ACCELERATED EVOLUTION OF LAND SNAILS MANDARINA IN THE OCEANIC BONIN ISLANDS: EVIDENCE FROM MITOCHONDRIAL DNA SEQUENCES

Arboreal snail genus Amphidromus Albers, 1850 of Southeast Asia: Shell polymorphism of Amphidromus cruentatus (Morelet, 1875) revealed by phylogenetic and morphometric analyses

Species of colourful arboreal snails of the genus Amphidromus from Southeast Asia commonly exhibit high intraspecific variation in shell morphology. Although highly polymorphic Amphidromus specimens with different colouration have been collected at the same locality and were revealed to possess similar genital organs, there is yet no morphometric or DNA analyses of these different shell morphs. This study is the first to reveal that both striped and stripeless morphs of A. cruentatus from Laos and Vietnam belong to the same mitochondrial (COI and 16S rRNA) lineage. Although the shell colouration between the striped and stripeless morphs is markedly different, morphometric and shell outline-based analyses indicated an overall similarity in shell shape. We also revised the systematics of A. cruentatus, in which we treated similar related species, namely A. eudeli, A. fuscolabris, A. thakhekensis, A. gerberi bolovenensis, A. goldbergi, A. pengzhuoani, A. eichhorsti and A. pankowskiae as junior synonyms of A. cruentatus. Amphidromus daoae, A. anhdaoorum, A. stungtrengensis, A. yangbayensis and A. yenlinhae, which were formerly regarded as junior synonyms, are considered as species different from A. cruentatus based on shell morphology and morphometric analyses. Preliminary phylogenetic analyses also retrieved some Amphidromus species groups as distinct mitochondrial lineages.

A small slug from a tropical greenhouse reveals a new rathouisiid lineage with triaulic tritrematic genitalia (Gastropoda: Systellommatophora)

A small slug found in the tropical greenhouse of the Science Museum (MUSE) of Trento (Italy) turned out to be a species of the little-known systellommatophoran family Rathouisiidae. We undertook detailed comparative anatomical and molecular studies using specimens of the MUSE slug, Rathouisia sinensis, and sequences of other systellommatophoran species deposited in GenBank to conduct a systematic and phylogenetic assessment. Analysis of the genitalia of the MUSE slug and R. sinensis revealed an unusual triaulic tritrematic structure: two separate female ducts – one for egg release (oviduct), the other for intake of allosperm (vagina) – and a separate male duct for autosperm release. Analysis of the nucleotide sequences of several mitochondrial (COI, 16S rDNA) and nuclear (18S rDNA, ITS2 flanked by 5.8S and 28S rDNA fragments, H3) gene fragments supported assignation of the MUSE slug to Rathouisiidae, but also its distinction from the other rathouisiid genera Atopos, Granulilimax, Rathouisia and an undescribed genus from the Ryukyu Islands (Japan). Therefore, we decided to describe the MUSE slug as a new species in a new genus: Barkeriella museensis gen. et sp. nov. The species is certainly an alien introduced into the tropical greenhouse of MUSE, but its origin is unknown and calls for further investigation.

Deep structure, long-distance migration and admixture in the colour polymorphic land snail Cepaea nemoralis

Although snails of the genus Cepaea have historically been important in studying colour polymorphism, an ongoing issue is that there is a lack of knowledge of the underlying genetics of the polymorphism, as well as an absence of genomic data to put findings in context. We, therefore, used phylogenomic methods to begin to investigate the post‐glacial history of Cepaea nemoralis, with a long‐term aim to understand the roles that selection and drift have in determining both European‐wide and local patterns of colour polymorphism. By combining prior and new mitochondrial DNA data from over 1500 individuals with ddRAD genomic data from representative individuals across Europe, we show that patterns of differentiation are primarily due to multiple deeply diverged populations of snails. Minimally, there is a widespread Central European population and additional diverged groups in Northern Spain, the Pyrenees, as well as likely Italy and South Eastern Europe. The genomic analysis showed that the present‐day snails in Ireland and possibly some other locations are likely descendants of admixture between snails from the Pyrenees and the Central European group, an observation that is consistent with prior inferences from mitochondrial DNA alone. The interpretation is that C. nemoralis may have arrived in Ireland via long‐distance migration from the Pyrenean region, subsequently admixing with arrivals from elsewhere. This work, therefore, provides a baseline expectation for future studies on the genetics of the colour polymorphism, as well as providing a comparator for similar species.

Phylogeny and evolution of the land snail tribe Clausiliini (Gastropoda: Clausiliidae)

The phylogenetic relationships within the land snail group Clausiliini were analysed based on an almost complete taxon sampling (28 of 29 extant species) and a set of mitochondrial and nuclear markers. The phylogenetic analyses and character state reconstructions revealed several trends in the group that resulted in repeated convergences. The N-type closing apparatus was convergently transformed into a G-type clausilial apparatus in Graciliaria, Ruthenica + Micridyla and probably three times within Neostyriaca. There were parallel changes in the length of the male copulatory organs and repeated reductions of the basal keel in several lineages. Such trends resulting in repeated convergences are characteristic for several radiations of stylommatophoran land snails. They may reflect parallel adaptations of related lineages to similar environmental constraints. However, it is also possible that some of these transformations are not adaptive, but represent random changes in a restricted morphospace. We explored the timing of the Clausiliini radiation using different calibration strategies. Despite large numbers of fossils of Clausiliidae from Western and Central Europe, the results of these analyses and the fossil evidence for a Cretaceous origin of the Clausiliidae indicate that there are large gaps in the fossil record of the Clausiliini. Especially the origin and early evolution of the Clausiliini in Southeastern Europe is obscured by our insufficient knowledge of Neogene deposits there.

