Several studies have demonstrated the importance of the bioavailability of particulate phosphorus (PP) exported from various watersheds, especially agricultural land. However, few studies have ...documented the influence of hydrological conditions on the sources and bioavailability of PP exported from watersheds with multiple land uses. In this study, to assess the sources and bioavailability of PP under different hydrological conditions, we conducted synoptic monitoring of compositional changes in the chemical fractions of PP exported from the Yasu River Watershed, which is covered with a mixture of forest (57.7%) and rice paddy (20.5%) areas. In this river, total phosphorus was composed mainly of PP at all monitoring sites and time points. The sequential extraction of PP revealed that a fraction bound to redox‐sensitive iron and manganese, regarded as bioavailable, was specific to the drainage waters of rice paddies, while a fraction bound to organic matter, regarded as less bioavailable, was specific to a forested stream. In the downstream of the Yasu River covering the whole watershed, PP exported under the base flow and small rainfall conditions was composed mainly of the rice paddy‐derived fraction, while most of the PP exported under heavy rainfall conditions was the forest‐derived fraction. These results suggest that the sources and bioavailability of PP can vary dynamically, depending on the hydrological regimes and land use pattern in the watershed. Even taking into account the fact that the large amount of PP exported during heavy rainfall is considered to be forest‐derived PP with low bioavailability, the monitoring results suggested that the annual amount of bioavailable PP exported is larger than that of dissolved phosphorus, and can have a large impact on phosphorus recycling in the downstream lake ecosystem through sedimentation and regeneration.
We assessed the influence of hydrological conditions on the sources and bioavailability of particulate phosphorus (PP) exported from watersheds with multiple land uses. In the downstream of the Yasu River covering the whole watershed, PP exported under the base flow and small rainfall conditions was composed mainly of the rice paddy‐derived fraction, while most of the PP exported under heavy rainfall conditions was the forest‐derived fraction. These results suggest that the sources and bioavailability of PP can vary dynamically, depending on the hydrological regimes and land use pattern in the watershed.
The construction of linkage maps is a first step in exploring the genetic basis for adaptive phenotypic divergence in closely related species by quantitative trait locus (QTL) analysis. Linkage maps ...are also useful for comparative genomics in non-model organisms. Advances in genomics technologies make it more feasible than ever to study the genetics of adaptation in natural populations. Restriction-site associated DNA (RAD) sequencing in next-generation sequencers facilitates the development of many genetic markers and genotyping. We aimed to construct a linkage map of the gudgeons of the genus Gnathopogon (Cyprinidae) for comparative genomics with the zebrafish Danio rerio (a member of the same family as gudgeons) and for the future QTL analysis of the genetic architecture underlying adaptive phenotypic evolution of Gnathopogon.
We constructed the first genetic linkage map of Gnathopogon using a 198 F2 interspecific cross between two closely related species in Japan: river-dwelling Gnathopogon elongatus and lake-dwelling Gnathopogon caerulescens. Based on 1,622 RAD-tag markers, a linkage map spanning 1,390.9 cM with 25 linkage groups and an average marker interval of 0.87 cM was constructed. We also identified a region involving female-specific transmission ratio distortion (TRD). Synteny and collinearity were extensively conserved between Gnathopogon and zebrafish.
The dense SNP-based linkage map presented here provides a basis for future QTL analysis. It will also be useful for transferring genomic information from a "traditional" model fish species, zebrafish, to screen candidate genes underlying ecologically important traits of the gudgeons.
