Freshwater Snail Research Articles

Love story or fling? The first observation of Vorticella sp. (Ciliophora: Peritrichia) on the freshwater snail Gyraulus rossmaessleri (Auerswald, 1852)

Love story or fling? The first observation of Vorticella sp. (Ciliophora: Peritrichia) on the freshwater snail Gyraulus rossmaessleri (Auerswald, 1852)

Characterisation of Nematoda and Digenea in selected Australian freshwater snails

Freshwater snails are integral to local ecosystems as a primary food source for various vertebrate species, thereby contributing significantly to ecological food webs. However, their role as intermediate hosts also makes them pivotal in the transmission of parasites. In Australia, research on freshwater snails has predominantly focused on their role as intermediate hosts for livestock parasites, while there has been limited exploration of the impact of these parasites on snail health and population dynamics. The aim of this study was to determine parasitic infection in freshwater snails. This study was conducted in the south-eastern region of Australia, in 2022. A total of 163 freshwater snails from four different species were collected and examined in the Murrumbidgee catchment area in the southeastern part of Australia during the Southern Hemisphere summer and autumn months (February to May). The species included Isidorella hainesii, Glyptophysa novaehollandica, Bullastra lessoni (endemic species), and Physella acuta (an introduced species). Through the analysis of sequence data from the various regions of the nuclear ribosomal DNA, we determined that the Digenea species in this study belonged to three distinct species, including Choanocotyle hobbsi, Petasiger sp. and an unidentified species belonging to Plagiorchioidea. Additionally, analysis of the sequences from Nematoda found in this study, revealed they could be categorized into two separate taxa, including Krefftascaris sp. and an unidentified nematode closely associated with plant and soil nematodes. This research holds significant implications for the future understanding and conservation of Australian freshwater ecosystems. Most parasites found in the present study complete their life cycle in snails and turtles. As many of freshwater snail and turtle species in Australia are endemic and face population threats, exploring the potential adverse impacts of parasitic infections on snail and turtle health, is crucial for advancing our understanding of these ecosystems and also paving the way for future research and conservation efforts. While none of the native snail species in the present study have been listed as endangered or threatened, this may simply be attributed to the absence of regular population surveys.

Influence of physicochemical parameters on the biodiversity indices of fresh water snails in selected rivers of Osun State, Nigeria

Studies have investigated the influence of environmental factors on distribution of vectors of parasites of public health importance but little is known on the role of these factors on the biodiversity indices of the vectors. This study is therefore set to assess the role of physicochemical parameters on biodiversity indices of fresh water snails. The study was carried out in three randomly selected communities across the three senatorial regions of Osun state namely Ere Ijesha, Ede and Erin-Osun. Through reports from community members, a mostly visited river from each community was selected. Three contact points with evident human water contact were identified for snail and water sampling. Morphological identification of snails was done. Physicochemical parameters of water were measured while snail biodiversity indices were determined using Shannon index, snail richness and abundance. Relationship between continuous variables was determined using Spearman’s correlation. There is a significant difference between pH values of Ere Ijesa and Erin Osun while Ede and Erin Osun also show a significant difference in their chloride concentration. A significant positive correlation was observed between pH and diversity (correlation coefficient (rho)= 0.64, P<0.05), pH and Bulinus abundance (rho= 0.68, P< 0.05), chloride and snail richness (rho= -0.65, P< 0.05), chloride and diversity (rho= -0.88, P< 0.01), BOD and snail richness (rho= -0.78, P < 0.05), BOD and diversity (rho= -0.64, P<0.05) COD and snail richness (rho= -0.61, P< 0.05). Ede had highest diversity index while Ere Ijesa had highest Bulinus abundance. Erin Osun was the least in terms of snail richness, diversity and Bulinus abundance. Snail diversity, snail richness and Bulinus abundance significantly differ across the sampling locations (P< 0.01). Physicochemical parameters such as pH, chloride content, BOD and COD have significant role to play in fresh water snail richness, snail diversity and Bulinus abundance.

