scispace - formally typeset
Search or ask a question
Author

Jun Yokoyama

Other affiliations: Tohoku University
Bio: Jun Yokoyama is an academic researcher from Yamagata University. The author has contributed to research in topics: Phylogenetic tree & Population. The author has an hindex of 29, co-authored 128 publications receiving 2680 citations. Previous affiliations of Jun Yokoyama include Tohoku University.


Papers
More filters
Journal ArticleDOI
TL;DR: A nested PCR assay is established that uses two pairs of PCR primers to amplify the internal transcribed spacer (ITS) region of a ribosomal RNA cassette to detect mild fungal infections from as little as 0.001 pg of B. dendrobatidis DNA.
Abstract: A serious disease of amphibians caused by the chytrid fungus Batrachochytrium dendrobatidis was first found in Japan in December 2006 in imported pet frogs. This was the first report of chytridiomycosis in Asia. To assess the risk of pandemic chytridiomycosis to Japanese frogs, we surveyed the distribution of the fungus among captive and wild frog populations. We established a nested PCR assay that uses two pairs of PCR primers to amplify the internal transcribed spacer (ITS) region of a ribosomal RNA cassette to detect mild fungal infections from as little as 0.001 pg (1 fg) of B. dendrobatidis DNA. We collected swab samples from 265 amphibians sold at pet shops, 294 bred at institutes and 2103 collected at field sites from northern to southwestern Japan. We detected infections in native and exotic species, both in captivity and in the field. Sequencing of PCR products revealed 26 haplotypes of the B. dendrobatidis ITS region. Phylogenetic analysis showed that three of these haplotypes were specific to the Japanese giant salamander (Andrias japonicus) and appeared to have established a commensal relationship with this native amphibian. Many other haplotypes were carried by alien amphibians. The highest genetic diversity of B. dendrobatidis was found in the American bullfrog (Rana catesbeiana). Some strains of B. dendrobatidis appeared to be endemic to Japanese native amphibians, but many alien strains are being introduced into Japan via imported amphibians. To improve chytridiomycosis risk management, we must consider the risk of B. dendrobatidis changing hosts as a result of anthropogenic disturbance of the host-specific distribution of the fungus.

207 citations

Journal ArticleDOI
TL;DR: It is suggested that competition for nest sites rather than flower resources is the major ecological mechanism for displacement of native bees, which may cause local extinction of native bumblebees.
Abstract: The introduced Bombus terrestris has recently been naturalized in Japan and become dominant in some local communities. We investigated potential niche overlaps between introduced and native bumblebees in terms of morphological characteristics, seasonal flight activity, foraging and nesting habitat use, and plant species visited. There were considerable niche overlaps in flower resource use between B. terrestris and B. hypocrita sapporoensis/B. pseudobaicalensis. Bombus terrestris also potentially competes for nest sites with B. hypocrita sapporoensis. During 3-year monitoring, B. pseudobaicalensis showed no noticeable change, but B. hypocrita sapporoensis decreased while B. terrestris increased. Abundant flower resources provided by exotic plants may buffer native bumblebees from competition for food with introduced species. By contrast, the number of nest usurpers found in B. terrestris nests increased between 2003 and 2005, indicating that availability of nest sites was limiting and queens strongly competed for nest sites. Our findings suggest that competition for nest sites rather than flower resources is the major ecological mechanism for displacement of native bees. The large reduction of B. hypocrita sapporoensis queen indicates that B. terrestris may cause local extinction of native bumblebees. Control of established B. terrestris populations and prevention of further range expansion are urgently needed.

167 citations

Journal ArticleDOI
TL;DR: To investigate phylogenetic and biogeographic relationships of the genus with emphasis on L. sandwicense, the coding region of matK, the two intergenic spacers trnT (UGU)-trnL (UAA) and trnF (GAA), and the trnL intron of chloroplast DNA (cpDNA) were sequenced.

128 citations

01 Jan 2004
TL;DR: The numbers of B. terrestris captured or observed have increased rapidly during the eight years since the evidence of its naturalization was found, and it clearly has the potential to compete with native bumblebees for floral resources and nest sites.
Abstract: In 1996, a naturally occurring nest of an introduced bumblebee, Bombus terrestris L., was found in Monbetsu in the Hidaka region of southern Hokkaido, indicating that it had become naturalized in Japan. In this region, monitoring of B. terrestris has been continued at two sites. The numbers of B. terrestris captured or observed have increased rapidly during the eight years since the evidence of its naturalization was found. Seasonally, the queens of naturalized B. terrestris have appeared as early as mid-April each spring. Queens were observed continuously during the period from April to October, workers from May to October, and males from July to October. B. terrestris was shown to forage among various flowering plants, 40% −70% of the species of flowering plants upon which native bumblebees fed. Nine of ten natural nests of B. terrestris discovered during the study were found in abandoned underground rodent nests. The nest sites of this species were similar to those of B. hypocrita sapporoensis Cockerell, and B. diversus tersatus Smith. B. terrestris clearly has the potential to compete with native bumblebees for floral resources and nest sites. The mean number of new queens born in the colonies of B. terrestris was 4.4 times larger than that of the native bumblebees. This strongly suggested superior reproductive ability of B. terrestris compared with native bumblebees in the region.

