A phylogeny for the pomatiopsidae (Gastropoda: Rissooidea): a resource for taxonomic, parasitological and biodiversity studies

A new species of freshwater snail of Fenouilia (Gastropoda, Pomatiopsidae) from northern Guangxi, China, based on morphological and DNA evidence

A new species of pomatiopsid freshwater snail, Fenouiliaundata Chen & He, sp. nov., is described from Guangxi, China, based on morphological and molecular evidence. The new species can be distinguished from its congeners by the following combination of characters: shell with low, prosocline, rounded axial ribs and fine spiral striae, broader than high; aperture broader than shell height; radula with lateral teeth have only two or three faint, wavy ridges on inner side. A molecular analysis of partial mitochondrial COI and 16S DNA sequences supports the systematic position of the new taxon.

Fifth mass extinction event triggered the diversification of the largest family of freshwater gastropods (Caenogastropoda: Truncatelloidea: Hydrobiidae)

The fifth mass extinction event (MEE) at the Cretaceous-Palaeogene (K-Pg) boundary 66 million years ago (Ma) led to massive species loss but also triggered the diversification of higher taxa. Five models have been proposed depending on whether this diversification occurred before, during or after the K-Pg boundary and the rate of species accumulation. While the effects of the K-Pg MEE on vertebrate evolution are relatively well understood, the impact on invertebrates, particularly in freshwater ecosystems, remains controversial. One example is the hyperdiverse Hydrobiidae-the most species-rich family of freshwater gastropods. Whereas some studies place its origin in the Jurassic or even Carboniferous, most fossil records postdate the K-Pg event. We therefore used robustly time-calibrated multi-locus phylogenies of >400 species representing >100 hydrobiid genera to unravel its evolutionary history and patterns of diversification. We found that the family started diversifying shortly after the K-Pg boundary (∼60 Ma; 95% highest posterior density 52-69 Ma). Lineage richness gradually increased to the present and phylogenetic diversity until ∼25 Ma. These findings suggest that diversification was not initially driven by ecological opportunity. Combining the two criteria of timing and rate of diversification, a soft-explosive diversification model of aquatic vertebrates best fits the patterns observed. We also show that most higher hydrobiid taxa (i.e. subfamilies) diversified from the Middle Oligocene to Middle Miocene (i.e. 12-28 Ma). Two of the 15 major clades delimited are described here as new subfamilies (i.e. Bullaregiinae n. subfam. and Pontobelgrandiellinae n. subfam.), whose members are restricted to subterranean waters. Our results are an important contribution to understanding how the fifth MEE has shaped evolution and patterns of biodiversity in continental aquatic systems. Given the high extinction risks faced by many hydrobiids today, they also emphasise the need to study the biodiversity of vulnerable ecosystems.

Phylogenetic position of the relict South American genus Idiopyrgus Pilsbry, 1911 (Gastropoda, Truncatelloidea), with the description of two new cave species

Idiopyrgus is a relict genus of freshwater snails from Brazil traditionally classified in the family Pomatiopsidae. Herein, we use molecular data from newly acquired specimens to test that classification through Bayesian inference phylogenetic analysis. We conclude that Idiopyrgus belongs in the Gondwanan family Tomichiidae, together with the African genus Tomichia and the Australian genus Coxiella. Furthermore, we reassess currently synonymized genus- and species-level names in Idiopyrgus. The genera Hydracme and Aquidauania are considered synonymous with Idiopyrgus. The species I. brasiliensis and I. pilsbryi are restored as accepted species; I. walkeri is considered a taxon inquirendum. Two new species from caves in Bahia state are described herein: Idiopyrgus adamanteussp. nov. and Idiopyrgus minorsp. nov.

