Ecology

Systematic paleontologyOrder Rodentia Bowdich, 182131Family Ischyromyidae Alston, 187632Genus Asiomys Qi, 198733Asiomys dawsoni Qi, 198733Figure 3A–EMaterial. Fragment of right calcaneus (IVPP V24417), early Middle Eocene, Huheboerhe, Irdin Manha Formation, Erlian Basin, China.Description. The bone is damaged and most probably that of a juvenile as it shows loss of the tissue in the extremities of the bone such as the calcaneal tuber and calcaneal eminence, which are usually less calcified in juveniles. The bone is relatively large (Table 1), with an elongated calcaneal tuber and a relatively short body (Fig. 3A–D). The sustentaculum tali is partly damaged; it has a subcircular articulation facet, which was probably more extended craniocaudally than mediolaterally. The caudal margin of the sustentaculum tali is inclined cranially, similar to the condition seen in species A and more than in species B (Fig. 3A). The sustentacular facet overlaps about one-half of the craniocaudal reach of the ectal facet. The groove for the ‘spring ligament’ (sensu Szalay and Decker34), which runs along the medial edge of the sustentaculum tali, is poorly pronounced. Likewise, the calcaneal groove for the tendon of the flexor fibularis muscle is shallow and poorly marked, most probably due to poor preservation. The ectal facet is relatively wide and similarly shaped as in species B (below). The peroneal process is completely damaged.Table 1 Measurements (in mm) of ischyromyid calcanei from the early middle Eocene of the Erlian Basin, Nei Mongol, China.Full size tableFigure 2Linear measurements of the calcaneus. Abbreviations: AEW, ectal facet anterior width; BL, calcaneal body length; BW, calcaneal body width; CCL, calcaneocuboid facet length; CCW, calcaneocuboid facet width; CL, calcaneus length; CMT, calcaneus maximum thickness; CW, calcaneal width; EL, ectal facet length; TEW, ectal facet total width; TL, tuber calcanei length; TT, tuber calcanei thickness; TW, tuber calcanei width; TWM, tuber calcanei width in mid-length. (Figure created in Corel Draw X4 (v.14.0.0.567) by Łucja Fostowicz-Frelik).Full size imageFigure 3Ischyromyid calcanei from the early middle Eocene of the Erlian Basin, Nei Mongol, China. (A–E), Asiomys dawsoni (IVPP V24417), right calcaneus, juvenile?; (F–K), species A (IVPP V24416), right calcaneus, adult; (L–Q), species B (IVPP V24418), right calcaneus, adult. In: A, F and L, dorsal; B, G and M, medial; C, H and N, lateral; D, I and O plantar; J and P caudal; E, K and Q, cranial views. Explanatory line drawings (right side) show important morphological features. Note sustentacular facet marked pale yellow. Scale bar equals 10 mm. (Photographs taken by Łucja Fostowicz-Frelik; drawings created in Corel Draw X4 (v.14.0.0.567) by Łucja Fostowicz-Frelik).Full size imageThe calcaneal tuber is strongly compressed, but it resembles in shape those of species A and B. A long groove for the calcaneofibular ligament is impressed on its lateral side.The anterior plantar tubercle is large and swollen, similar to that in species A, and touches the brim of the calcaneocuboid surface. The latter, only slightly damaged laterally, is round in outline, without a distinct pit, and inclined about 20–30°.Systematic remark: The fossil was associated with Asiomys dentition found in the same spot. We attribute specimen IVPP V24417 to Asiomys dawsoni, based on this fact and its distinctive size (Asiomys being the largest rodent in the assemblage). Asiomys is the only ischyromyid rodent known from the basal strata of the Irdin Manha Formation of Huheboerhe.Genus indet.Species AFigure 3F–KMaterial. Right calcaneus (IVPP V24416), early Middle Eocene, Irdin Manha Escarpment, Irdin Manha Formation, Erlian Basin, China.Description. The right almost complete calcaneus of an adult specimen is relatively large (Table 1), comparable in length to the calcaneus of a coypu (Myocastor coypus) or Asiatic brush-tailed porcupine (Atherurus macrourus). The bone has a characteristically elongated calcaneal tuber and rather short body (Fig. 3F–I). The calcaneal tuber is quite slender in comparison with the structure found in the coypu and porcupines. The shape of the bone resembles most closely the calcaneus of Paramys wortmani (see35: Fig. 12B), although in Paramys the calcaneal tuber is more compressed mediolaterally.The sustentaculum tali is large and eminent, reaching far medially and tapering, although its medial end forms a blunt edge parallel to the long axis of the bone. This medial edge also bears a well-marked but not deep groove of the calcaneonavicular (or ‘spring’) ligament (Fig. 3G). The sustentacular facet (facies articularis talaris media in Fostowicz-Frelik36: Fig. 12B2) is round, with only slight anteroposterior compression. It occupies almost the whole dorsal surface of the sustentaculum, encroaching slightly onto the calcaneal body. In that it differs from Notoparamys and Paramys wortmani, which both have a much more medially placed sustentacular facet, which does not encroach on the calcaneal body. The range of the sustentacular facet overlaps less than one-third of the ectal facet (posterior facies articularis talaris in Fostowicz-Frelik36: Fig. 12B2) on its anterior and medial sides. The calcaneal eminence is slightly longer than that in Marmota and Sciurus, in proportions closer to that of porcupines and of similar size as in Paramys wortmani. The ectal facet is wide, long, and has a distinctly helical course, even more strongly marked than in North American ischyromyids (see Rose and Chinnery35: Fig. 12A). It is, however, inclined more strongly mediolaterally than in Notoparamys and Paramys, and faces strongly medially. On the dorsal side of the calcaneal eminence, posterolateral to the ectal facet, there is a flattened rough area (finely pitted), marking the place of attachment of the lateral collateral ligaments binding the distal fibula and the astragalus with the calcaneus and stabilizing the astragalocalcaneal joint.A calcaneal body is short and stocky with poorly marked tendon ridges at the dorsal surface. A large peroneal process is partly damaged at its lateral margin. The process is placed closer to the cuboid surface than the sustentaculum tali. The position of the sustentaculum tali and the proportions of the calcaneal body of specimen IVPP V24416 resemble rather closely the calcaneus of Paramys wortmani (see35).The calcaneal tuber is not ‘pinched’ at its dorsal side but moderately