model‐based methods for evaluating historical gene flow—to measure the extent and tempo of introgression over the evolutionary history of an allopolyploid lineage of all‐female salamanders and two ancestral sexual species. Our analyses support a scenario in which the genomes sampled in unisexual salamanders last shared a common ancestor with genomes in their parental species ～3.4 million years ago, followed by a period of divergence between homologous genomes. Recently, secondary introgression has occurred at different times with each sexual species during the last 500,000 years. Sustained introgression of sexual genomes into the unisexual lineage is the defining characteristic of their reproductive mode, but this study provides the first evidence that unisexual genomes have undergone long periods of divergence without introgression. Unlike other sperm‐dependent taxa in which introgression is rare, the alternating periods of divergence and introgression between unisexual salamanders and their sexual relatives could explain why these salamanders are among the oldest described unisexual animals.     

一种银耳段木栽培杂菌的形态学鉴定与分子生物学分析

从四个不同银耳段木栽培场地采集杂菌样本,经初步鉴定后纯化得到48个菌株。通过对子实体、孢子及菌丝等的形态观察确认从银耳栽培段木上分离的48株杂菌隶属于炭团菌属,在形态上与截头炭团菌Annulohypoxylon annulatum最为相似。为了进一步确认从银耳栽培段木上分离的48株杂菌的分类地位,对其中14个供试菌株进行了ITS系统发育分析,结果表明:14个供试菌株之间的遗传距离为0.036时可以形成两个明显分枝,且分枝与地理来源之间并无明显相关性;供试菌株在分类地位上属于炭团菌属,与形态学鉴定结果一致,并与截头炭团菌的关系最为接近,遗传距离在0.2左右;与银耳伴生菌香灰菌的遗传距离为0.29左右。从75条引物中筛选出13条引物对所有48个供试菌株进行ISSR扩增,扩增共获得103条带,其中多态性条带72条,占条带总数的69.9%。聚类分析结果表明:在相似水平为75%时,48个菌株可以划分为5个类群,且类群的划分与地理来源之间并无明显相关性;多数供试菌株之间的遗传相似性较低,这表明供试菌株在DNA水平上存在比较显著的遗传变异,具有较丰富的遗传多样性。