Phylogenomics and Diversification of the Schistosomatidae Based on Targeted Sequence Capture of Ultra-Conserved Elements

Schistosomatidae Stiles and Hassall 1898 is a medically significant family of digenetic trematodes (Trematoda: Digenea), members of which infect mammals or birds as definitive hosts and aquatic or amphibious gastropods as intermediate hosts. Currently, there are 17 named genera, for many of which evolutionary interrelationships remain unresolved. The lack of a resolved phylogeny has encumbered our understanding of schistosomatid evolution, specifically patterns of host-use and the role of host-switching in diversification. Here, we used targeted sequence capture of ultra-conserved elements (UCEs) from representatives of 13 of the 17 named genera and 11 undescribed lineages that are presumed to represent either novel genera or species to generate a phylogenomic dataset for the estimation of schistosomatid interrelationships. This study represents the largest phylogenetic effort within the Schistosomatidae in both the number of loci and breadth of taxon sampling. We present a near-comprehensive family-level phylogeny providing resolution to several clades of long-standing uncertainty within Schistosomatidae, including resolution for the placement of the North American mammalian schistosomes, implying a second separate capture of mammalian hosts. Additionally, we present evidence for the placement of Macrobilharzia at the base of the Schistosoma + Bivitellobilharzia radiation. Patterns of definitive and intermediate host use and a strong role for intermediate host-switching are discussed relative to schistosomatid diversification.

The genus Erhaia (Gastropoda, Truncatelloidea, Amnicolidae), with a new species from Bhutan

The distribution of the five Erhaia (Gastropoda, Truncatelloidea, Amnicolidae) species that are diagnosed by both morphological and molecular data is combined with several records of less completely diagnosed nominal Erhaia species. The resulting distribution pattern is summarized in a map and is discussed herein. Erhaia norbuisp. nov. is described from Bhutan on the basis of shell morphology and two mitochondrial DNA barcoding markers. A molecular phylogeny is presented for the five Erhaia species for which molecular data are available, three of which form a separate clade and are from Bhutan.

First report of Schistosoma sinensium infecting Tupaia belangeri and Tricula sp. LF

Schistosoma sinensium belongs to the Asian Schistosoma and is transmitted by freshwater snails of the genus Tricula. Rodents are known definitive hosts of S. sinensium. In 2016, suspected schistosome eggs were found in the feces of the northern tree shrew (Tupaia belangeri) in a field in Lufeng County (latitude, 25°04'50″ N; longitude, 102°19'30″ E; altitude 1820 m), Yunnan Province, China. Morphological analysis suggested that the schistosome was S. sinensium. 18S, 12S and CO1 genes sequencing and phylogenetic analysis showed that this species had the highest similarity to and occupied the same evolutionary branch as S. sinensium from Mianzhu, Sichuan, China. Meanwhile, based on 16S and 28S rDNA sequencing and morphological identification, the snail intermediate host was identified as a species of Tricula, and was found in irrigation channels. Phylogeny indicated that Tricula sp. LF was a sister taxon to T. bambooensis, T. ludongbini. The S. sinensium was able to experimentally infect the captive-bred Tupaia belangeri, and Schistosoma eggs were recovered from all Tupaia belangeri exposed. In this study, we report the infection of Tupaia belangeri and Tricula sp. LF with S. sinensium in Lufeng, Yunnan, southwest China. These findings may improve our understanding of the host range, evolution, distribution, and phylogenetic position of S. sinensium.

The genera Erhaia and Tricula (Gastropoda, Rissooidea, Amnicolidae and Pomatiopsidae) in Bhutan and elsewhere in the eastern Himalaya

Shells of the Rissooidea species that are known from Bhutan are characterized. Triculamontana is reported from that country for the first time. Two Erhaia species from Bhutan are described as new to science, viz. E.janneisp. nov., and E.pelkiaesp. nov., The holotypes of the Erhaia species that were described from Nepal are figured with photographs for the first time and compared with the congeneric taxa from Bhutan and India. Erhaianainitalensis is considered a senior synonym of E.chandeshwariensis. An identification key is presented for the Erhaia species of the Himalayan foothills.

