Aquatic Gastropods Research Articles

Complex “simple nervous systems”

Terrestrial gastropods have evolved new structures in the nervous system compared to marine and aquatic snails in order to adapt to their new habitat. The behavior of these animals is qualitatively different from the behavior of aquatic gastropods, includes not only the possibility of active interaction with other animals, but also the demonstration of interest by active approach, avoidance or escape in certain cases. The “arrow of love” used in copulation is unique to Nature. Almost all types of associative memory can be formed in these animals, consolidation and reconsolidation of memory can be demonstrated, and mechanisms of memory maintenance and modification can be analyzed. At the level of functionally identified neurons and neural clusters, it is possible to study associative processes in vitro, a 3-neural model of associative longterm changes in synaptic efficiency has been developed.

Co-introduction into a delicate island ecosystem: metastrongyloid nematodes (superfamily Metastrongyloidea) of veterinary and medical importance circulating in aquatic and terrestrial environments of Tenerife (Canary Islands).

Metastrongyloid nematodes typically reside as adults in the cardiopulmonary systems of their mammalian definitive hosts, potentially causing severe diseases. Of particular concern are Angiostrongylus cantonensis and A. costaricensis, which can cause eosinophilic meningitis and abdominal angiostrongyliasis, respectively, in their accidental human hosts. Several metastrongyloid species of medical and veterinary importance have been documented in the Canary Islands. However, the gastropod species acting as intermediate hosts for some of these nematodes in the archipelago remained unknown. This study aimed to investigate the occurrence of metastrongyloid nematodes in terrestrial and aquatic gastropods, including both endemic and non-native species, on Tenerife. Foot samples from terrestrial and aquatic gastropods were analyzed using a multiplex PCR targeting the Internal Transcribed Spacer 1 (ITS1), allowing the specific detection of A. cantonensis, A. vasorum, Aelurostrongylus abstrusus, Crenosoma striatum, Troglostrongylus brevior, and Crenosoma vulpis. Five metastrongyloid species, namely C. striatum, A. cantonensis, Ae. abstrusus, A. vasorum, and an unidentified metastrongyloid, were identified within both non-native and endemic terrestrial gastropods. In the aquatic snail Physella acuta, only A. cantonensis and C. striatum were detected. This study confirms the introduction of various metastrongyloids associated with non-native mammalian fauna and provides new data on the occurrence of these nematodes in non-native and endemic gastropod species, including their presence in aquatic environments on the Canary Islands.

Glutamate, glycine, and especially the secretions of Ruditapes phillipinarum induce efficient foraging by juvenile Rapa whelks

Chemical signals are known to influence interactions within and among species of aquatic organisms, including gastropods. However, despite the indispensable roles of chemical signals in species interactions, little is known about their effectiveness, especially in gastropods. The rapa whelk Rapana venosa (Valenciennes, 1846) is an ecologically and economically important gastropod, but it has also become a global invasive species. Currently, bottlenecks exist in the breeding of R. venosa related to foraging behaviour and efficiency in juveniles, while significant problems also exist in controlling invasive populations of the gastropod. Here, we aimed to identify chemical signaling molecules that could effectively improve their foraging behaviour and efficiency and potentially solve the bottlenecks in aquaculture production and control the invasiveness of R. venosa. The foraging behaviour of R. venosa during the search phase was evaluated in response to various signaling molecules as to activity time, motion path, and successful perception rate, and a standard scoring metric was proposed. The results showed that bivalve (Ruditapes philippinarum) secretion and glutamic acid and glycine, could effectively induce foraging behaviour in R. venosa. In contrast, 4-dodecylbenzene sulfonic acid and dodecyl sulfate, did not induce significant foraging behaviour. The induced foraging behaviour by a single amino acid was less effective than that of the entire bivalve secretion. These findings could be helpful in improving breeding efficiency, efficient trapping, and controlling invasive populations of aquatic gastropods.

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.

Theoretical morphological analysis of differential morphospace occupation patterns for terrestrial and aquatic gastropods.