compressed, thus there is no coracoid ridge posterior to the ectal facet. At the lateral side of the tuber, there is a long groove for the calcaneofibular ligament running askew, towards the dorsal surface of the calcaneal tuber. The groove for the calcaneofibular ligament is more weakly expressed than in the North American paramyines and arboreal sciurids, but similar to that of Marmota.The caudal surface of the calcaneal tuber is subcircular (only slightly more extended dorsoplantarly than mediolaterally, see Fig. 3 and Table 1). The groove for the calcaneal tendon (= Achilles tendon) is deep and placed asymmetrically at the surface (Fig. 3J). Also, the medial process of the calcaneal tuber is much better developed and extending medially.The plantar surface of the bone is almost straight with a delicate flexure cranially to a well-developed plantar heel process (Fig. 3G). The anterior plantar tubercle is relatively large, swollen, but shifted medially, towards the sustentaculum tali. It is placed very close to the cuboid surface, almost touching its margin; such location and the medial shifting resembles the condition in some ground squirrels, e.g., Cynomys (see Fostowicz-Frelik et al.8: Fig. 3D–F). The anterior plantar tubercle is also somewhat flattened and inclined medially and forms a well-marked calcaneal groove for the tendon of the flexor fibularis muscle.The calcaneocuboid articular surface is semicircular, slightly wider mediolaterally than long dorsoplantarly, which distinguishes species A from Marmota and paramyines (see35). It is almost transversally positioned, not inclined, as in most of the rodent taxa (coypu and porcupines included), and gently concave; it is also confluent and level with the cuboid pit, forming one round surface at the cranial end of the bone.Genus indet.Species BFigure 3L–QMaterial Right calcaneus (IVPP V24418), early Middle Eocene, Daoteyin Obo, Irdin Manha Formation, Erlian Basin, China.Description The bone is complete, slightly larger than in species A (Table 1), matching in length the calcaneus of the coypu. Its overall structure is very similar to the calcaneus of Paramys (either P. wortmani or P. taurus, see Rose and Chinnery35: Fig. 12B, C). It has a long and strong calcaneal tuber and a relatively strong but short calcaneal body (Fig. 3L). The tuber is more compressed mediolaterally than in species A; thus, the caudal surface of the tuber is extended more dorsoplantarly than mediolaterally (Fig. 3P). The attachment for the calcaneal tendon forms a rounded concavity at the caudal side of the tuber, and is more horizontally and symmetrically located at the surface than in species A. The lateral surface of the calcaneal tuber bears a marked scar from the calcaneofibular ligament, although the scar is convex, not concave as in species A and in other compared taxa (e.g., Cynomys).The sustentaculum tali is large and round; it is located relatively close to the calcaneal body, not extending as far medially as in the North American paramyines (see35). It is slightly longer anteroposteriorly and located more caudally (closer to the ectal facet) than in species A. Thus, the sustentacular surface overlaps ca. one-half of the cranial part of the ectal facet. The medial edge of the sustentacular shelf bears a deep groove for the ‘spring ligament’.The ectal facet is large, equally wide throughout its length, long and helical, although its course is straighter along the proximodistal direction than in species A. The ectal surface faces mediodorsally, with a slightly weaker medial component than in species A. The dorsal surface of the tuber, just caudal to the ectal facet, is not typically ‘pinched’ into a sagittally oriented crest, but it is, nevertheless, more mediolaterally compressed than in the species A, similar to Marmota.The calcaneal body forms about one-third of the bone length. Its dorsal surface is carved by deep longitudinal marks indicating the position of the extensor digitorum brevis muscle (Fig. 3). A middle-size peroneal process is located cranially at the calcaneal body. It is strong and long anteroposteriorly, reaching almost the edge of the calcaneocuboid surface. Its lateral edge shows a deep groove for the tendon of the peroneus longus muscle, while its dorsal surface forms a groove for the peroneus brevis muscle tendon (Fig. 3). Species B differs from the ground squirrels in the shape and location of the peroneal process, which is less extended laterally in species B than e.g., in marmots, although it is relatively much larger than in the coypu and porcupines.The anterior plantar tubercle looks less swollen than in species A; it is located at the very margin of the calcaneocuboid surface and as in species A is shifted medially (Fig. 3O, Q). The calcaneocuboid surface is slightly inclined (ca. 25°) anteromedially, which distinguishes the bone from species A, Marmota, and Notoparamys, which all have the calcaneocuboid facet almost transversal and perpendicular to the long axis of the calcaneus. In this respect, the calcaneocuboid surface resembles more closely the calcaneus of Paramys taurus (Rose and Chinnery35: Fig. 12C). The calcaneocuboid surface is almost round, slightly wider mediolaterally, resembling that of species A. A relatively small calcaneal pit (extending only to a half of the anterior plantar tubercle base, see Fig. 3Q), smaller but deeper than in species A, forms a shallow sink at the medial side of the surface, cranially to the sustentaculum tali.PCA analysisA Principal Component Analysis (PCA) was performed based on 14 measurements of the calcaneus. The analysis included the calcaneal measurements of five ischyromyid species (two described here as species A and B, and three comparative species from North America) and 16 extant large rodent species (Supplementary Table S1). The extant taxa represent six basic types of locomotor adaptations found in rodents: ambulatorial (terrestrial generalists), amphibious (swimming), arboreal (tree climbing), cursorial (four-pedal runners), ricochetal (bipedal jumpers), and semi-fossorial (burrowing).Principal Components 1 and 2 (PC1 and PC2) represent 87.48% and 5.75% of the variance, respectively, whereas Principal Components 3–4 represent further 4% of the variance (Supplementary Table S2). All the variables are positively correlated with PC1 and their loadings are very balanced (Fig. 4). Thus, it implies that the PC1 represents a proxy for the size of the bone. PC2 is most strongly correlated