Green synthesis of silver nanoparticles using Croton urucurana and their toxicity in freshwater snail species Biomphalaria glabrata

Green silver nanoparticles (G-Ag NPs) have contributed to the development of ecological technologies with low environmental impact and safer for human health, as well as demonstrating potential for the control of vectors and intermediate hosts. However, knowledge about its toxicity in the early stages of gastropod development remains scarce. Therefore, the current study aimed to investigate the toxicity of G-Ag NPs synthesized from Croton urucurana leaf extracts in snail species Biomphalaria glabrata, which is an intermediate host for Schistosoma mansoni parasite. G-Ag NPs were synthesized using two types of plant extracts (aqueous and hydroethanolic) and characterized using multiple techniques. Bioassays focused on investigating G-Ag NPs and plant extracts were carried out with embryos and newly hatched snails, for 144 h and 96 h, respectively; toxicity was analyzed based on mortality, hatching, development inhibition, and morphological changes. Results have shown that both G-Ag NPs were more toxic to embryos and newly hatched snails than the investigated plant extracts. G-Ag NPs deriving from aqueous extract have higher molluscicidal activity than those deriving from hydroethanolic extract. Both G-Ag NPs induced mortality, hatching delay, development inhibition, and morphological changes (i.e., hydropic embryos), indicating their molluscicidal activities. Moreover, embryos were more sensitive to G-Ag NPs than newly hatched snails. Thus, the toxicity of G-Ag NPs to freshwater snails depends on the type of extracts and the snail's developmental stages. These findings can contribute to the development of green nanobiotechnologies applicable to control snails of medical importance.

Combining a transcriptomic approach and a targeted metabolomics approach for deciphering the molecular bases of compatibility phenotype in the snail Biomphalaria glabrata toward Schistosoma mansoni

Biomphalaria glabrata is a freshwater snail and the obligatory intermediate host of Schistosoma mansoni parasite, the etiologic agent of intestinal Schistosomiasis, in South America and Caribbean. Interestingly in such host-parasite interactions, compatibility varies between populations, strains or individuals. This observed compatibility polymorphism is based on a complex molecular-matching-phenotype, the molecular bases of which have been investigated in numerous studies, notably by comparing between different strains or geographical isolates or clonal selected snail lines. Herein we propose to decipher the constitutive molecular support of this interaction in selected non-clonal resistant and susceptible snail strain originating from the same natural population from Brazil and thus having the same genetic background. Thanks to a global RNAseq transcriptomic approach on whole snail, we identified a total of 328 differentially expressed genes between resistant and susceptible phenotypes among which 129 were up-regulated and 199 down-regulated. Metabolomic studies were used to corroborate the RNAseq results. The activation of immune genes and specific metabolic pathways in resistant snails might provide them with the capacity to better respond to parasite infection.

Salt tolerance and survival of the freshwater bioinvasive gastropod Melanoides tuberculata (Thiariidae): when different methodologies tell us different stories

ABSTRACT The study of the ecophysiology of invasive species is one of the main steps in understanding the dynamics of territorial expansion of these species and establishing prevention, control, and combat measures and protocols. For freshwater molluscs, one of the main limiting factors is salinity. Laboratory tests closer to reality are needed to make more efficient models. Melanoides tuberculata is an invasive freshwater snail monitored worldwide, and it also has implications for human health. Recent studies supported that its rapid expansion has been enabled through its adaptation to both estuarine conditions and saline waters. The present study aims to determine the real tolerance range of M. tuberculata through a stepwise acclimation test as a more realistic model of a transitional gradient from a lentic to an estuarine environment and so determine the real potential for salinity adaptation. It also aims to check differences in the tolerance responses between age groups and life history, using two distinct populations subject to distinct ambient conditions. The stepwise acclimation test was effective in proving that M. tuberculata may be highly adaptable to salinity variation, contrasting with all previous tests. Thus, the results support the hypothesis of dispersion via estuaries by salinity-tolerant M. tuberculata juveniles.

Freshwater trematodes differ from marine trematodes in patterns connected with division of labor.

