Phylogenetic variations in a novel family of hyperstable apple snail egg proteins: insights into structural stability and functional trends.

The relationship between protein stability and functional evolution is little explored in proteins purified from natural sources. Here, we investigated a novel family of egg proteins (Perivitellin-1, PV1) from Pomacea snails. Their remarkable stability and clade-related functions in most derived clades (Canaliculata and Bridgesii) make them excellent candidates for exploring this issue. To that aim, we studied PV1 (PpaPV1) from the most basal lineage, Flagellata. PpaPV1 displays unparalleled structural and kinetic stability, surpassing PV1s from derived clades, ranking among the most hyperstable proteins documented in nature. Its spectral features contribute to a pale egg coloration, exhibiting a milder glycan binding lectin activity with a narrower specificity than PV1s from the closely related Bridgesii clade. These findings provide evidence for substantial structural and functional changes throughout the genus' PV1 evolution. We observed that structural and kinetic stability decreased in a clade-related fashion and was associated with large variations in defensive traits. For instance, pale PpaPV1 lectin turns potent in the Bridgesii clade, adversely affecting gut morphology, while giving rise to brightly colored PV1s providing eggs with a conspicuous, probably warning signal in the Canaliculata clade. This work provides a comprehensive comparative analysis of PV1s from various apple snail species within a phylogenetic framework, offering insights into the interplay among their structural features, stability profiles and functional roles. More broadly, our work provides one of the first examples from natural evolution showing the crucial link among protein structure, stability and evolution of new functions.

Melanella martarum sp. nov. (Gastropoda: Eulimidae): the first parasitic deep-sea snail reported for the Salas & Gomez Ridge.

Eulimidae is a highly diverse family of gastropods that are often parasites of echinoderms. They are cosmopolitan and live from the intertidal to great depths. Despite its wide geographic and bathymetric distribution, no species of Eulimidae have been reported for the Salas & Gómez Ridge to date. In this study, we describe Melanella martarum sp. nov., which was collected during the EPIC oceanographic cruise onboard RV Mirai (JAMSTEC, Japan) in 2019. Seven specimens were collected with a modified Agassiz trawl on the summit of seamount "Pearl" (Zhemchuznaya) in the Salas & Gómez Ridge (25.59°S, 89.13°W) at 545 m depth. The morphology of M. martarum sp. nov. was compared with other Melanella species reported for the area, including Chile and Rapa Nui. DNA was extracted and partial sequences of the mitochondrial genes Cytochrome Oxidase 1 (COI) and 16S rDNA, and the nuclear gene Histone 3 (H3) were sequenced. Melanella martarum sp. nov. has morphological characteristics that separate it from other species of Melanella, such as the thickness and color of the shell, and the shape of the protoconch. In addition, M. martarum sp. nov. was genetically differentiated from other Melanella spp. sequences (uncorrected p distances from 18,1-8.6% in mitochondrial COI and 16S rDNA to 3% in nuclear H3 sequences). Although there is not much molecular data available for Eulimidae, the phylogenetic analysis confirms the results obtained by morphology, placing the species found on the Salas & Gómez Ridge within the genus Melanella. The current study advances the understanding of the poorly known benthic fauna found on seamounts in the easternmost part of the Sala & Gómez ridge, a location distinguished by a high level of endemism.

VECTOR COMPATIBILITY OF NEW MEXICO GALBA SPECIES WITH THE CANINE SCHISTOSOME HETEROBILHARZIA AMERICANA, INCLUDING THE FIRST REPORT OF GALBA SCHIRAZENSIS AS A COMPATIBLE HOST.

