Evolution of reproductive strategies in the species-rich land snail subfamily Phaedusinae (Stylommatophora: Clausiliidae)

Genome Evolution and Introgression in the New Zealand mud Snails Potamopyrgus estuarinus and Potamopyrgus kaitunuparaoa

We have sequenced, assembled, and analyzed the nuclear and mitochondrial genomes and transcriptomes of Potamopyrgus estuarinus and Potamopyrgus kaitunuparaoa, two prosobranch snail species native to New Zealand that together span the continuum from estuary to freshwater. These two species are the closest known relatives of the freshwater species Potamopyrgus antipodarum-a model for studying the evolution of sex, host-parasite coevolution, and biological invasiveness-and thus provide key evolutionary context for understanding its unusual biology. The P. estuarinus and P. kaitunuparaoa genomes are very similar in size and overall gene content. Comparative analyses of genome content indicate that these two species harbor a near-identical set of genes involved in meiosis and sperm functions, including seven genes with meiosis-specific functions. These results are consistent with obligate sexual reproduction in these two species and provide a framework for future analyses of P. antipodarum-a species comprising both obligately sexual and obligately asexual lineages, each separately derived from a sexual ancestor. Genome-wide multigene phylogenetic analyses indicate that P. kaitunuparaoa is likely the closest relative to P. antipodarum. We nevertheless show that there has been considerable introgression between P. estuarinus and P. kaitunuparaoa. That introgression does not extend to the mitochondrial genome, which appears to serve as a barrier to hybridization between P. estuarinus and P. kaitunuparaoa. Nuclear-encoded genes whose products function in joint mitochondrial-nuclear enzyme complexes exhibit similar patterns of nonintrogression, indicating that incompatibilities between the mitochondrial and the nuclear genome may have prevented more extensive gene flow between these two species.

Further notes on the taxonomy of the land snail family Clausiliidae Gray, 1855 (Stylommatophora, Helicina) from Myanmar with description of two new species

This study presents a complete species list of the door snails inhabiting Myanmar, updated to now include 33 taxa, and provides taxonomic notes together with a re-description of the shell, radula, and genitalia for 13 species and subspecies, including Oospiraphilippiana, the type species of the genus Oospira. The snails previously treated as subspecies or synonyms of Oospiragracilior and Oospiramagna are reclassified and recognized as distinct species. The lectotype of Oospirainsignis has been clarified and an illustration of the original type specimen provided. A long-overlooked species, Oospiraandersoniana, has been collected and redescribed herein. Two new species from the limestone karsts in the Salween River Basin are introduced: Oospiraluneainopsis Man & Panha, sp. nov. and Oospirazediopsis Man & Panha, sp. nov. A synoptic view of all clausiliid taxa known from Myanmar is presented along with taxonomic information and distributional records. Photographs of the type materials for all taxa are provided for further comparison or, if unavailable, photographs of the examined specimens or the original figure from the literature.

Flexible embryonic shell allies large offspring size and anti-predatory protection in viviparous snails

The evolutionary conflicts between viviparous reproductive mode and skeleton shape may occur whenever the space available for embryo development or delivery is limited by hard inflexible structures of a parent (bones, shell, etc.). In tetrapods, offspring size is at odds with female locomotion efficiency, which results in obstetric selection. We suggest a similar relationship for viviparous gastropods, where spacious canal needed for embryo delivery may interfere with anti-predatory role of narrow and toothed shell aperture. We explored this hypothesis in the group of viviparous land snails (Clausiliidae, subfamily Phaedusinae), known for complex apertural barriers protecting the shell interior. Most of the shell structure modifications we recorded facilitate the delivery of embryos but simultaneously reduce the safeguard of a narrow shell opening. However, we also observed highly flexible embryonic shells that may withstand squeezing between apertural barriers during birth. We investigated the microstructure of these flexible embryonic shells, compared to the typical hard shells of clausiliid embryos, which are rigid and unpliable already in the genital tract of the parent. Our results suggest that the unusual flexibility, which is related to a low number of organomineral layers in the shell, evolved in two phylogenetically distant lineages of Phaedusinae. This adaptation reduces mechanical constraints for birth of the neonates but allows to maintain the protective function of the apertural barriers.

