A roadmap for the conservation of freshwater mussels in Europe.

Europe has a long history of human pressure on freshwater ecosystems. As pressure continues to grow and new threats emerge, there is an urgent need for conservation of freshwater biodiversity and its ecosystem services. However, whilst some taxonomic groups, mainly vertebrates, have received a disproportionate amount of attention and funds, other groups remain largely off the public and scientific radar. Freshwater mussels (Bivalvia, Unionida) are an alarming example of this conservation bias and here we point out six conceptual areas that need immediate and long-term attention: knowledge, threats, socioeconomics, conservation, governance and education. The proposed roadmap aims to advance research, policy and education by identifying the most pressing priorities for the short- and long-term conservation of freshwater mussels across Europe.

Regional impacts of warming on biodiversity and biomass in high latitude stream ecosystems across the Northern Hemisphere.

Warming can have profound impacts on ecological communities. However, explorations of how differences in biogeography and productivity might reshape the effect of warming have been limited to theoretical or proxy-based approaches: for instance, studies of latitudinal temperature gradients are often conflated with other drivers (e.g., species richness). Here, we overcome these limitations by using local geothermal temperature gradients across multiple high-latitude stream ecosystems. Each suite of streams (6-11 warmed by 1-15°C above ambient) is set within one of five regions (37 streams total); because the heating comes from the bedrock and is not confounded by changes in chemistry, we can isolate the effect of temperature. We found a negative overall relationship between diatom and invertebrate species richness and temperature, but the strength of the relationship varied regionally, declining more strongly in regions with low terrestrial productivity. Total invertebrate biomass increased with temperature in all regions. The latter pattern combined with the former suggests that the increased biomass of tolerant species might compensate for the loss of sensitive species. Our results show that the impact of warming can be dependent on regional conditions, demonstrating that local variation should be included in future climate projections rather than simply assuming universal relationships.

Trapped on the Roof of the World: taxonomic diversity and evolutionary patterns of Tibetan Plateau endemic freshwater snails (Gastropoda: Lymnaeidae: Tibetoradix).

The high-elevation Tibetan Plateau (western China) is inhabited by a unique, though not particularly species-rich, community of organisms. We explored the species content and evolutionary history of the Tibetan Plateau endemic freshwater snail genus Tibetoradix. Phylogenetic relationships within the genus were reconstructed based on available sequence data. We used a single-rate Poisson Tree Processes approach for species delimitation and compared putative species-level clades with already described taxa. We found that the genus consists of at least 6 species, of which we described 4 as new to science. Shell and soft body morphology was examined and the radula in Tibetoradix was described for the first time. Based on our findings, the diversification of the genus did not result in a prominent morphological differentiation and a number of species can be regarded as morphologically cryptic. Single species found in different drainage areas indicate relatively good passive dispersal abilities of the snails. The allopatric distribution of the species could result from competitive exclusion between them. The absence of Tibetoradix spp. outside the Tibetan Plateau could be explained by a scenario of an "evolutionary trap", where adaptations to high elevation conditions prevented the taxa from a successful colonization of lower elevations.

Cryptic taxonomic diversity and high-latitude melanism in the glossiphoniid leech assemblage from the Eurasian Arctic.

The family Glossiphoniidae is a diverse and widespread clade of freshwater leeches, playing a significant role in functioning of aquatic ecosystems. The taxonomy and biogeography of leeches from temperate, subtropical, and tropical regions attracted much attention of zoologists, while their taxonomic richness and distribution in the Arctic are poorly understood. Here, we present an overview of the Eurasian Arctic Glossiphoniidae based on the most comprehensive occurrence and DNA sequence datasets sampled to date. This fauna contains 14 species, belonging to five genera and three subfamilies. One genus and five species are new to science and described here. The world's northernmost occurrences of glossiphoniids are situated on the Taymyr Peninsula at 72° N, although further records at higher latitudes are expected. Most Arctic leeches are characterized by broad ranges crossing several climatic zones (e.g., Glossiphonia balcanica and G. nebulosa), although the distribution of two new species may be confined to the high-latitude areas. The Taymyr Peninsula with the nearby Putorana Plateau represents the most species-rich area (totally 9 species), while the European Arctic, Iceland, Kolyma Highland, and Chukotka Peninsula house depleted faunas (2-4 species per subregion). Finally, we show that the high-latitude melanism is a common phenomenon in glossiphoniid leeches.