Population genetic structure and geographical variation in Neotricula aperta (Gastropoda: Pomatiopsidae), the snail intermediate host of Schistosoma mekongi (Digenea: Schistosomatidae)

Background

Neotricula aperta is the snail-intermediate host of the parasitic blood-fluke Schistosoma mekongi which causes Mekong schistosomiasis in Cambodia and the Lao PDR. Despite numerous phylogenetic studies only one DNA-sequence based population-genetic study of N. aperta had been published, and the origin, structure and persistence of N. aperta were poorly understood. Consequently, a phylogenetic and population genetic study was performed, with addition of new data to pre-existing DNA-sequences for N. aperta from remote and inaccessible habitats, including one new taxon from Laos and 505 bp of additional DNA-sequence for all sampled taxa,.

Principal findings

Spatial Principal Component Analysis revealed the presence of significant spatial-genetic clustering. Genetic-distance-based clustering indicated four populations with near perfect match to a priori defined ecogeographical regions. Spring-dwelling taxa were found to form an ecological isolate relative to other N. aperta. The poor dispersal capabilities suggested by spatial-genetic analyses were confirmed by Bayesian inference of migration rates. Population divergence time estimation implied a mid-Miocene colonisation of the present range, with immediate and rapid radiation in each ecogeographical region. Estimated effective population sizes were large (120–310 thousand).

Conclusions

The strong spatial-genetic structure confirmed the poor dispersal capabilities of N. aperta—suggesting human-mediated reintroduction of disease to controlled areas as the primary reason for control failure. The isolation of the spring-dwelling taxa and ecogeographical structure suggests adaptation of sub-populations to different habitats; the epidemiological significance of this needs investigation. The large effective population sizes indicate that the high population densities observed in surveyed habitats are also present in inaccessible areas; affording great potential for recrudescence driven by animal-reservoir transmission in remote streams. Mid-Miocene colonisation implies heterochronous evolution of these snails and associated schistosomes and suggests against coevolution of snail and parasite. Heterochronicity favours ecological factors as shapers of host-parasite specificity and greater potential for escape from schistosomiasis control through host-switching.

The disease Mekong schistosomiasis poses a threat to the health of about 1.5 million people living near the Mekong river and its tributaries in Cambodia and Laos. It is a water-borne parasite transmitted by direct contact with water in which freshwater snails of the species Neotricula aperta live. Control of the snails is an effective approach to control of the parasite; however, because many suitable habitats for N. aperta occur in remote and inaccessible areas, knowledge of N. aperta population sizes and interconnectivity is insufficient for the design of effective snail control interventions. Although much of the region is difficult to survey by conventional means, population genetics can be used to estimate population structure and total size from small samples of accessible populations. The study added to existing data-sets, to give more population samples and longer DNA-sequences, together with improved analytical approaches to provide a better overview of N. aperta. The findings suggest that N. aperta in different kinds of habitats are also genetically different, with very low levels of migration between them; this genetic clustering is greater than expected from spatial distance alone. Further work is needed to determine if these different clusters vary in ability to transmit the parasite. The overall population size estimates were very large; thus suggesting that high snail population densities observed in accessible habitats are also characteristic of inaccessible populations—parasites are therefore more likely to return after disease control by immigration from remote areas. Finally, the timing of evolutionary events for snails and parasites was found to differ; this implies that the parasite may not be as strongly restricted to one species of snail as originally thought, which has implications for avoidance of parasite control by host-switching.

First intermediate hosts of Paragonimus spp. in Vietnam and identification of intramolluscan stages of different Paragonimus species

Background

Members of the genus Paragonimus require at least three hosts in their life-cycles. The obligatory first intermediate hosts are freshwater snails. In Vietnam, although seven Paragonimus species have been recorded, the natural first intermediate hosts of almost all species have not been confirmed. The aim of this study was, therefore, to investigate snail hosts of Paragonimus species in Vietnam, and to identify Paragonimus species at intramolluscan stages.

Methods

Freshwater snails were collected from streams in Yen Bai and Quang Tri Provinces, where high prevalences of Paragonimus metacercariae in crab hosts have been reported. Snails were morphologically identified and then examined individually for Paragonimus cercariae using shedding and crushing methods. Chaetomicrocercous cercariae, the morphological class to which Paragonimus cercariae belong, were collected for morphological description and molecular species identification by analyses of ITS2 sequences. The infected snail species were identified based on analyses of nucleotide sequences of the cox1 gene.

