Does vicariance shape biotas? Biogeographical tests of the vicariance model in the north‐west European land snail fauna

Aim To investigate the importance of vicariance in shaping the north‐west European land snail fauna. Location North‐west Europe. Methods We tested whether there is a non‐random congruence, i.e. a clustering of species ranges, using a Monte Carlo procedure with a null model that generates range data sets such that their range size distribution, the species richness distribution of the geographic cells and the spatial autocorrelation of the occurrences of a taxon approach the parameters in the real data set. Biotic elements, groups of species with similar ranges, were delimited with Model based Gaussian clustering. The prediction that closely related species belong to different biotic elements, has been tested with a chi‐square test. Results The distribution areas of the north‐west European land snail species are significantly clustered as predicted by the vicariance model. One widespread and seven regional biotic elements were identified. Contrary to the predictions of the vicariance model, closely related north‐west European land snail species belong significantly more often to the same biotic element than should be expected by chance. Main conclusions The clustering of closely related north‐west European land snail species within the same biotic element indicates that speciation modes other than vicariance were frequent or that the imprint of vicariance on the ranges was obscured by extensive post‐speciational dispersal. Extensive dispersal may have been caused by Pleistocene climatic fluctuations. The core areas of the regionally restricted biotic elements might indicate the positions of glacial refugia of land snails.     

Distribution patterns of land snails in Ugandan rain forests support the existence of Pleistocene forest refugia

Aim We investigated whether the biogeographical patterns expected if the East African fauna was affected by cycles of contraction to refugia and expansion of ranges, as has been previously hypothesized, can be found in the land snail fauna of rain forests in Uganda. Location The Albertine Rift region and the Lake Victoria forest belt in Uganda. Methods Snails and slugs were sampled in 60 plots in 13 rain forests, and small species were extracted from 5‐L leaf litter samples. Relative species richness was calculated by rarefaction. The influence of putative determinants of species richness was examined by bivariate correlation and multiple regression. Clustering and nestedness were tested by Monte Carlo simulations with a null model that considers the range size distribution, the species richness distribution of the forests, and the spatial autocorrelation of the occurrences of each species. Biotic elements were determined by model‐based Gaussian clustering. Results A total of 169 land snail species were recorded from 13 Ugandan rain forests. Relative species richness increases with rainfall and altitude, and decreases with evaporation and distance from the putative East Congolian refugia. Mean annual rainfall and distance from the putative East Congolian refugia were included in the best multiple regression model. The distribution areas of the Ugandan land snails are significantly clustered. Two montane, two lowland and a northern biotic element were found. The mean range extension increases with increasing distance from the putative East Congolian refugia. Moreover, the ranges of the Ugandan land snails are significantly nested. The centre of the sets of nested subsets is in the Virunga Mountains, close to the putative East Congolian refugia. Main conclusions The decrease of diversity with increasing distance from the putative East Congolian refugia, the clustering and nestedness of ranges, and the range size increase with increasing distance from the refugia indicate that the East African land snail fauna was affected by cycles of contraction to refugia and expansion of ranges. The significant clustering and nestedness cannot be explained by current environmental conditions. Given the environmental history, it can be supposed that the lowland elements expanded post‐glacially, whereas the ranges of the montane species are probably currently contracting.     

Biogeography of the Helicoidea (Mollusca: Gastropoda: Pulmonata): land snails with a Pangean distribution

The biogeography of helicoid land snails was investigated using cladistic methods. Parsimony analysis under Assumption 0 yielded twelve area cladograms (length=25, c.i.=0.76, r.i.=0.86). The pattern of vicariance for the Helicoidea indicated that families originated with the break up of eastern Gondwana and Laurasia between the late Mesozoic and mid-Tertiary, and possible vicariance events are identified. It is proposed that Asian terranes, located between India and Australia, maintained contact with northern Australia until the late Cretaceous, which is later than is suggested in current palaeogeographical hypotheses.     

The influence of recent geography, palaeogeography and climate on the composition of the fauna of the central Aegean Islands

Partial Mantel tests and structural equation models were used to investigate the influence of recent geography, palaeogeography and climate on the composition of the fauna of the central Aegean Islands. The composition of land snail and isopod island faunas was significantly influenced by recent and by Pliocene geography. Only Pleistocene palaeogeography had a significant influence on the composition of tenebrionid beetle island faunas. The composition of butterfly island faunas was influenced by recent and by Miocene geographical distances. The composition of reptile island faunas was correlated with recent and Pliocene geography as well as with Pleistocene and/or Miocene geographical distances. Island area influenced only the composition of the island faunas of the volant butterflies, and not that of the less mobile land snails, land isopods, tenebrionid beetles and reptiles. This might indicate that butterflies are able to colonize large islands with suitable habitats even if such islands are comparatively far from source areas more frequently than can the nonvolant groups. Influence of a climatic parameter, namely annual precipitation, on faunal composition was found only for reptiles.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 785–795.     

