Copse snail Arianta arbustorum (Linnaeus, 1758) (Gastropoda: Helicidae) in the Baltic Sea region: Invasion or range extension? Insights from phylogeographic analysis and climate niche modeling

The range of Arianta arbustorum is spreading eastwards across the Baltic Sea region. Because A. arbustorum is a common pest in agriculture and horticulture, understanding the origin and factors involved in the eastward range expansion of the land snail are important for future planning of species management. In the present study, we compared the genetic diversity of A. arbustorum in the recently established easternmost populations and across Europe using standard phylogeographic analyses on a mitochondrial marker (cytochrome c oxidase I). We also applied bioclimatic envelope modeling to determine the environmental factors responsible for the ongoing range shifts of A. arbustorum. The unique haplotype lineage was found in all Baltic Sea populations in contrast with the highly polymorphic populations from Central Europe and the Alps. The peripheral easternmost populations were fixed for the dominant haplotype of the Baltic lineage. Retrospective niche modeling confirmed previous assumptions of multiple glacial refugia of A. arbustorum in Europe. Our results also show that the emergence of new populations in the easternmost part of the A. arbustorum range and the presumptive loss of rear-edge populations in western Europe are most plausibly caused by ongoing climate change, which will have a remarkable effect on the future distribution of genetic diversity within the range of the copse snail.     

Geographic variation of resting behaviour in the land snail Arianta arbustorum (L.): Does gene flow prevent local adaptation?

The resting behaviour of the land snail Arianta arbustorum (L.) from different geographic areas in the eastern Swiss Alps was compared under uniform conditions in order to examine whether local populations had evolved adaptive differences.Differences were observed in resting site preferences of snails from different geographic provenances, which did not seem to be associated with any environmental variables. The observed patterns support the electrophoretic evidence from other studies that there is gene flow between geographically very close populations, above all, along streams. This gene flow may swamp incipient behavioural changes. Morphological differences in shell features, however, appear to take place in spite of gene flow.     

SPATIAL RELATIONSHIP AND GENE FLOW PATHS BETWEEN POPULATIONS OF THE ALPINE SNAIL ARIANTA ARBUSTORUM (PULMONATA: HELICIDAE)

The alpine snail Arianta arbustorum (Pulmonata, Helicidae) was sampled along an 8-km contour line in the Swiss Alps orthogonal to well-known altitudinal clines in life history and shell traits. The allele frequencies and the morphs of 16 populations were compared with habitats. Two hypotheses about the recolonization of the mountain slopes after the last glaciation were tested against the present population structure. The allele frequencies are best explained by the spatial structure whereas the morphs are better explained by the habitats. The genotypic distances point to a historical explanation by recolonization processes, the phenotypical dissimilarities to a selectionistic interpretation of the present distribution of the populations. The following conclusions are from the study of the spatial relationship and the gene flow paths for A. arbustorum at Mount Martegnas: (1) Streams are the main gene flow paths; gene flow is low, allowing differentiation of local populations. (2) Morphs and habitats are correlated, but the interpretation has to be made carefully. The spatial dependence of habitats has to be included into the analysis of selection. (3) The random assumption for gene flow of A. arbustorum is not a spatial isolation-by-distance model, but a functional isolation-by-distance model, assuming gene flow over the drainage system.     

Allozymic differentiation in the land snail Arianta arbustorum (Stylommatophora, Helicidae): historical inferences

The intraspecific genetic differentiation depends to a large part on historical factors. The mode of dispersal is an important determinant of the genetic diversity especially of newly founded populations. Fast long-distance colonization of formerly unsuitable habitats results in reduced genetic diversity and lineages originating from different glacial refugia form well-defined hybrid zones, where they meet. Slow dispersers, on the other hand, preserve their refugial genetic diversity. Paleontological findings and a previous analysis of mtDNA suggest that the land snail Arianta arbustorum, which today is widely spread across Europe, has survived the Pleistocene glaciations within the boundaries of permafrost. In the present paper, we asked, whether the differentiation of nuclear markers, i.e. allozymes, supports these results. We investigated the allozymic differentiation at 15 polymorphic loci in 14 Alpine and one English populations of the land snail A. arbustorum. Various tests of genetic population differentiation yielded ambiguous results. Allele frequencies differed significantly across populations and all but five pairwise F_ST values were significant. Genetic distances between populations were comparatively high. On the other hand, an exact test of population differentiation found no differences and the assignment of individuals to their populations of origin was poor. This indicates that allozymic differentiation is constrained. Whether these constraints are of natural or methodological nature remains open. Matrices of genetic and geographical distances were correlated only after removal of the English population from the analysis. Similarly, with one exception F_ST values increased as the number of regions included in the calculations increased. Thus, on a regional scale, we largely observed a pattern of isolation by distance, which does no longer hold on a larger scale. This is well in accordance with the previous findings based on mtDNA. Mitochondrial lineages were widely distributed across Europe and overlapped extensively. Considering the low potential for dispersal of a land snail, the patchy distribution of lineages, and the high genetic diversity also found in the present study suggests that A. arbustorum has survived the Pleistocene within the boundaries of permafrost.     

