Acheilognathus Longipinnis Research Articles

Next-generation phylogeography reveals unanticipated population history and climate and human impacts on the endangered floodplain bitterling (Acheilognathus longipinnis)

BackgroundFloodplains harbor highly biodiverse ecosystems, which have been strongly affected by both past climate change and by recent human activities, resulting in a high prevalence of many endangered species in these habitats. Understanding the history of floodplain species over a wide range of timescales can contribute to effective conservation planning. We reconstructed the population formation history of the Itasenpara bitterling Acheilognathus longipinnis, an endangered floodplain fish species in Japan, over a broad timescale based on phylogenetic analysis, demographic modeling, and historical demographic analysis using mitogenome and whole-genome sequences. A genome sequence was newly assembled as a reference for the resequencing analysis. This bitterling is distributed in three plains separated by high mountain ranges and exhibits ecological characteristics well adapted to floodplain environments.ResultsOur analyses revealed an unexpected population branching pattern, gene flow, and timing of the differentiation that occurred within a few hundred thousand years, i.e., long after the mountain uplift that was assumed to be the primary geological cause of the population differentiation. The analyses also showed that all local populations experienced a severe decline during the last glacial and post-glacial periods.ConclusionsOur results suggest that the floodplain bitterling was able to disperse through unknown routes after mountain uplift and that its populations were strongly influenced by climatic and geographic changes in glacial–interglacial cycles and subsequent human activities, probably related to its floodplain-dependent ecology. The genomic data highlight the unanticipated distribution process of this species and the magnitude of the impact of human activities, with important implications for its conservation.

Autumn dispersal and limited success of reproduction of the deepbody bitterling (Acheilognathus longipinnis) in terrestrialized floodplain

The terrestrialization of floodplains has become a concern to river managers and ecologists because it has degraded habitats for floodplain-dependent organisms. We examined the temporal distributions of the endangered deepbody bitterling (Acheilognathus longipinnis) throughout its life history, which is an autumn-spawning annual fish spending its egg and larval stages in unionid mussels and emerging in spring, to understand its population decline in the terrestrialized floodplains of the Kiso River, central Japan. We first validated our A. longipinnis environmental DNA (eDNA) sampling method and observed an 89.3% probability of consistency between the eDNA and the direct capture surveys of 56 floodplain waterbodies (FWBs). Subsequently, the temporal distributions with autumn dispersal (9 of 14 FWBs) were found using time-series eDNA samples collected from 14 FWBs on a floodplain with a length and width of 1.4 and 0.2 km, respectively. In the following spring, juveniles were only detected in the two FWBs connected to the river channel. Moreover, the direct capture data revealed that juveniles occurred in 52.9% (9/17) of the connected FWBs, but only in 5.1% (2/39) of the FWBs isolated from the river channel. Autumn dispersal of A. longipinnis would be disadvantageous for reproduction in terrestrialized floodplains with numerous isolated FWBs.

Fine-scale genetic structure of the endangered bitterling in the middle river basin of the Kiso River, Japan.

Recently, anthropogenic alterations have had severe and negative impacts on the terrestrial and aquatic species and environments. To conserve species that have a small and limited habitat, it is necessary to focus on fine-scale population structure and its effects on persistence. The deepbodied bitterling Acheilognathus longipinnis is an endangered freshwater fish that occupies ponds scattered in lateral bars in the Kiso River. In this study, we conducted multi-locus microsatellite DNA analysis to evaluate both fine-scale population structure and genetic diversity, in order to conserve A. longipinnis. The smaller number of loci deviating from the Hardy-Weinberg equilibrium in ponds scattered in individual lateral bars compared to the whole river system suggests that A. longipinnis forms a local breeding population in units of ponds. The population was roughly split between the river banks and the local population located in ponds in the mid-channel bar showed intermediate relationships with the river bank populations. Gene flow between local populations was not always homogeneous and was not influenced by geographical distances between local populations or the direction of river flow. The dispersal of A. longipinnis across both river bank sides may be constrained and is probably affected by the ecological characteristics of A. longipinnis and the hydrological regimes. Consequently, A. longipinnis in the Kiso River is maintained as a complex of multiple local populations with appropriate gene flow among them. To conserve A. longipinnis, both the persistence of the unstable ponds and moderate genetic exchanges by individual migration are required.