The indigenous North American mammalian schistosome Heterobilharzia americana has recently attracted attention for causing outbreaks in dogs in states outside of its southeastern U.S. distribution. Although H. americana has yet to be reported in New Mexico, we examined 2 New Mexico isolates of Galba snails to determine their susceptibility to experimental infection with an isolate of H. americana from Utah. One of the Galba isolates from the Rio Grande bosque in the Albuquerque suburb of Corrales was identified as Galba humilis, and like specimens of the same taxon from Utah, proved susceptible to H. americana (27.6% of exposed surviving snails positive). The second Galba isolate sourced from the northern mountains of New Mexico, which surprisingly was revealed to be Galba schirazensis based on cytochrome c oxidase 1, 16S rRNA, and the internal transcribed spacer 2 markers, was also susceptible to H. americana (56.3% of exposed surviving field-derived snails and 46.4% first generation [F1] snails positive). This is the first report of the latter snail being a compatible snail host for H. americana. As G. schirazensis has a wide, albeit spotty, distribution and is considered an invasive species, it provides yet another opportunity for H. americana to expand its known range, potentially including the state of New Mexico as well.

Comparative Mitogenome Analysis of Two Native Apple Snail Species (Ampullariidae, Pomacea) from Peruvian Amazon.

Apple snails of the genus Pomacea Perry, 1810 (Mollusca: Caenogastropoda: Ampullariidae) are native to the Neotropics and exhibit high species diversity, holding cultural and ecological significance as an important protein source in Peru. However, most genetic studies in Pomacea have focused mostly on invasive species, especially in Southeast Asia, where they are considered important pests. In this study, we assembled and annotated the mitochondrial genomes of two Pomacea species native to the Peruvian Amazon: Pomacea reevei Ampuero & Ramírez, 2023 and Pomacea aulanieri (Deville & Hupé, 1850). The mitogenomes of P. reevei and P. aulanieri comprise 15,660 and 16,096 bp, respectively, and contain the typical 37 genes of the animal mitochondria with a large control region of 292 bp in P. reevei and 524 bp in P. aulanieri-which fall within the range of what is currently known in Pomacea. Comparisons with previously published mitogenomes in Pomacea revealed differences in the overlapping of adjacent genes, the size of certain protein-coding genes (PCGs) and the secondary structure of some tRNAs that are consistent with the phylogenetic relationships between these species. These findings provide valuable insights into the systematics and genomics of the genus Pomacea.

Molecular phylogeny of the Orthalicoidea land snails: Further support and surprises.

The superfamily Orthalicoidea comprises approximately 2,000 species of terrestrial gastropods, mostly concentrated in the Neotropics but also present in southern Africa and Oceania. We provide a multi-marker molecular phylogeny of this superfamily, reassessing its family- and genus-level classification. We exclude two families from the group, Odontostomidae and Vidaliellidae, transferring them to Rhytidoidea based on their phylogenetic relationships as recovered herein. Two new families are recognized herein as members of Orthalicoidea, Tomogeridae and Cyclodontinidae fam. nov. The family Megaspiridae and the subfamily Prestonellinae are paraphyletic but are retained herein for taxonomic stability. The subfamily Placostylinae is synonymized with Bothriembryontinae. The new genera Alterorhinus gen. nov. and Sanniostracus gen. nov. containing some Brazilian species are described here to better reflect the phylogeny. The fossil record and paleobiogeographic history of the group is explored under the new phylogenetic framework.

STENOPHYSA MARMORATA (MOLLUSCA: PHYSIDADE) AS AN INTERMEDIATE HOST OF A SNAKE TREMATODE OF THE FAMILY RENIFERIDAE IN BRAZIL.

Species of the family Reniferidae are trematodes found in the oral cavity and esophagus of snakes from Nearctic and Neotropical regions. Although Renifer heterocoelium has been reported in different snake species from South America, the snails involved in its transmission remain unknown. In this study, a xiphidiocercaria emerged from the physid snail Stenophysa marmorata from Brazil and was subjected to morphological and molecular study. The general morphology, including the shape of the stylet and arrangement of penetration glands, resembles that described for reniferid trematodes from North America. Phylogenetic analysis on the basis of nuclear sequences (28S ribosomal deoxyribonucleic acid gene [1,072 base pairs {bp}] and internal transcribed spacer region [ITS, 1,036 bp]) supports identifying this larva as a member of the family Reniferidae, very possibly a species of the genus Renifer. In the 28S analysis, low molecular divergences were found to Renifer aniarum (1.4%) and Renifer kansensis (0.6%), but also concerning other 2 reniferid species, i.e., Dasymetra nicolli (1.4%) and Lechriorchis tygarti (1.0%). Regarding ITS, the divergences between this Brazilian cercaria and R. aniarum or L. tygarti were 1.9% and 8.5%, respectively. In the case of the mitochondrial marker cytochrome oxidase subunit 1 (797 bp), our Reniferidae gen. sp. differs 8.6-9.6% from Paralechriorchis syntomentera, the only reniferid with sequences available for comparison. We discuss the probable conspecificity of the larval stages here reported with R. heterocoelium, the reniferid species reported in South America.