Despite the morphological diversity of organisms, they only occupy a fraction of the theoretically possible spectrum (i.e., morphospace) and have been studied on several taxa. Such morphospace occupation patterns are formed through evolutionary processes under multiple constraints. In this study, we discovered a differential morphospace occupation pattern between terrestrial and aquatic gastropods, and subsequently attempted to quantitatively understand these differences through morphospace analysis. These differential occupation patterns between terrestrial and aquatic species were observed in the morphospace of spire height and aperture inclination, including a bimodal distribution of shell height in terrestrial species alongside an absence of high-spired shells with high aperture inclination. Although terrestrial species were distributed along optimal lines of shell instability and shell hindrance to locomotion, aquatic species were distributed not only along this line but also within a suboptimal region of the low spire with low inclination. Based on numerical simulation and biometric analysis, here we propose the hypothesis that this difference was caused by the aquatic species being able to adopt a posture with the growth direction perpendicular to the substrate due to reduced functional demands. Our results provided an ultimate explanation for the differential occupation patterns between habitats alongside an overview of the morphospace.

Fluvial response to Quaternary hydroclimate in eastern Africa: Evidence from Gona, Afar, Ethiopia

The Busidima Formation in the Afar region, Ethiopia, spans the Quaternary and records the cultural evolution of the genus Homo. Yet, the Middle Pleistocene to Holocene fluvial environments in which early humans lived are undersampled in eastern Africa. This paper examines the stratigraphy, geochronology and paleoenvironments of the newly designated Odele Member of the uppermost Busidima Formation (<152 thousand years ago (ka)), which has received little attention despite representing a critical period in the evolution of early Homo sapiens and its migration out of Africa. The Odele Member is 40–50 m thick and is dated using tephrochronology, radiometric, luminescence, and electron spin resonance techniques. The member spans 151 to 7 ka, defined at the base by the widespread Waidedo Vitric Tuff (WAVT, 151 ± 16 ka modeled age and 95.4% credible interval - C.I.). There are two prominent erosional unconformities in the Odele Member, a lower one after the WAVT deposition with a modeled 95.4% C.I. range of 124–97 ka; and an upper one involving widespread alluvial fan incision commencing between 21.7 and 12.9 ka. The uppermost Odele Member also contains black, organic-rich mats, redox features, reed casts, and freshwater gastropods marking wetter conditions during the terminal Pleistocene and Early Holocene. A black, fine-grained relict soil coeval with the Halalalee paleosol bounds the top of the Odele Member and has mollic and vertic properties, weathering since ∼12 ka. These incision events and prominent paleosol development near/at the top of the Busidima Formation document Middle to Late Pleistocene Awash River incision to its present-day course. Paleo-rainfall estimates suggest that the Early Holocene-age Halalalee paleosol weathered under a climate with mean annual rainfall 10–15% higher than today. A compilation of radiocarbon ages from aquatic gastropods, carbonized wood and charcoal from the upper Odele Member shows wetter and possibly more vegetated conditions during late marine isotope stage (MIS) 3 and the African Humid Period (AHP) that are tightly coupled with precession-driven summer insolation maxima. These key findings suggest that periods of incision, aggregation, and landscape stability in the Odele Member have an orbital precession pacing. The Odele Member revises upward the age of the Busidima Formation to 7 ka, showing that it spans into the Holocene and now includes Middle and Later Stone Age archaeological traditions.

The Ins and Outs of Urea: Identification of Putative DUR3-like Urea Transporters in the Oligohaline Nerite Snail Theodoxus fluviatilis and Their Expression under Changing Salinities

Theodoxus fluviatilis (Linnaeus, 1758) (Gastropoda: Neritidae) is an oligohaline aquatic gastropod that inhabits most of Europe and adjacent areas of Asia. Two different ecotypes can be distinguished: One in freshwater (FW) and another along the Baltic Sea coast in brackish water habitats (BW). Individuals of either ecotype use free amino acids and urea as organic osmolytes to adjust body fluid osmolality to the external medium; however, the BW ecotype is able to accumulate them in larger quantities. The use of urea as an organic osmolyte in aquatic gastropods such as T. fluviatilis has only recently been initially described and raised the question of how urea transport between body fluids and the environment is balanced. Upon examining transcriptome and preliminary genome sequence data of T. fluviatilis, we identified putative homologues of DUR3 genes, which code for urea transporters (UTs) in other organisms. In this study, we provide evidence for the presence of four different subtypes of DUR3-like UTs that belong to two distinct families. Two of the UT subtypes were subject to qRT-PCR analyses to investigate differences in mRNA expression during the acclimation of individuals of both ecotypes to different salinities. Our results indicate that only BW animals regulate DUR3 gene expression in the context of osmoregulation.