Patterns of diversification of the operculate land snail genus Cyclophorus (Caenogastropoda: Cyclophoridae) on the Ryukyu Islands, Japan

The Ryukyu Islands, an island chain in southwestern Japan, originated from land masses that separated from the Eurasian continent due to the formation of sea barriers about 1.55 million years ago. In this study, we investigated the phylogenetic relationships of the operculate land snail genus Cyclophorus (Caenogastropoda: Cyclophoridae) in the Ryukyu Archipelago and surrounding regions based on DNA sequence data. According to our results, all studied Cyclophorus specimens from Japan form a monophyletic group containing eight subclades. Six of these subclades were found only on the Ryukyu Islands. On most islands of the Ryukyu Archipelago, no more than one Cyclophorus subclade was recorded, which may be due to limited ecological niche space and competition. No subclade was found to occur on both sides of the Watase Line, a regional zoogeographical boundary. Divergence times were estimated based on a time-calibrated phylogeny. We found that multiple splits among the Japanese Cyclophorus subclades predate the emergence of major sea barriers in the Ryukyu Archipelago. Vicariance due to sea barrier formation, as assumed for many other taxa from the region, was thus likely not the main driver for subclade divergence in these snails. Instead, certain geographical features might have shaped the diversification of subclades prior to sea barrier formation. Given that Cyclophorus populations were also present on islands that have never been connected to other land masses, the snails must have colonized them via oversea dispersal. As not all nominal taxa corresponded to monophyletic groups, our molecular phylogenetic approach revealed that a taxonomic revision of the Japanese Cyclophorus fauna is necessary. The eight subclades may be regarded as potential species-level groups based on COI p-distances. A canonical discriminant analysis using shell morphological data revealed slight differences among the subclades.

Life histories of three Serrulinini species (Stylommatophora: Clausiliidae) from Georgia kept under laboratory conditions

The Serrulinini, a small relict group of clausiliids occurring in coastal regions of the Black and Caspian Seas and the Caucasus, are currently classified within the Phaedusinae, however paraphyletic origin of the Serrulinini is also widely debated with Pontophaedusa funiculum (Mousson) being most phylogenetically distinct from other taxa. As life history data may have taxonomical value, we conducted long-term observations in laboratory culture to assess reproductive modes, fecundity and growth pattern of three serruline species. Caspiophaedusa perlucens (O. Boettger) and Pravispira semilamellata (Mousson) produced partly calcified eggs with regular, spiral arrangement of crystals; their juveniles hatched after 17–18 days; the generation time was long and significantly exceeded one year. P. funiculum laid heavily calcified, elongated eggs. The incubation time in P. funiculum varied depending on the humidity, with a tendency towards short embryo-retention. The generation time in P. funiculum was one year. In all the studied species, egg calcification differed from the pattern common for other oviparous Phaedusinae which produce partly calcified eggs with homogeneous distribution of crystals. The calcite crystal distribution in the egg membranes reported here for the Serrulinini suggests some potential of these characters in phylogenetic context.

Pontophaedusa funiculum (Mousson, 1856) (Gastropoda: Eupulmonata: Clausiliidae) lived in captivity for 15 years

A specimen of the clausiliid snail Pontophaedusa funiculum (Mousson, 1856) was kept alive for 15 years after it was collected as an adult. This is the longest direct observation of the lifespan in the Clausiliidae, and one of the longest in all land snails.

A new species and new genus of Clausiliidae (Gastropoda: Stylommatophora) from south-eastern Hubei, China

A new clausiliid species, in a newly proposed genus, Probosciphaedusa mulini gen. et sp. nov. is described from south-eastern Hubei, China. The new taxon is characterised by having thick and cylindrical apical whorls, a strongly expanded lamella inferior and a lamella subcolumellaris that together form a tubular structure at the base of the peristome, and a dorsal lunella connected to both the upper and the lower palatal plicae. Illustrations of the new species are provided.