with the length of the calcaneal body, BL (-0.86) and more weakly correlated with the width of the cuboid facet (CCW) and anterior width of the ectal facet (AEW), 0.31 and 0.21, respectively (Fig. 4). The correlation with the length of the calcaneal body is an especially important factor for estimating an animal’s vertical jumping ability; the species with elongated calcaneal bodies are generally better jumpers (see8,36). The strong negative correlation of the length of the calcaneal body in the second component is illustrated by grouping the species with a strong jumping locomotor repertoire (e.g., squirrels and chinchillas) towards the left side of the plot (Fig. 4). Incidentally, this phenomenon does not concern the calcanei of ricochetal species (see the position of Pedetes versus that of Sciurus and Chinchilla: Fig. 4), where the mechanics of a jump are differently realized, and the stabilisation and relative stiffness of the ankle joint plays the most important role (thus, the calcaneal body and calcaneal tuber are more similar in size).Figure 4Principal component analysis of 14 metric parameters of rodent calcanei. The morphospace including paramyid calcanei from Nei Mongol in yellow circle. Lines connecting all data points represent a minimum spanning tree (MST) based on a Euclidean distance matrix. The loadings of the Components 1 and 2 shown at the corresponding axes. Strictly fossil taxa marked in red and pink, extant in black. (Figure created in Corel Draw X4 (v.14.0.0.567) by Łucja Fostowicz-Frelik).Full size imageIn the plot of PC1 against PC2, ischyromyids do not cluster together. Instead, the PCA morphospace is divided into two (or even three) broad groups of ischyromyid locomotor adaptations: the ambulatorial species and those with more pronounced jumping or cursorial ability. Chinese taxa fall among typically large ambulatorial rodents, such as the coypu (Myocastor) and porcupines (Atherurus and Hystrix). Closest to them there is the North American ischyromyid Quadratomus, which is somewhat shifted towards the cursorial species and can be thus distinguished as differently specialized (more cursorial). Two other North American ischyromyids, Ischyromys and Reithroparamys, are grouped with Chinchilla and Ondatra, respectively, which may imply some jumping and slightly scansorial locomotor adaptations for Ischyromys and those of typical agile generalist species for Reithroparamys.Although the sample is limited, the results of the PCA analysis point to general differences in the structure of the calcaneus, and thus, locomotor specialisation, between Asian and North American ischyromyid species. Moreover, Asian species seem to differ less from each other than the North American ones do, reflecting the overall greater species diversity and coverage of a wider niche spectrum of the North American ischyromyids.Functional and paleoecological implicationsThe studied calcanei add to our knowledge on the functional aspects of locomotion of ischyromyid rodents. Proximal tarsal morphology has been recently used to interpret the locomotor behavior of some extinct rodents (see e.g.,8,37,38,39). In the scheme of locomotor categories of Samuels and Van Valkenburgh40, attributions proposed for early ischyromyids fit into generally terrestrial41, arboreal42 or a mixture of those two35.A relatively short calcaneal body, widely spread sustentaculum tali, and a large peroneal process observed in most ischyromyid species (including these studied herein) indicate rather poor cursoriality. Instead, their ankle joint structure allows for a large freedom of foot movements in different planes. A medially extended sustentaculum tali together with a long and helically twisted ectal facet indicate a large degree of sliding between the calcaneus and astragalus along their articular facets, which makes possible a great degree of foot torsion resulting in foot eversion and inversion. This effect is further enhanced by an extended calcaneocuboid facet that is gently concave and oriented perpendicularly to the long axis of the calcaneus in species A.Such adaptations are helpful for both clinging to branches and adjusting to uneven or inclined substrate during climbing. A great degree of freedom of movement may be helpful also during burrowing, when the hind legs are used to push forward loose soil out of a burrow or an animal is forced to maintain a crouched posture, when it digs with its forelegs and head. Nevertheless, as much as the calcaneal structure may suggest some burrowing ability in ischyromyids (see Rose and Chinnery35), the rest of the postcranial skeleton known from the more complete specimens of North American representatives41 does not support fossorial adaptations. In particular, a long tail in the pre-Oligocene North American (see e.g., Paramys or Reithroparamys in Wood41: figs. 8 and 44, respectively) suggests some arboreal adaptations or at least occasional climbing, as such a tail greatly enhances balancing on uneven terrain. In contrast, typically fossorial mammals have reduced tails43.The overall morphology of dental and mandibular remains16,18 of Asian ischyromyids is similar to that of their North American counterparts16,19. As complete or even partial postcranial skeletons are unknown for the Asian ischyromyids, we can surmise their general locomotor adaptations based on calcaneal morphology which, although not in striking contrast with their North American counterparts, shows some differences.Overall, the calcaneal morphology of Chinese ischyromyids is closest to that of ground squirrels and especially porcupines (both Atherurus and Hystrix) and the coypu; the similarity to the last one is supported also by the PCA analysis. The calcaneal morphology and proportions may therefore reflect their locomotion behavior as generalized terrestrials, with a somewhat limited ability to climb (a rare but observed behavior in Hystrix) and to dig burrows (as does Atherurus43). A transverse and gently concave calcaneocuboid facet of species A facilitates foot rotation along the long axis, useful on an uneven, rocky terrain or while traversing branches, when an animal needs a flexible foot for a better grip (see Chester et al.44). On the other hand, the lack of both a characteristically bent calcaneal tuber and posteriorly located peroneal process in all ischyromyids (except for Notoparamys, see Rose and Chinnery35) argues against the arboreal adaptations characteristic of tree squirrels. More