Trophic Ecology of African Dwarf Crocodiles (Osteolaemus spp.) in Perennial and Ephemeral Aquatic Habitats

Crocodilians occupy diverse aquatic and riparian habitats, and through their movements and ontogenetic niche shifts, link the flow of energy and nutrients between aquatic and terrestrial food webs. We analyzed the trophic ecology of African dwarf crocodiles Osteolaemus tetraspis and O. osborni at one site for each species in Cameroon by analyzing carbon and nitrogen stable isotope ratios. We hypothesized that Osteolaemus species inhabiting a perennial river would be primarily associated with aquatic food webs, whereas those inhabiting a small ephemeral stream would assimilate significant fractions of terrestrial-derived material into their biomass. We also hypothesized that Osteolaemus species would undergo ontogenetic trophic shifts, including changes in vertical trophic position (TP). We found that crocodiles in both systems assimilated material from both terrestrial and aquatic-based food chains, and therefore provide a trophic link between habitats. In the perennial river, aquatic gastropods, fish, and amphibians were estimated to have higher maximum feasible contributions to crocodile biomass than terrestrial invertebrates. Prey contributions to crocodile biomass in the ephemeral stream could not be estimated because model results suggested that at least one important prey had not been sampled. Even though isotopic overlap was high between juveniles and adults, and between sexes, ontogenetic shifts in TP were apparent in both Osteolaemus populations.

Gastropod chemoreception behaviors—Mechanisms underlying the perception and location of targets and implications for shellfish fishery development in aquatic environments

Chemoreception is one of the most important senses and it plays a key role in the survival and adaptation of animals to their environments. Many gastropods, such as Rapana venosa and Neptunea cumingii, have emerged as economically important shellfish. Meanwhile, invasive gastropods have destroyed commercial shellfisheries in many countries. Given the importance of chemoreception in the behavior of aquatic gastropods, the mechanism of their chemical perception has recently garnered attention. To provide a foundation for understanding the chemoreception of aquatic gastropods, we reviewed recent studies and summarized the chemoreception behaviors and mechanisms that gastropods use to perceive and locate targets in aquatic environments, along with relevant molecular and genetic insights. We highlight several of the implications of these studies for chemoreception-related research and shellfish fishery development. This review should aid in the rational development and utilization of gastropod resources as well as in controlling the populations of invasive species.

Warming and phosphorus enrichment alter the size structure and body stoichiometry of aquatic gastropods

Aquatic gastropods are important integral components of the macroinvertebrate community in freshwater ecosystems and play critical roles in freshwater ecosystems by contributing to biodiversity, nutrient cycling, and water quality. However, the variation of aquatic gastropods’ community structure under the combined effects of warming and nutrient enrichment remains largely unknown. To investigate this question, we performed an outdoor mesocosm experiment examining the interaction of warming (a 4.5 °C increase in mean temperature above ambient conditions) and nutrient enrichment (phosphorus addition) on the aquatic gastropods’ community and dominant population (Bellamya aeruginosa). We analyzed the changes in community dynamics (abundance and biomass), size structure, and stoichiometric traits (only B. aeruginosa). Results showed that phosphorus enrichment alone had a positive effect on the total abundance and biomass of gastropods, as well as the abundance and biomass of B. aeruginosa. Warming alone only produced a positive effect on total abundance. However, the combined effects of warming and phosphorus enrichment negatively affected the biomass and abundance of the whole gastropod community and the dominant gastropod population. The body mass of B. aeruginosa increased because of warming, whereas the body mass of the gastropod community negatively responded to warming. Phosphorus enrichment alone had no remarkable effects on body mass. The combined effects of warming and phosphorus enrichment negatively affected the whole community’s body mass but had no substantial effect on the body mass of B. aeruginosa. For body stoichiometric traits, warming or phosphorus enrichment alone produced positive effects on the nitrogen and phosphorus contents of B. aeruginosa. The combined effects caused adverse effects on the contents of the two elements. The effect of warming alone only decreased the ratio of nitrogen to phosphorus. Results suggested that the response levels in size structure between the gastropod community and the dominant population differed remarkably. Composition species shift was the main cause of the decrease in aquatic gastropods’ community size structure. The shift in species composition at the whole gastropod community level caused by warming and phosphorus enrichment may result in more complex and unpredicted consequences through cascade effects on the structure and function of freshwater ecosystems.

