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The distribution of neutral genetic variation in subdivided populations is driven by the interplay between genetic drift, migration, local extinction and colonization. The influence of environmental and demographic factors has also been increasingly examined in empirical studies, but generally focusing on a single species. An open question is whether these factors will similarly, or idiosyncratically, affect a guild of species occupying the same, though exhibiting different traits, mating systems and histories. We addressed it by comparing the population genetic structure of the four most common species of hermaphroditic freshwater snails in Guadeloupe (Lesser Antilles), which occupy a network of patchily distributed sites experiencing temporal variation in water availability. We analyzed microsatellite variability in 21 to 43 populations per species, and built predictions on how several environmental and demographic variables, quantified from a long-term annual survey, as well as species traits, may affect the distribution of genetic variation. These species displayed similarities, such as fairly high levels of variation, but with marked differences among sites, as well as strong genetic differentiation and limited isolation by distance, which can be explained by passive dispersal (strong role of site connectivity), extinction/colonization dynamics and variation in local population size. They also exhibit differences, largely due to the mating system with less genetic diversity and more genetic differentiation in the two selfing species when compared to the two outcrossing ones. These differences can also be attributed to interspecific interactions resulting from the ongoing invasion of Guadeloupe by one of the species studied, which affects the demography of other species, and, to a limited extent, to local environmental factors. Our comparative approach shows both differences and uniqueness in the way species occupy the same landscape, and provides a possible entry to interspecific interactions in community assembly.

Background: Biological invasions pose risks to the normal functioning of ecosystems by altering the structure and composition of several communities. Molluscs stand out as an extensively studied group given their long history of introduction by either natural or anthropogenic dispersal events. An alien population of the lymnaeid species Orientogalba viridis was first sighted in 2009 in southern Spain. In its native range (Australasian), this species is one of the main intermediate hosts of Fasciola hepatica, a major worldwide trematode parasite largely affecting humans, domestic animals and wildlife. Methods: We collected field populations of O. viridis from its native (Malaysia) and invaded (Spain) ranges. We performed detailed morphoanatomical drawings of the species and screened for natural infection of parasites. Individuals were molecularly characterized using ITS2 for comparison with existing sequences in a fine phylogeography study. We founded experimental populations at two different conditions (tropical, 26 °C and temperate, 21 °C) to study the life-history traits of exposed and non-exposed individuals to different F. hepatica isolates. Results: We found a 9% natural prevalence of trematode infection (98% similarity with a sequence of Hypoderaeum conoideum [Echinostomatidae]) in the Spanish field population. The haplotypes of O. viridis found in our study from Spain clustered with Australian haplotypes. Experimental infection with F. hepatica was successful in both experimental conditions but higher in tropical (87% prevalence) than in temperate (73%). Overall lifespan, however, was higher in temperate conditions (mean 32.5 ± 7.4 weeks versus 23.3 ± 6.5) and survivorship remained above 70% during the first 20 weeks. In parasite-exposed populations, life expectancy dropped from an overall 37.75 weeks to 11.35 weeks but still doubled the time for initial cercariae shedding. Cercariae shedding started at day 23 post-exposure and peaked between days 53 and 67 with an average of 106 metacercariae per snail. Conclusions: Whether O. viridis will succeed in Europe is unknown, but the odds are for a scenario in which a major snail host of F. hepatica occupy all available habitats of potential transmission foci, ravelling the epidemiology of fasciolosis. This research provides a comprehensive understanding of O. viridis biology, interactions with parasites and potential implications for disease transmission dynamics, offering valuable insights for further research and surveillance. [ABSTRACT FROM AUTHOR]

Fasciolosis is a widely distributed disease in livestock in South America but knowledge about the epidemiology and the intermediate hosts is relatively scarce in Ecuador. For three months, lymnaeid snails were sampled (n = 1482) in Pichincha Province at two sites located in a highly endemic area. Snails were identified (based on morphology and ITS-2 sequences) and the infection status was established through microscopic dissection and a multiplex polymerase chain reaction (PCR)-based technique. Techniques based on morphology were not useful to accurately name the collected snail species. Comparison with available DNA sequences showed that a single snail species was collected, Galba schirazensis. Live rediae were observed in 1.75% (26/1482) and Fasciola sp. DNA was detected in 6% (89/1482) of collected snails. The COX-1 region permitted identification of the parasite as Fasciola hepatica. The relative sensitivity and specificity of the microscope study, compared to PCR results, were 25.84% and 99.78%, respectively. The mean size of the snails recorded positive for F. hepatica through crushing and microscopy was significantly higher than the mean size of negative snails, but there was no such difference in PCR-positive snails. The role of G. schirazensis as an intermediate host of F. hepatica in Ecuador is discussed and the hypothesis of an adaptation of the parasite to this invasive snail is proposed. For the first time, an epidemiological survey based on molecular biology-based techniques assessed the possible role of lymnaeid snails in the epidemiology of fasciolosis in Ecuador.