Prior research suggests that trematode rediae, a developmental stage of trematode parasites that reproduce clonally within a snail host, show evidence of division of labor (DOL). Single-species infections often have two morphologically distinct groups: small rediae, the 'soldiers', are active, aggressive, and do not appear to reproduce; large rediae, the 'reproductives', are larger, sluggish, and full of offspring. Most data supporting DOL come from trematodes infecting marine snails, while data from freshwater trematodes are more limited and generally do not supported DOL. The shorter lifespan typical of freshwater snails may partially explain this difference: defending a short-lived host at the expense of reproduction likely provides few advantages. Here, we present data from sixty-one colonies spanning twenty species of freshwater trematode exploring morphological and behavioral patterns commonly reported from marine trematodes believed to have DOL. Trematode rediae were obtained from sixty-one infected snails collected in central Vermont, USA. A portion of the COI gene was sequenced to make tentative species identifications ('COI species'). Samples of rediae were photographed, observed, and measured to look for DOL-associated patterns including a bimodal size distribution, absence of embryos in small rediae, and pronounced appendages and enlarged pharynges (mouthparts) in small rediae. Additional rediae were used to compare activity levels and likelihood to attack heterospecific trematodes in large vs. small rediae. Many of the tests for DOL-associated patterns showed mixed results, even among colonies of the same COI species. However, we note a few consistent patterns. First, small rediae of most colonies appeared capable of reproduction, and we saw no indication (admittedly based on a small sample size and possibly insufficient attack trial methodology) that small rediae were more active or aggressive. This differs from patterns reported from most marine trematodes. Second, the small rediae of most colonies had larger pharynges relative to their body size than large rediae, consistent with marine trematodes. We also observed that colonies of three sampled COI species appear to produce a group of large rediae that have distinctly large pharynges. We conclude that these freshwater species likely do not have a group of specialized non-reproductive soldiers because small rediae of at least some colonies in almost every species do appear to produce embryos. We cannot rule out the possibility that small rediae act as a temporary soldier caste. We are intrigued by the presence of rediae with enlarged pharynges in some species and propose that they may serve an adaptive role, possibly similar to the defensive role of small 'soldier' rediae of marine trematodes. Large-pharynx rediae have been documented in other species previously, and we encourage future efforts to study these large-pharynx rediae.

Reproductive performance of freshwater snail, Helisoma duryi under the effect of bulk and nano zinc oxide.

Nanotechnology has been used to apply nanoparticle essential elements to enhance the ability of animals to absorb these elements and consequently improve their reproductive performance. High concentrations of nanoparticles (NPs) can directly harm a range of aquatic life forms, ultimately contributing to a decline in biodiversity. Helisoma duryi snails are a good model for studying the toxicological effects of bulk zinc oxide (ZnO-BPs) and nano zinc oxide (ZnO-NPs) on freshwater gastropods. This study aimed to compare the toxic effects of ZnO-BPs and ZnO-NPs on H. duryi snails and explore how waterborne and dietary exposure influenced the reproductive performance of this snail. ZnO-BPs and ZnO-NPs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray powder (XRD). This study revealed that the size of ZnO-BPs and ZnO-NPs were 154 nm and 11-31 nm, respectively. The results showed that exposure of adult snails to sub-lethal concentrations of both ZnO forms (bulk and nano) for 24 h/week for 4 weeks markedly changed their reproductive performance in a concentration-dependent manner, where fecundity was negatively affected by high concentrations. It was concluded that dietary exposure to the lowest tested concentration of ZnO-NPs (1 ppm) has a positive effect as the number of eggs and egg masses/snails increased and the incubation period decreased. Also, poly-vitelline eggs (The formation of twins) were observed. ZnO-NPs at low concentrations positively affect the reproductive performance of snails, especially after dietary exposure. The results revealed that 1 ppm ZnO-NPs could be supplementary provided to snails to improve their fertility, reduce the developmental time course, increase hatchability percentage, and produce poly-vitelline eggs.