The enhancement of human well-being is one of the ultimate goals of resource management; however, it is not explicitly considered by forest policy indicators. Our previous studies examined how ...Japanese citizens in the Yasu River watershed of the Shiga Prefecture perceived subjective well-being related to forests (forest SWB). We found a negative correlation between forest SWB and forest ownership, suggesting dissatisfaction with the low profitability of forest ownership. Based on this result, in this paper, we argue that forest SWB can be an important indicator for policymaking in the context of urbanization and forest restoration and can complement existing forest indicators focusing mainly on physical and objective properties. First, we propose that a direct measurement of well-being (e.g., forest SWB) is preferable over an indirect measurement (e.g., GDP), for policymaking processes related to forests. Second, forest SWB can reflect the quality of our interactions with forests, which is important in urbanized societies which tend to have reduced experiences with nature. Third, forest SWB could identify inequalities between the users of forest ecosystem services and forest managers. Overall, forest SWB can be a holistic indicator to capture a variety of perspectives held by citizens.
The purpose of this study is to assess the effects of natural capital on overall subjective well-being and forest-related subjective well-being. A questionnaire survey of 1698 urban and rural ...residents living in a watershed of Japan was conducted in February and March of 2016. Multiple regression and moderation effect analyses are conducted to statistically estimate the respective influences of natural capital, human-made capital, social capital, human capital, and other demographic factors on the above-mentioned two types of subjective well-being. Forest-related activities, human engagement with forests, are supposed to be of great societal and political importance for Japanese society, where past management practices have, at least quantitatively, restored forests from past deforestation. Our statistical analysis tests whether specific engagement with natural capital (forest-related activities) is positively related to subjective well-being. Following the capability approach developed by Amartya Sen, forest-related activities are interpreted as functionings, and the analysis highlights the importance of functionings as links between natural capital and subjective well-being. The results show several forest-related activities have statistically significant effects on overall and forest-related well-being. For respondents living in less forested areas and with less social capital, forest-related activities have stronger effects on their subjective well-being, suggesting that the individual subjective well-being of urban residents and those with less social capital can be enhanced through engagement with forests.
•We measured subjective well-being (SWB) related to forests in a watershed, Japan.•Forest-related activities are functionings linking resources and well-being.•Certain forest-related activities have effects on overall and forest-related well-being.•In less forested areas, forest-related activities have stronger SWB effects.•For people with less social capital, forest-related activities have more SWB effects.
Resource availability often determines the intensity of cannibalism, which has a considerable effect on population size distribution and individual life history. Larvae of the caddisfly Psilotreta ...kisoensis build portable cases from sedimentary sands and often display cannibalism. For this species, the availability of preferable case material is a critical factor that affects larval fitness, and material is locally variable depending on the underlying geology. In this study, we investigated how sand quality as a case material determines cannibalism frequency among larvae and, in turn, how the differential cannibalism frequency affects the body-size distribution and voltinism. Rearing experiments within a cohort revealed that a bimodal size distribution developed regardless of material quality. However, as the preferable material became abundant, the proportion of larger to smaller individuals increased. Consecutive experiments suggested that smaller larvae were more frequently cannibalized by larger ones and excluded from the population when preferable smooth material was abundant. This frequent cannibalism resulted in a bimodal size distribution with a significantly higher proportion of larger compared to smaller individuals. The size-dependent cannibalism was significantly suppressed when the larvae were raised in an environment with a scarcity of the preferable case material. This is probably because larvae cannot enjoy the benefit of rapid growth by cannibalism due to the difficulties in enlarging their case. At low cannibalism the growth of smaller individuals was stunted, and this was probably due to risk of cannibalism by larger individuals. This growth reduction in small individuals led to a bimodal size-distribution but with a lower proportion of larger to smaller individuals compared to at high cannibalism. A field study in two streams showed a similar size distribution of larvae as was found in the rearing experiment. The bimodal ratio has consequences for life history, since a size-bimodal population causes a cohort splitting: only larvae that were fully grown at 1 year had a univoltine life cycle, whereas larvae with a stunted growth continued their larval life for another year (semivoltine). This study suggests that availability of preferable case building material is an important factor that affects cannibalism, which in turn affects larval population size structure and cohort splitting.