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Present results showed that Hilsa shad had low nucleotide diversity (0.001809–0.008811) like most of the Clupeiforms, e.g., Elongate ilisha (0.001–0.010), Tapertail anchovy (0.0011–0.0029) in Yangtze river and Japanese anchovy (0.0014–0.0090)44,45,46. Sea fish population had higher genetic diversity than anadromous population within same species or among same group47. Although, Hilsa and Kelee shad belonged to the same subfamily Dorosomantinae but Hilsa shad is anadromous in nature and Kelee shad is exclusively marine48. Because of this habit, nucleotide diversity of Hilsa shad was lower than Kelee shad (Hilsa kelee) (0.010337–0.014690)49. Correspondingly, marine Pacific herring (0.020)50 also had higher nucleotide diversity than Hilsa shad. There were several researchers also reported low nucleotide diversity of Hilsa shad population in the Hoogli, the Ganges and the Brahmaputra river of India10,17,18. Low genetic diversity suggested that only small portion of the total population had the scope of successful spawning. That might be associated with their long anadromous breeding migration journey. At that time huge numbers of individuals were caught in their long migratory routes by the fishermen. Frequent changing of spawning pattern is another reason of unsuccessful spawning51. Therefore, Government of Bangladesh should place some safety and protection actions including, public conscious, restriction on fishing gear, Hilsa fisheries management activities and proper timing of the fishing ban period.Previous studies on genetic population structure of T. ilisha were mostly based on allozymes, allele frequencies, microsatellite DNA markers and mitochondrial DNA regions: Cytochrome b (CytB), ATPase 6&8 (ATPase), 12 s and 16 s rRNA10,15,16,17,18. However, genomic data is more powerful marker than previous markers to present the history, evolution, population status and phylogeny of a fish. Recently, A study discover the population genomics and structure of Hilsa shad in Bangladesh waters based on genomic data at NGS platform by NextRAD sequencing, however they mistakenly assigned samples collected from the confluent of the Meghna River as the north-eastern riverine group19,20. Our study was also based on genomic data at the NGS platform. Conversely, we collected sequence data of 4434 nuclear genes applying a cross-species gene enrichment method22, to examine the genetic diversity and population status of hilsa shad from the Bay of Bengal, its estuaries and all possible lotic and lentic waters and two migratory cohorts.. This study provided a solid estimation of the population status of Hilsa shad using genome-wide data and to infer its genetic diversity.Result of the maximum likelihood IQtree and the population structure suggested that the fresh, estuarine and marine water of Bangladesh have a single population of Hilsa shad. In-addition DAPC, dendrogram and network on SNP loci analysis also represented the same trend. In the phylogenetic tree, samples of all locations were mixed together without making any specific cluster. In the population structure analysis, a single population was present with some admixtured individuals bearing small portion of genes from other group. Pairwise FST value between most locations were poor with non-significant P value (P  > 0.05), that support the deprived local population differences and homogeneity of this fish population throughout our studied locations. The hilsa shad population in Bangladesh might retrieve from a collapsed population. Once upon a time (upto first half of 1990s), this fish was most available and cheap fish in Bangladesh. Because of overexploitation and lack of proper management, the fish population was collapsed more than one decade. After that period, because of fishing ban period and public consciousness (first imposed in 2011), the population started to increase. Hilsa fish production in Bangladesh has doubled in a decade from 2006–2007 (279,189 MT) to 2017–2018 (517,189 MT)4,64. This fact probably caused low genetic diversity and divergence among populations of hilsa shad in the Bangladesh waters.Bangladesh has diversified fresh water habitats for Hilsa shad migration including main river system, coastal and freshwater small rivers, hill stream rivers, haors etc. but anadromous migration of this shad starts from same marine water body, the Bay of Bengal, which is their living ground. Furthermore, this fish has highly migratory nature among marine, estuarine and fresh water bodies. Therefore, it is difficult to draw a conclusion that there is more than one population in this water system. Low variation among groups and among population within groups also did not support more than one population. FST value between most of the locations was poor with non-significant P value, which suggested that the population differences were not significant. Although in some cases, P value was significant but due to their poor FST value that did not provide strong support of local population differences. Here present findings of this study were supported by the findings of some previous researchers who represented the single gene pool or stock of this species in the Bay of Bengal with a substantial gene flow18,52,53.All of the spawning grounds of Hilsa shad were identified in the coastal areas of Bangladesh especially at the lower stretches of the Meghna, the Tetulia, the Ander Manik and the Shahabazpur River e.g., Hatia (Moulavir char) Sandwip (Kalir char) and Bhola (Dhal char and Monpura)6,21. However, migratory plan is mainly initiated during the spawning season, which is activated with follow of fresh water runoff from the inland rivers, and naturally it occurs with the commencement of the south-west monsoon and consequent flooding of all the major rivers draining down to the upper Bay of Bengal and there are no considerable differences in any context. Isolation of spawning ground is an important factor for population differentiation11. Due to presence of un-alienated spawning grounds, it is less feasible to draw population differences of Hilsa shad in the upper streams of different rivers and in their living ground, Bay of Bengal. Therefore, the unique spawning grounds and sole major migratory down-stream route strengthen the presence of single population in all over the Bangladesh water without any significant population clusters. Without specify exact spawning grounds for every cluster, it is unrealistic to draw several clusters in this population.Hilsa population studies in Indian part across the Hoogli, the Bhagirathi, the Ganges and the Brahmaputra Rivers also suggested single and genetically homogeneous population in Indian part10,17,18. Hilsa shad population of the Hoogli-Bhagirathi river system and Hilsa stock of Bangladesh water used same natal habitat, Bay of Bengal. Moreover, the River Ganges is the upstream of the Padma River (Bangladesh) and the Bhagirathi River (India) as well as the Brahmaputra is the upstream of the Jamuna River (Bangladesh). Most of the Hilsa shad of River Ganges comes from the Padma River and as the same way the Brahmaputra river has no other significant source of this fish except the Jamuna River. So genetic homogeneity and unique population across these rivers of Indian part also supported the Hilsa shad’s single population in the Bangladesh water.Nevertheless, Rahman and Naevdal (2000) based on allozymes and muscle proteins as well as Mazumder and Alam (2009) based on mitochondrial D-loop region figured out more than one Hilsa population in Bangladesh waters15,54. Rahman and Naevdal (2000) mentioned two populations: 1. Marine and 2. Estuary and fresh water but they processed without explaining how this highly migratory species was separated into two distinct cohorts. Mazumder and Alam (2009) divided the population into two clusters like previous study but poor pairwise FST value between two groups showed that there were no differences between fresh water and marine-estuarine locations. Recently Asaduzzaman et al. (2020) reported three clusters in the Hilsa population in Bangladesh waters, first one was in marine and estuarine waters