The geographic distribution of mitochondrial DNA haplotypes from Japanese river sculpin Cottus pollux large‐egg type (LE), collected from 55 locations in 22 rivers over most of the species’ range in ...Japan, was examined to assess for patterns of population genetic structure. The 87 haplotypes observed from C. pollux LE were distinguishable from C. pollux middle‐egg type and small‐egg type haplotypes from previously published research. Cottus pollux LE from each river were largely represented by diagnostic mtDNA haplotypes, with limited geographical associations of haplotypes, suggesting that each river must be treated as a separate management unit.
In Japan, numerous artificial dams constructed for erosion control or hydroelectric power generation have affected almost all rivers and resulted in isolation and fragmentation of many freshwater ...fish populations. We examined genetic structure and diversity of two temporally isolated samples (spanning 15 years) from 23 white-spotted charr (
Salvelinus leucomaenis
) populations, including above- and below-dam populations, on Hokkaido Island. We used microsatellite DNA markers to elucidate how habitat fragmentation by damming can spatiotemporally alter population genetic structure. An isolation-by-distance genetic structure was found for anadromous populations on Hokkaido Island, which indicates substantial gene flow among populations. After habitat fragmentation by damming, isolated populations were indiscriminately subjected to genetic differentiation from anadromous (below-dam) populations within river systems, and to the subsequent loss of genetic diversity. Effective population sizes of isolated populations were less than 50. We found that substantial decreases in heterozygosity and allelic richness occurred in some isolated white-spotted charr populations over 15 years. This study shows that habitat fragmentation by damming induces significant spatial changes in population genetic structure and genetic diversity within river systems. Our findings also provide an important implication that most isolated white-spotted charr populations will continuously lose genetic diversity in the future.
We examined the radiocesium concentration, age, standard length, and stomach contents of smallmouth bass
Micropterus dolomieu
collected from Lake Hayama, Fukushima Prefecture, Japan, in 2014. Across ...three seasons sampled, fish and aquatic insects were common foods for
M. dolomieu
; the most frequently occurring forage items were Osteichthyes. The mean radiocesium concentration in
M. dolomieu
muscle was 582 Bq kg
–1
wet weight, and the concentrations in different categories of stomach contents ranged from 297 to 811 Bq kg
–1
wet weight. Considering the radiocesium concentrations in the lake water and in plankton (which included some particulate organic matter), it was possible that
M. dolomieu
radiocesium contamination is mainly transferred via the food chain. A positive correlation existed between
M. dolomieu
standard length and radiocesium concentration
.
However, in
M. dolomieu
of the same size range, the concentrations did not differ significantly between fish that existed at the time of the Fukushima Daiichi Nuclear Power Plant accident and those born afterward. Although some fish sampled in 2014 were highly contaminated, the initial Fukushima fallout does not necessarily explain the high radiocesium concentrations in some
M. dolomieu
in the lake several years after the accident. The contamination levels observed in
M. dolomieu
might result from radiocesium concentrations in their available food at any time, whether immediately or several years after the Fukushima accident.
Abstract
The area around the Sea of Okhotsk and the Sea of Japan in the north-western North Pacific provides opportunities for studying the impact of climate oscillations on the evolutionary history ...of cold-temperate species independent of direct ice sheet development. We conducted a range-wide collection survey of white-spotted charr, Salvelinus leucomaenis, and integrated nuclear DNA and mitochondrial DNA (mtDNA) data to reveal the evolutionary history of this species. Phylogeographic analyses using genome-wide SNP data revealed the presence of five geographically distinct groups with slightly overlapping ranges. Of these, a northern group was widely distributed along the coast of the Sea of Okhotsk, the Sea of Japan and the northern region of Honshu Island, whereas the other four groups were only found on Honshu Island. The population structure of Honshu Island was largely divided into the Sea of Japan and Pacific Ocean groups by the mountain ranges running through the centre of Honshu Island, and was further subdivided by many geological factors, such as river capture and other vicariance processes. There was a discrepancy in the phylogeographic patterns between nuclear DNA and mtDNA, which was likely influenced by a complex population history that involved multiple dispersal and secondary contact events during several glacial-interglacial cycles.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The origin of 137Cs contamination, contamination levels, and its effective ecological half-life can differ among fish species, but until recently it was unknown whether interspecific differences in ...radiocaesium metabolism existed. We compare the trophic transfer of 137Cs in five salmonid species under controlled conditions. Fish were fed a diet containing 200 Bq kg−1 wet wt concentration of 137Cs for a fixed period of time. While there were almost no differences in contamination levels among individual fish within a species during fixed periods, the rate of 137Cs uptake was statistically different among the species examined, for which the effective half-life of 137Cs ranged 49–84 days. No significant difference in rate of decline in the quantity of 137Cs was apparent among species in two experiments after correcting for differences in growth. The effective half-life was shortest in Oncorhynchus mykiss and O. masou—two species exhibiting the best growth rate in both experiments—indicating an influence of the dilution effect associated with growth. When continuously fed 200 Bq kg−1 wet wt concentration of 137Cs for a period of 209–294 days, contamination levels in the five species ranged 216–240 Bq kg−1 wet wt, and reached a steady state value. Our results indicate metabolic rate, although accompanying a change of body size, did not affect 137Cs contamination levels in fish, which implies that contamination levels in the diet strongly determined contamination levels in fish.