Results

Three snail species were found to be infected with Paragonimus cercariae at low infection rates, ranging between 0.07–1.0%. The molecular analyses identified them as Sulcospira quangtriensis and 2 species of subfamily Triculinae. In a phylogenetic tree, these two triculine snails were related to the genera Gammatricula and Tricula with low posterior probabilities. Thus we named them as Triculinae sp. 1 and Triculinae sp. 2. Cercariae from the three snail species, Sulcospira quangtriensis, Triculinae sp. 1 and Triculinae sp. 2, were molecularly identified as Paragonimus westermani, P. heterotremus and P. proliferus, respectively. The cercariae of the three species are morphologically similar to each other, but their daughter rediae can be distinguished by the length of the intestine and the number of cercariae per redia. The rediae of P. westermani have a long intestine and each contain 6–8 cercariae. In contrast, those of P. heterotremus and P. proliferus have a short intestine and each redia contain 10–12 and 5–6 cercariae, respectively.

Conclusions

Three snail species, Sulcospira quangtriensis, Triculinae sp. 1 and Triculinae sp. 2, serve as the first intermediate hosts of P. westermani, P. heterotremus and P. proliferus, respectively, in Vietnam. The length of the intestine of rediae and the number of cercariae per redia are valuable characteristics for distinguishing between larvae of these Paragonimus species.

Erhaia Davis & Kuo (Gastropoda, Rissooidea, Amnicolidae) also in Bhutan

The occurrence of at least one species of Erhaia in Bhutan, viz. Erhaiawangchukisp. n., is confirmed by DNA sequencing. A second unnamed species from Bhutan, that might be congeneric, is known from only a single shell. According to the molecular analysis, E.wangchuki is most closely related to a still undescribed Erhaia species from China. These two species together with E.jianouensis and Akiyoshiakobayashii, both also from China, form a well supported clade. Awaiting additional molecular data, the apparent inconsistency regarding Erhaia versus Akiyoshia is not dealt with here. The extant true sister species of E.wangchuki could be among the four SE Himalayan species from Bhutan and Nepal that are classified with Erhaia on the basis of conchological data only.

Recent range expansion of an intermediate host for animal schistosome parasites in the Indo-Australian Archipelago: phylogeography of the freshwater gastropod Indoplanorbis exustus in South and Southeast Asia

Background

The planorbid snail Indoplanorbis exustus is the sole intermediate host for the Schistosoma indicum species group, trematode parasites responsible for cattle schistosomiasis and human cercarial dermatitis. This freshwater snail is widely distributed in Southern Asia, ranging from Iran to China eastwards including India and from the southeastern Himalayas to Southeast Asia southwards. The veterinary and medical importance of this snail explains the interest in understanding its geographical distribution patterns and evolutionary history. In this study, we used a large and comprehensive sampling throughout Indo-Malaya, including specimens from South India and Indonesia, areas that have been formerly less studied.

Results

The phylogenetic inference revealed five highly divergent clades (genetic distances among clades: 4.4–13.9%) that are morphologically indistinguishable, supporting the assumption that this presumed nominal species may represent a cryptic species complex. The species group may have originated in the humid subtropical plains of Nepal or in southern adjacent regions in the Early Miocene. The major cladogenetic events leading to the fives clades occurred successively from the Early Miocene to the Early Pleistocene, coinciding with major periods of monsoonal intensification associated with major regional paleogeographic events in the Miocene and repeated climate changes due to the Plio-Pleistocene climatic oscillations. Our coverage of the Indo-Australian Archipelago (IAA) highlights the presence of a single clade there. Contrary to expectations, an AMOVA did not reveal any population genetic structure among islands or along a widely recognised zoogeographical regional barrier, suggesting a recent colonisation independent of natural biogeographical constraints. Neutrality tests and mismatch distributions suggested a sudden demographic and spatial population expansion that could have occurred naturally in the Pleistocene or may possibly result of a modern colonisation triggered by anthropogenic activities.