An integrative study of the invasive jumping-snail Ovachlamys fulgens (Gastropoda, Helicarionidae) in Rio de Janeiro and its fast spreading in Southeastern and Southern Brazil.

The Japanese invasive jumping snail Ovachlamys fulgens is a pest of ornamental plants and an intermediate host of a nematode that causes eosinophilic meningitis. We expand its distribution to eight municipalities from Rio de Janeiro State, and one locality from the Paraná State, and generated for the first time partial sequences of the cytochrome c oxidase subunit I (COI) gene for Brazilian populations. External morphology, reproductive system, shell, radula, and jaw were also analyzed and described. Twenty-one lots were collected from Rio de Janeiro, Niterói, Magé, Miguel Pereira, Petrópolis, Teresópolis, Nova Friburgo, Bom Jardim and Paraty, in Rio de Janeiro State, and from Foz do Iguaçu, Paraná State. External morphology, shell and reproductive system were typical of O. fulgens, with some peculiarities found in the shell and radula. A single haplotype was found, which was 100% similar to sequences of COI available in GenBank for specimens from Japan and Argentina. The species seems to be adapted to many habitats and be rapidly expanding its distribution in Southeastern and Southern Brazil, and other South America countries. We highlight the importance of monitoring O. fulgens, considering its potential to compete with native mollusks, attack several plants, and be a transmitter of diseases.

Morphological and molecular identification of the invasive freshwater snail Physa acuta (Gastropoda: Physidae) into Llanquihue Lake, Chilean Patagonia.

The sewage snail Physa acuta, native to North America, is an effective invasive species around the world. In Chile, it was first reported in 2014 in the north central area of the country. So far, the species has not been recorded in southern Chile. Sampling performed in 2015 in three localities from Llanquihue Lake, Chilean Patagonia, only provided native freshwater snails. However, new collections performed in February 2018 in the same three sites were successful for physid specimens suggesting a biological invasion entailing a large southward range expansion of these snails. Here we performed morphological, microstructural and phylogenetic analyses to investigate whether the new samples belong to Physa acuta. The shell morphology, male copulatory complex and radula microstructure of the new material agree with those of the sewage snail. The molecular phylogenetic analyses using the cytochrome c oxidase subunit 1 (COI) gene confirmed morphological identification. We suggest to take prompt measures to prevent the expansion of Physa acuta in Llanquihue Lake or nearby aquatic ecosystems.

Lymnaeidae from Santander and bordering departments of Colombia: Morphological characterization, molecular identification and natural infection with Fasciola hepatica.

The Lymnaeidae constitute a family of freshwater gastropod molluscs whose diversity and ecology have been infrequently studied throughout Colombia. Some lymnaeid species act as intermediate hosts of trematode parasites, which are of great importance in both the veterinary and medical fields. Among trematode parasites, Fasciola hepatica is best known for being an important parasite of sheep and cattle for decades and causes significant economic losses in these livestock species. The main objective of this work is to identify the various species of lymnaeids that occupy different geographical regions of Santander and its bordering departments within Colombia. This will expand the knowledge of lymnaeid diversity in Colombia and provide further insight into their role in the transmission of F. hepatica. A total of 118 georeferenced sites between 126 m.a.s.l. and 3870 m.a.s.l. were sampled in Santander, Boyacá, Norte de Santander and Cundinamarca, respectively. Lymnaeid snails were identified according to the morphology of their shells and by several characteristics of their reproductive systems. Species identification was confirmed using DNA barcoding. Four lymnaeid species are reported in the study area: the native Galba cousini and three exotic species, Pseudosuccinea columella, G. truncatula and G. schirazensis. The four species were examined for natural infection with F. hepatica. Infected variants of the main snail host, G. cousini, were found in the Onzaga, Encino and Vetas municipalities of Santander, as well as in the Belén municipality of Boyacá. A second species, G. truncatula was also found naturally infected in Mutiscua municipality of Norte de Santander. The two other species, P. columella and G. schirazensis were found free of infection.