Biotic element analysis in biogeography

Biotic element analysis is an alternative to the areas-of-endemism approach for recognizing the presence or absence of vicariance events in a given region. If an ancestral biota was fragmented by vicariance events, biotic elements or clusters of distribution areas should emerge. We propose a statistical test for clustering of distribution areas based on a Monte Carlo simulation with a null model that considers the spatial autocorrelation in the data. The hypothesis tested is that the observed degree of clustering of ranges can be explained by the range size distribution, the varying number of taxa per cell, and the spatial autocorrelation of the occurrences of a taxon alone. A method for the delimitation of biotic elements which uses model-based Gaussian clustering is introduced. We demonstrate our methods and show the importance of grid size by means of a case study, an analysis of the distribution patterns of southern African species of the weevil genus Scobius. The example highlights the difficulties in delimiting areas of endemism if dispersal has occurred and illustrates the advantages of the biotic element approach.     

Where and why? Bees,snail shells and climate: Distribution of Rhodanthidium (Hymenoptera: Megachilidae) in the Iberian Peninsula

Species distribution patterns are widely studied through species distribution models (SDMs), focusing mostly on climatic variables. Joint species distribution models (JSDMs) allow inferring if other factors (biotic interactions, shared phylogenetic history or other unmeasured variables) can also have an influence on species distribution. We identified current distributional areas and optimal suitability areas of three species of the solitary snail‐shell bee Rhodanthidium (Hymenoptera: Megachilidae), and their host gastropod species in the Iberian Peninsula. We undertook SDMs using Maxent software, based on presence points and climatic variables. We also undertook JSDMs for the bees and the snails to infer if co‐occurrence could be a result of biotic interactions. We found that the three bee species: (1) use at least five different species of Mediterranean snails; (2) use empty shells not only for nesting but also for sheltering when there is adverse weather and during the night; (3) have their most suitable areas in the eastern and southern Iberian Peninsula, mostly on limestone areas; and (4) have their optimal range under Mediterranean climatic values for the studied variables. There is positive co‐occurrence of Rhodanthidium with the gastropod species, especially with the snail Sphincterochila candidissima. The contribution of the environmental component to the co‐occurrence is less than that of the residual component in those cases, suggesting that: (i) the use of biotic resources (between Rhodanthidium and the gastropod species); (ii) shared phylogenetic history (between R. septemdentatum and R. sticticum); or (iii) unmeasured variables are largely responsible for co‐occurrence.     

Evolutionary relationships among the Pulmonate land snails and slugs (Pulmonata, Stylommatophora)

We have incorporated an additional 56 species of land snails and slugs in our ribosomal (r) RNA molecular phylogeny. The new taxa include representatives of several important groups. The molecular tree now includes 160 species of stylommatophoran land snails and slugs in 144 genera in 61 families. In the rDNA tree, the Stylommatophora are principally divided into an 'achatinoid' and a 'non-achatinoid' clade. Within these clades, several major land snail groups, including the Orthurethra, Elasmognatha, Limacoidea, and Helicoidea, are supported. Overall, the rDNA molecular phylogeny has remained stable following the incorporation of the additional taxa, with these additions having little impact on the major evolutionary patterns in the tree. Taxonomic coverage of the Orthurethra, Orthalicidae, Camaenidae, and Bradybaenidae is increased significantly. The camaenids and bradybaenids form a complex, and both appear to be paraphyletic. Several families of uncertain affinity, such as the Sagdidae and Thyrophorellidae, are included for the first time. The Sagdidae are shown to belong to the Helicoidea, and the Thyrophorellidae to the Achatinoidea.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 593–610.     