A new fossil piddock (Bivalvia: Pholadidae) may indicate estuarine to freshwater environments near Cretaceous amber-producing forests in Myanmar.

The lower Cenomanian Kachin amber from Myanmar contains a species-rich assemblage with numerous plant and animal fossils. Terrestrial and, to a lesser degree, freshwater species predominate in this assemblage, while a few taxa with marine affinities were also discovered, e.g. isopods, ammonites, and piddocks. Here, we describe the Kachin amber piddock †Palaeolignopholas kachinensis gen. & sp. nov. It appears to be an ancestral stem lineage of the recent Lignopholas piddocks, which are estuarine to freshwater bivalves, boring into wood and mudstone rocks. Frequent occurrences and high abundance of †Palaeolignopholas borings and preserved shells in the Kachin amber could indicate that the resin-producing forest was partly situated near a downstream (estuarine to freshwater) section of a river. Multiple records of freshwater invertebrates (caddisflies, mayflies, stoneflies, odonates, and chironomids) in this amber could also manifest in favor of our paleo-environmental reconstruction, although a variety of local freshwater environments is known to occur in coastal settings.

New freshwater mussel taxa discoveries clarify biogeographic division of Southeast Asia.

While a growing body of modern phylogenetic research reveals that the Western Indochina represents a separate biogeographic subregion having a largely endemic freshwater fauna, the boundaries of this subregion are still unclear. We use freshwater mussels (Unionidae) as a model to reconstruct spatial patterns of freshwater biogeographic divides throughout Asia. Here, we present an updated freshwater biogeographic division of mainland Southeast Asia and describe 12 species and 4 genera of freshwater mussels new to science. We show that the Isthmus of Kra represents a significant southern biogeographic barrier between freshwater mussel faunas of the Western Indochina and Sundaland subregions, while the Indian and Western Indochina subregions are separated by the Naga Hills, Chin Hills, and Rakhine Yoma mountain ranges. Our findings highlight that the freshwater bivalve fauna of Southeast Asia primarily originated within three evolutionary hotspots (Western Indochina, Sundaland, and East Asian) supplemented by ancient immigrants from the Indian Subcontinent.

Integrative taxonomy, biogeography and conservation of freshwater mussels (Unionidae) in Russia.

Freshwater mussels are ecosystem engineers and keystone species in aquatic environments. Unfortunately, due to dramatic declines this fauna is among the most threatened globally. Here, we clarify the taxonomy and biogeography of Russian Unionidae species based on the most comprehensive multi-locus dataset sampled to date. We revise the distribution and assess the conservation status for each species. This fauna comprises 16 native species from 11 genera and 4 tribes: Anodonta, Pseudanodonta (Anodontini); Amuranodonta, Beringiana, Buldowskia, Cristaria, Sinanodonta (Cristariini); Middendorffinaia, Nodularia, Unio (Unionini); and Lanceolaria (Lanceolariini). No country-level endemic species are known in Russia, except for Buldowskia suifunica that may also occur in China. Sinanodonta woodiana, a non-native species, was introduced from China. Russia comprises the northern parts of Western and Eastern Palearctic subregions. The first subregion with six species encompasses a huge area from the western boundary of Russia to the Lena Basin in Siberia. The second subregion with 10 species covers the Amur Basin, rivers east of the Lena Basin, coastal basins of the Japan Sea, and the North Pacific Islands. The fauna of Russia primarily includes widespread generalist species that are here considered Least Concern (LC). However, Buldowskia suifunica and Sinanodonta lauta have restricted distributions and are assessed here as Vulnerable (VU) and Endangered (EN), respectively.

A new genus and two new species of freshwater mussels (Unionidae) from western Indochina.