and another two belonged to north–western riverine (turbid freshwater) and north-eastern riverine (clear freshwater) ecotypes20. Existing of a single population, the most likely assumption from the present research varied with their findings. Our result suggested that as a highly migratory species, Hilsa shad is incapable to belong to more than one population when sampled at different sections of their migration route. Our postulation is the presence of single cluster in the Bangladesh water because all water bodies are almost connected to each other, raising high rate of gene flow and created large population size. Western and eastern river systems of Bangladesh have immaterial dissimilar water quality (e.g., turbidity) but this is not enough to make population differences of Hilsa shad since they migrate and start their life from same spawning grounds and used almost same route across the lower stream and coastal estuaries during their breeding migration. Asaduzzaman et al. (2020) reported that samples of the Meghna river (MR) was included in the north-eastern riverine (clear freshwater) ecotypes by DAPC and neighbor-joining tree analysis20. However, their sample collection site (MR) was located in the common migratory route for north–western riverine (turbid freshwater) and north-eastern riverine (clear freshwater) ecotypes. Therefore, this site should be representing the samples of both ecotypes rather than specific one.If we draw several specific populations or clusters in the upper streams of Bangladesh that means we had the scope to find this shad in the freshwater all over the year round. However, in the freshwater of Bangladesh, this fish was available in the summer (June–October) and winter season (January-March) only; these were related to their summer and winter migration respectably55. If one or two groups of this fish, continue their complete lifecycle in the freshwater (Western/Eastern part of Bangladesh) that states the assurance of continuous supply of this fish almost year round. However, the original scenario does not support this hypothesis. Finally we can conclude that, only one population of this fish inhabit in the Bangladesh waters without any instance of different populations and clusters (2–4) but in some specific locations, they had some particular characteristics. The Bay of Bengal is their main living ground, at the time of their breeding they come to the freshwater upper streams, spawn in the estuaries and finally return to the sea. Therefore, using all the same ecosystems (sea, estuary and freshwater rivers) in a cyclic fashion is essential to support their life cycle, which certainly pushes all the individuals to belong a unique population.In the population structure analysis, only one population of Hilsa shad was identified with some admixtured individuals (32%) containing partial genes from other population in the water bodies of Bangladesh. The mentioned other population might not represent the Hilsa population of the Hoogly and Bhagirathi river system, India because, the Hilsa shads of both migratory routes of Bangladesh and India showed genetic homogeneity10,17. The Ganges and Brahmaputra rivers of Indian part are the upstream of the Padma and the Jamuna river of Bangladesh and might be belonged to the same population. However, Hilsa population of the Arabian Sea was genetically heterogeneous from the Bay of Bengal18 and those different population genes of admixtured individuals might come from the Arabian Sea by oceanographic dispersion. Once (almost 18,000 years ago) the Arabian Sea had a close connection with the Bay of Bengal through the Laccadive Sea, the Gulf of Mannar and the Palk Bay. Therefore, this likely was an easy way for oceanographic dispersion of Hilsa shad between these two water bodies. After that period, a bridge of limestone shoals, coral reefs and tombolo called as ‘Ram Bridge’ or ‘Adam’s Bridge’ (about 48 km) originated between Pamban Island off the south-eastern coast of Tamil Nadu, India, and Mannar Island, off the north-western coast of Sri Lanka 56,57. Sarker et al. (2020) also mentioned that type of oceanographic dispersion between these two water bodies for another Clupeid fish species, Hilsa kelee49. The Irrawaddy, the Naaf and the Sittang River of Myanmar were also regarded as another important route for Hilsa migration6,58. There is also a possibility of inflowing of these different genes of other population from such population. Still there is no population structure study was conducted in the Myanmar part. Therefore, there is no scope to compare those admixtured individuals with the Hilsa population of Myanmar. However, for completing the full scenario, the Hilsa population of Myanmar also claims research attention in population genomics field.In the present study, Samples of both migration cohorts (summer and winter) were studied. The maximum likelihood IQ tree, population structure and DAPC suggested that samples of both migration cohorts were homogenous. Similarly, Jhingran and Natarajan (1969) and Ramakrishnaiah (1972) also did not find any significant temporal population differences in their previous studies59,60. Dwivedi (2019) found morphometric variations between seasonal migrants of Hilsa shad from Hooghly estuary, India using geometric morphometrics (GM) data61. They explained that these morphotypes might be related to the food availability and temperature fluctuation of summer and winter season but they did not incorporate that to the genetic level of the population. Quddus et al. (1984) reported two seasonal migratory populations of Hilsa shad in Bangladesh water based on spawning, fecundity and sex ratio8. Based on our findings and previous studies we can conclude these mentioned seasonal cohorts might be associated with their food availability and breeding rather than genome level.Hill stream river and haor were two important and unique ecosystems for fish diversity in Bangladesh, they belong to the unique characteristics in the ecological factors as well as fish diversity62,63. Infrequently Hilsa shad use these two water bodies as their migratory routes. Samples were collected from the Shomeswari River and the Dingapota Haor, Mohanganj as the representatives of hill stream river and haor population respectively. However, Hilsa shad of these two exclusive water bodies were similar to the samples of the some other fresh water bodies (i.e., CM, CN and MG) as they were belonging to the Hilsa population without any admixtured individuals. Samples of SS do not have any significant P value with other locations whereas MO samples had significant P value with five other locations but having poor FST value with three locations (i.e., BL, PP, MG). MO samples had only mentionable FST value with MP (estuarine) and MK (marine), which might be the result of differences in water quality of these two water bodies. In DAPC, phylogenetic tree and in network, the samples of hill stream river and haor failed to make any unique cluster or monophyletic clade that represent they are also the part of single unique Hilsa population of Bangladesh waters.Main migration was occurred through the Meghna river estuary, which is connected to the Padma, Meghna and Jamuna river system. However, there are some other alternative routes through some small coastal rivers e.g., the Pashur, the Bishkhali, the Balaswar, the Kocha river, which are connected to the Padma river through the Modhumati and the Gorai river. These coastal rivers passed through or beside the world largest mangrove forest Sundarban. Thus, these two routes are ecologically different from each other. Samples of these two routes have some genetic differences, because most of the locations (MK, CF and BL with PP and KN) of these two estuarine routes had significant P value, but their FST value was not satisfactorily high to make population differences. Ecological differences of these two routes might be played an important role to create this type of slight differences among them. Therefore, these scenarios were not significant enough to describe noteworthy differences in the population level, but may make a sign of upcoming population differences. More