On the verge of extinction - revision of a highly endangered Swiss alpine snail with description of a new genus, Raeticella gen. nov. (Gastropoda, Eupulmonata, Hygromiidae)

The phylogenetic status of the alpine land snail Fruticicolabiconica has remained questionable since it was described by Eder in 1917. Considered a microendemic species from mountain tops in Central Switzerland, the shell is specially adapted for life under stones. Herein, we show via molecular and anatomical investigations that F.biconica neither belongs to the land snail genus Trochulus, nor to any other genus within Trochulini, but rather warrants placement within the newly established genus Raeticella Kneubühler, Baggenstos & Neubert, 2022. Phylogenetic analyses reveal that R.biconica is clearly separated from Trochulus. These findings are supported by morphological investigations of the shell and genitalia.

Convergent evolution of

East Asian terrestrial snails of the family Camaenidae Pilsbry, 1895a are diverse in terms of genus and species numbers, shell morphology and mode of living. This family also includes colourful conical arboreal snails that traditionally have been assigned to the genus Amphidromus Albers, 1850. Yet, the present study shows that, despite their deceiving conchological similarity, some of these East Asian arboreal snails do not belong to the genus Amphidromus or the subfamily Camaeninae Pilsbry, 1895a. The presence of a dart complex comprising a mucous gland, a dart sac, an accessory sac and a proximal accessory sac, along with a pronounced penial caecum and molecular phylogenetic analyses revealed that former ‘Amphidromus’ dautzenbergi, ‘A.’ roemeri and ‘Camaena’ mirifica, and one additional new species belong to Aegistohadra Wu, 2004 (subfamily Bradybaeninae Pilsbry, 1934). Aegistohadra dautzenbergi, comb. nov. and Aegistohadra roemeri, comb. nov. are conical with colourful spiral bands, whereas Aegistohadra mirifica, comb. nov. and Aegistohadra zhangdanae, sp. nov. are heliciform to conical with colourful, variegated spiral and transverse banding patterns. DNA sequence analyses also revealed that each variety of Aegistohadra dautzenbergi could not be differentiated by mitochondrial (cytochrome c oxidase subunit I and 16S rRNA) gene fragments. The phylogenetic position of Aegistohadra within the East Asian camaenids revealed that the similar appearance in shell morphology, microhabitat use and diet to arboreal snails in the genus Amphidromus is homoplastic. Moreover, the presence or absence of a dart complex is also homoplastic and is unsuitable for suprageneric classification. By contrast, the presence of a flagellum and a penial caecum is useful for the suprageneric classification.

Diversity of Land Snail Tribe Helicini (Gastropoda: Stylommatophora: Helicidae): Where Do We Stand after 20 Years of Sequencing Mitochondrial Markers?

Sequences of mitochondrial genes revolutionized the understanding of animal diversity and continue to be an important tool in biodiversity research. In the tribe Helicini, a prominent group of the western Palaearctic land snail fauna, mitochondrial data accumulating since the 2000s helped to newly delimit genera, inform species-level taxonomy and reconstruct past range dynamics. We combined the published data with own unpublished sequences and provide a detailed overview of what they revealed about the diversity of the group. The delimitation of Helix is revised by placing Helix godetiana back in the genus and new synonymies are suggested within the genera Codringtonia and Helix. The spatial distribution of intraspecific mitochondrial lineages of several species is shown for the first time. Comparisons between species reveal considerable variation in distribution patterns of intraspecific lineages, from broad postglacial distributions to regions with a fine-scale pattern of allopatric lineage replacement. To provide a baseline for further research and information for anyone re-using the data, we thoroughly discuss the gaps in the current dataset, focusing on both taxonomic and geographic coverage. Thanks to the wealth of data already amassed and the relative ease with which they can be obtained, mitochondrial sequences remain an important source of information on intraspecific diversity over large areas and taxa.

A misinterpreted disjunction: the phylogenetic relationships of the North African land snail Gyrostomella (Gastropoda: Stylommatophora: Helicidae)

The North African helicid Gyrostomella has been considered closely related to Levantina, suggesting a disjunct distribution with a distribution gap of almost 2000 km in North Africa. We studied this disjunction and the systematics of Helicinae using molecular markers. Our analyses indicate an affiliation of Gyrostomella with the radiation of Helicinae in the Maghreb, especially with Maurohelix. The occurrence of Gyrostomella in Libya does not represent a western outpost of Helicini in North Africa, but an eastern outpost of the Maghreb radiation of Helicinae. The disjunction of Gyrostomella in Libya and Maurohelix in Algeria may be the result of a long-distance dispersal or may represent relicts of a larger range of the lineage in the past as a consequence of aridification processes in North Africa. Taking into account biogeographic patterns, we suggest a subdivision of Helicinae into four tribes: Allognathini, Helicini, Maculariini trib. nov. and Thebini. The Eastern Mediterranean Helicini diverged from the Western Mediterranean clade in the Eocene. The Western Mediterranean clade then split into Allognathini in the Iberian Peninsula, Maculariini in the region of the future western Alps and Thebini on terranes probably including the Rif-Betic and Kabylies blocks that now form part of the Maghreb region.