The biogeography of land snails in the islands of the Gulf of Guinea

Data on land snail diversity in the Gulf of Guinea islands is presented and the biogeography of the Gulf of Guinea fauna is discussed with reference to island snail faunas in the other areas of the world. Although the land snail faunas of the four islands clearly have west and central African affinities, speciation events following rare colonizations have led to high rates of endemism at the species and generic levels. The influence of island size, altitude, isolation and other factors on the development of the land snail faunas is discussed. The effect of land use changes on the land snail fauna over the last 150 years is evaluated. Current threats include recent changes in agricultural practice leading to the destruction of snail habitats in both forest and plantation areas. The potential threat posed by introduced species is also discussed. The Gulf of Guinea snail faunas appear to be in relatively good health in comparison to many other island snail faunas. However, the uniqueness of the faunas makes it imperative that further ecological and taxonomic research is undertaken both to understand the processes by which they developed and to evaluate the current status of many species in terms of distribution and threats.     

Inference of evolutionary patterns of the land snail Albinaria in the Aegean archipelago: is vicariance enough?

Mitochondrial DNA sequences from 16S rRNA and ATPase8 genes were used to investigate phylogeographic patterns of the land snail Albinaria (Gastropoda: Clausiliidae) in the Aegean archipelago. Forty-two populations of Albinaria were analyzed, mainly A. turrita, A. caerulea and A. brevicollis, collected from 22 Aegean islands and certain surrounding regions. Maximum parsimony, maximum likelihood and Bayesian analyses on 16S rRNA and combined datasets produced trees that share significant similarity and reveal a phylogeny with distinct branches which are in general, but not full, agreement with current taxonomy. The Aegean taxa are not monophyletic as a whole, since A. turrita does not cluster with A. caerulea and A. brevicollis. The latter form a distinct monophyletic cluster, within which two groups are evident. These groups do not readily correspond to currently accepted morphospecies; one contains the populations that inhabit the central part of the archipelago plus some eastern islands, while the other contains populations whose geographic distribution is restricted to the southeastern part of the archipelago. The divergence between these two groups is attributed to vicariance events that primarily shape contemporary distributions. Although dispersal may also be present, certain small- and large-scale vicariance events can be traced; alternative phylogeographic hypotheses are discussed in view of the historical biogeography of the region.     

Southern isolation and northern long‐distance dispersal shaped the phylogeography of the widespread,but highly disjunct,European high mountain plant Artemisia eriantha (Asteraceae)

We investigated the range dynamics of Artemisia eriantha, a widespread, but rare, mountain plant with a highly disjunct distribution in the European Alpine System. We focused on testing the roles of vicariance and long‐distance dispersal in shaping the current distribution of the species. To this end, we collected AFLP and plastid DNA sequence data for 17 populations covering the entire distributional range of the species. Strong phylogeographical structure was found in both datasets. AFLP data suggested that almost all populations were genetically strongly differentiated, with 58% of the overall genetic variation partitioned among populations. Bayesian clustering identified five groups of populations: Balkans, Pyrenees, Central Apennines, one southwestern Alpine population and a Widespread cluster (eastern Pyrenees, Alps, Carpathians). Major groups were supported by neighbor‐joining and NeighbourNet analyses. Fourteen plastid haplotypes were found constituting five strongly distinct lineages: Alps plus Pyrenees, Apennines, Balkans, southern Carpathians, and a Widespread group (eastern Pyrenees, northern Carpathians, Mt. Olympus). Plastid DNA data suggested that A. eriantha colonized the European Alpine System in a westward direction. Although, in southern Europe, vicariant differentiation among the Iberian, Italian and Balkan Peninsulas predominated, thus highlighting their importance as glacial refugia for alpine species, in temperate mountain ranges, long‐distance dispersal prevailed. This study emphasizes that currently highly disjunct distributions can be shaped by both vicariance and long‐distance dispersal, although their relative importance may be geographically structured along, for instance, latitude, as in A. eriantha. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174 , 214–226.     

Invasive Temperate Species are a Threat to Tropical Island Biodiversity

To protect the remaining biodiversity on tropical islands it is important to predict the elevational ranges of non-native species. We evaluated two hypotheses by examining land snail faunas on the eastern (windward) side of the island of Hawaii: (1) the latitude of a species' native region can be used to predict its potential elevational range and (2) non-native temperate species, which experience greater climatic fluctuations in their native range, are more likely to become established at higher elevations and to extend over larger elevational ranges than non-native tropical species. All non-native tropical species were distributed patchily among sites ≤500 m and occupied small elevational ranges, whereas species introduced from temperate regions occupied wide elevational ranges and formed a distinct fauna spanning elevations 500–2000 m. Most native land snail species and ecosystems occur >500 m in areas dominated by temperate non-native snail and slug species. Therefore, knowing the native latitudinal region of a non-native species is important for conservation of tropical island ecosystems because it can be translated into potential elevational range if those species are introduced. Because temperate species will survive in tropical locales particularly at high elevation, on many tropical islands the last refuges of the native species, preventing introduction of temperate species should be a conservation priority.     