Rice fields serve as alternative habitats for wetland species, and their recent reduction in area due to land conversion is considered one of the main human drivers of wetland biodiversity loss. Even ...for existing rice fields, physico‐chemical disturbances, such as farmland consolidation and agrochemical application, also have negative effects on wetland biodiversity. For fish that inhabit rice fields for at least part of their life history, differences in water level between rice fields and irrigation ditches caused by irrigation system improvements are critical to their abundance by preventing their access.
The ecological impact of differences in water level may extend to the foraging habits and trophic positions of the top predators in rice fields, resulting in the alteration of wetland food webs. Here, we investigated how physical disruptions to habitat networks affect food‐web properties in rice‐field ecosystems.
We conducted stable nitrogen and carbon isotope analysis on a threatened giant water bug, Kirkaldyia deyrolli, to estimate its trophic position as an indicator of food‐chain length. Based on field observations, we found that fish that were at a high trophic position were only available to K. deyrolli in rice fields where there were no physical barriers blocking access to the network of habitats, and the diets of K. deyrolli included fish prey (18%, based on visual observation). The stable isotope analysis revealed that the trophic position of K. deyrolli was significantly lower in rice fields with physical barriers (no fish/10 dips by a dip net) than in those without physical barriers (5.6 fish) due to the absence of fish in locations with barriers.
In conclusion, our study demonstrates that physical alterations are important to community composition and food‐web properties in rice‐field ecosystems because they can act as barriers to fish.
Evolution of ecomorphologically relevant traits such as body shapes is important to colonize and persist in a novel environment. Habitat‐related adaptive divergence of these traits is therefore ...common among animals. We studied the genomic architecture of habitat‐related divergence in the body shape of Gnathopogon fishes, a novel example of lake–stream ecomorphological divergence, and tested for the action of directional selection on body shape differentiation. Compared to stream‐dwelling Gnathopogon elongatus, the sister species Gnathopogon caerulescens, exclusively inhabiting a large ancient lake, had an elongated body, increased proportion of the caudal region and small head, which would be advantageous in the limnetic environment. Using an F2 interspecific cross between the two Gnathopogon species (195 individuals), quantitative trait locus (QTL) analysis with geometric morphometric quantification of body shape and restriction‐site associated DNA sequencing‐derived markers (1622 loci) identified 26 significant QTLs associated with the interspecific differences of body shape‐related traits. These QTLs had small to moderate effects, supporting polygenic inheritance of the body shape‐related traits. Each QTL was mostly located on different genomic regions, while colocalized QTLs were detected for some ecomorphologically relevant traits that are proxy of body and caudal peduncle depths, suggesting different degree of modularity among traits. The directions of the body shape QTLs were mostly consistent with the interspecific difference, and QTL sign test suggested a genetic signature of directional selection in the body shape divergence. Thus, we successfully elucidated the genomic architecture underlying the adaptive changes of the quantitative and complex morphological trait in a novel system.
Identifying nonpoint phosphorus (P) sources in a watershed is essential for addressing cultural eutrophication and for proposing best-management solutions. The oxygen isotope ratio of phosphate ...(δ18OPO4 ) can shed light on P sources and P cycling in ecosystems. This is the first assessment of the δ18OPO4 distribution in a whole catchment, namely, the Yasu River Watershed in Japan. The observed δ18OPO4 values in the river water varied spatially from 10.3‰ to 17.6‰. To identify P sources in the watershed, we used an isoscape approach involving a multiple-linear-regression model based on land use and lithological types. We constructed two isoscape models, one using data only from the whole watershed and the other using data from the small tributaries. The model results explain 69% and 96% of the spatial variation in the river water δ18OPO4 . The lower R 2 value for the whole watershed model is attributed to the relatively large travel time for P in the main stream of the lower catchment that can result in cumulative biological P recycling. Isoscape maps and a correlation analysis reveal the relative importance of P loading from paddy fields and bedrock. This work demonstrates the utility of δ18OPO4 isoscape models for assessing nonpoint P sources in watershed ecosystems.
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