Random mating with respect to mating status in the simultaneously hermaphroditic land snail Arianta arbustorum

In promiscuous species with sperm storage, males are expected to show a preference for mating with virgin and young females to reduce the risk of sperm competition. In the simultaneous hermaphrodite land snail Arianta arbustorum, sperm production precedes egg production by 2–4 weeks, resulting in a short period of protandric hermaphroditism before shell growth is completed. In natural populations, copulating pairs involving individuals which have not yet completed shell growth (virgins) have been observed. We ran a series of mate-choice experiments to examine whether virgin and nonvirgin (experienced) individuals of A. arbustorum discriminate between virgin and nonvirgin mating partners. We also assessed the number of sperm delivered to partners with different mating status. Neither virgin nor nonvirgin snails showed any preference for mating with a virgin partner. In all test situations mating was random and the number of sperm delivered was not adjusted to the mating status of the partner. Mating success was mainly determined by the activity of the individual. The random mating pattern does not imply random fertilization of eggs because the presence of a sperm-digesting organ and the morphology of the sperm storage organ allow a selective storage and use of sperm in A. arbustorum.     

Density-dependent effects in a parasitic nematode,Elaphostrongylus rangiferi,in the snnail intermediate host

Summary Density-dependent effects in Elaphostrongylus rangiferi, a parasitic nematode in the CNS and muscular system of reindeer, were studied in a laboratory population of the snail intermediate host, Arianta arbustorum. The rates in parasite growth, development and mortality were all affected by parasite density. The effects on growth and development were, however, much more marked, than the effect on mortality.All density-dependent rates were intensified by decreasing snail size, and by snail starvation. The snail host showed marked tissue reactions against infection, and the intensity of these reactions increased with increasing parasite density. The mechanism behind the observed density-dependent rates is discussed, and is tentatively concluded to be competition for nutritive substances in the host tissue.The importance of a density-dependent developmental rate in natural populations of this parasite is discussed, and it is hypothesized that this effect may counteract the strong temperature-dependent developmental rate of E. rangiferi In a more general context it is pointed out that density-dependent developmental rates, although common amongst animal populations, has been neglected in models of population dynamics. Developmental rates are usually represented by a constant time lag in such models, but should be treated as a density-dependent variable.     

AGE DETERMINATION OF ARIANTA ARBUSTORUM (L.) (PULMONATA) BASED ON GROWTH BREAKS AND INNER LAYERS

The pulmonate snail Arianta arbustorum from the Swiss Alps wasaged using thin sections of the shell margins cut from markedindividuals. Shell layers at the apertural lip and growth breaksin the juvenile can give a reliable estimate of age. (Received 16 May 1986;     

Altitudinal variation in Arianta arbustorum (Mollusca,Pulmonata) in the Swiss Alps

Arianta arbustorum is a highly variable helieid snail found in Europe. We have studied biometrically its transition from low altitude where large dark phenotypes are typical, to higher altitudes in the Alps, where small light ones are found. Seven measurements and 10 colour characters were considered. Size varies with altitude while colours rather vary with habitats. Our observations on 5 alpine transects agree with those of previous authors who sampled other alpine areas. It indicates that the species' reaction to alpine conditions is general to large mountain regions. This provides a striking example of consistent variation. Previous authors claim that midland and alpine Arianta stem from different colonizing stocks. However, part of the variation found in the present study appears to be adaptive. Both interpretations can be reconciled.     