Mitogenomes do not substantially improve phylogenetic resolution in a young non-model adaptive radiation of freshwater gastropods

BackgroundSpecies flocks in ancient lakes, and particularly those arising from adaptive radiation, make up the bulk of overall taxonomic and morphological diversity in these insular ecosystems. For these mostly young species assemblages, classical mitochondrial barcoding markers have so far been key to disentangle interspecific relationships. However, with the rise and further development of next-generation sequencing (NGS) methods and mapping tools, genome-wide data have become an increasingly important source of information even for non-model groups.ResultsHere, we provide, for the first time, a comprehensive mitogenome dataset of freshwater gastropods endemic to Sulawesi and thus of an ancient lake invertebrate species flock in general. We applied low-coverage whole-genome sequencing for a total of 78 individuals including 27 out of the 28 Tylomelania morphospecies from the Malili lake system as well as selected representatives from Lake Poso and adjacent catchments. Our aim was to assess whether mitogenomes considerably contribute to the phylogenetic resolution within this young species flock. Interestingly, we identified a high number of variable and parsimony-informative sites across the other ‘non-traditional’ mitochondrial loci. However, although the overall support was very high, the topology obtained was largely congruent with previously published single-locus phylogenies. Several clades remained unresolved and a large number of species was recovered polyphyletic, indicative of both rapid diversification and mitochondrial introgression.ConclusionsThis once again illustrates that, despite the higher number of characters available, mitogenomes behave like a single locus and thus can only make a limited contribution to resolving species boundaries, particularly when introgression events are involved.

Effect of pollutants on the oviposition and embryo development of the invasive snail Physella acuta (Gastropoda: Physidae)

ABSTRACT The varied types of detergent are considered as contaminants in the freshwater environment and interfere with the bio-ecology of macroinvertebrates. Based on this proposition, a study was conducted to examine the impact of detergents and acidic bathroom cleaners on the oviposition and embryo development of the invasive snail Physella acuta (Draparnaud, 1805) (Gastropoda: Physidae). Laboratory-based experiments were carried out to observe the oviposition pattern and embryo development under varied concentrations of commercially available detergent and bathroom cleaner. The invasive snail, P. acuta, breeds throughout the year, and its reproduction positively correlates with shell length. The results of this study implied that the fecundity and hatching rate were reduced and varied with detergent and bathroom cleaner concentrations compared to the control group. Among the treatments, the higher doses of bathroom cleaners impaired the embryo development of P. acuta. The results suggest that the colonization and establishment of the invasive snail P. acuta in the new habitats may be affected by detergent contamination of the freshwater habitats. While the present study aims to provide a link between the detergent and oviposition pattern of the freshwater snail, further studies should be carried out to deduce the long-term effects of the detergents on the population dynamics of P. acuta.

Toxic responses of environmental concentrations of bifenthrin in larval freshwater snail Bellamya aeruginosa

Bifenthrin (BF) is ubiquitous in aquatic environments, and studies have indicated that environmental concentrations of BF could cause neurotoxicity and oxidative damage in fish and decrease the abundance of aquatic insects. However, little information is available on the toxicity of BF in freshwater benthic mollusks. Bellamya aeruginosa (B. aeruginosa) is a key benthic fauna species in aquatic ecosystems, and has extremely high economic and ecological values. In this study, larval B. aeruginosa within 24 h of birth were exposed to 0, 30 or 300 ng/L of BF for 30 days, and then the toxic effects from molecular to individual levels were comprehensively evaluated in all the three treatment groups. It was found that BF at 300 ng/L caused the mortality of snails. Furthermore, BF affected snail behaviors, evidenced by reduced crawling distance and crawling speed. The hepatopancreas of snails in the two BF exposure groups showed significant pathological changes, including increase in the number of yellow granules and occurrence of hemocyte infiltration, epithelial cell thinning, and necrosis. The levels of ROS and MDA were significantly increased after exposure to 300 ng/L BF, and the activities of two antioxidant enzymes SOD and CAT were increased significantly. GSH content decreased significantly after BF exposure, indicating the occurrence of oxidative damage in snails. Transcriptomic results showed that differentially expressed genes (DEGs) were significantly enriched in pathways related to metabolism and neurotoxicity (e.g., oxidative phosphorylation and Parkinson disease), and these results were consistent with those in individual and biochemical levels above. The study indicates that environmental concentration of BF results in decreased survival rates, sluggish behavior, histopathological lesions, oxidative damage, and transcriptomic changes in the larvae of B. aeruginosa. Thus, exposure of larval snails to BF in the wild at concentrations similar to those used in this study might have adverse consequences at the population level. These findings provide a theoretical basis for further assessing the ecological risk of BF to aquatic gastropods.