Vicariance and endemism in a Neotropical savanna hotspot: distribution patterns of Cerrado squamate reptiles

Aim To test predictions of the vicariance model, to define basic biogeographical units for Cerrado squamates, and to discuss previous biogeographical hypotheses. Location Cerrado; South American savannas south of the Amazon, extending across central Brazil, with marginal areas in Bolivia and Paraguay and isolated relictual enclaves in adjacent regions. Methods We compiled species occurrence records via field sampling and revision of museum specimens and taxonomic literature. All species were mapped according to georeferenced locality records, and classified as (1) endemic or non‐endemic, (2) typical of plateaus or depressions, and (3) typical of open or forested habitats. We tested predictions of the vicariance model using biotic element analysis, searching for non‐random clusters of species ranges. Spatial congruence of biotic elements was compared with putative areas of endemism revealed by sympatric restricted‐range species. Effects of topographical and vegetational mosaics on distribution patterns were studied according to species composition in biotic elements and areas of endemism. Results We recorded 267 Cerrado squamates, of which 103 (39%) are endemics, including 20 amphisbaenians (61% endemism), 32 lizards (42%) and 51 snakes (32%). Distribution patterns corroborated predictions of the vicariance model, revealing groups of species with significantly clustered ranges. An analysis of endemic species recovered seven biotic elements, corroborating results including non‐endemics. Sympatric restricted‐range taxa delimited 10 putative areas of endemism, largely coincident with core areas of biotic elements detected with endemic taxa. Distribution patterns were associated with major topographical and vegetational divisions of the Cerrado. Endemism prevailed in open, elevated plateaus, whereas faunal interchange, mostly associated with forest habitats, was more common in peripheral depressions. Main conclusions Our results indicate that vicariant speciation has strongly shaped Cerrado squamate diversity, in contrast to earlier studies emphasizing faunal interchange and low endemism in the Cerrado vertebrate fauna. Levels of squamate endemism are higher than in any other Cerrado vertebrate group. The high number of recovered endemics revealed previously undetected areas of evolutionary relevance, indicating that biogeographical patterns in the Cerrado were poorly represented in previous analyses. Although still largely undocumented, effects of vicariant speciation may be prevalent in a large fraction of Cerrado and Neotropical biodiversity.     

History, island area and habitat availability determine land snail species richness of Aegean islands

Aim We examined the species-area relation of Aegean land snails, comparing different models to describe the relation. By examining those factors other than area that may also affect species richness, we tested whether the Aegean land snail fauna was more influenced by equilibrial migration and colonization processes, or rather is conservative and relictual. Location The Aegean archipelago (Greece). Methods Sixty-five islands were examined. Data were taken from own collections and from literature sources. Multiple regression analysis was used to test the null hypothesis of no relationship between species richness and island area, elevation, distance to the next larger island, and the presence and extent of calcareous substrate. Results The single most important factor determining land snail species number was area. While colonization-extinction dynamics have frequently been cited to explain this result, this conclusion was not tenable in this study as it was contradicted by species number not being related to the islands’ distances to neighbouring larger islands, after accounting for other factors affecting species number. We also found that habitat diversity affected species richness even after accounting for the effects of area: both increased elevation and greater extent of calcareous substrate on islands resulted in higher species number. This effect was most likely due to the fact that particular ecological conditions increased the probability that particular species could survive on an island. We compared the utility of the power and extreme-value function models of the species-area relation and found that both gave substantially the same results. However, fitting the power function model using nonlinear regression was of questionable utility. Main conclusions We conclude that the snail fauna of the Aegean is relictual, not equilibrial. The unusually high number of land snail species found on Crete is consistent with this conclusion. Crete is a currently united island which was separated into at least six smaller islands for 7–9 million years during the Neogene. Our results are consistent with the hypothesis that Crete still hosts a large number of endemic species of these paleoislands, resulting in a total number of species in excess of what would be expected based on area alone.     