The systematics of Oriental freshwater mussels (Bivalvia: Unionidae) is poorly known. Here, we present an integrative revision of the genus Trapezoideus Simpson, 1900 to further understanding of freshwater mussel diversity in the region. We demonstrate that Trapezoideus as currently circumscribed is non-monophyletic, with its former species belonging to six other genera, one of which is new to science and described here. We recognize Trapezoideus as a monotypic genus, comprised of the type species, T. foliaceus. Trapezoideus comptus, T. misellus, T. pallegoixi, and T. peninsularis are transferred to the genus Contradens, T. subclathratus is moved to Indonaia, and T. theca is transferred to Lamellidens. Trapezoideus prashadi is found to be a junior synonym of Arcidopsis footei. Trapezoideus dallianus, T. nesemanni, T. panhai, T. peguensis, and two species new to science are placed in Yaukthwa gen. nov. This genus appears to be endemic of the Western Indochina Subregion. The two new species, Yaukthwa paiensis sp. nov. and Y. inlenensis sp. nov., are both endemic to the Salween River basin. Our results highlight that Southeast Asia is a species-rich freshwater mussel diversity hotspot with numerous local endemic species, which are in need of special conservation efforts.

Eight new freshwater mussels (Unionidae) from tropical Asia.

Freshwater mussels are sensitive to habitat and water quality, revealing the fastest rates of human-mediated global extinction among aquatic animals. These animals are especially diverse in tropical Asia, the faunas of which are characterized by high levels of endemism. Here we describe four new species and four new subspecies of freshwater mussels from Myanmar. Leoparreysia whitteni sp. nov., the smallest representative of this genus, was discovered from the Ayeyarwady and Chindwin rivers. Radiatula myitthanensis sp. nov. and R. chindwinensis sp. nov. were recorded from the Chindwin Basin, and R. mouhoti haungthayawensis ssp. nov. has been discovered from the Haungthayaw River. Indochinella pugio has been revised with a description of three subspecies: I. pugio viridissima ssp. nov. from the Sittaung, Bilin and Bago rivers, I. pugio daweiensis ssp. nov. from the Dawei River, and I. pugio paradoxa ssp. nov. from the Haungthayaw River. Yaukthwa elongatula sp. nov., a peculiar species, conchologically resembling representatives of the genus Solenaia (Gonideinae) with ultra-elongated shell was found in the Chindwin Basin. Our records highlight that tropical Asia harbors numerous, but still overlooked local endemic lineages of freshwater bivalves, which may be on the brink of extinction due to the high anthropogenic and climate change impacts.

Freshwater mussels house a diverse mussel-associated leech assemblage.

Freshwater mussels (Unionida) are one of the most imperiled animal groups worldwide, revealing the fastest rates of extinction. Habitat degradation, river pollution and climate change are the primary causes of global decline. However, biological threats for freshwater mussels are still poorly known. Here, we describe a diverse ecological group of leeches (Hirudinea: Glossiphoniidae) inhabiting the mantle cavity of freshwater mussels. So far, examples of mussel-associated leech species are recorded from East Asia, Southeast Asia, India and Nepal, Africa, and North America. This group comprises a dozen glossiphoniid species with a hidden life style inside the mantle cavity of their hosts largely overlooked by researchers. We show that the association with freshwater mussels evolved independently in three leech clades, i.e. Batracobdelloides, Hemiclepsis, and Placobdella, at least since the Miocene. Seven mussel-associated leech species and two additional free-living taxa are described here as new to science.

Discovery of Novaculina myanmarensis sp. nov. (Bivalvia: Pharidae: Pharellinae) closes the freshwater razor clams range disjunction in Southeast Asia.

The razor clam genus Novaculina represents an example of a marine-derived, secondary freshwater group. It was thought to comprise three species: N. gangetica (Ganges and smaller basins in Bangladesh and northwestern Myanmar), N. siamensis (Bang Pakong and Pasak rivers in Thailand and Mekong River in Vietnam), and N. chinensis (lower Yangtze River, China). Here we describe Novaculina myanmarensis sp. nov., an additional species from the Ayeyarwady and Salween basins representing a divergent lineage that appears to be sister to N. gangetica. This new record closes a Novaculina range disjunction between northwestern Myanmar and Thailand. The populations of this novel species share a shallow molecular divergence from each other indicating potential dispersal events between the two distant freshwater basins during the Late Pleistocene. Our ancestral area modeling suggests that the MRCA of Novaculina crown group was a salt-tolerant freshwater species. The recent Novaculina species most likely originated via allopatric speciation. Our findings highlight that generalist estuarine species could have played the role as a source for bivalve expansions into freshwater and that western Indochina is a separate biogeographic subregion, which is clearly distinct from India. A new synonymy is proposed as follows: Pharellinae Stoliczka, 1870 = Novaculininae Ghosh, 1920 syn. nov.