In search of the glow—Three‐dimensional reconstruction of Latia neritoides with specific focus on the mantel cavity (Mollusca; Gastropoda; Hygrophila)

AbstractThe freshwater snail Latia neritoides occurs in certain streams and lakes of New Zealand's North Island. It defends itself against predators with a unique mechanism – the release of sticky, glowing mucus. Two possible origins of this defence mucus had earlier been suggested: the foot and the pneumostome area. After examining the glandular system of the foot in a previous study, in the present study we examined the general morphology of L. neritoides, focusing on the mantle cavity. With the first complete 3D model of L. neritoides now available, it is possible to evaluate previous morphological studies and to give non‐specialists a better understanding of the soft part anatomy of this fascinating gastropod. As a by‐product of this, we also compared the capabilities of μ‐CT and HREM on a methodological level. We characterized the two most common gland types in the mantel cavity (Lmcg1/Lmcg2) on the basis of their ultrastructure. They are present in large numbers and, therefore, regarded as likely candidates for being the producers of one or more components of the defence mucus. This notion was confirmed by histochemical analyses of Lmcg1 and Lmcg2 and other gland types in L. neritoides.

THE COCCIDIA SPECIES PFEIFFERINELLA ELLIPSOIDES EXHIBITS SPATIAL AND SPECIES-SPECIFIC VARIATION IN PREVALENCE AMONG FRESHWATER SNAILS.

Freshwater snails are commonly studied within the context of their role as intermediate hosts for digenetic trematodes. However, there are fundamental data deficiencies related to our understanding of directly transmitted parasites, such as coccidia, for freshwater snails. Because variation in coccidia pathogenicity and transmission among snail species likely has major impacts on snail community structure, we aimed to investigate the spatial distribution and prevalence of coccidia in several freshwater snail species throughout the Ozark and Ouachita Mountains ecoregions in Arkansas. We opportunistically collected 220 freshwater snails from 24 Ozark sites in summer 2022 and scanned fecal slides for the presence of coccidia. In summer 2023, we surveyed an additional 146 snails from 19 Ouachita sites. To test for apparent interactions among coccidia and trematodes, we scanned feces from a subset of snails (Physa and Planorbella in the Ozarks) that did not have concurrent trematode infections and from those that did. We observed oocysts that morphologically conformed to Pfeifferinella ellipsoides in 2 of the 9 snail taxa from 7 of the 43 sites. Planorbella trivolvis was infected at 2 of 6 sites in the Ozarks and 0 of 5 sites in the Ouachitas. Physa species were infected at 6 of 14 sites in the Ozarks and 0 of 12 sites in the Ouachitas. In the Ozarks, Pl. trivolvis had an overall prevalence of 0.13 (6 of 47), whereas individuals in the genus Physa had an overall prevalence of 0.08 (8 of 97). Our chi-square and Fisher exact tests revealed no significant evidence for trematode-coccidia competition or synergism within the two snail species. There were no other species infected, and we did not observe any coccidia in the snails from the Ouachitas. Our survey of 366 snails among 9 taxa and 43 sites represents the largest survey for freshwater snail coccidia to date and indicates that both Pl. trivolvis and Physa spp. may be primary hosts and/or reservoir hosts for Pf. ellipsoides in freshwater snail communities. The highly aggregated distribution of Pf. ellipsoides in northwestern Arkansas requires further investigation. Our results led to proposal of several hypotheses for additional research, including questions regarding the variation of coccidia host specificity and virulence.