118 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: The nature and extent of reported declines, and the potential drivers of pollinator loss are described, including habitat loss and fragmentation, agrochemicals, pathogens, alien species, climate change and the interactions between them are reviewed.
Abstract: Pollinators are a key component of global biodiversity, providing vital ecosystem services to crops and wild plants. There is clear evidence of recent declines in both wild and domesticated pollinators, and parallel declines in the plants that rely upon them. Here we describe the nature and extent of reported declines, and review the potential drivers of pollinator loss, including habitat loss and fragmentation, agrochemicals, pathogens, alien species, climate change and the interactions between them. Pollinator declines can result in loss of pollination services which have important negative ecological and economic impacts that could significantly affect the maintenance of wild plant diversity, wider ecosystem stability, crop production, food security and human welfare.

4,608 citations

Journal ArticleDOI
27 Mar 2015-Science
TL;DR: The stresses bees are experiencing from climate change, infectious diseases, and insecticides are reviewed, with concern that the authors may be nearing a “pollination crisis” in which crop yields begin to fall.
Abstract: Bees are subject to numerous pressures in the modern world. The abundance and diversity of flowers has declined, bees are chronically exposed to cocktails of agrochemicals, and they are simultaneously exposed to novel parasites accidentally spread by humans. Climate change is likely to exacerbate these problems in the future. Stressors do not act in isolation; for example pesticide exposure can impair both detoxification mechanisms and immune responses, rendering bees more susceptible to parasites. It seems certain that chronic exposure to multiple, interacting stressors is driving honey bee colony losses and declines of wild pollinators, but such interactions are not addressed by current regulatory procedures and studying these interactions experimentally poses a major challenge. In the meantime, taking steps to reduce stress on bees would seem prudent; incorporating flower-rich habitat into farmland, reducing pesticide use through adopting more sustainable farming methods, and enforcing effective quarantine measures on bee movements are all practical measures that should be adopted. Effective monitoring of wild pollinator populations is urgently needed to inform management strategies into the future.

2,526 citations

Journal ArticleDOI
12 Apr 2012-Nature
TL;DR: It is argued that nascent fungal infections will cause increasing attrition of biodiversity, with wider implications for human and ecosystem health, unless steps are taken to tighten biosecurity worldwide.
Abstract: The past two decades have seen an increasing number of virulent infectious diseases in natural populations and managed landscapes. In both animals and plants, an unprecedented number of fungal and fungal-like diseases have recently caused some of the most severe die-offs and extinctions ever witnessed in wild species, and are jeopardizing food security. Human activity is intensifying fungal disease dispersal by modifying natural environments and thus creating new opportunities for evolution. We argue that nascent fungal infections will cause increasing attrition of biodiversity, with wider implications for human and ecosystem health, unless steps are taken to tighten biosecurity worldwide.

2,408 citations

Journal ArticleDOI
TL;DR: The results of this study show that a survey using as few as three representative taxa can be predictive of the amount of phylogenetic information offered by a cpDNA region and that rate heterogeneity exists among noncoding cpDNA regions.
Abstract: Chloroplast DNA sequences are a primary source of data for plant molecular systematic studies. A few key papers have provided the molecular systematics community with universal primer pairs for noncoding regions that have dominated the field, namely trnL-trnF and trnK/matK. These two regions have provided adequate information to resolve species relationships in some taxa, but often provide little resolution at low taxonomic levels. To obtain better phylogenetic resolution, sequence data from these regions are often coupled with other sequence data. Choosing an appropriate cpDNA region for phylogenetic investigation is difficult because of the scarcity of information about the tempo of evolutionary rates among different noncoding cpDNA regions. The focus of this investigation was to determine whether there is any predictable rate heterogeneity among 21 noncoding cpDNA regions identified as phylogenetically useful at low levels. To test for rate heterogeneity among the different cpDNA regions, we used three species from each of 10 groups representing eight major phylogenetic lineages of phanerogams. The results of this study clearly show that a survey using as few as three representative taxa can be predictive of the amount of phylogenetic information offered by a cpDNA region and that rate heterogeneity exists among noncoding cpDNA regions.

1,763 citations

Journal ArticleDOI
TL;DR: Comparison of the total plastid genomes of tobacco and deadly nightshade enhanced with trials on widely divergent angiosperm taxa suggest that the sequences in this pair of loci have the potential to discriminate among the largest number of plant species for barcoding purposes.
Abstract: Methods for identifying species by using short orthologous DNA sequences, known as “DNA barcodes,” have been proposed and initiated to facilitate biodiversity studies, identify juveniles, associate sexes, and enhance forensic analyses. The cytochrome c oxidase 1 sequence, which has been found to be widely applicable in animal barcoding, is not appropriate for most species of plants because of a much slower rate of cytochrome c oxidase 1 gene evolution in higher plants than in animals. We therefore propose the nuclear internal transcribed spacer region and the plastid trnH-psbA intergenic spacer as potentially usable DNA regions for applying barcoding to flowering plants. The internal transcribed spacer is the most commonly sequenced locus used in plant phylogenetic investigations at the species level and shows high levels of interspecific divergence. The trnH-psbA spacer, although short (≈450-bp), is the most variable plastid region in angiosperms and is easily amplified across a broad range of land plants. Comparison of the total plastid genomes of tobacco and deadly nightshade enhanced with trials on widely divergent angiosperm taxa, including closely related species in seven plant families and a group of species sampled from a local flora encompassing 50 plant families (for a total of 99 species, 80 genera, and 53 families), suggest that the sequences in this pair of loci have the potential to discriminate among the largest number of plant species for barcoding purposes.

1,702 citations