The introduction of the European Caucasotachea vindobonensis (Gastropoda: Helicidae) in North America, its origin and its potential range

We report the introduction of the central and eastern European helicid land snail Caucasotachea vindobonensis in North America. It was first recorded from Rensselaer County in the state of New York in 2015 by a community scientist. From 2016 to 2020, 14 additional occurrences in Rensselaer County, neighbouring Albany County and an imprecisely localized site in the Adirondack Mountains were recorded by community scientists. In 2020, the species was newly recorded at two sites in Schoharie County, NY, and at three sites in Québec, one of them approximately 700 km to the north of the initial record. Partial mitochondrial cox1 sequences from Rensselaer differ from an eastern Ukrainian haplotype only in a single substitution. Therefore, a Ukrainian origin for this introduction is likely, although not certain: the Rensselaer haplotype also differs in only two substitutions from a more widespread haplotype known from Ukraine, Hungary, Slovakia, Czechia, Serbia, and Bulgaria. An environmental niche model of the species based on occurrence data from central and eastern Europe indicated that a large region from the northern east coast to the midwestern United States is suitable for C. vindobonensis. The Canadian occurrences may indicate that the North American lineage is able to survive colder winters than predicted by the environmental niche model. Caucasotachea vindobonensis is not listed as a pest in Europe and it is unlikely to become an agricultural pest in North America as it prefers rotting plant material over living parts of plants, but its impact on native organisms can hardly be predicted.

Shell colour diversification induced by ecological release: A shift in natural selection after a migration event

Ecological release is often attributed to the rapid adaptive diversification of phenotypic traits. However, it is not well understood how natural selection changes its strength and direction through the process of ecological release. Herein, we demonstrated how shell colour of the Japanese land snail Euhadra peliomphala simodae has diversified via a shift in natural selection due to ecological release after migration from the mainland to an island. This snail's shell colour diversified on the island due to disruptive selection after migration from the mainland. We used trail camera traps to identify the cause of natural selection on both the mainland and the island. We then conducted a mark-recapture experiment while collecting microhabitat use data. In total, we captured and marked around 1,700 snails on the mainland, some of which were preyed upon by an unknown predator. The trail camera traps showed that the predator is the large Japanese field mouse Apodemus speciosus, and the predatory frequency was higher on the mainland than on the island. However, this predation did not correlate with shell colour. Microhabitat use on the island was more extensive than on the mainland, with snails on the island using both ground and arboreal microhabitats. A Bayesian estimation showed that the stabilizing selection on shell colour came from factors other than predation. Our results suggest that the course of natural selection was modified due to ecological release after migration from the mainland, explaining one cause of the phenotypic diversification.

Systematic revision of Stegodera Martens, 1876 (Gastropoda, Stylommatophora, Camaenidae), with description of a new genus

The monotypic genus Stegodera Martens, 1876 is systematically revised based on anatomical and morphological examination of freshly collected specimens. A new species from southern Hunan, which resembles Stegoderaangusticollis, is confirmed to represent a new genus evidenced by comparative shell morphology and anatomy as well as by molecular phylogenetic analyses. The new genus might be more closely related to Stegodera and Nesiohelix Kuroda & Emura, but differs anatomically from the latter two genera by the absence of a dart apparatus.

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.

Incorporating palaeogeography into ancestral area estimation can explain the disjunct distribution of land snails in Macaronesia and the Balearic Islands (Helicidae: Allognathini)

The systematics and biogeographical history of the Eastern Mediterranean and Macaronesian land snail tribe Allognathini (Helicidae: Helicinae) is investigated based on mitochondrial and nuclear DNA sequence data. Our molecular phylogenetic analyses indicate that the genus-group systematics of the tribe needs to be revised. We show for the first time that the narrow-range endemics Lampadia and Idiomela from the Madeira Archipelago belong to Allognathini and represent together the sister group of the diverse Canary Island Hemicycla radiation. We therefore suggest synonymising Lampadiini with Allognathini. Sister to these Macaronesian genera was the Balearic Island Allognathus radiation. Pseudotachea was not recovered as a monophyletic group and the two currently recognised species clustered in Iberus. Similarly, Adiverticula was not recovered as a monophyletic group and clustered in Hemicycla. We therefore suggest synonymising Pseudotachea with Iberus and Adiverticula with Hemicycla. The six genera in Allognathini, which we distinguish here (Cepaea, Iberus, Allognathus, Hemicycla, Idiomela and Lampadia), originated in Western to South-western Europe according to our ancestral area estimation and the fossil record. The disjunct distribution of the Balearic Islands and Macaronesian sister clades and the mainly Iberian Iberus clade that separated earlier can be explained by the separation of the Betic-Rif System from the Iberian Peninsula during the late Oligocene to early Miocene, along with independent Miocene dispersals to the Balearic Islands and Macaronesia from the Iberian Peninsula, where the ancestral lineage became extinct.

Comparative phylogeography of two Northern Rocky Mountain endemics: the widespread Anguispira kochi occidentalis and the narrow-range Anguispira nimapuna (Gastropoda: Discidae)

The Northern Rocky Mountain ecosystem supports rich biological diversity with many endemic and rare species. Extant endemics display two biogeographic patterns: widespread species with fragmented populations, and narrow-range endemics. These distributions are shown by the congeneric snails Anguispira kochi occidentalis and Anguispira nimapuna. These two taxa are disjunct from the remaining species of the genus, which achieves its greatest diversity in eastern North America. Given the disjunct nature of A. k. occidentalis and A. nimapuna, we here present a mtDNA phylogeny of the genus that includes both eastern and western species to assess the phylogenetic position of A. k. occidentalis and A. nimapuna. We then reconstruct the demographic history of A. k. occidentalis and A. nimapuna by analysing current patterns of genetic variation and interpreting the results considering the historical biogeography of the region. Both A. k. occidentalis and A. nimapuna represent unique taxa that are genetically and geographically distinct from their congeners. The current distribution and genetic structure of A. k. occidentalis has been shaped by both historical isolation in refugia and more recent northward shifts, whereas A. nimapuna is represented by two populations with shallow divergence in an area of long-term habitat stability.