Archipelago-Wide Patterns of Colonization and Speciation Among an Endemic Radiation of Galápagos Land Snails.

Newly arrived species on young or remote islands are likely to encounter less predation and competition than source populations on continental landmasses. The associated ecological release might facilitate divergence and speciation as colonizing lineages fill previously unoccupied niche space. Characterizing the sequence and timing of colonization on islands represents the first step in determining the relative contributions of geographical isolation and ecological factors in lineage diversification. Herein, we use genome-scale data to estimate timing of colonization in Naesiotus snails to the Galápagos islands from mainland South America. We test inter-island patterns of colonization and within-island radiations to understand their contribution to community assembly. Partly contradicting previously published topologies, phylogenetic reconstructions suggest that most Naesiotus species form island-specific clades, with within-island speciation dominating cladogenesis. Galápagos Naesiotus also adhere to the island progression rule, with colonization proceeding from old to young islands and within-island diversification occurring earlier on older islands. Our work provides a framework for evaluating the contribution of colonization and in situ speciation to the diversity of other Galápagos lineages.

Patterns of distribution, population genetics and ecological requirements of field-occurring resistant and susceptible Pseudosuccinea columella snails to Fasciola hepatica in Cuba.

Pseudosuccinea columella snails transmit the trematode Fasciola hepatica, but in Cuba, six naturally occurring populations successfully resist parasite infection. Here, we present an updated distribution of P. columella in Cuba; 68 positive sites with the earliest records more abundant in west-central Cuba and with east-central populations generally corresponding to the newest samples. No records were found farther east. The IPA site reported 10.5% prevalence of F. hepatica-infected snails. Population genetics, studied through microsatellites, showed low allelic and multilocus genotypic richness (MLGT), mainly in susceptible populations, strong deviations from panmixia and high self-fertilization rates. Susceptible individuals were grouped in one major cluster containing the majority of MLGT, and two independent clusters grouped the MLGT of resistant individuals from western and central populations, respectively. From these, we propose that several introductions of P. columella occurred in Cuba, primarily in the west, with the early arrivals deriving on the resistant populations. A more recent introduction of susceptible P. columella carrying MLGT T and Y may have occurred, where the latter spread quickly through the island and possibly increase the risk of parasite transmission in Cuba since all snails naturally infected with F. hepatica were carriers of the MLGT Y. Interestingly, even though resistant populations are highly diverse and are likely the oldest within Cuba, they are only found in six localities characterized by soft (total hardness, TH = 6.3 ± 1.03°d) and slightly acidic (pH = 6.2 ± 0.12) waters with low richness in snail species (3.2 ± 1.02). This tendency was also observed in a two-year follow-up ecological study that was conducted on a farm where both phenotypes occurred in sympatry; colonization events by resistant over susceptible snails coincided with a reduction in the pH and TH of the water. A comparison of life traits in susceptible and resistant isolates reared at two different pH/TH conditions (5.9/4°d or 7.8/14°d) showed that low pH/TH negatively affects P. columella, irrespective of the phenotype. However, evidence of higher tolerance (higher survival, life expectancy, egg viability) to such conditions was observed in resistant isolates. Finally, we speculate that the limited distribution of resistant populations might be related to a better exploitation of sites that are less suitable to snails (thus, with lower competition), rather than to a differential ecological restriction to specific environmental conditions from susceptible P. columella.

Integrative Proteomic Analysis of Digestive Tract Glycosidases from the Invasive Golden Apple Snail, Pomacea canaliculata.