The development of massive sequencing has provided a relatively inexpensive method to obtain the transcriptome of a species. Taking advantage of this technique, we used a previously obtained transcriptome of P. acuta to identify 18 genes related to different pathways of interest in ecotoxicology and then examined how exposure to phthalates changed the transcription of these genes. The processes of interest include DNA repair, the stress response, detoxification, apoptosis, immunity, energy reserves, and lipid transportation. There is a growing interest in combining ecologically relevant endpoints with biochemical and molecular parameters to seek a more integrative analysis. In this sense, increasing the number of described genes will allow for the design of standard arrays that could be used in combination with toxicity tests. In this way, initiatives such as the Adverse Outcome Pathway wiki24 will increase its relevance in assessing old and new compounds and provide putative mechanisms of action to explain the differences to the animals’ specific physiology. Furthermore, increasing knowledge at the molecular level in P. acuta supports its use as a representative of freshwater gastropods in toxicity analysis. There is a lack of model freshwater mollusks, which is one of the animal groups whose pollution response is currently less known.The 18 newly identified genes evaluated in this work show homology with those previously described in other species, as expected, mainly with the freshwater snail Biomphalaria glabrata, which belongs to the Planorbidae family. rad21 and rad50 are both involved in DNA repair: rad21 is an essential gene encoding a DNA double-strand break repair protein21, and rad50 is a member of the protein complex MRN (including Mre11, RAD50, and Nbs1) that functions in DNA double-strand break repair to recognize and process DNA ends as well as a signal for cell cycle arrest25. There is very little information about these genes in mollusks, with only one report in Crassostrea gigas for rad5026. The relevance of these genes is that their detection can be combined with other methodologies, such as the comet assay, to perform an integrated study to determine whether a compound is genotoxic and whether the organism has the ability to compensate for the damage.The Cat and SOD Mn genes allow us to evaluate the status of oxidative stress. Oxidative stress analysis is usually focused on biochemical parameters, such as enzyme activity. However, it should also include a transcriptional activity study because it can provide additional information about the mid- and long-term responses. Protein turnover can also be relevant in the response, especially in chronic exposure to toxicants. Detoxification mechanisms are also important to assess the response to toxicants. GST activity is one of the most used methods to assess detoxification27, but it does not differentiate between the members involved. The situation is similar regarding cytochrome P450s, which show high diversity with many roles in the cell28. Our identification of the Cyp72a15 gene increases the number of cytochromes 450 s described in P. acuta. Evaluating changes in these genes can help to elucidate how the organism can process the toxicants.The sHSP17.9 and HSC70-4 genes extend the battery of genes available to assess the stress response of P. acuta. sHSP17.9 is difficult to match with other species’ genes because while they all have an alpha-crystallin domain, there is no other sequence that presently allows for homology to be established. Additional functional studies will help to search for homology. It is worth mentioning that HIF1α offers a new aspect of stress related to hypoxia29. The stress response mainly focuses on the canonical heat shock proteins, so other mechanisms involved in specific stresses, such as hypoxia, are usually neglected. With the identification of HIF1a in P. acuta, researchers can evaluate the effect of a toxicant on oxygen intake in this species.The remaining identified genes allow for the analysis of pathways that can also be altered by toxicants, like apoptosis (AIF3), the immune system (ApA), energy reserves (PYGL), and lipid transport (ORP8). To our knowledge, in this study these genes have been analyzed for the first time concerning pollution in freshwater mollusks. The last three genes, DNMT1, KATB6, and HDAC1, are involved in epigenetic mechanisms. There is increasing evidence that epigenetic regulation is one of the long-term effects of toxicants. However, the genes involved in this process in invertebrates are still poorly represented in toxicity analysis. The description of these three genes opens the possibility of analyzing their role in the epigenetic response and its relevance in the transgenerational effects that have started to be described with different toxicants30,31,32.Plastics in the environment are a growing problem. During the degradation process, the polymers themselves and the compounds used as additives, including phthalates, are released. Hence, the presence of phthalates is increasing in the environment5,33,34. We analyzed three phthalates in this work, namely BBP, DEP, and DEHP; they showed a differential impact in P. acuta. DEP and DEHP, did not alter any of the mRNA levels. Researchers have described previously that both phthalates can alter the physiology of invertebrates16,35,36,37,38, including mollusks39,40,41. Other phthalates can also alter development and growth, which could be related to the endocrine-disrupting activity described for those chemicals. The molecular mechanisms involved are still under investigation, but some data are available. In the clam Venerupis philippinarum, DEHP alters the immune response40. In H. diversicolor, DBP affects oxidative stress, lipid and energy metabolism, and osmoregulation17. In other invertebrates, including Chironomus riparius42, Drosophila melanogaster43, and Caenorhabditis elegans15, phthalates alter endocrine pathways. The changes affect the ecdysone response as well as the expression of insulin-like peptide. Other pathways are also affected by phthalates, such as oxidative stress and detoxification routes44 and the stress response14. Finally, in C. elegans, exposure to environmentally relevant concentrations of diethylhexyl phthalate produces genomic instability by altering the expression of genes involved in DNA repair during meiosis37. It is clear then that phthalates can have a broad spectrum of actions in the cell, with a significant alteration of metabolism but primarily affecting oxidative stress and the endocrine system.The previous studies performed in mollusks have revealed alterations in several physiological processes; the analyzed molecular mechanisms mainly involved oxidative stress and immunity17,41. A recent review of the impact of phthalates on aquatic animals summarizes the effects observed, suggesting that activation of the detoxification system (cytochrome P450s) and endocrine system receptors of aquatic animals cause oxidative stress, metabolic disorders, endocrine disorders, and immunosuppression8. It would activate a cascade response that could cause genotoxicity and cell apoptosis, resulting in the disruption of growth and development. Considering this, the absence of a response observed in P. acuta exposed to DEP and DEHP is striking. The differences observed can be assigned to the type of analysis (molecular vs. physiological), the exposure time (1 week vs. a few hours or days), the concentration used (μg/L vs. mg/L), and evidently, the species used. Additional research will help elucidate the differential response in P. acuta compared with other organisms. However, it is essential to highlight that the obtained results suggest that P. acuta can manage the environmentally relevant doses of DEP and DEHP used in this work. This species may be less sensitive to these phthalates, but this eventually will require further research, including the use of other methodological approaches, to confirm it.In contrast to DEP and DEHP, BBP showed a marked effect: it increased the mRNA levels of almost all the analyzed genes. It is essential to consider that most studies on invertebrates that involve transcriptional activity analysis use arthropods and short exposure times14,44,45,46. Limited data are available on mollusks and, usually, they are marine representatives40,47. To our knowledge, this is the first study on a freshwater snail that shows that BBP can produce a substantial effect on cell metabolism. Several of the altered pathways can explain, in some way, the effects observed in other organisms, like DNA repair by the alteration of rad21 and rad50, which are related to DNA damage, or the alteration of the genes involved in histone and DNA modification (KAT6B, HDAC1, and DNMT1), which are related to epigenetic regulation. Apoptosis, which phthalates can also alter, also seems to be modulated in P. acuta by altering the AIF3 and the casp3 genes. Furthermore, the three phases of the detoxification could be acting since the genes tested (three cytochrome P450s, three GSTs, and MRP-1) were upregulated.Genes involved in oxidative stress and the stress response were also altered, as shown by the changes in the mRNA levels of Cat, SODs, stress proteins, and the hypoxia-related transcription factor genes. These changes support the alteration of oxidative stress, the stress response, and detoxification, backing previous analysis and adding new insight about the mechanisms involved in modulating these processes. In this sense, the absence of changes in GSTm1 supports a differential role for each GST family member in the response to toxicants. The altered acetylcholinesterase mRNA level also suggests effects in the nervous system, requiring additional research to elucidate the damage to the central nervous system. Finally, the alteration of PYGL, ApA, and ORP8, involved in energy metabolism, immunity, and lipid transport, respectively, shows that P. acuta responds to BBP in a way that has been observed in other organisms. In summary, the present gene profile obtained in response to BBP in P. acuta supports the proposed mechanisms and cellular processes in studies with other animals8. Immunity, oxidative stress, the stress response, detoxification, apoptosis, epigenetic modulation, DNA repair, lipid metabolism, and energy metabolism are modulated. The nervous system could also be affected. Of note, some genes showed differences in transcription based on the phthalate concentration. These findings suggest there are subtle differences, and additional kinetic analysis is required to elucidate early and late activated genes and the relevance of the damage for the population’s future.The obtained results are in line with previous studies in other organisms, which have confirmed that BBP can induce different types of damage such as apoptosis48, genotoxicity49, oxidative stress50, stress response activation45, or endocrine disruption14. Although there are studies in invertebrates showing the impact on development and other physiological processes39,51, most of them did not focus on the putative mode of action, with only a few of them trying to delve into the response mechanisms. Here we have shown that BBP can extensively affect the cell transcriptional activity in P. acuta. These results could be considered to reflect specific alterations on these pathways. This scenario would mean that BBP is the most active phthalate in P. acuta, with a broad spectrum of action and a potential effect on many pathways. However, the more probable picture is something that has been recently proposed: alterations in the oxidative stress response and the endocrine system cause a cascade of responses that affect different pathways and ultimately block growth and development8. It is relevant to keep in mind that BBP is a known endocrine disruptor47. A recent study in Daphnia magna provides some insight. Specifically, RNA-Seq revealed that genes involved in signal transduction, cell communication, and embryonic development were significantly down-regulated, while those related to biosynthesis, metabolism, cell homeostasis, and redox homeostasis were remarkably upregulated upon BBP exposure46. Although the organism and the stage analyzed are different from our study, those results support the idea that BBP can simultaneously alter multiple pathways, and it fits better with the regulatory role of the endocrine system and the extensive affection by oxidative stress.As stated before, the results obtained in this work show that DEP and DEHP had no apparent effect to P. acuta after 1 week exposure to environmentally relevant concentrations. However, BBP showed a strong effect. The difference in response could be due to several reasons that need to be explored in future work. One possibility is the structure of each compound. In this sense, BBP has two benzene rings while DEP and DEHP have only one. This factor could determine the biological activity of these compounds. Another possibility is that DEP and DEHP have effects earlier than the time studied, and the cell returned to the basal state, being able to process and remove the compounds. Finally, it cannot be dismissed that DEP and DEHP are not toxic to P. acuta, at least at environmentally relevant concentrations. In any case, BBP alters the metabolism of this species and produces a broad impact on different pathways. Additional research should be done in P. acuta and other freshwater species to determine the impact on organisms based on the freshwater ecosystem food web. More