One, two or three? Integrative species delimitation of short-range endemic Hemicycla species (Gastropoda: Helicidae) from the Canary Islands based on morphology, barcoding, AFLP and ddRADseq data

Hemicycla mascaensis and H. diegoi are short-range endemics that occur allopatrically in small areas in the Teno Mountains in the western part of Tenerife (Canary Islands). Both taxa have been recognised as distinct species based on differences in shell morphology and genital anatomy. Preliminary molecular analyses using mitochondrial markers suggested a potential paraphyly of H. diegoi with regard to H. mascaensis. We here use multilocus AFLP data and ddRADseq data as well as distribution data, data on shell morphology and genital anatomy to assess the status of these taxa using phylogenetic analyses, species tree reconstruction and molecular species delimitation based on the multispecies coalescent as implemented in BFD* and BPP in an integrative approach. Our analyses show that, based on the analysis of multilocus data, the two taxa are reciprocally monophyletic. Species delimitation methods, however, tend to recognise all investigated populations as distinct species, albeit neither lending unambiguous support to any of the species hypotheses. The comparison of the anatomy of distal genital organs further suggests differentiation within H. mascaensis. This highlights the need for a balanced weighting of arguments from different lines of evidence to determine species status and calls for cautious interpretations of the results of molecular species delimitation analyses, especially in organisms with low active dispersal capacities and expected distinct population structuring such as land snails. Taking all available evidence into account, we favour to recognise H. mascaensis and H. diegoi as distinct species, acknowledging, though, that the recognition of both taxa as subspecies (with possibly a third yet undescribed) would also be an option as morphological differentiation is within the limits of other land snail species that are traditionally subdivided into subspecies.

Geographic isolation and human-assisted dispersal in land snails: a Mediterranean story of Helix borealis and its relatives (Gastropoda: Stylommatophora: Helicidae)

The Mediterranean basin is a major centre for land-snail diversity, with many localized endemics, but there are also species widely spread by humans. Both endemics and introductions can be found in the snail genus Helix, which comprises many large-bodied species used for human consumption in the past and present. The Mediterranean clade of Helix is currently distributed throughout this region, but the phylogenetic and biogeographic relationships among its forms from different parts of the basin remain enigmatic. The reasons include insufficient sampling, taxa with unclear taxonomy and a significant impact of human-assisted transport obscuring the natural distribution of phylogenetic lineages. We provide evidence that European and Anatolian populations of H. cincta and its relatives are not native to those regions, but originate from the northern Levant. These results have implications for taxonomy of the genus, but also for the understanding of its evolutionary history. We posit that the Mediterranean clade consists of four geographically separated groups, which diversified in Northern Africa, the Apennine Peninsula and Corsica, the Aegean and Greece, and the northern Levant. This geographic pattern has been subsequently blurred by multiple instances of human-assisted dispersal. However, revealing the founding populations with certainty requires thorough sampling in currently inaccessible countries.

Repeated evolution of an undescribed morphotype of Rhagada (Gastropoda : Camaenidae) from the inland Pilbara, Western Australia

An undescribed small, banded morphotype of Rhagada land snails occurs widely in the rocky inland Pilbara region, Western Australia. Phylogenetic analysis of mitochondrial COI and 16S rRNA genes revealed that this novel morphotype is polyphyletic, comprising four distinct major clades, with divergences up to 21.4% at COI. These clades are apparently morphologically cryptic, with no obvious shell differences. Two of these species are associated with the major clade of Rhagada in the Pilbara mainland, one of which appears to be a variant of the larger, more globose species R. pilbarana, which occurs within 20km proximity. The other two small, banded species are phylogenetically distinct from each other and all other known Rhagada. This small, banded morphotype shows evidence for both plesiomorphy and homoplasy. The morphotype has evolved independently at least twice, and is associated with the reasonably uniform habitat and harsh conditions in the elevated hinterland of the inland Pilbara. The broad distribution of the inland, small, banded morphotype conforms to the pattern of broad-scale uniformity of shells of the more coastal species of Rhagada. Its repeated evolution, however, confirms that the morphological uniformity is not simply because of common ancestry, supporting the theory that shell form in Rhagada is adapted to a broadly homogenous environment. Shell morphology in this genus has been demonstrated on more than one occasion to have the potential to adapt to different available environments, and hence shells should be used with a degree of caution for taxonomic interpretation.

Taxonomic study of a new green alga, Annulotesta cochlephila gen. et sp. nov. (Kornmanniaceae, Ulvales, Ulvophyceae), growing on the shells of door snails

Some algae are known to grow on shellfish shells. Most of these have been reported in aquatic environments. The species specificity for substrate shells varies, and some algae grow only on the shells of a certain species of shellfish, such as Pseudocladophora conchopheria (Cladophorales, Ulvophyceae) on Lunella coreensis (Trochida, Gastropoda). There are very few reports of algae that grow on land snails. In this study, we discovered green algae growing on the shells of six species of door snails (Clausiliidae) from nine localities in Japan. These green algae formed a green mat composed of thalli embedded in the extracellular matrix. The thallus was composed of aggregated oval cells and peripheral branched filaments. The cells possessed a single parietal chloroplast with a pyrenoid surrounded by two starch sheaths and transversed by a thylakoid. Oil droplets in the cell and ring-like structures on the cell wall surface were frequently observed. The 18S rDNA sequences of all shell-attached algae on different clausiliid species from different localities were almost identical and formed a new clade in the family Kornmanniaceae (Ulvales, Ulvophyceae). No other algae forming visible colonies on the clausiliid shell were found. These findings indicate the presence of specificity between the alga and clausiliid shells. Based on the results of morphological observation and molecular phylogenetic analysis, we propose a new genus and new species of shell-attached green alga, Annulotesta cochlephila.