Multi-biomarker approach to evaluate the toxicity of chlorpyrifos (active ingredient and a commercial formulation) on different stages of Biomphalaria straminea

Biomphalaria straminea is a freshwater gastropod native to South America and used in toxicological assessments. Our aim was to estimate 48 h-LC50 and sub-chronic effects after the exposure to low concentrations of chlorpyrifos as commercial formulation (CF) and active ingredient (AI) on B. straminea adult, embryos and juveniles. Concentrations between 1 and 5000 μg L−1 were chosen for acute exposures and 0.1 and 1 μg L−1 for the sub-chronic one. After 14 days biochemical parameters, viability and sub-populations of hemocytes, reproductive parameters, embryotoxicity and offspring' survival were studied. Egg masses laid between day 12 and 14 were separated to continue the exposure and the embryos were examined daily. Offspring' survival and morphological changes were registered for 14 days after hatching. 48 h-LC50, NOEC and LOEC were similar between CF and AI, however the CF caused more sub-lethal effects. CF but not the AI decreased carboxylesterases, catalase and the proportion of hyalinocytes with respect to the total hemocytes, and increased superoxide dismutase and the % of granulocytes with pseudopods. Also CF caused embryotoxicity probably due to the increase of embryos' membrane permeability. Acetylcholinesterase, superoxide dismutase, hemocytes sub-populations, the time and rate of hatching and juveniles' survival were the most sensitive biomarkers. We emphasize the importance of the assessment of a battery of biomarkers as a useful tool for toxicity studies including reproduction parameters and immunological responses. Also, we highlight the relevance of incorporating the evaluation of formulations in order to not underestimate the effects of pesticides on the environment.

Both nuclear and cytoplasmic polymorphisms are involved in genetic conflicts over male fertility in the gynodioecious snail Physa acuta.

Gynodioecy, the coexistence of hermaphrodites with females, often reflects conflicts between cytoplasmic male sterility (CMS) genes and nuclear genes restoring male fertility. CMS is frequent in plants, and has been recently discovered in one animal: the freshwater snail Physa acuta. In this system, CMS was linked to a single divergent mitochondrial genome (D), devoid of apparent nuclear restoration. Our study uncovers a second, novel CMS-associated mitogenome (K) in Physa acuta, demonstrating an extraordinary acceleration of molecular evolution throughout the entire K mitochondrial genome, akin to the previously observed pattern in D. This suggests a pervasive occurrence of accelerated evolution in both CMS-associated lineages. Through a 17-generation introgression experiment, we further show that nuclear polymorphisms in K-mitogenome individuals contribute to the restoration of male function in natural populations. Our results underscore shared characteristics in gynodioecy between plants and animals, emphasizing the presence of multiple CMS mitotypes and cyto-nuclear conflicts. This reaffirms the pivotal role of mitochondria in influencing male function and in generating genomic conflicts that impact reproductive processes in animals.

Population dynamics of freshwater snails in three towns in Ekiti State, Nigeria

Many rivers and streams in Nigeria are habitats of freshwater snails. Many of these snails are edible, whereas others are intermediate hosts of various flatworms. Nine rivers and streams from three towns in Ekiti State, Nigeria, were examined for the presence of freshwater snails. Each freshwater habitat was sampled for snails at the designated sites for 15 min on a monthly basis using a 0.2 mm mesh scoop. The collected snails were transported to the laboratory in pre-labelled plastic containers. Two thousand three hundred and thirty-one (2331) freshwater snails were collected from all habitats. Lanistes libycus had the highest population, 1044 (44.8%). The other species were Melanoides tuberculata 550 (23.6%), Bulinus globosus 401 (17.2%), and Potadoma moerchi 336 (14.4%). Freshwater snails were more abundant at the beginning of the rainy season (March-May) than during heavy rainfall (July–October). The environmental conditions of the study area supported the occurrence of these snail species. Although some species of these snails are edible, others can serve as intermediate hosts for parasitic flatworms, which requires urgent attention.

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.