Disappearance or overlooked or untouched? - A brief history of aquatic gastropods of Malaysian Borneo

The aquatic gastropods (marine and freshwater) in Malaysian Borneo (MYB) have an ancient history of 255 years, while the first record was observed in 1767 by the pioneer Carl Linnaeus. Over time, many European, native taxonomists and conservationists have worked on the diverse group of gastropods in the Malaysian part of Borneo (states of Sabah and Sarawak). No previous work has been conducted to assess the historical status of this particular class of Mollusca. The study objective was to reveal the types of aquatic gastropods and the number of published research and expeditions conducted in MYB. The bibliometric analysis found 145 research publications mentioning the names of the region and reporting at least one gastropod species from this geographic region. Over the history of 255 years, a total of 559 gastropod species were reported by different research groups. Between 1767 and 1900, a total of 150 gastropod species were reported, followed by 79 species from 1900 to 2000 and 330 species from 2001 to 2022. The Grubbs test (p<0.05) identified outlier years for the reporting of gastropod species from MYB with 54 new species each in 2011 and 2020 and 39 species in 2001. Over the history of aquatic gastropod research in MYB, the taxonomists making the greatest contribution were Han Raven and his colleagues from Naturalis Biodiversity Center, The Netherlands, The Netherlands, who reported 111 new species from the region, followed by Nur Leena Wong from Universiti Putra Malaysia (54 new species). The results suggested that reporting of new species from MYB is increasing, which may reflect the many unexplored sites and suggests the existence of as yet unrecorded species in this ecoregion. In this regard further expeditions and research should improve estimates of the true number of aquatic gastropod species in this area. These results can help the regional governments in making a regional biodiversity database as well as in taking decisions regarding aquatic gastropod research and management.

Surface crawling and pedal surface collecting in aquatic gastropods: A case of scientific amnesia

Aquatic gastropods, both freshwater and marine, often crawl along the water surface with the sole of the foot facing upward. Differential regulation of the activity of cilia on the sole turns the gliding mechanism into pedal surface collecting, by which food particles floating on the water are collected on the sole. Over the last 300 years, surface crawling and pedal surface collecting have been studied in numerous species, but the accumulated knowledge has fallen victim to scientific amnesia. Today, pedal surface collecting usually is considered a unique behaviour that evolved in the family Ampullariidae (Caenogastropoda), which includes the genus Pomacea with some of the globally worst invasive pests. Consequently it may appear feasible to tackle invasive Pomacea species specifically by delivering molluscicides via the water surface. Based on a review of our forgotten literature, I here argue that such an approach would have potentially devastating, unintended effects on native gastropod faunas.

Distinct stages of the intestinal bacterial community of Ampullaceana balthica after salinization.

Environmental disturbances influence bacterial community structure and functioning. To investigate the effect of environmental disturbance caused by changes in salinity on host-protected bacterial communities, we analyzed the microbiome within the gastrointestinal tract of Ampullaceana balthica in different salinities. A. balthica is a benthic gastropod found in fresh- and mesohaline waters. Whereas the total energy reserves of A. balthica were unaffected by an increase of salinity to 3, a high mortality rate was detected after a shift from freshwater to salinity 6 suggesting a major disruption of energy homeostasis. The shift to salinity 6 also caused a change in the gastrointestinal bacterial community composition. At salinity 3, the bacterial community composition of different host individuals was related either to the freshwater or salinity 6 gastrointestinal bacterial community, indicating an ambivalent nature of salinity 3. Since salinity 3 represents the range where aquatic gastropods are able to regulate their osmolarity, this may be an important tipping point during salinization. The change in the intestinal microbiome was uncoupled from the change in the water bacterial community and unrelated to the food source microbiome. Our study shows that environmental disturbance caused by salinity acts also on the host-protected microbiome. In light of the sea-level rise, our findings indicate that salinization of the near-shore freshwater bodies will cause changes in organisms’ intestinal microbiomes if a critical salinity threshold (presumably ∼3) is exceeded.