Phylogeny, species delimitation and population structure of the steppe-inhabiting land snail genus Helicopsis in Eastern Europe

We here study the steppe-inhabiting land snail genus Helicopsis (Gastropoda: Geomitridae: Helicellinae) across Eastern Europe using mitochondrial 16S rDNA sequences and nuclear AFLP markers and compare the biogeographical patterns with those of other steppe-inhabiting organisms. The subdivision of Central and Eastern European Helicopsis reflects the geographical subdivision of the European steppe belt in Pontic, Pannonian and Northern steppes. The subdivision within Helicopsis is deeper, at the species level, than in most other steppe-inhabiting groups. Helicopsis populations from the Pontic steppes can be classified into two sister-species. Helicopsis lunulata includes mainly populations with depressed conical shells previously identified as H. striata, but also populations with disc-like shells previously identified as H. instabilis, and it is distributed mainly west of the Dnieper River. Most Helicopsis populations from east of the Dnieper, especially from Crimea, belong to the variable H. filimargo that includes H. gasprensis, H. retowskii, H. arenosa, H. luganica, H. martynovi and H. subfilimargo. The species inhabiting the Pannonian Basin and the Northern steppes form a well-supported monophylum, including H. hungarica in the Pannonian Basin, H. austriaca at the fringe of the Eastern Alps and H. striata mainly in the Northern steppes.

Biogeography of land snail genus Acusta (Gastropoda: Camaenidae): Diversification on East Asian islands

East Asia has highly diverse and endemic biota due to its complex geological and climatic history and its diversified topography. The continental and insular distributions of land snail genus Acusta in East Asia provide a good opportunity to compare the evolutionary processes in this group under different biogeographical conditions. In this study, we inferred the evolutionary history of the land snail genus Acusta by a molecular phylogeny and investigated how the palaeogeographic events shaped species diversity and the distribution of the Acusta genus within the island arc. A concatenated dataset generated from sequences of one nuclear (ITS2) and two mitochondrial (16S, COI) gene fragments, include most of nominal taxa of the genus, four related species and one outgroup. We constructed the phylogeny and the evolutionary history of the genus through maximum-likelihood and Bayesian inference methods, using a Bayesian molecular clock and ancestral range estimation. Our results suggested that currently recognized species in Acusta are polyphyletic. The traditionally accepted concept of the affinity of Acusta and Bradybaena is not supported. The hypothesis of colonization via land bridges during the Pleistocene glaciations for the biota of East Asian islands is not supported. Instead, the origin and diversification of the genus Acusta was dated to the late Miocene-Pliocene from an area around North and Northeast China to South China and East Asian islands Three major evolutionary lineages were identified. Two of the major lineages demonstrate distinct evolutionary histories, as sympatric speciation is the major speciation process for the continental clade, while the insular clade originated from founder events. Taiwan functioned as an important source of diversification for species on the East Asian islands possibly through passive dispersal of different mechanisms. The sea level fluctuations caused by the Pleistocene glacial cycles play a role in the subsequent dispersion and diversification of species of the continental clade, such as the more recent range expansion of A. redfieldi from South China to Taiwan and Japan.

A Sicilian–Cretan biogeographical disjunction in the land snail genus Cornu (Gastropoda: Helicidae)

We report an unusual biogeographical disjunction between the western and the eastern Mediterranean region. Cornu (Gastropoda: Helicidae) is a western Mediterranean land snail genus. It includes Cornu (Cornu) aspersum, which originated in north-western Africa and was distributed by humans for food or accidentally, first throughout the Mediterranean region and, subsequently, to all continents except Antarctica. It also includes three species belonging to the subgenus Erctella, which are all endemic to Sicily. We discovered a new species of Cornu on the Greek island of Crete. The morphological and molecular genetic analyses showed that the species from Crete is a disjunct representative of the subgenus Erctella. We hypothesize that the disjunction originated by a long-distance dispersal event of the ancestors of the Cretan species from Sicily by birds or by sea currents, perhaps facilitated by a tsunami or a similar event. The Cretan lineage separated from the Sicilian species in the Late Miocene or Early Pliocene. This divergence time is compatible with the hypothesis that the ancestor of Cornu cretense sp. nov. was washed from Sicily to Crete by the Zanclean flood that refilled the Mediterranean basin after it had dried up during the Messinian salinity crisis.

Phylogenetic relationships of ghost slugs (Selenochlamys) and overlooked instances of limacization in Western Palaearctic Limacoidei (Gastropoda: Stylommatophora)

We analysed the phylogenetic relationships of the enigmatic ghost slug Selenochlamys with other Western Palaearctic Limacoidei based on mitochondrial and nuclear sequences. Selenochlamys is a carnivorous slug group from the Caucasus region. Until now, it has been classified in Trigonochlamydidae, which includes several carnivorous slug groups from the Caucasus region. However, the molecular phylogenetic analyses revealed that Selenochlamys originated from omnivorous snails belonging to Oxychilidae. The similarities of Selenochlamys and Trigonochlamydidae are convergences resulting from limacization, the evolutionary transition from shelled snails to slugs, and from the transition from herbivory or detritivory via omnivory to obligate carnivory. These two evolutionary trends occurred repeatedly within the Limacoidei. Phylogenetic analyses based on morphological characters are prone to underestimate the instances with which such recurrent evolutionary trends occurred, as they depend on the parsimony criterion. The molecular phylogenetic analyses revealed that Limacoidea and Parmacelloidea, which were at least partly based on characters associated with limacization, are polyphyletic. The molecular phylogenetic tree implied that 5-7 independent limacizations occurred in the Western Palaearctic Limacoidei. Half of these limacizations remained undetected in a previous parsimony analysis based on morphological characters. Moreover, the analyses revealed that Godwiniinae belong to Gastrodontidae, not Oxychilidae.