Interpopulational and intrapopulational genetic diversity of the endangered Itasenpara bitterling (Acheilognathus longipinnis) with reference to its demographic history

To conserve endangered species, maintenance of both interpopulational and intrapopulational genetic diversity is often required in wild populations. For the Itasenpara bitterling (Acheilognathus longipinnis), its limited number of habitats in three areas of Japan are all threatened. In this study, microsatellite data were obtained from DNA sampled from all three wild populations to evaluate the interpopulational and intrapopulational genetic diversity of A. longipinnis. The genetic uniqueness of each population and genetic differentiation among populations were determined, which are probably due to both spatial and temporal isolation among populations. Both the long-term and contemporary effective population sizes (Ne) were estimated for all populations. In all populations, the presence of historic and recent bottlenecks was estimated. For the population from the Moo River, which has the smallest habitat area and the highest number of individuals, Bayesian skyline plots demonstrated a drastic decrease in effective population size, likely caused by anthropogenic habitat modification in the past. The population from the Kiso River demonstrated a similar trend in genetic demography to the population from the Moo River. In contrast, a gradual decline in Ne was observed in the population from the Yodo River, which continued until recently. The populations from the Moo and Kiso rivers are deemed to be critically endangered due to the loss of heterozygosity. Therefore, conservation efforts are needed to maintain and promote genetic diversity in each population, both through habitat conservation and captive breeding efforts.

Morphological changes and habitat shifts with growth of endangered floodplain fish: Possible adaptations to fluctuating environments

AbstractAdaptations that maximise food intake are dependent on food and/or habitat types. However, there have been few studies on the ability of floodplain primary freshwater fish to rapidly change their morphology, especially the internal one, to maximise utilisation efficiency of food resources in response to environmental fluctuations during their life history. We investigated morphological changes of an Acheilognathinae species (Acheilognathus longipinnis) that inhabits creeks in Japan to determine whether body shape variation correlated with environmental characteristics, including water depth, current velocity, vegetation cover and food availability. When shifting from floodwater‐level to low‐water‐level season, the current velocity of the study area increased as the water level decreased, causing a significant increase in periphyton and a significant decline in zooplankton and phytoplankton. Concurrently, during the short period when A. longipinnis grow from the juvenile to the premature stage, changes in internal morphology, that is intestinal elongation, and changes in external morphology such as an increase of body depth were observed. In contrast, intestinal length significantly decreased in the adult stage. Our findings suggest that morphological changes between floodwater‐level and low‐water‐level seasons associated with juvenile to premature development are an adaptation to changes in food availability due to environmental fluctuations. Additionally, the shortening of the intestine from the premature to the adult stage may be an adaptive strategy for reproduction.

淀川城北ワンド群における外来魚駆除とその効果 －「淀川水系イタセンパラ保全市民ネットワーク」を中心とした 多様な主体の連携事例－

淀川城北ワンド群における外来魚駆除とその効果 －「淀川水系イタセンパラ保全市民ネットワーク」を中心とした 多様な主体の連携事例－

Seasonal variations in bacterioplankton community structures in two small rivers in the Himi region of central Japan and their relationships with environmental factors.

The aim of this study was to improve our understanding of seasonal variations and the effects of physicochemical conditions on the bacterioplankton communities in two small rivers, the Moo and Nakayachi Rivers in the Himi region of central Japan. These rivers are inhabited by unionid freshwater mussels, which are used for oviposition by the endangered Itasenpara bitterling (Acheilognathus longipinnis). Water samples were collected every month between March 2011 and February 2012. Changes in bacterioplankton community structures were analysed using an approach that did not require cultivating the bacteria and involved PCR and denaturing gradient gel electrophoresis. The bacterioplankton community structures in the two rivers were similar in all seasons except winter. The bacterial sequences identified were dominated by typical freshwater Actinobacteria, Bacteroidetes, Cyanobacteria, α-Proteobacteria, and β-Proteobacteria bacterioplankton. Many β-Proteobacteria species were detected in all seasons, but Bacteroidetes species were dominant in the winter. The bacterioplankton community structures were affected by biochemical oxygen demand, chemical oxygen demand, chlorophyll-a concentration, water depth, and water temperature. These results provide a foundation for a more detailed understanding of the conditions that provide a suitable unionid habitat.

Paddy management for potential conservation of endangered Itasenpara bitterling via zooplankton abundance

Abstract In recent decades, the decline of biodiversity due to land-use changes in agricultural landscapes has become a central issue in ecology. Paddy management practices support animal diversity in agricultural landscapes. Using an endangered fish (the Itasenpara bitterling) inhabiting rivers connected to paddy fields as its subject, this study investigated two hypotheses: first, paddy field management affects the spatial distribution of Itasenpara bitterling in the adjacent river, and second, zooplankton and warm water supplied by paddy fields to the adjacent river are the primary factors influencing bitterling abundance. To model habitat suitability for the juvenile Itasenpara bitterling, rivers around paddy fields were examined using geographical information system tools and field survey methods in conjunction with a generalized linear model. The supply of zooplankton from paddy fields to the adjoining river positively contributed to juvenile Itasenpara bitterling abundance. This finding suggests that paddy management practices contribute to zooplankton abundance, and thus increase habitat suitability for juvenile Itasenpara bitterling.