Diversity and Biotic Homogenization of Urban Land-Snail Faunas in Relation to Habitat Types and Macroclimate in 32 Central European Cities

The effects of non-native species invasions on community diversity and biotic homogenization have been described for various taxa in urban environments, but not for land snails. Here we relate the diversity of native and non-native land-snail urban faunas to urban habitat types and macroclimate, and analyse homogenization effects of non-native species across cities and within the main urban habitat types. Land-snail species were recorded in seven 1-ha plots in 32 cities of ten countries of Central Europe and Benelux (224 plots in total). Each plot represented one urban habitat type characterized by different management and a specific disturbance regime. For each plot, we obtained January, July and mean annual temperature and annual precipitation. Snail species were classified into either native or non-native. The effects of habitat type and macroclimate on the number of native and non-native species were analysed using generalized estimating equations; the homogenization effect of non-native species based on the Jaccard similarity index and homogenization index. We recorded 67 native and 20 non-native species. Besides being more numerous, native species also had much higher beta diversity than non-natives. There were significant differences between the studied habitat types in the numbers of native and non-native species, both of which decreased from less to heavily urbanized habitats. Macroclimate was more important for the number of non-native than native species; however in both cases the effect of climate on diversity was overridden by the effect of urban habitat type. This is the first study on urban land snails documenting that non-native land-snail species significantly contribute to homogenization among whole cities, but both the homogenization and diversification effects occur when individual habitat types are compared among cities. This indicates that the spread of non-native snail species may cause biotic homogenization, but it depends on scale and habitat type.     

Species richness, environmental heterogeneity and area: a case study based on land snails in Skyros archipelago (Aegean Sea, Greece)

Aim To test the performance of the choros model in an archipelago using two measures of environmental heterogeneity. The choros model is a simple, easy‐to‐use mathematical relationship which approaches species richness as a combined function of area and environmental heterogeneity. Location The archipelago of Skyros in the central Aegean Sea (Greece). Methods We surveyed land snails on 12 islands of the archipelago. We informed the choros model with habitat data based on natural history information from the land snail species assemblage. We contrast this with habitat information taken from traditional vegetation classification to study the behaviour of choros with different measures of environmental heterogeneity. R² values and Akaike's information criterion (AIC) were used to compare the choros model and the Arrhenius species–area model. Path analysis was used to evaluate the variance in species richness explained by area and habitat diversity. Results Forty‐two land snail species were recorded, living in 33 different habitat types. The choros model with habitat types had more explanatory power than the classic species–area model and the choros model using vegetation types. This was true for all islands of the archipelago, as well as for the small islands alone. Combined effects of area and habitat diversity primarily explain species richness in the archipelago, but there is a decline when only small islands are considered. The effects of area are very low both for all the islands of the archipelago, and for the small islands alone. The variance explained by habitat diversity is low for the island group as a whole, but significantly increases for the small islands. Main conclusions The choros model is effective in describing species‐richness patterns of land snails in the Skyros Archipelago, incorporating ecologically relevant information on habitat occupancy and area. The choros model is more effective in explaining richness patterns on small islands. When using traditional vegetation types, the choros model performs worse than the classic species–area relationship, indicating that use of proxies for habitat diversity may be problematic. The slopes for choros and Arrhenius models both assert that, for land snails, the Skyros Archipelago is a portion of a larger biogeographical province. The choros model, informed by ecologically relevant habitat measures, in conjunction with path analysis points to the importance of habitat diversity in island species richness.     

Drivers of Central European urban land snail faunas: the role of climate and local species pool in the representation of native and non-native species

The importance of macroclimate and dispersal limitation in the broad-scale variation of European urban land snail assemblages is likely to differ between native and non-native species because of the southern origin of many non-native snails, often spread by humans. We sampled land snails in each of 32 European cities and compiled from the literature a list of land snail species reported from the surroundings of each city. To quantify the predictive power of climate and local species pools, beta-sim dissimilarity matrices of both native and non-native species were explored using MDS and RDA ordination methods, Mantel tests with bootstrapping of each dataset, and multivariate homogeneity analysis of group variances. We observed no significant relation between the numbers of non-native species found in the cities and their surroundings (p > 0.133), while the percentage of native species in the cities derived from their local species pools decreased significantly with the increasing species richness of local faunas (r_S = ?0.75, p < 0.001). Assemblage variation of urban native species was explained mostly by the difference between mean January and July temperatures (21.3 %), with the major role of July temperature (18.0 %). In contrast, variation of non-native species assemblages was mainly explained by January temperature (19.9 %). The congruence in faunal similarities between the cities and the surrounding areas was higher in native (r = 0.46, p < 0.001) than in non-native species (r = 0.36, p < 0.001). Overall native faunas were significantly more homogeneous than the non-native faunas. Our results suggest that recent climate warming may foster geographical expansions of many non-native land snail species as their distributions are controlled mainly by January temperature.     