Structure-behaviour correlations between two genetically closely related snail species

Species, through their structure and composition, have evolved to respond to environmental constraints. Predator-prey interactions are among environmental pressures that can lead to speciation, but it remains unclear how this pressure can be related to the material structure and performance. Recently, two land snails, Karaftohelix editha and Karaftohelix gainesi, were found to exhibit divergent phenotypes and responses to predation despite sharing the same habitat and most of their genome. Indeed, under attack from a beetle, K. editha snails retract into their shell whereas K. gainesi snails swing their shell. In this paper, we looked at the microstructure, composition, morphology and mechanics of the shells of those two species and discuss potential relationships between material structure and the snail defence behaviour. The results of this study provide additional arguments for the role of predator-prey interactions on speciation, as well as an unusual approach for the design of biomimetic structures adapted to a particular function.

Cretaceous amber fossils highlight the evolutionary history and morphological conservatism of land snails

Other than hard bones and shells, it is rare for soft tissues to fossilize, but occasionally they are well-preserved in amber. Here, we focus on both modern and fossilized species of the land snail superfamily Cyclophoroidea. Phylogenetic relationships within the Cyclophoroidea were previously studied using extant species, but timing of divergence within the group remains unclear. In addition, it is difficult to observe morphological traits such as the chitinous operculum and periostracum of fossil snails due to their poor preservation potential. Here we describe nine species including a new genus and five new species of well-preserved fossil cyclophoroideans from the mid-Cretaceous Burmese amber. These fossils include not only the shell, but also the chitinous operculum and periostracum, soft body, and excrements. We present the first estimation of divergence time among cyclophoroidean families using fossil records and molecular data, suggesting extreme morphological conservatism of the Cyclophoroidea for nearly 100 million years.

Comparison of the Whole-Plastome Sequence between the Bonin Islands Endemic Rubus boninensis and Its Close Relative, Rubus trifidus (Rosaceae), in the Southern Korean Peninsula

Rubus boninensis is a rare endemic species found on the Bonin Islands with a very restricted distribution. It is morphologically most closely related to Rubus trifidus, occurring widely in the southern Korean peninsula and Japan. This species pair provides a good example of anagenetic speciation on an oceanic island in the northwestern Pacific Ocean-R. trifidus as a continental progenitor and R. boninensis as an insular derivative species. In this study, we firstly characterized the complete plastome of R. boninensis and R. trifidus and compared this species pair to another anagenetically derived species pair (R. takesimensis-R. crataegifolius). The complete plastome of R. trifidus was 155,823 base pairs (bp) long, slightly longer (16 bp) than that of R. boninensis (155,807 bp). No structural or content rearrangements were found between the species pair. Eleven hotspot regions, including trnH/psbA, were identified between R. trifidus and R. boninensis. Phylogenetic analysis of 19 representative plastomes within the family Rosaceae suggested sister relationships between R. trifidus and R. boninensis, and between R. crataegifolius and R. takesimensis. The plastome resources generated by the present study will help elucidate plastome evolution and resolve phylogenetic relationships within highly complex and reticulated lineages of the genus Rubus.

Ecological specialization resulting in restricted gene flow promotes differentiation in door snails

We tested the hypothesis that ecological specialization that affects dispersal promotes diversification by a comparison of the genetic structure of two sister species of door snails across their broadly overlapping ranges in the Crimean Mountains. The hypothesized effect of ecological specialization on diversification is supported by STRUCTURE analyses that showed that Mentissa gracilicosta that is restricted to limestone rocks, is subdivided into several distinct clusters, whereas all populations of the species adapted to more continuous habitat, the forests-dwelling Mentissa canalifera, were assigned to a single cluster. Furthermore, it is supported by AMOVAs that showed that a larger part of the genetic variation of M. gracilicosta is apportioned among populations than in M. canalifera. The stronger genetic differentiation of the M. gracilicosta populations corresponds to their more distinct morphological differentiation that resulted in the classification of M. gracilicosta into several geographical subspecies, whereas the more continuously distributed M. canalifera was not subdivided into subspecies. The stronger differentiation of populations of M. gracilicosta compared to M. canalifera can be ascribed to reduced gene flow between the isolated populations of M. gracilicosta and to founder events associated with the long distance dispersal events that are necessary for the colonization of isolated rocks by M. gracilicosta. In Central Europe, the Pleistocene climatic oscillations selected for species with high dispersal abilities, whereas the more stable climate in southern Europe facilitated the non-adaptive radiation of rock-dwelling door snails. Thus, the intrinsic ecological properties of these species groups contributed to the latitudinal diversity gradient.