The freshwater snail Pomacea canaliculata, an invasive species of global significance, possesses a well-developed digestive system and diverse feeding mechanisms enabling the intake of a wide variety of food. The identification of glycosidases in adult snails would increase the understanding of their digestive physiology and potentially generate new opportunities to eradicate and/or control this invasive species. In this study, liquid chromatography coupled to tandem mass spectrometry was applied to define the occurrence, diversity, and origin of glycoside hydrolases along the digestive tract of P. canaliculata. A range of cellulases, hemicellulases, amylases, maltases, fucosidases, and galactosidases were identified across the digestive tract. The digestive gland and the contents of the crop and style sac yield a higher diversity of glycosidase-derived peptides. Subsequently, peptides derived from 81 glycosidases (46 proteins from the public database and 35 uniquely from the transcriptome database) that were distributed among 13 glycoside hydrolase families were selected and quantified using multiple reaction monitoring mass spectrometry. This study showed a high glycosidase abundance and diversity in the gut contents of P. canaliculata which participate in extracellular digestion of complex dietary carbohydrates. Salivary and digestive glands were the main tissues involved in their synthesis and secretion.

Morphological and molecular analysis of cryptic native and invasive freshwater snails in Chile.

Species delimitation in minute freshwater snails is often difficult to perform using solely shell morphology. The problem intensifies when invasive species spread within the distribution range of morphologically similar native species. In Chile, the Truncatelloidean snails are represented by the native genera Heleobia and Potamolithus plus the invasive mudsnail Potamopyrgus antipodarum, which can easily be confused. Using an integrative approach, we performed molecular phylogenetic analysis and studied reproductive and morphological features to identify superficially similar forms inhabiting the central area of the country. Truncatelloidean snails were identified in 40 of 51 localities sampled, 10 containing Potamopyrgus antipodarum, 23 Heleobia and 7 Potamolithus. Based on these results and previously published data, the known distribution of the mudsnail in Chile encompasses 6 hydrological basins, including 18 freshwater ecosystems. The finding of the mudsnails in several type localities of native species/subspecies of "Heleobia" that were not find in situ suggests species replacement or significant extinction of native fauna, a hypothesis supported by the restudy of type material that shows that endemic forms belong to the genus Potamolithus. This study shows the usefulness of integrative taxonomy not only resolving complex taxa with cryptic morphology but also measuring the extent of an ongoing invasion.

Asymmetric evolutionary responses to sex-specific selection in a hermaphrodite.

Sex allocation theory predicts that simultaneous hermaphrodites evolve to an evolutionary stable resource allocation, whereby any increase in investment to male reproduction leads to a disproportionate cost on female reproduction and vice versa. However, empirical evidence for sexual trade-offs in hermaphroditic animals is still limited. Here, we tested how male and female reproductive traits evolved under conditions of reduced selection on either male or female reproduction for 40 generations in a hermaphroditic snail. This selection favors a reinvestment of resources from the sex function under relaxed selection toward the other function. We found no such evolutionary response. Instead, juvenile survival and male reproductive success significantly decreased in lines where selection on the male function (i.e., sexual selection) was relaxed, while relaxing selection on the female function had no effect. Our results suggest that most polymorphisms under selection in these lines were not sex-antagonistic. Rather, they were deleterious mutations affecting juvenile survival (thus reducing both male and female fitness) with strong pleiotropic effects on male success in a sexual selection context. These mutations accumulated when sexual selection was relaxed, which supports the idea that sexual selection in hermaphrodites contributes to purge the mutation load from the genome as in separate-sex organisms.

Phylogenetic relationships of the conoidean snails (Gastropoda: Caenogastropoda) based on mitochondrial genomes.