FLYING SNAILS--HOW FAR CAN TRUNCATELLINA (PULMONATA: VERTIGINIDAE) BE BLOWN OVER THE SEA?

With populations of land snails of very small size like Vertiginidae,questions have arisen as to whether populations of relativelydistant islands in archipelagos are really isolated from eachother. Apart from other flight agencies, airborne transportof loose specimens is not improbable in stormy weather conditions.Currently, mechanisms of wind-borne transport of sand particlesover short and long distances have been intensively studied.The results are available in the literature on sediments, allowingthe calculation of probable flight distances for particles insuspension. For living snails of the Aegean species Truncatel-lina rothi,an average fall velocity of 2.6–2.7 m s^–1 has beendetermined in experiments under laboratory conditions. Applyingthese results, Truncatellina living on an island at 100 m altitudeand close to the coast could be transported up to several kilometersin heavy storms, which are not uncommon in the Aegean archipelago(Greece). This would imply that many of the Aegean islands arenot effectively isolated for minute snail species, and thatgenetic interchange between island populations is probably frequent. (Received 3 April 1996; accepted 27 January 1997)     

A biogeographical analysis of terrestrial isopods (Isopoda, Oniscidea) from the central Aegean islands (Greece)

Abstract. Terrestrial isopods (Isopoda, Oniscidea) of forty-three central Aegean islands and islets are analysed from a biogeographical point of view. The oniscid fauna consists of sixty-nine species, thirty-two genera and fourteen families and is characterized by Aegean elements that have an eastern Mediterranean origin. Endemism is at the level of 20%, similar to that of oniscids from other Mediterranean archipelagoes. Analysis of species distribution through both idiographic and quantitative approaches (faunal similarity among islands using Jaccard's index, simple matching indices and the UPGMA clustering technique) resulted in the recognition of a major disjunction between Kykladesplus-Ikaria and eastern islands-plus-Astypalea and four noteworthy island groups: the eastern islands, Naxos-Ikaria, Amorgos, and all other Kyklades. Island similarities are generally consistent with the known palaeogeography of the area with the exception of Ikaria's placement with Naxos among the Kyklades. Also, the 'eastern' character of Astypalea is in conflict with evidence from other known taxa.     

Polymorphism of a genital organ under sexual selection in Monacha kuznetsovi from the Caucasus (Gastropoda: Hygromiidae)

During mating the dart apparatus of the land snail group Helicoidea transfers an allohormone that increases paternity success. Thus, this organ is under sexual selection. Despite this selective advantage, the dart sac has independently been lost in many lineages in the Helicoidea, presumably because natural selection counteracts sexual selection. However, the selective pressures that result in the loss of the organ have not been examined experimentally because most species show no variation in the presence or absence of the dart sac. Using nuclear multilocus data and mitochondrial sequences, we show that a so far misidentified morph of the genus Monacha without appendicula, a homologue of the dart sac, is conspecific with M. kuznetsovi with appendicula. This is only the second case of polymorphy with regard to the presence or absence of the dart sac or its homologue in the Helicoidea. Monacha kuznetsovi might therefore be a suitable model organism to study how the interplay between sexual selection and natural selection may affect the evolution of the genital organs.     

Exceptionally poor land snail fauna of central Yakutia (NE Russia): climatic and habitat determinants of species richness

There is an ongoing debate on the causes of the latitudinal diversity gradient, but diversity decline towards high latitudes is poorly documented for many invertebrate taxa. Therefore, we sampled land snail assemblages at 79 sites and in various habitat types in central Yakutia, a region with extremely continental, cool and dry climate. We tested whether habitats lacking suitable shelters for winter survival harbour less species than those with vegetation cover that softens climatic extremes. Both local species diversity and regional species diversity were extremely low: 13 species were recorded in total with an average of 1.4 species per site. While the majority of grassland sites were without snails (26 of 34 sites), forest sites supported at least one snail species in most cases (38 of 45 sites). Within grasslands, snail occurrences were associated with a higher herb-layer biomass. Numbers of snail species correlated with the amount of available calcium only in forests, in which species accumulation towards more favourable habitats was possible due to softening of climate harshness. As minute snails are known to be effective passive dispersers and the study area was not glaciated during the last glacial stage, there was certainly enough time for colonization of all favourable habitats. Our results suggest climatically driven limitations of both local and regional land snail diversity in central Yakutia. We conclude that the hypothesis of climate harshness remains the most probable explanation of a sharp drop in land snail diversity in high-latitude areas with cold climate.