Měkkýši přírodních památek Kalábová a Kalábová 2 v CHKO Bílé Karpaty [Molluscs of the Kalábová and Kalábová 2 Nature Monuments in the White Carpathians PLA

The Kalábová (K1) and Kalábová 2 (K2) Nature Monuments are located in the central part of the White Carpathians PLA near the village of Březová. Both monuments protect treeless wet grasslands and tufa forming spring fens, which were originally part of a larger wetland complex. A total of 51 species were recorded in K1 (47 terrestrial and two aquatic gastropods and two bivalves). Of these, 30 species (56%) are woodland dwellers that were recorded during the survey in 2000, shortly after the area was logged. In contrast, none of these species was detected during the recent survey in 2021. However, these species are widespread in the region and Nature Monuments surroundings and some are likely present also in the ecotones of the spring meadow and adjacent forest. Currently, hygrophilous and wetland dwellers dominate (9 spp.; 17%), followed by ubiquitous (7; 15%), open-ground (4; 8%) and aquatic species (4; 8%). At K2, 19 species were recorded, including 15 terrestrial and two aquatic gastropods, and two bivalves. The two most species-rich ecogroups were hygrophilous and wetland dwellers (5; 26%) and woodland dwellers (5; 26%), the latter were prevailing probably due to relatively recent deforestation between 2012–2014. Aquatic species were represented by four species (21%), followed by three ubiquitous (16%) and one open-ground (5%) species. The spring dweller Bythinella austriaca (NT) and the declining wetland umbrella species Vertigo angustior (VU; NATURA 2000) inhabited both localities in high densities. To maintain the favourable habitat conservation status of the reserves, the sites should be managed extensively by grazing or mowing.

Egg-Laying Behavior in Lithasia armigera (Say, 1821) (Gastropoda: Cerithioidea: Pleuroceridae)

Lithasia armigera (Armored Rocksnail) is an imperiled pleurocerid (Gastropoda: Cerithioidea: Pleuroceridae) historically found throughout the Ohio River drainage. Its reproductive behaviors, like most aquatic gastropods, are poorly understood. We began propagating Armored Rocksnail in captivity, and herein report on the egg-laying behaviors of the species. These data can help natural resource and conservation managers prepare propagation and recovery plans to help conserve at-risk species.

Study of Aquatic Gastropods (Mollusca) in Shatt Al-Arab River, Iraq.

Study of Aquatic Gastropods (Mollusca) in Shatt Al-Arab River, Iraq.

Evaluation of terrestrial gastropods as possible intermediate hosts of Gurltia paralysans in southern Chile.

Gurltia paralysans is the causal agent of gurltiosis in domestic cats in South America. Although the life cycle of G. paralysans is unknown, it is thought that gastropods could act as intermediate hosts (IHs), as is the case for several nematodes in the Angiostrongylidae family. The aim of this study was to search for G. paralysans larvae in terrestrial gastropods and determine their role in the life cycle of this nematode species. Terrestrial gastropod samples (n=835) were collected in Punucapa, Valdivia, southern Chile, where cases of gurltiosis had been reported before. The samples included species from the families Arionidae, Limacidae, Helicidae and Milacidae. All gastropods were subjected to enzymatic digestion to isolate G. paralysans larvae. Ten percent of the gastropod samples were analyzed using seminested PCR targeting the 28S rRNA gene, while 2.6% were analyzed by histopathological examination. The results indicated the absence of G. paralysans when using any of the three methods. In conclusion, further studies are needed to evaluate specific species of aquatic or native gastropods acting as possible IHs (in this geographic location).

Chemical-neuroanatomical organization of peripheral sensory-efferent systems in the pond snail (Lymnaea stagnalis)

Perception and processing of chemical cues are crucial for aquatic gastropods, for proper elaboration of adaptive behavior. The pond snail, Lymnaea stagnalis, is a model species of invertebrate neurobiology, in which peripheral sensory neurons with different morphology and transmitter content have partly been described, but we have little knowledge regarding their functional morphological organization, including their possible peripheral intercellular connections and networks. Therefore the aim of our study was to characterize the sensory system of the tentacles and the lip, as primary sensory regions, and the anterior foot of Lymnaea with special attention to the transmitter content of the sensory neurons, and their relationship to extrinsic elements of the central nervous system. Numerous bipolar sensory cells were demonstrated in the epithelial layer of the peripheral organs, displaying immunoreactivity to antibodies raised against tyrosine hydroxylase, histamine, glutamate and two molluscan type oligopeptides, FMRFamide and Mytilus inhibitory peptide. A subepithelial plexus was formed by extrinsic serotonin and FMRFamide immunoreactive fibers, whereas in deeper regions axon processess of different origin with various immunoreactivities formed networks, too. HPLC–MS assay confirmed the presence of the low molecular weight signal molecules in the three examined areas. Following double-labeling immunohistochemistry, close arrangements were observed, formed by sensory neurons and extrinsic serotonergic (and FMRFamidergic) fibers at axo-dendritic, axo-somatic and axo-axonic levels. Our results suggest the involvement of a much wider repertoire of signal molecules in peripheral sensory processes of Lymnaea, which can locally be modified by central input, hence influencing directly the responses to environmental cues.