Managing Water Levels in Rice Paddies to Conserve the Itasenpara Host MusselUnio douglasiae nipponensis

ABSTRACT Floodplains, considered hotspots of biodiversity, are used by a wide range of aquatic and terrestrial species. Over recent decades, floodplains have been modified for cultivation. This contributes to a loss of biodiversity, which has become a key issue in biological conservation in recent years. Paddy agriculture impacts substantially on the biodiversity of floodplains, including freshwater mussels and bitterlings. To model the habitat suitability for Unio douglasiae nipponensis, the itasenpara bitterling host mussel, we used geographical information system tools and field survey methods along with a generalized linear model to examine the environmental conditions of rivers surrounding paddy fields that were subject to water management practices. Water level fluctuations on the floodplains and artificial management of the water level in rivers around the paddy fields both influenced the spatial distribution of U. d. nipponensis, which suggests that traditional rice paddy management practices prov...

Population viability analysis predicts decreasing genetic diversity in ex situ populations of the Itasenpara bitterling Acheilognathus longipinnis from the Kiso River, Japan

To conserve endangered species, the maintenance of ex situ captive populations with sustainable genetic diversity is often required, in combination with population viability analysis (PVA). Since 2010, the threatened Itasenpara bitterling Acheilognathus longipinnis lineages in the Kiso region, Japan, have been maintained in ex situ rearing facilities to allow for conservation efforts. In this study, we obtained microsatellite data from DNA extracted from these captive populations to elucidate their genetic diversity and effective population size. The populations of several initial generations indicated a deviation from Hardy–Weinberg equilibrium, probably due to the limited number of extracted founder individuals analyzed. The effective population size of the captive population tended to increase over the course of generations, although the degree of genetic diversity tended to decrease highlighting the concern for the progression of inbreeding. Our prediction based on the PVA suggests that the maintenance of the captive population under the current conditions could lead to extinction of the Itasenpara bitterling in 50 years. In contrast, simultaneously increasing the carrying capacity and individual exchange among populations appears to enhance the effective management of captive Itasenpara bitterling populations.

Environmental factors affecting growth and survival of the Itasenpara bitterling in a small aquarium

Environmental factors affecting growth and survival of the Itasenpara bitterling in a small aquarium

Life history and reproductive ecology of the endangered Itasenpara bitterling Acheilognathus longipinnis (Cyprinidae) in the Himi region, central Japan.

The life history, reproductive ecology and habitat utilization of the Itasenpara (deepbody) bitterling Acheilognathus longipinnis were investigated in a lowland segment of the Moo River in Toyama Prefecture, central Honshu, Japan. Analysis of 1285 individuals revealed that the study population comprised a single size class, an age at maturation of 3 months and a life span of 1 year. On the basis of the growth pattern, the life cycle was divided into two stages: the juvenile stage, characterized by rapid growth, and the adult stage at which growth ceased. Spawning by A. longipinnis was recorded between early September and late October. Female A. longipinnis in the 0+ year age class began to mature when they reached a standard length (LS ) of 56·4 mm. Mature females had a large clutch size (maximum 273 eggs) and deposited highly adhesive and relatively large eggs (2·55 mm(3) ; major axis, 3·12 mm; minor axis, 1·22 mm) via a short ovipositor (mean length, 21·5 mm) into freshwater mussels. The embryos remained in the gill cavities of the freshwater mussels (used as a spawning substratum) and emerged as juveniles (LS , 9 mm). Habitat utilization during spawning was analysed using a generalized linear model. The best-fit model showed that three environmental factors (freshwater mussel availability, water depth and vegetation cover) were important variables for habitat utilization by A. longipinnis. Shallow areas (water depth, 250-330 mm) created for rice paddy management and areas with an abundance of cover were particularly effective for predator avoidance. These results suggest that maintenance of water level fluctuations corresponding with rice cultivation and the abundance of vegetation on the river bank (particularly avoidance of concrete revetments) is essential for conservation of this species under current practices for rice cultivation in Japan.

English

Wando and tamari are water bodies in the floodplain of a river and play an important role in maintaining valuable ecosystems. There are over 100 wando and tamari in the middle and lower basin of the Kiso River. An Acheilognathus longipinnis, Itasenpara Bitterling, which is designated as an endangered species, has been identified in these areas. The habitat of these valuable wando and tamari species is endangered by the development of large land plants around these reservoirs caused by river dredging for flood protection. Therefore, it is essential to collect detailed data about the habitat, hydraulic water flow, physical structures and landscape in order to preserve this species, but so far little attention has been given to water quality. The purpose of our research was to classify the water quality of wando and tamari water, especially ions, and to determine the water type based on its origin. Samples were collected at 10 wando sites and 15 tamari sites from August 2011 to February 2013 along the Kiso River. As our analysis by trilinear diagram shows, the waters of wando and tamari almost all belong to the category of Type I (Ca-HCO3), which forms in shallow aquifers. The two reservoirs that do not belong to Type I are presumably contaminated by drainage water from human activities.