With more than 5,000 species, Conoidea is one of the most diversified superfamilies of Gastropoda. Recently, the family-level classification of these venomous predator snails has undergone substantial changes, on the basis of a phylogenetic tree reconstructed combining partial mitochondrial and nuclear gene sequences, and up to 16 families are now recognized. However, phylogenetic relationships among these families remain largely unresolved. Here, we sequenced 20 complete or nearly complete mitochondrial (mt) genomes, which were combined with mt genomes available in GenBank to construct a dataset that included representatives of 80% of the known families, although for some we had only one species or genus as representative. Most of the sequenced conoidean mt genomes shared a constant genome organization, and observed rearrangements were limited exclusively to tRNA genes in a few lineages. Phylogenetic trees were reconstructed using probabilistic methods. Two main monophyletic groups, termed "Clade A" and "Clade B", were recovered with strong support within a monophyletic Conoidea. Clade A (including families Clavatulidae, Horaiclavidae, Turridae s.s., Terebridae, Drilliidae, Pseudomelatomidae, and Cochlespiridae) was composed of four main lineages, one of which was additionally supported by a rearrangement in the gene order. Clade B (including families Conidae, Borsoniidae, Clathurellidae, Mangeliidae, Raphitomidae, and Mitromorphidae) was composed of five main lineages. The reconstructed phylogeny rejected the monophyly of Clavatulidae, Horaiclavidae, Turridae, Pseudomelatomidae, and Conidae, indicating that several of the currently accepted families may be ill-defined. The reconstructed tree also revealed new phylogenetic positions for genera characterized as tentative (Gemmuloborsonia, Lucerapex, and Leucosyrinx), enigmatic (Marshallena) or challenging to place (Fusiturris), which will potentially impact the classification of the Conoidea.

The exotic jumping snail Ovachlamys fulgens (Gude, 1900) (Gastropoda: Helicarionidae) in urban areas of the Upper-Paraná Atlantic Forest.

The exotic land gastropod Ovachlamys fulgens (Gude, 1900), aka the jumping snail, was registered in Eldorado city, Misiones province, constituting the first documented record of that species in Argentina-and for all of South America as well. Identities of the individuals were confirmed through morphological examination, and by a DNA sequencing of the cytochrome oxidase subunit I gene. DNA sequences for the mitochondrial 16S-rRNA and the nuclear 18S-rRNA genes were also obtained from the morphologically-confirmed specimens to gain insights into the genetic background of this species in Argentina, and as additional markers for enhancing the rapidity of identification by governmental authorities who are responsible for managing the presence of exotic species. Different size classes suggested that the species had successfully reproduced and become established in the locality. Ovachlamys fulgens is emphasized in the literature as being a serious pest to orchids. Misiones province harbors a high species richness of orchids, representing about one half of the known species in Argentina. Owing to the use of the orchid as an ornamental plant, the commercial trade could have facilitated the introduction of the species into Argentina. Control measures, preventive education, and surveillance are needed to prevent the further spread of this snail.

Convergent evolution of plant and animal embryo defences by hyperstable non-digestible storage proteins.

Plants have evolved sophisticated embryo defences by kinetically-stable non-digestible storage proteins that lower the nutritional value of seeds, a strategy that have not been reported in animals. To further understand antinutritive defences in animals, we analysed PmPV1, massively accumulated in the eggs of the gastropod Pomacea maculata, focusing on how its structure and structural stability features affected its capacity to withstand passage through predator guts. The native protein withstands >50 min boiling and resists the denaturing detergent sodium dodecyl sulphate (SDS), indicating an unusually high structural stability (i.e., kinetic stability). PmPV1 is highly resistant to in vitro proteinase digestion and displays structural stability between pH 2.0-12.0 and 25-85 °C. Furthermore, PmPV1 withstands in vitro and mice digestion and is recovered unchanged in faeces, supporting an antinutritive defensive function. Subunit sequence similarities suggest a common origin and tolerance to mutations. This is the first known animal genus that, like plant seeds, lowers the nutritional value of eggs by kinetically-stable non-digestible storage proteins that survive the gut of predators unaffected. The selective pressure of the harsh gastrointestinal environment would have favoured their appearance, extending by convergent evolution the presence of plant-like hyperstable antinutritive proteins to unattended reproductive stages in animals.

Transcriptome mining of immune-related genes in the muricid snail Concholepas concholepas.