Relationship between individual metabolic rate and patch departure behaviour: evidence from aquatic gastropods

Individual energy requirements are tightly related to individual resource use and by extension of space‐use patterns and other traits at higher levels of the ecological hierarchy. However, there is still little experimental evidence linking individual energetics and space‐use behaviour. Individual energy requirements scale mainly with body size and temperature, but these do not explain all individual variation. Therefore, studies focused on inter individual variation in resource and space use behaviour can be used to frame foraging dynamics in an energy perspective. We empirically tested the hypothesis of a relationship between individual energetics and patch departure behaviour using as model organisms four small species (body mass ranging from 0.4 to 14 mg AFDW) of aquatic gastropods strongly differing in adult size: Galba truncatula, Bithynia tentaculata, Theodoxus fluviatilis and Ecrobia ventrosa (in descending order of size). Motility tests were performed in controlled microcosm conditions. The tests were designed to classify the specimens as either low motility (not inclined to abandon the patch) or high motility (likely to abandon the patch). The tests entailed measuring the propensity of the individuals to abandon a limited resource patch (2 g DW of conditioned Phragmites australis leaves) within a given amount of time (24 h) when foraging with conspecifics under conditions where competition for food is expected to increase over time due to resource depletion. The individual standard metabolic rate of the tested specimens was measured via open flow respirometry and compared across motility classes at intra‐ and interspecific level. At both levels, we observed that individuals with higher standard metabolic rates were more inclined to abandon the patch. This finding establishes a link between foraging theory and competitive coexistence mechanisms.

An Inventory of Springsnails (Pyrgulopsis spp.) in and Adjacent to the Spring Mountains, Nevada

Springsnails (genus Pyrgulopsis, hereafter pyrgs) are small freshwater aquatic gastropods that occur in isolated springs in western North America. Pyrgs are species of conservation concern, but patterns of occupancy and speciation are complex. We investigated patterns of occurrence for pyrgs in the Spring Mountains, Clark County, Nevada. We were primarily concerned with identifying springs containing the species P. deaconi, the Spring Mountains pyrg, and P. turbatrix, the southeast Nevada pyrg. We identified species through genetic analysis of the COI-1 mitochondrial region and examined patterns of genetic structure. We located aquatic gastropods in 26 springs and analyzed 420 aquatic gastropods, of which 392 were pyrgs, the remainder representing an unknown species of Physa. Of the 26 springs, 25 contained pyrgs and 5 contained Physa sp. For pyrgs, at COI-1 we identified a total of 29 haplotypes that formed 6 distinct monophyletic groups. Five of the 6 groups were consistent with pyrgs previously identified: P. bacchus, P. deaconi, P. fausta, P. turbatrix, and an unknown species which had been identified previously in the Grapevine Springs. The sixth group, found in 2 springs, does not match any reference specimen and is genetically divergent from the other 5 groups. It is most closely related to P. micrococcus. Prior to this study, P. bacchus had not been located in the Spring Mountains. Both P. deaconi and P. turbatrix were located in multiple springs on both the east and west sides of the Spring Mountains, even though the Las Vegas Valley (east) and Pahrump Valley (west) are hydrologically distinct. At the scale of the hydrologic basin, genetic structure was not discernable; haplotype divergence did not align with basin boundaries and the most common haplotype for P. turbatrix occurred on both the east and west sides of the Spring Mountains. While there was little evidence for genetic structuring at the hydrologic-basin level, there was good evidence for structuring at the level of the individual spring. All told, 79% (23/29) of pyrg haplotypes were unique to specific springs, suggesting that pyrg diversity primarily occurs at the level of the individual spring.