Volcanic ash soilWe used commercially available Kanuma soil as volcanic ash soil (fine-grained pumice, Akagi Engei Co., Ltd.) for growth experiment 1. Kanuma soil is a fully weathered pyroclastic fall from the eruption of Mt. Akagi 44,000 years ago19. The soil contains 30.8% aluminum (allophane and imogolite) and 1.4% iron (ferrihydrite)20. For growth experiment 2, we used three natural volcanic ash soil types—immature soil of pumice (Kanuma soil, C horizon), as well as mature soils of andosol (A–B horizon) and topsoil (the surface of andosol, P to A horizon)—collected from a riverbed in Kanuma City (36°35′ N, 139°44′ E; 200 m a.s.l.), central Japan, where the vegetation is a cypress forest. This place is managed by the Kanuma Civil Engineering Office. The topsoil was collected at a depth of approximately 0–10 cm from the soil surface after removing the fallen leaves on the soil surface. The andosol layer, typically distributed at a depth of approximately 10–75 cm, was collected from a depth of approximately 10–30 cm. Below the andosol layer, the Akadama soil layer is distributed; further below, the pumice Kanuma soil is distributed. The pumice was collected approximately 50 cm under the Akadama layer.Temporal information on soil formation was confirmed by direct radiocarbon dating of the soil samples. After removing soil carbonate with 1.0 M HCl, the total organic fraction was analyzed using an accelerator mass spectrometer (0.5MV compact AMS system, NEC) at the laboratory of radiocarbon dating, University of Tokyo. Conventional radiocarbon age after correction of isotopic fractionation with δ13C values was calibrated to a calendar date with the calibration dataset IntCal1321.The elemental analysis of total phosphorus, nitrogen, and carbon in the soil samples was performed by Createrra Inc. (http://www.createrra.co.jp/english/top.html).Plant speciesOn the volcanic ash soil of Mt. Fuji, Japan’s highest volcano, vegetation in primary succession generally changes from herbaceous plants such as Fallopia japonica (Houtt.) Ronse Decr. var. japonica to nitrogen-fixing alder plants, and finally to non-nitrogen fixing Betula ermanii Cham22,23. Hence, we used three species—F. japonica, the alder species Alnus inokumae Murai et Kusaka, and B. ermanii—owned by and grown in our research institute, Nikko Botanical Garden, for the growth experiments. Experimental research on these plants, including the collection of plant material, comply with the relevant institutional, national, and international guidelines and legislation.Litter incubation experimentSamples (1 g) of F. japonica litter leaves—collected upon leaf fall on an autumn day, dried at 80 °C for at least 48 h, and then crushed—were placed in cultivating tubes (n = 5). Then, 5 g of wet soil from the Nikko Botanical Garden (36°45′ N, 139°35′ E; 647 m a.s.l.) in Nikko, central Japan, was added to 500 mL of water and stirred (solution I). As inoculation, 0.1 mL of the supernatant of solution I was added to the tubes24. Considering that the amounts of phosphorus and nitrogen in the solution I were approximately 0.003 mg/L and 0.3 mg/L, respectively, they were determined to have not affected the initial value (t = 0). Next, 2 mL of water was added to the tubes, which were then kept at 30 °C. The tubes were left open to maintain an aerobic environment. The efflux of phosphorus and nitrogen from the leaves was measured every week for ten weeks. For these measurements, 5 mL of water was added and the tube was centrifuged for 10 min (solution II). The supernatant of solution II was then used for phosphorus and nitrogen measurements, and the residue was continuously kept at 30 °C.Growth experimentsGrowth experiments were conducted in an open-type greenhouse in Nikko Botanical Garden. The greenhouse is only vinyl on the ceiling and good ventilation to keep the temperature constant. The mean monthly highest and lowest temperatures and the monthly precipitation observed in the botanical garden during the cultivation period are provided in Table 1. In the growth experiments, irrigation with tap water was provided to the plants and litter leaves in the morning and evening. The phosphorus and nitrogen concentration of the tap water were approximately 0.03 mg/L and 0.25 mg/L respectively.Table 1 Nikko botanical garden weather data (May–October 2019).Full size tableGrowth experiment 1: Comparative experiment on the growth of plant species with and without litterThe seedlings used for the experiment were from the species F. japonica, A. inokumae, and B. ermanii. A similar seedling size was used for each plant species. Seedlings of A. inokumae coexist with N-fixing actinomycetes.Six plants per species were collected before cultivation (t = 0) and dried in an oven at 80 °C for at least 48 h to measure the dry weight. There were four experimental groups for each species: a control (Con), a nitrogen addition (N: 10 mM NH4NO3), a phosphorus addition (P: 10 mM NaH2PO4), and a nitrogen and phosphorus addition (NP: 10 mM NH4NO3 + 10 mM NaH2PO4). Once a week, 50 mL of each nutrients was added to a 0.25-L garden pot. To verify whether the addition of litter (denoted by +) improved plant growth, litter leaves of F. japonica were placed on the soils. To verify if nutrients leached from litter sustained plant growth, we also combined nutrient and litter additions (Con+, N+, P+, NP+). When nutrients were added to the soil once a week, litter bag was removed before fertilizer application and returned after that.To reproduce how litter is deposited and supplies nutrients on volcanic ash soil in primary succession, F. japonica litter was collected in Nikko in the autumn of 2018 and dried at 80 °C or 2 days or more (the same litter was used in incubation). Approximately 9 g of litter leaves was packed in a tea mesh bag25 to prevent it from flying in the wind and placed on the soil surface of the garden pots. As indicated by the equation below, the amount of litter added to the 8 × 8 cm (0.0064 m2) garden pot used in this experiment amounts to approximately three years of litter production when converted to the amount of leaf litter in a 15-year-old alder forest, i.e., about 430 g/m2 per year26.$$frac{9,g}{{430frac{g}{{ m^{2} }} yr times 0.0064 m^{2} }} cong 3.3 yr$$Six seedlings per group of A. inokumae and B. ermanii were cultivated for approximately 2 months (June 7–August 22, 2019) and 12 seedlings per group of F. japonica were cultivated for about 1 month (September 10–October 15, 2019). The experiment was stopped after 1 month for F. japonica as it grew rapidly in 2 nutrient conditions (NP, NP+) and the roots overflowed from the garden pot. At the end of the experiment, growth was evaluated by measuring dry weight after drying seedlings at 80 °C for at least 48 h. Subsequently, the total phosphorus and nitrogen content of the dried seedlings were also measured (chemical analysis).The mass of phosphorus leached from litter during the cultivation period was calculated from the difference in the phosphorus contents of the litter before and after cultivation.Growth experiment 2: Comparative experiment on plant growth with old organic matterEight F. japonica seedlings were cultivated in three different soil-types (pumice, andosol, and topsoil, as mentioned above) under three experimental conditions (Con, N, P, same nutrition as growth experiment 1) from May 29 to July 12, 2019. These plants were then harvested and oven-dried at 80 °C for at least 48 h to measure dry weight. Subsequently, the total phosphorus and nitrogen content of the seedlings were also measured (chemical analysis).Chemical analysisPhosphorusWe used the dry destruction method to pretreat total phosphorus measurements in plant tissue27. A sample of the plant (0.05 g) was burned at 550 °C for 1 h. The plant ash was dissolved in 10 mL of 2 M H2SO4 and shaken for over 16 h; then, the solution was filtered. The filtrate was diluted at a 1:10 ratio with tris(hydroxymethyl)aminomethane (pH 8.0).The soil for available phosphorus were pretreated by Truog’ s method28. The soil (0.05 g) was dissolved in 10 mL of 0.002 M H2SO4, shaken for 30 min, and the solution was filtered. The filtrate was diluted at a 1:10 ratio with water.The amount of phosphorus in the sample solution was measured by the molybdenum blue colorimetric method29.NitrogenThe total nitrogen in plant tissue was measured using an elemental analyzer (EA; Vario Macro cube, Elementar, Germany). A few milligrams of the dried plant sample were placed in a tin capsule for EA combustion. EA carried out sample combustion and N2 separation/detection from the combusted gases and provided us with nitrogen contents.The soil sample preparation for available nitrogen measurements was based on the incubation methodology30. Half of the sampled soils were analyzed fresh, and the other half incubated for four weeks at 30 °C before analysis. 2 M KCl (20 mL) was added to 2 g of the soil sample; the solution was shaken for 1 h and filtered. The filtrate was collected, and the volume of nitrogen was measured by indophenol blue absorptiometry after reducing all to ammonia using Pack Test WAK-TNi (Kyoritsu Chemical-Check Lab., Corp, Tokyo, Japan). Available nitrogen was taken as the difference in the concentration of inorganic nitrogen (NO3-N, NO2-N and NH4-N) between incubated and fresh soil.Statistical analysisAll statistical analyses were performed with EZR31 (Saitama Medical Center, Jichi Medical University, Saitama, Japan), which is a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria). More precisely, it is a modified version of R commander designed to add statistical functions frequently used in biostatistics. The figure’s values are mean ± SE. Intergroup differences for nutrition conditions in soil, and soil-types were evaluated using non-parametric Kruskal–Wallis with post-hoc Steel–Dwass tests. In addition, comparisons between with or without litter were evaluated using two-tailed Mann–Whitney U-test. p values are * p  More