The population of the Chilean endemic marine gastropod Concholepas concholepas locally called "loco" has dramatically decreased in the past 50 years as a result of intense activity of local fisheries and high environmental variability observed along the Chilean coast, including episodes of hypoxia, changes in sea surface temperature, ocean acidification and diseases. In this study, we set out to explore the molecular basis of C. concholepas to cope with biotic stressors such as exposure to the pathogenic bacterium Vibrio anguillarum. Here, 454pyrosequencing was conducted and 61 transcripts related to the immune response in this muricid species were identified. Among these, the expression of six genes (CcNFκß, CcIκß, CcLITAF, CcTLR, CcCas8 and CcCath) involved in the regulation of inflammatory, apoptotic and immune processes upon stimuli, were evaluated during the first 33 h post challenge (hpc). The results showed that CcTLR, CcCas8 and CcCath have an initial response at 4 hpc, evidencing an up-regulation from 4 to 24 hpc. Notably, the response of CcNFKB occurred 2 h later with a statistically significant up-regulation at 6 hpc and 10 hpc. Furthermore, the challenge with V. anguillarum induced a statistically significant down-regulation of CcIKB between 2 and 10 hpc as well as a down-regulation of CcLITAF between 2 and 4 hpc followed in both cases by an up-regulation between 24 and 33 hpc. This work describes the first transcriptomic effort to characterize the immune response of C. concholepas and constitutes a valuable transcriptomic resource for future efforts to develop sustainable aquaculture and conservations tools for this endemic marine snail species.

Bioinvasion Triggers Rapid Evolution of Life Histories in Freshwater Snails.

Biological invasions offer interesting situations for observing how novel interactions between closely related, formerly allopatric species may trigger phenotypic evolution in situ. Assuming that successful invaders are usually filtered to be competitively dominant, invasive and native species may follow different trajectories. Natives may evolve traits that minimize the negative impact of competition, while trait shifts in invasives should mostly reflect expansion dynamics, through selection for colonization ability and transiently enhanced mutation load at the colonization front. These ideas were tested through a large-scale common-garden experiment measuring life-history traits in two closely related snail species, one invasive and one native, co-occurring in a network of freshwater ponds in Guadeloupe. We looked for evidence of recent evolution by comparing uninvaded or recently invaded sites with long-invaded ones. The native species adopted a life history favoring rapid population growth (i.e., increased fecundity, earlier reproduction, and increased juvenile survival) that may increase its prospects of coexistence with the more competitive invader. We discuss why these effects are more likely to result from genetic change than from maternal effects. The invader exhibited slightly decreased overall performances in recently colonized sites, consistent with a moderate expansion load resulting from local founder effects. Our study highlights a rare example of rapid life-history evolution following invasion.

Self-fertilization, long-distance flash invasion and biogeography shape the population structure of Pseudosuccinea columella at the worldwide scale.

Population genetic studies are efficient for inferring the invasion history based on a comparison of native and invasive populations, especially when conducted at species scale. An expected outcome in invasive populations is variability loss, and this is especially true in self-fertilizing species. We here focus on the self-fertilizing Pseudosuccinea columella, an invasive hermaphroditic freshwater snail that has greatly expanded its geographic distribution and that acts as intermediate host of Fasciola hepatica, the causative agent of human and veterinary fasciolosis. We evaluated the distribution of genetic diversity at the largest geographic scale analysed to date in this species by surveying 80 populations collected during 16 years from 14 countries, using eight nuclear microsatellites and two mitochondrial genes. As expected, populations from North America, the putative origin area, were strongly structured by selfing and history and harboured much more genetic variability than invasive populations. We found high selfing rates (when it was possible to infer it), none-to-low genetic variability and strong population structure in most invasive populations. Strikingly, we found a unique genotype/haplotype in populations from eight invaded regions sampled all over the world. Moreover, snail populations resistant to infection by the parasite are genetically distinct from susceptible populations. Our results are compatible with repeated introductions in South America and flash worldwide invasion by this unique genotype/haplotype. Our study illustrates the population genetic consequences of biological invasion in a highly selfing species at very large geographic scale. We discuss how such a large-scale flash invasion may affect the spread of fasciolosis.