Parasitic mites influence intra‐ and interpopulational variation in sperm length in a simultaneous hermaphrodite land snail (Gastropoda: Helicidae)

Sperm morphology can be highly variable among species, but less is known about patterns of population differentiation within species. Sperm morphology is under strong sexual selection, may evolve rapidly, and often co‐varies with other reproductive traits that differ between populations. We investigated variation in sperm morphology in the simultaneous hermaphrodite land snail Arianta arbustorum in relation to parasitic mite infection. Variation in total sperm length and sperm head length was assessed in 23 populations sampled across the distributional range of the species in Central and Northern Europe. We found a pronounced variation in total sperm length among the populations studied, with a difference of 11.0% of total sperm length between the shortest and longest population means. Differences among populations explained 62.9% of the variance in total sperm length, differences among individual snails within population 23.4% and differences within individual snail 13.7%. Mantel tests showed that interpopulation differences in total sperm length increased significantly with geographical distance between populations. A minimal adequate model revealed that parasitic infection had a positive effect and longitude a negative effect on total sperm length. Thus, independent of the population examined, mite‐infected individuals of A. arbustorum produced larger sperm than uninfected snails and total sperm length decreased from west to east. Sperm head length also varied among populations, but it was not influenced by any of the factors examined. In a subsample of 12 populations restricted to the mountains of Switzerland (elevational range 440–2485 m a.s.l.), total sperm length decreased with increasing elevation. Our results suggest that selection pressures acting among populations may differ from those acting within. Stabilizing selection might be a possible mechanism for producing the reduced variation observed in sperm length within a population. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 1036–1046.     

Effects of population subdivision and catastrophes on the persistence of a land snail metapopulation

We modeled the dynamics of a metapopulation of the land snail Arianta arbustorum in north-eastern Switzerland to investigate the effect of population subdivision on the persistence of a land snail metapopulation and to analyze the interaction between spatial factors, population subdivision, and catastrophes. We developed a spatially structured, stochastic, age-structured metapopulation model with field data from previous studies on the metapopulation in Switzerland and experimental and meteorological data. The model incorporated distance-dependent dispersal through stream banks, correlated environmental fluctuations, and catastrophes resulting from heavy rains. The results point to various complex interactions among factors involved in metapopulation dynamics and suggest that in some cases population subdivision may act to decrease threats from environmental fluctuations and catastrophes.     

ALTITUDINAL VARIATION AND ADAPTIVE ZONES IN ARIANTA ARBUSTORUM: A NEW LOOK AT A WIDESPREAD SPECIES

Arianta arbustorum is a European land snail, occurring in bothlowland and mountainous regions. Its shell is usually globular,which makes the species aberrant among the Campylaeinae in shellshape, habitat, and wide, not exclusively montane range. Withincreasing altitudes, the shells usually decrease in size andbecome more conical. However, in some mountain stocks thereare populations with depressed shells, provided with an openumbilicus. This form (subspecies) is only known from formerPleistocene refugia. It is hypothesized that in the Pliocene, the primary montaneA. arbustorum, with a depressed shell, entered an additional,adaptive zone, while conquering damp lowland habitats. Thisresulted in an enormous range extension. In the new habitata different (globular) shell shape evolved and the species becamepolytypic. The subsequent glaciations wiped out most of theoriginal montane A. arbustorum with depressed shells. Wherethis had occurred, post-Pleistocene re-colonizing conspecificsnails with globular shells, found vacant territory and coulddevelop the dines mentioned before. The invading populationsdid not regain the original, montane, depressed shell shape.This shape was only retained in a few refugia, where the populationssurvived amidst the glaciers. (Received 9 February 1990; accepted 31 May 1990)     

Population regulation in the land snail Arianta arbustorum: density effects on adult size,clutch size and incidence of egg cannibalism

Summary The relationships between local population density and adult size, clutch size and spatial distribution of egg batches were investigated in 11 natural populations of the land snail Arianta arbustorum in a forest near Uppsala, Sweden. Shell size of adults decreased with increasing population density as did clutch size. Within populations, clutch size scaled allometrically with shell size indicating size-specific fecundity. It is hypothesized that food unpalatability caused by mucus deposition slows down juvenile growth rate in high density populations, resulting in small adults and thus reducing their fecundity in subsequent years. The influence of the distance between batches on the incidence of egg cannibalism by hatchlings was examined in a laboratory experiment. In this experiment the number of eggs cannibalized increased with decreasing distance to the batch of hatching snails. Thus, in the field, eggs of highly aggregated batches suffer a high risk of cannibalism. In the 3 populations with the highest snail density, 21–39% of all batches were deposited close to each other (nearest neighbour distance 5 cm, i.e. less than hatchlings more within 1 day). These findings indicate that egg cannibalism can act as a population regulating factor.     