Found, forgotten, and found again: systematics and distribution of Cooper’s Rocky Mountain snail (Oreohelix cooperi) on a sky island in the Canadian Prairies

The results of phylogeographic and biogeographic studies of organisms residing in isolated habitats provide key insights into processes of population differentiation, speciation, and endemicity. Several of the approximately 70 species of land snail in the genus Oreohelix Pilsbry, 1904 occur only on isolated sky islands on the North American Great Plains. The restricted distributions of these snails have led to concerns regarding their conservation status, particularly in western Canada where their systematics and distributions are poorly known. Cooper’s Rocky Mountain snail (Oreohelix cooperi (Binney, 1858)) has been reported from several sky islands in the northern United States. We evaluated morphological characteristics and sequence data for samples of putative O. cooperi collected from a sky island in the Cypress Hills area of southeastern Alberta and southwestern Saskatchewan. COI sequences matched O. cooperi from snails collected on sky islands in South Dakota and Wyoming and morphological analyses of shell shape and male genitalia were consistent with published descriptions of this species. COI and ITS2 sequences and morphological characteristics of these snails did not match other Oreohelix spp. found in the Cypress Hills and in the adjacent Rocky Mountains. Our results extend the distribution of O. cooperi into southern Canada and confirm its endemicity within sky islands of western North America.

Morphometrics and phylogeography of the cave-obligate land snail Helicodiscus barri (Gastropoda, Stylommatophora, Helicodiscidae)

Molecular studies have recently led to the detection of many cryptic species complexes within morphologically ambiguous species formerly undescribed by the scientific community. Organisms such as land snails are at a particularly higher risk of species misidentification and misinterpretation, in that gastropod systematics are based almost entirely on external shell morphology. Subterranean ecosystems are associated with especially high degrees of cryptic speciation, largely owing to the abiotic similarities of these systems. In this study, we attempt to diagnose the potential cryptic diversity in the troglobitic land snail Helicodiscusbarri. Land snails are generally associated with having low vagility, and as such this species’ broad, mosaic distribution indicates the misdiagnosis of this organism as a single species. We analyze both mitochondrial (16S, CO1) and nuclear (28S, H3) genetic data for 23 populations. Phylogeny for H.barri was reconstructed using both maximum-likelihood and Bayesian approaches to assess relationships among populations, and two species delimitation methods (mPTP and ABGD) were used to detect the presence of unique molecular operational taxonomic units (MOTUs). Species delimitation results revealed seven and sixteen MOTUs respectively, suggesting the presence of several cryptic lineages within H.barri. To assess how external shell morphology corresponds with patterns of genetic and environmental variation, two morphometric approaches were used incorporating 115 shells from 31 populations. Both morphometric approaches reveal a significant environmental influence on shell morphology, and one approach showed the significance of MOTU groups. We discuss the delimitation and morphometric results and additionally provide discussion on the taxonomic and conservation implications of this study.

Complex interplay of ancient vicariance and recent patterns of geographical speciation in north-western North American temperate rainforests explains the phylogeny of jumping slugs (Hemphillia spp.)

The history of the currently disjunct temperate rainforests of the Pacific Northwest of North America has shaped the evolution and diversity of endemics. This study focuses on how geological and climatic perturbations have driven speciation in the area by isolating lineages. We investigated the phylogenetic relationships and historical biogeography of the endemic jumping slugs (genus Hemphillia) using a multi-locus phylogeny. We evaluated the spatial distribution and divergence times of major lineages, generated ancestral area probabilities and inferred the biogeographical history of the genus. Our study revealed eight genetic lineages that formed three clades: one clade consisting of two Coast/Cascade lineages, and two reciprocally monophyletic clades that each contain a Coast/Cascade and two Rocky Mountains taxa. The results of the biogeographical analysis suggest that the ancestral range of the genus occupied Coast/Cascade habitats and then spread across into Northern Rocky Mountain interior habitats with subsequent fragmentations isolating coastal and inland lineages. Finally, there have been more recent speciation events among three lineage pairs that have shaped shallow structures of all clades. We add to our knowledge of the biogeographical history of the region in that we discovered diversification and speciation events that have occurred in ways more complex than previously thought.

Enigmatic incongruence between mtDNA and nDNA revealed by multi-locus phylogenomic analyses in freshwater snails

Phylogenetic incongruence has frequently been encountered among different molecular markers. Recent progress in molecular phylogenomics has provided detailed and important information for evolutionary biology and taxonomy. Here we focused on the freshwater viviparid snails (Cipangopaludina chinensis chinensis and C. c. laeta) of East Asia. We conducted phylogenetic analyses and divergence time estimation using two mitochondrial markers. We also performed population genetic analyses using genome-wide SNPs. We investigated how and which phylogenetic patterns reflect shell morphology. The results showed these two species could be separated into four major mitochondrial clades, whereas the nuclear clusters supported two groups. The phylogenetic patterns of both mtDNA and nDNA largely reflected the geographical distribution. Shell morphology reflected the phylogenetic clusters based on nDNA. The findings also showed these two species diversified in the Pliocene to early Pleistocene era, and occurred introgressive hybridisation. The results also raise the taxonomic issue of the two species.