Impacts of water physicochemical parameters on schistosomiasis vector snail distributional-abundance and infectivity rate in South-Eastern Nigeria.

Schistosomiasis, an NTD, poses public health problems for rural communities. The parameters controlling its intermediate hosts are scarcely studied. 24 human-water contacts were sampled for 12 months to understand the impacts of water parameters on the vector. Sampling was done by monthly handpicking of the snail vector with a net to analyze the water parameters (temperature, dissolved oxygen, conductivity, depth, and rainfall). 546 snails recovered from the water sites showed that Bulinus globosus had the highest occurrence (50.5%), followed by Lanistes varicus (27.7%), and Bulinus truncatus species (3.7%). Ohaukwu LGA recorded the highest occurrence of freshwater snails at 55.3%, while Amovu stream had the highest number of snails with an overall abundance of 35.9%. May had the highest cercariae shedding at 26%, followed by June at 20%. No shedding occurred in September, November, December, and January. The infectivity rate of freshwater snails collected showed a significant difference based on the month (X2=6590.079, p- value=0.006). The study reveals that water physicochemical parameters significantly influence the abundance of intermediate snail hosts, with all parameters positively correlated except for temperature, conductivity, and TDS. This poses a significant public health threat due to vector snails' presence.

Plasticity of circadian and circatidal rhythms in activity and transcriptomic dynamics in a freshwater snail

Organisms have diverse biological clocks synchronised with environmental cycles depending on their habitats. Anticipation of tidal changes has driven the evolution of circatidal rhythms in some marine species. In the freshwater snail, Semisulcospira reiniana, individuals in nontidal areas exhibit circadian rhythms, whereas those in tidal areas exhibit both circadian and circatidal rhythms. We investigated whether the circatidal rhythms are genetically determined or induced by environmental cycles. The exposure to a simulated tidal cycle did not change the intensity of circatidal rhythm in individuals in the nontidal population. However, snails in the tidal population showed different activity rhythms depending on the presence or absence of the exposure. Transcriptome analysis revealed that genes with circatidal oscillation increased due to entrainment to the tidal cycle in both populations and dominant rhythmicity was consistent with the environmental cycle. These results suggest plasticity in the endogenous rhythm in the gene expression in both populations. Note that circatidal oscillating genes were more abundant in the tidal population than in the nontidal population, suggesting that a greater number of genes are associated with circatidal clocks in the tidal population compared to the nontidal population. This increase of circatidal clock–controlled genes in the tidal population could be caused by genetic changes in the biological clock or the experience of tidal cycle in the early life stage. Our findings suggest that the plasticity of biological rhythms may have contributed to the adaptation to the tidal environment in S. reiniana.

Surveys that prioritize site number over time per site will result in better gastropod status assessments: a case study on the rediscovery of Big Black Rocksnail

Freshwater gastropods are among the most imperiled organisms on Earth. Yet, they are among the most understudied freshwater taxa. Numerous freshwater gastropod species have gone extinct in the last 100 years, but recent rediscoveries indicate that some species were prematurely declared extinct. Such premature extinction declarations remove legal protections, which could facilitate actual extinction. Thus, research and policy recommendations are needed so surveys provide the best information possible for conservation. Here, we examined the case of Lithasia hubrichti, a freshwater gastropod endemic to the Big Black River in Mississippi that was last seen in 1965. In 2022, a freshwater mollusk survey resulted in finding L. hubrichti alive. An additional survey effort in 2023 that prioritized sampling as many sites as possible in a single day clarified the current range of L. hubrichti. Genomic analyses indicated that the species has persisted with a large population size for thousands of years, rather than ever falling below a survey detection limit. When considering the case of L. hubrichti and other recent freshwater gastropod rediscoveries, we conclude that freshwater gastropod surveys should emphasize sampling as many sites as possible under favorable sampling conditions when targeting rare species, rather than expending high sampling effort at a small number of sites or when stream conditions may impact ability to detect target species. We also advocate for policies that encourage partnerships with landowners, which was required to rediscover L. hubrichti.