Decreasing genetic diversity in wild and captive populations of endangered Itasenpara bittering (Acheilognathus longipinnis) in the Himi region, central Japan, and recommendations for conservation

Biodiversity is increasingly declining as a result of direct human impact and structural alteration of ecosystems resulting from changes in human life styles. Itasenpara bittering (Acheilognathus longipinnis), which has been maintained in floodplain and paddy fields, is a threatened cyprinid fish endemic to central Japan. To aid in the preservation of this species, information on genetic diversity and demographic variables in wild and captive populations was obtained using microsatellite DNA analysis. Temporal changes in genetic diversity and effective population size (N e) tended to be relatively stable in the wild Moo River population, although lower values were detected in the wild Busshouji River population, suggesting an extremely high risk of extinction in the latter. Captive populations derived from the Busshouji River population demonstrated significant genetic divergence even among intrapopulational cohorts, suggesting the influence of genetic drift caused by geographic isolation and small population size. Active maintenance of genetic diversity in captive population is a necessary part of conservation programs, as are continuous addition of wild individuals and replacement of individuals among captive populations. In addition, increasing or maintaining suitable floodplain areas and artificial habitats such as paddy fields might contribute to the conservation of genetic diversity in the Itasenpara bittering.

Strong population genetic structure and its implications for the conservation and management of the endangered Itasenpara bitterling

To infer the population genetic structure and genetic diversity of Itasenpara bitterling (Acheilognathus longipinnis), a cyprinid species endemic to Japan and distributed in only three specific regions, we investigated mitochondrial DNA variation. The distribution of the haplotypes among the three regions showed distinct geographic structure, and no common haplotypes were observed among regions. Analysis of molecular variance revealed a significant proportion of the genetic variance was partitioned among regions (93.1 %, P < 0.001), and pairwise estimates of DA and ΦST between regions also revealed strong population structure. Given the strong genetic structure and low genetic diversity within regions, we strongly suggest that each region should be treated as a separate unit in any conservation program and any inter-regional translocations should be avoided.

Patterns of genetic diversity of mitochondrial DNA within captive populations of the endangered itasenpara bitterling: implications for a reintroduction program

In this study, the level of genetic diversity of captive populations of the itasenpara bitterling (Acheilognathus longipinnis) was assessed to obtain information useful for successful captive breeding and reintroduction; this analysis was performed using mitochondrial DNA (mtDNA) sequence data. Comparison of the captive and wild populations showed low levels of genetic diversity within the captive population and significant genetic differentiation among the captive populations and also between the wild and captive populations, suggesting at chance effect during the founding process for the captive population and a subsequent genetic drift. Therefore, for successful reintroduction, it is important that the reintroduced population reflects all the genetic diversity available from the captive populations, and that releasing a large number of individuals that consist of all captive populations.

Host mussel utilization of the Itasenpara bitterling (Acheilognathus longipinnis) in the Moo River in Himi, Japan

Bitterling are fishes that use freshwater mussels for oviposition. The pattern of mussel utilization of an endangered bitterling species, Acheilognathus longipinnis, which spawned in autumn, was investigated in a lowland river. Six Unio douglasiae nipponensis (1.5% of total 388 individuals) hosted A. longipinnis embryos consistently in their outer gills, and they inhabited areas along the river bank where mussel density was relatively high on a less compacted mud substrate. Unexpectedly low rates of host utilization and the rare occurrence of juvenile (shell length, <40 mm) hosts (<0.8% of total individuals) suggest the need for greater attention to the conservation of A. longipinnis.

Low temperature requirement for embryonic development of Itasenpara bitterlingAcheilognathus longipinnis

The Itasenpara bitterling has an embryonic period up to 7 months, when the embryo experiences large seasonal temperature changes. We examined the temperature requisites for normal development during the embryonic stage. Fertilized eggs reared under any of the constant temperatures ranging from 5 degrees C to 30 degrees C did not achieve complete embryogenesis, and none reached the swim-up stage. The optimum temperature for normal embryonic development was found to be stage-dependent: 10-30 degrees C for fertilization, 15-25 degrees C for hatching, 5 degrees C for the requisite low temperature, 10-15 degrees C for eye pigmentation, and 20-30 degrees C for swim-up. These temperatures correlated well with the embryo's natural environmental conditions. Embryos raised at these temperatures sequentially grew normally, with 70% of the fertilized eggs achieving complete embryogenesis and, for the first time, developed to the swim-up stage. These results indicate that the low temperature, as required by the bitterling embryo, is an essential factor and correlates well with the embryo's natural ambient temperatures. Since the populations of Itasenpara bitterlings have been declining in Japan, this study is the first to provide additional information for successful artificial breeding of this endangered species.