Conclusions

Even though Indoplanorbis is the main focus of this study, our findings may also have important implications for fully understanding its role in hosting digenetic trematodes. The existence of a cryptic species complex, the historical phylogeographical patterns and the recent range expansion in the IAA provide meaningful insights to the understanding and monitoring of the parasites potential spread. It brings a substantial contribution to veterinary and public health issues.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2043-6) contains supplementary material, which is available to authorized users.

Comparative Phylogenetic Studies on Schistosoma japonicum and Its Snail Intermediate Host Oncomelania hupensis: Origins, Dispersal and Coevolution

BACKGROUND

Schistosoma japonicum causes major public health problems in China and the Philippines; this parasite, which is transmitted by freshwater snails of the species Oncomelania hupensis, causes the disease intestinal schistosomiasis in humans and cattle. Researchers working on Schistosoma in Africa have described the relationship between the parasites and their snail intermediate hosts as coevolved or even as an evolutionary arms race. In the present study this hypothesis of coevolution is evaluated for S. japonicum and O. hupensis. The origins and radiation of the snails and the parasite across China, and the taxonomic validity of the sub-species of O. hupensis, are also assessed.

METHODOLOGY/PRINCIPAL FINDINGS

The findings provide no evidence for coevolution between S. japonicum and O. hupensis, and the phylogeographical analysis suggests a heterochronous radiation of the parasites and snails in response to different palaeogeographical and climatic triggers. The results are consistent with a hypothesis of East to West colonisation of China by Oncomelania with a re-invasion of Japan by O. hupensis from China. The Taiwan population of S. japonicum appears to be recently established in comparison with mainland Chinese populations.

CONCLUSIONS/SIGNIFICANCE

The snail and parasite populations of the western mountain region of China (Yunnan and Sichuan) appear to have been isolated from Southeast Asian populations since the Pleistocene; this has implications for road and rail links being constructed in the region, which will breach biogeographical barriers between China and Southeast Asia. The results also have implications for the spread of S. japonicum. In the absence of coevolution, the parasite may more readily colonise new snail populations to which it is not locally adapted, or even new intermediate host species; this can facilitate its dispersal into new areas. Additional work is required to assess further the risk of spread of S. japonicum.

Reprint of "An overview of freshwater snails in Asia with main focus on Vietnam"

Freshwater snails have received much attention for their role as intermediate hosts for trematodes causing disease in people and animals such as schistosomiasis and various food-borne trematodes. While effective medical treatment exists for some of these diseases there is need for preventive measures to reduce transmission, e.g. control of intermediate hosts because transmission patterns are often complicated due to presence of reservoir final hosts. In order to implement control measures against the intermediate host snails with minimal impact on the freshwater ecosystems and their biodiversity, a profound knowledge on transmission patterns of the trematodes is required and this is partly related to distribution, habitat preferences, and seasonal variation in density of the intermediate host species. Identification of snail species can be problematic on the basis of morphological and anatomical characters alone as some species show morphological plasticity and similarly morphological differentiation of cercariae found in snails may be difficult and this could lead to biased perceptions of intermediate host spectra and transmission patterns. In this paper, we give an overview of the snail families and their medical and veterinary importance in Asia but with main focus on Vietnam.

An overview of freshwater snails in Asia with main focus on Vietnam

Freshwater snails have received much attention for their role as intermediate hosts for trematodes causing disease in people and animals such as schistosomiasis and various food-borne trematodes. While effective medical treatment exists for some of these diseases there is need for preventive measures to reduce transmission, e.g. control of intermediate hosts because transmission patterns are often complicated due to presence of reservoir final hosts. In order to implement control measures against the intermediate host snails with minimal impact on the freshwater ecosystems and their biodiversity, a profound knowledge on transmission patterns of the trematodes is required and this is partly related to distribution, habitat preferences, and seasonal variation in density of the intermediate host species. Identification of snail species can be problematic on the basis of morphological and anatomical characters alone as some species show morphological plasticity and similarly morphological differentiation of cercariae found in snails may be difficult and this could lead to biased perceptions of intermediate host spectra and transmission patterns. In this paper, we give an overview of the snail families and their medical and veterinary importance in Asia but with main focus on Vietnam.