A new genus and tribe of freshwater mussel (Unionidae) from Southeast Asia.

The freshwater mussel genus Oxynaia Haas, 1911 is thought to be comprised of two geographically disjunct and morphologically variable species groups but the monophyly of this taxon has yet to be tested in any modern cladistic sense. This generic hypothesis has important systematic and biogeographic implications as Oxynaia is the type genus of the currently recognized tribe Oxynaiini (Parreysiinae) and is one of the few genera thought to cross several biogeographically important barriers in Southeast Asia. Morphological and molecular data clearly demonstrate that Oxynaia is not monophyletic, and the type species and its allies (O. jourdyi group) belong to the Unioninae, and more specifically as members of the genus Nodularia Conrad, 1853. Therefore, neither Oxynaia syn. nov. nor Oxynaiini Starobogatov, 1970 are applicable to the Parreysiinae and in the absence of an available name, Indochinella gen. nov. and Indochinellini trib. nov. are described. Several combinations are proposed as follows: Indochinella pugio (Benson, 1862) gen. et comb. nov., Nodularia jourdyi (Morlet, 1886) comb. res., N. gladiator (Ancey, 1881) comb. res., N. diespiter (Mabille, 1887) comb. res. and N. micheloti (Morlet, 1886) comb. res. Finally, we provide an updated freshwater biogeographic division of Southeast Asia.

Species Richness, Molecular Taxonomy and Biogeography of the Radicine Pond Snails (Gastropoda: Lymnaeidae) in the Old World.

The radicine pond snails represent a species-rich and widely distributed group, many species of which are key vectors of human and animal trematodoses. Here we clarify the taxonomy, distribution and evolutionary biogeography of the radicine lymnaeids in the Old World based on the most comprehensive multi-locus molecular dataset sampled to date. We show that the subfamily Amphipepleinae is monophyletic and contains at least ten genus-level clades: Radix Montfort, 1810, Ampullaceana Servain, 1881, Peregriana Servain, 1881, Tibetoradix Bolotov, Vinarski & Aksenova gen. nov., Kamtschaticana Kruglov & Starobogatov, 1984, Orientogalba Kruglov & Starobogatov, 1985, Cerasina Kobelt, 1881, Myxas G. B. Sowerby I, 1822, Bullastra Bergh, 1901, and Austropeplea Cotton, 1942. With respect to our phylogeny, species-delimitation model and morphological data, the Old World fauna includes 35 biological species of radicines. Tibet and Eastern Europe harbor the richest faunas, while East Asia and Africa appear to be the most species-poor areas. The radicine clade could have originated near the Cretaceous - Paleocene boundary. The Miocene great lakes in Eurasia seems to be the most important evolutionary hotspots shaping spatial patterns of recent species richness. Finally, we present the first DNA barcode reference library for the reliable molecular identification of species within this group.

Discovery of a silicate rock-boring organism and macrobioerosion in fresh water.

Macrobioerosion is a common process in marine ecosystems. Many types of rock-boring organisms break down hard substrates, particularly carbonate rocks and calcareous structures such as dead corals and shells. In paleontology, the presence of rocks with boreholes and fossil macroboring assemblage members is one of the primary diagnostic features of shallow marine paleo-environments. Here we describe a silicate rock-boring organism and an associated community in submerged siltstone rock outcrops in Kaladan River, Myanmar. The rock-boring mussel Lignopholas fluminalis is a close relative of the marine piddocks, and its borings belong to the ichnospecies Gastrochaenolites anauchen. The neotectonic uplift of the area leading to gradual decrease of the sea level with subsequent shift from estuarine to freshwater environment was the most likely driver for the origin of this community. Our findings highlight that rocks with macroborings are not an exclusive indicator of marine paleo-ecosystems, but may also reflect freshwater habitats.