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CORRESPONDENCE
01 June 2021

French vote for river barriers defies biodiversity strategy

Simon Blanchet

 ORCID: http://orcid.org/0000-0002-3843-589X

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Pablo A. Tedesco

 ORCID: http://orcid.org/0000-0001-5972-5928

1

Simon Blanchet

National Centre for Scientific Research (CNRS), Moulis, France.

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Pablo A. Tedesco

French National Research Institute for Development (IRD), Toulouse, France.

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Europe’s rivers are disrupted by more than one million artificial barriers, including small dams, weirs and fords (see, for example, B. Belleti et al. Nature 588, 436–441; 2020). There is strong scientific evidence that such obstructions can harm both hydrological and ecological systems, yet the French parliament has voted to leave them in place (see go.nature.com/3ck9mxq).By limiting the transfer of sediments and movement of organisms, these small barriers create a succession of reaches of warming, stagnant water that threatens freshwater biodiversity (M. R. Fuller et al. Ann. NY Acad. Sci. 1335, 31–51; 2015). Dismantling such small barriers is the most effective way to restore river connectivity and is now a worldwide objective (J. E. O’Connor et al. Science 348, 496–497; 2015).The French parliament’s decision flies in the face of the EU Biodiversity Strategy. It also has no economic justification. Most small barriers cannot generate hydroelectricity and those that can contribute less than 1% to France’s electricity (see go.nature.com/2rphjch).In our view, the fate of each barrier should be decided by balancing its ecological benefits and socioeconomic costs.

Nature 594, 26 (2021)
doi: https://doi.org/10.1038/d41586-021-01467-0

Competing Interests
The authors declare no competing interests.

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