Purification of cadmium-binding proteins from related species of terrestrial helicidae (gastropoda,mollusca): A comparative study

Summary Three species of terrestrial Helicidae (Helix pomatia, Cepaea hortensis andArianta arbustorum) were fed cadmium-rich diet in the laboratory. The snails accumulated high amounts of the metal in their hepatopancreas. Most cadmium and some zinc were found, after centrifugation, in the soluble fractions from which a cadmium-binding protein was isolated for each species by ion exchange and gel chromatography. The proteins contained different amounts of cadmium, but little or no zinc, and showed high absorption at 254 nm indicating the presence of cadmium-mercaptide bonds. After gel filtration, a molecular weight of 12000 was found for cadmium-binding proteins fromHelix pomatia andArianta arbustorum, whereas a molecular weight of 10 000 was found for a cadmium-binding protein fromCepaea hortensis. SDS-polyacrylamide gel electrophoresis showed one single band for each protein fromHelix pomatia andArianta arbustorum and suggested a molecular weight of 11000 for both species. Amino acid analysis revealed, for each protein, high amounts of cysteine (12–20%), glycine (15–19%), and serine (12–14%), and moderately elevated contents of lysine (9–13%) and alanine (4–8%), but no methionine and only traces, if any, of aromatic amino acids. The ratios of cadmium to cysteine were 1:5, 1:10 and 1:3 in the proteins fromHelix pomatia,Cepaea hortensis andArianta arbustorum, respectively. Some features of the isolated proteins resembled mammalian metallothioneins. Most characteristics, however, differed from true metallothioneins and were similar to cadmium-binding proteins found in some marine molluscs.     

DIFFERENCES IN RESTING-SITE PREFERENCE IN TWO COEXISTING LAND SNAILS, ARIANTA ARBUSTORUM AND ARIANTA CHAMAELEON (HELICIDAE), ON ALPINE SLOPES

Resting-site preference and patterns of spatial distributionwere examined in the sympatric land snails Arianta arbustorumand A. chamaeleon on two opposite slopes in the south-easternAlps, Austria. The two slopes did not differ in proportion ofA. arbustorum and A. chamaeleon (74.4% vs. 25.6% on the NNE-exposedslope and 68.3% vs. 31.7% on the SSW-exposed slope). Individualsof both species showed aggregated dispersion patterns. The nearest-neighbourmethod indicated that in both species snail aggregations predominantlyconsisted either of A. arbustorum or A. chamaeleon on the NNE-exposedslope with a mosaic of rocks and distinct patches of differentplants. On the SSW-exposed slope, which was less variable invegetation cover, snail aggregations consisted of conspecificand hetero-specific individuals. Juvenile and adult A. arbustorumpreferred to rest attached to leaves of Adenostyles alliariae,but avoided rock surfaces and patches of grass on the NNE-exposedslope. In contrast, juvenile and adult A. chamaeleon preferentiallyrested on rock surfaces, and also avoided grass patches. Juvenileand adult A. chamaeleon did not differ in resting-site preference,whereas small differences in resting sites were observed betweenjuvenile and adult A. arbustorum. Differences in resting-sitepreference is one way of niche differentiation which may allowindividuals of the two Arianta species to coexist. (Received 14 March 1996; accepted 8 July 1996)     

Contact-based transmission models in terrestrial gastropod populations infected with parasitic mites

Parasite transmission fundamentally affects the epidemiology of host-parasite systems, and is considered to be a key element in the epidemiological modelling of infectious diseases. Recent research has stressed the importance of detailed disease-specific variables involved in the transmission process. Riccardoella limacum is a hematophagous mite living in the mantle cavity of terrestrial gastropods. In this study, we experimentally examined whether the transmission success of R. limacum is affected by the contact frequency, parasite load and/or behaviour of the land snail Arianta arbustorum, a common host of R. limacum. In the experiment the transmission success was mainly affected by physical contacts among snails and slightly influenced by parasite intensity of the infected snail. Using these results we developed two different transmission models based on contact frequencies and transmission probability among host snails. As parameters for the models we used life-history data from three natural A. arbustorum populations with different population densities. Data on contact frequencies of video-recorded snail groups were used to fit the density response of the contact function, assuming either a linear relationship (model 1) or a second-degree polynomial relationship based on the ideal gas model of animal encounter (model 2). We calculated transmission coefficients (β), basic reproductive ratios (R₀) and host threshold population densities for parasite persistence in the three A. arbustorum populations. We found higher transmission coefficients (β) and larger R₀-values in model 1 than in model 2. Furthermore, the host population with the highest density showed larger R₀-values (16.47-22.59) compared to populations with intermediate (2.71-7.45) or low population density (0.75-4.10). Host threshold population density for parasite persistence ranged from 0.35 to 2.72 snails per m². Our results show that the integration of the disease-relevant biology of the organisms concerned may improve models of host-parasite dynamics.     