•Rates of 137Cs uptake can differ among salmonid species within a single water body.•The effective half-life of 137Cs in five salmonid taxa ranged 49–84 days.•Salmonid taxa did not bioaccumulate 137Cs at levels exceeding that of their diet.•Body weight did not affect 137Cs after contamination levels reached a steady state.
Dam construction has serious consequences for aquatic ecosystems, and one of the most serious is the "barrier effect," the prevention of organism migration throughout a system. We assessed the effect ...of habitat fragmentation by damming on the population persistence of a stream-dwelling fish, the white-spotted charr (Salvelinus leucomaenis), in streams of southwestern Hokkaido, Japan. We sampled for charr at 52 dammed-off sites by electrofishing or snorkeling and measured five habitat characteristics: isolation period, watershed area, gradient, elevation, distance from sea. Of the 52 study sites above dams, white-spotted charr were absent at 17 sites and were present at 35 sites. Because the charr occupied all undammed upstream reaches, the damming would cause the absence of charr upstream. Among five habitat characteristics examined, stepwise logistic-regression analysis showed that disappearance was promoted with increasing isolation period, with decreasing watershed area (i.e., habitat size), and with decreasing gradient. The resulting logistic model explained 82.7% of the present white-spotted charr occurrence and forecasted that 12 of 35 extant populations will disappear after 50 years. Our findings imply that extirpation of small, dammed-off populations is inevitable unless efficient fish ladders are installed or dams are removed.
The geographic distribution pattern of mitochondrial DNA (control region) sequence polymorphisms from 73 populations of a salmonid fish, Dolly Varden Salvelinus malma, over most of its range in the ...North Pacific rim, was examined to assess how its spatial population genetic structure has been molded. The observed 68 haplotypes were grouped into three main lineages, which correspond to western, central, and eastern regions in the North Pacific. The two outlier-haplotype groups gave close agreement with DNA types from two congeneric species, white-spotted charr S. leucomaenis and Arctic charr S. alpinus, respectively. These results suggest that the present-day genetic structure of S. malma reflects historical patterns of isolation and re-colonization, and also historical hybridization with co-distributed species. We also placed the haplotypes of S. malma within our study areas into a pre-existing evolutionary relationship of S. alpinus and S. malma throughout the Northern Hemisphere. Phylogenetic analysis revealed that the Western Lineage S. malma was basal to all other lineages of S. malma and S. alpinus. Our data serve as a biogeographic hypothesis for salmonid fishes that the Sea of Japan and/or Sea of Okhotsk regions represents a place of origin for S. malma and S. alpinus groups currently distributed in circumpolar regions.
The process tomography (PT) method using ultrasonic waves or electromagnetic waves has been proposed to measure the bubble distribution in a pipe where a liquid containing bubbles flows, but it has a ...problem of making the equipment larger and more complicated. In this paper, we propose a simpler method for imaging the distribution of air bubbles in a pipe by using an M-sequence coded array probe as the ultrasonic transmitter and receiver. In this paper, the effectiveness of the proposed method was verified by simulation using the finite difference time domain (FDTD) method and actual experiments. As a result, it was found that it was possible to image objects in a circular area in water in both simulation and actual experiments, suggesting that this method can be used to instantly image objects flowing in a pipe.
Isolation by distance is usually tested by the correlation of genetic and geographic distances separating all pairwise populations’ combinations. However, this method can be significantly biased by ...only a few highly diverged populations and lose the information of individual population. To detect outlier populations and investigate the relative strengths of gene flow and genetic drift for each population, we propose a decomposed pairwise regression analysis. This analysis was applied to the well‐described one‐dimensional stepping‐stone system of stream‐dwelling Dolly Varden charr (Salvelinus malma). When genetic and geographic distances were plotted for all pairs of 17 tributary populations, the correlation was significant but weak (r2 = 0.184). Seven outlier populations were determined based on the systematic bias of the regression residuals, followed by Akaike's information criteria. The best model, 10 populations included, showed a strong pattern of isolation by distance (r2 = 0.758), suggesting equilibrium between gene flow and genetic drift in these populations. Each outlier population was also analysed by plotting pairwise genetic and geographic distances against the 10 nonoutlier populations, and categorized into one of the three patterns: strong genetic drift, genetic drift with a limited gene flow and a high level of gene flow. These classifications were generally consistent with a priori predictions for each population (physical barrier, population size, anthropogenic impacts). Combined the genetic analysis with field observations, Dolly Varden in this river appeared to form a mainland‐island or source‐sink metapopulation structure. The generality of the method will merit many types of spatial genetic analyses.