A revision of Peronina Plate, 1893 (Gastropoda : Euthyneura : Onchidiidae) based on mitochondrial and nuclear DNA sequences, morphology and natural history

Peronina Plate, 1893 is a genus of onchidiids that live on the mud in mangrove forests. Peronina can be identified in the field by the lung opening at the margin between the ventral hyponotum and the dorsal notum, and by the distinctive scalloped notum edge. This genus was previously known only from the holotype of the type species, Peronina alta Plate, 1893, from eastern India. Onchidium tenerum Stoliczka, 1869 is moved to Peronina and applies to the same species as Peronina alta. Peronina species are described using an integrative approach (natural history, comparative anatomy and DNA sequences). Mitochondrial COI and 16S sequences and nuclear ITS2 and 28S sequences are used to independently test species boundaries. Mitochondrial sequences yielded three units separated by a large barcode gap, but nuclear sequences yielded two units. Because these two units are congruent with differences in the male copulatory apparatus, they are accepted as species. Explanations for highly divergent COI haplotypes within one species are discussed. Peronina tenera (Stoliczka, 1869) is distributed in the Bay of Bengal and the Strait of Malacca, while P. zulfigari Goulding & Dayrat, sp. nov. is endemic to the Strait of Malacca. The two species differ internally but are cryptic externally.

Molecular phylogeny of Candidula (Geomitridae) land snails inferred from mitochondrial and nuclear markers reveals the polyphyly of the genus

The genus Candidula (Geomitridae), consisting of 28 species in Western Europe as currently described, has a disjunct distribution in the Iberian Peninsula, Italy, the Balkans, the Aegean Islands, and one species on the Canary Islands. Although the genus is seemingly well defined by characters of the reproductive system, the relationships within the genus are still unclear and some authors have indicated a possible subgeneric division based on the internal morphology of the dart sac. Despite substantial phylogenetic incongruence, we present a well-resolved molecular phylogeny of Candidula based on two mitochondrial genes (COI and 16S rRNA), the nuclear rDNA region (5.8S rNRA + ITS2 + 28S rRNA) and seven additional nuclear DNA regions developed specifically for this genus (60SL13, 60SL17, 60SL7, RPL14, 40SS6, 60SL9, 60SL13a), in total 5595 bp. Six reciprocally monophyletic entities including Candidula species were recovered, grouping into two major clades. The incorporation of additional geomitrid genera allowed us to unequivocally demonstrate the polyphyly of the genus Candidula. One major clade grouped species from southern France and Italy with the widely distributed species C. unifasciata. The second major clade grouped all the species from the Iberian Peninsula, including C. intersecta and C. gigaxii. Candidula ultima from the Canary Islands was recovered as separated lineage within the latter clade and related to African taxa. The six monophyla were defined as six new genera belonging to different tribes within the Helicellinae. Thus, we could show that similar structures of the stimulatory apparatus of the genital system in different taxa do not necessarily indicate a close phylogenetic relationship in the Geomitridae. More genera of the family are needed to clarify their evolutionary relationships, and to fully understand the evolution of the stimulatory apparatus of the genital system within the Geomitridae.

At home at least: the taxonomic position of some north African Xerocrassa species (Pulmonata, )

In order to clarify the systematic position of Helix latastei Letourneux in Letourneux & Bourguignat, 1887, and Helix latasteopsis Letourneux & Bourguignat, 1887, a comprehensive approach using morphological and molecular methods is presented. The investigation of the genital organs of both species showed that they belong to the genus Xerocrassa Monterosato, 1892 with two very small dart sacs and a few tubiform glandulae mucosae. In our phylogenetic analysis using the mitochondrial markers COI, 16S and the nuclear cluster 5.8-ITS2-28S, the results of the anatomical research were confirmed. Thus, the genus Ereminella Pallary, 1919, which is based on H. latastei, becomes a junior synonym of Xerocrassa. A review of the genus-level taxa Xerobarcana Brandt, 1959, and Xeroregima Brandt, 1959, showed that these should also be considered as synonyms of Xerocrassa. A third species, Helix lacertara Bourguignat, 1863 from Algeria was found to be closely related to X. latastei based on its shell morphology. A map showing the distribution of the three species treated is supplied.

Burrowers from the Past: Mitochondrial Signatures of Ordovician Bivalve Infaunalization

Bivalves and gastropods are the two largest classes of extant molluscs. Despite sharing a huge number of features, they do not share a key ecological one: gastropods are essentially epibenthic, although most bivalves are infaunal. However, this is not the ancestral bivalve condition; Cambrian forms were surface crawlers and only during the Ordovician a fundamental infaunalization process took place, leading to bivalves as we currently know them. This major ecological shift is linked to the exposure to a different redox environoments (hypoxic or anoxic) and with the Lower Devonian oxygenation event. We investigated selective signatures on bivalve and gastropod mitochondrial genomes with respect to a time calibrated mitochondrial phylogeny by means of dN/dS ratios. We were able to detect 1) a major signal of directional selection between the Ordovician and the Lower Devonian for bivalve mitochondrial Complex I, and 2) an overall higher directional selective pressure on bivalve Complex V with respect to gastropods. These and other minor dN/dS patterns and timings are discussed, showing that the Ordovician infaunalization event left heavy traces in bivalve mitochondrial genomes.

High unexpected genetic diversity of a narrow endemic terrestrial mollusc

The Iberian Peninsula has an extensive record of species displaying strong genetic structure as a result of their survival in isolated pockets throughout the Pleistocene ice ages. We used mitochondrial and nuclear sequence data to analyze phylogeographic patterns in endemic land snails from a valley of central Portugal (Vale da Couda), putatively assigned to Candidula coudensis, that show an exceptionally narrow distributional range. The genetic survey presented here shows the existence of five main mitochondrial lineages in Vale da Couda that do not cluster together suggesting independent evolutionary histories. Our results also indicate a departure from the expectation that species with restricted distributions have low genetic variability. The putative past and contemporary models of geographic distribution of Vale da Couda lineages are compatible with a scenario of species co-existence in more southern locations during the last glacial maximum (LGM) followed by a post-LGM northern dispersal tracking the species optimal thermal, humidity and soil physical conditions.