Climate Warming as a Possible Trigger of Keystone Mussel Population Decline in Oligotrophic Rivers at the Continental Scale.

The effects of climate change on oligotrophic rivers and their communities are almost unknown, albeit these ecosystems are the primary habitat of the critically endangered freshwater pearl mussel and its host fishes, salmonids. The distribution and abundance of pearl mussels have drastically decreased throughout Europe over the last century, particularly within the southern part of the range, but causes of this wide-scale extinction process are unclear. Here we estimate the effects of climate change on pearl mussels based on historical and recent samples from 50 rivers and 6 countries across Europe. We found that the shell convexity may be considered an indicator of the thermal effects on pearl mussel populations under warming climate because it reflects shifts in summer temperatures and is significantly different in viable and declining populations. Spatial and temporal modeling of the relationship between shell convexity and population status show that global climate change could have accelerated the population decline of pearl mussels over the last 100 years through rapidly decreasing suitable distribution areas. Simulation predicts future warming-induced range reduction, particularly in southern regions. These results highlight the importance of large-scale studies of keystone species, which can underscore the hidden effects of climate warming on freshwater ecosystems.

New taxa of freshwater mussels (Unionidae) from a species-rich but overlooked evolutionary hotspot in Southeast Asia.

Southeast Asia harbors a unique and diverse freshwater fauna of Mesozoic origin, which is under severe threat of extinction because of rapid economic development and urbanization. The largest freshwater basins of the region are certainly the primary evolutionary hotspots and they attract the most attention as key biodiversity areas for conservation. In contrast, medium-sized rivers are considered low-importance areas with secondary biodiversity, whose faunas originated via founder events from larger basins during the Pleistocene, although such a scenario has never been tested by using a phylogenetic approach. In this investigation, we used freshwater mussels (Unionidae) as a model to estimate the levels of endemism within the Sittaung, a little-known remote basin in Myanmar, compared with the surrounding larger rivers (Irrawaddy, Salween and Mekong). We discovered that the Sittaung represents an exceptional evolutionary hotspot with numerous endemic taxa of freshwater mussels. On the basis of our extensive dataset, we describe two new tribes, two genera, seven species and a subspecies of Unionidae. Our results highlight that medium-sized basins may represent separate evolutionary hotspots that harbor a number of endemic lineages. These basins should therefore be a focus of special conservation efforts alongside the largest Southeast Asian rivers.

Ancient River Inference Explains Exceptional Oriental Freshwater Mussel Radiations.

The concept of long-lived (ancient) lakes has had a great influence on the development of evolutionary biogeography. According to this insight, a number of lakes on Earth have existed for several million years (e.g., Baikal and Tanganyika) and represent unique evolutionary hotspots with multiple intra-basin radiations. In contrast, rivers are usually considered to be variable systems, and the possibility of their long-term existence during geological epochs has never been tested. In this study, we reconstruct the history of freshwater basin interactions across continents based on the multi-locus fossil-calibrated phylogeny of freshwater mussels (Unionidae). These mussels most likely originated in Southeast and East Asia in the Jurassic, with the earliest expansions into North America and Africa (since the mid-Cretaceous) following the colonization of Europe and India (since the Paleocene). We discovered two ancient monophyletic mussel radiations (mean age ~51-55 Ma) within the paleo-Mekong catchment (i.e., the Mekong, Siam, and Malacca Straits paleo-river drainage basins). Our findings reveal that the Mekong may be considered a long-lived river that has existed throughout the entire Cenozoic epoch.

First molecular identification of Australapatemon burti (Miller, 1923) (Trematoda: Digenea: Strigeidae) from an intermediate host Radix labiata (Rossmaessler) (Gastropoda: Lymnaeidae) in Europe.

The strigeid digenean species Australapatemon burti (Miller, 1923) (Trematoda: Digenea: Strigeidae) was originally described from North America, but recorded in the Neotropical region (Drago et al. 2007; Hernández-Mena et al. 2014; Blasco-Costa et al. 2016) and in Central Europe (Faltýnková et al. 2007). In Europe, this species is rare, and there is not much information about its range (Faltýnková et al. 2007; Soldánová et al. 2012). Australapatemon burti has a complex life cycle with three larval stages, two of which (sporocyst and cercaria) use several species of freshwater snails, and the third stage (metacercaria) use non-specific host hirudineans (Dubois 1968; Davies & Ostrowski de Núñez 2012; Blasco-Costa et al. 2016). Adult flukes are parasitic in the intenstines of various waterfowl species, such as ducks and swans (Drago et al. 2007; Hernández-Mena et al. 2014). Currently, the molecular data on this parasite species includes only nucleotide sequences of four adult specimens from Mexico (Hernández-Mena et al. 2014). Their hosts were Mexican duck, Anas diazi Ridgway, American Wigeon, Anas americana Gmelin, Cinnamon Teal, Anas cyanoptera Vieillot, and Ruddy Duck, Oxyura jamaicensis (Gmelin) (Anserformes: Anatidae).

Radix dolgini: The integrative taxonomic approach supports the species status of a Siberian endemic snail (Mollusca, Gastropoda, Lymnaeidae).

The molecular techniques are the standard tool for the study of the taxonomic position and phylogenetic affinities of the lymnaeid genus Radix Montfort, 1810, and the majority of the European representatives of this taxon have been studied in this respect. However, a plethora of nominal species of Radix described from Northern Asia (Siberia and the Russian Far East) are still characterized only morphologically, raising some doubts concerning their validity. In this paper, we present the triple (morphological, molecular, and zoogeographical) evidence that there is at least one endemic species of Radix, Radix dolgini (Gundrizer and Starobogatov, 1979), widely distributed in Siberia and Western Mongolia. Phylogenetically, it is a sister species to the European R. labiata (Rossmaessler, 1835) [=R. peregra auct.], and their common ancestor most probably lived in the Pliocene, nearly 3.25Myr ago. Our results assume the existence of an extended dispersal barrier for freshwater hydrobionts between Europe and Siberia in the Late Pliocene that may be important for biogeographical explanations. Three other nominal Siberian species of Radix: R. kurejkae (Gundrizer and Starobogatov, 1979), R. gundrizeri (Kruglov and Starobogatov, 1983), and R. ulaganica (Kruglov and Starobogatov, 1983) proved to be the junior synonyms of R. dolgini.

Taxonomy and distribution of freshwater pearl mussels (Unionoida: Margaritiferidae) of the Russian Far East.

The freshwater pearl mussel family Margaritiferidae includes 13 extant species, which are all listed by IUCN as endangered or vulnerable taxa. In this study, an extensive spatial sampling of Margaritifera spp. across the Russian Far East (Amur Basin, Kamchatka Peninsula, Kurile Archipelago and Sakhalin Island) was conducted for a revision of their taxonomy and distribution ranges. Based on their DNA sequences, shell and soft tissue morphology, three valid species were identified: Margaritifera dahurica (Middendorff, 1850), M. laevis (Haas, 1910) and M. middendorffi (Rosén, 1926). M. dahurica ranges across the Amur basin and some of the nearest river systems. M. laevis is distributed in Japan, Sakhalin Island and the Kurile Archipelago. M. middendorffi was previously considered an endemic species of the Kamchatka. However, it is widespread in the rivers of Kamchatka, Sakhalin Island, the Kurile Islands (across the Bussol Strait, which is the most significant biogeographical boundary within the archipelago), and, likely, in Japan. The Japanese species M. togakushiensis Kondo & Kobayashi, 2005 seems to be conspecific with M. middendorffi because of similar morphological patterns, small shell size (<100 mm long) and overlapped ranges, but it is in need of a separate revision. Phylogenetic analysis reveals that two NW Pacific margaritiferid species, M. laevis and M. middendorffi, formed a monophyletic 18S rDNA clade together with the North American species M. marrianae and M. falcata. The patterns that were found in these Margaritifera spp. are similar to those of freshwater fishes, indicating multiple colonizations of Eastern Asia by different mitochondrial lineages, including an ancient Beringian exchange between freshwater faunas across the Pacific.