Expandable spermatheca influences sperm storage in the simultaneously hermaphroditic snail Arianta arbustorum

Summary

In many simultaneously hermaphroditic land snail species, the sperm storage organ (spermatheca) is highly structured, suggesting that the female function might be able to influence offspring paternity. Physical properties of the sperm storage organ, including its initial size and sperm storage capacity, may also affect fertilization patterns in multiply mated snails. We examined the structure, volume and tubule length of empty spermathecae in the land snail, Arianta arbustorum, and assessed differences in spermatheca size following a single copulation. The number of spermathecal tubules ranged from 2–7, but was not correlated with the volume of empty spermathecae. The volume of sperm stored in the spermatheca after a copulation was correlated with neither the number of spermathecal tubules nor copulation duration. Mean spermathecal volume more than doubled between two and thirty-six hours after sperm uptake, but the length of the spermathecal tubules did not change. Interestingly, the volume of sperm stored in the spermatheca seems not to be related to the size of the spermatophore and thus not to the number of sperm received (= allosperm). The amount of allosperm digested in the bursa copulatrix was highly variable and no significant relationship with the size of the spermatophore received was found. These findings suggest that numerical aspects of sperm transfer are less important in influencing fertilization success of sperm in A. arbustorum than properties of the female reproductive tract of the sperm receiver.     

Variation in multiple paternity and sperm utilization patterns in natural populations of a simultaneous hermaphrodite land snail

Mating frequency has important implications for patterns of sexual selection and sexual conflict, and hence for issues such as the maintenance of genetic diversity and speciation. We assessed the level of multiple paternity and sperm utilization patterns in four natural populations of the simultaneous hermaphrodite land snail Arianta arbustorum using four polymorphic microsatellite loci. A total of 1088 offspring from 26 wild‐caught snails were genotyped to determine the number of fathers siring each brood and paternity skew in succeeding clutches. Multiple paternity was detected in the offspring of all 26 mother snails examined with the contribution of two to six fathers. The four populations examined differed in the level of multiple paternity. Snails in the population with the highest density of adults showed the highest level of multiple paternity, whereas snails in the population with the lowest density exhibited the lowest value of multiple paternity. Highly skewed paternity patterns were found in the progeny of 15 (57.7%) of the 26 mother snails. The number and identity of fathers siring the offspring of single mothers also varied among successive clutches. Furthermore, genetic analyses indicate a low level of self‐fertilization in one of the four populations. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 350–361.     

Character coupling for taxa discrimination: a critical appraisal of quadratic assignment procedures (QAP)1

Taxa can be characterized by character coupling represented in similarity matrices. The customary methods of testing equality of variance-covariance matrices are based upon the multinormality assumption which is, however, frequently unacceptable in reality. Quadratic assignment procedures (QAP) have proved to be an alternative. They represent a type of computer-based test and utilize a random-permutation strategy to discover significant pattern correspondences between matrices. A comparison of the applicability of both testing methods requires an example with underlying multinormality. The samples of two species of land snails (Pulmonata, Helicidae), i. e. Arianta arbustorum (n = 104) and Arianta chamaeleon (n = 36), fulfil this requirement. Four parameters of shape and two parameters of spiral change were determined in each shell. The data serve as the basis for similarity matrices (variance-covariance, product-moment and rank order correlations). The inspection of methods reveals that QAP are suitable for correlation matrices, but can be applied for variance-covariance matrices with limitations only. Nevertheless, they are recommended procedures in taxonomy and evolutionary biology. Straightforward application, independence from distributional assumptions, and the possibility to test hypotheses of character coupling are advantageous features. The snail species are significantly discriminated by character coupling. Also, their parameters of shape and spiral change are morphologically integrated in a different way.     

Vegetation differentiation and secondary succession on a limestone hill in southern Poland

Abstract. The vegetation of the SkoHzanka Reserve, situated on a limestone hill near Krakow, was examined over a 30 year period, using the Braun-Blanquet method. With the help of a numerical classification eight types of grassland communities were distinguished, belonging to the classes Sedo-Scleranthetea, Nardo-Callunetea and Festuco-Brometea, and 11 types of woodland communities, both remnants of ancient woodlands from the classes Querco-Fagetea and Vaccinio-Piceetea and more recent woods. In the case of grasslands the results of detrended correspondence analysis (DCA) indicated that the largest variation was associated with the soil type. Woods on sandy soils are very different from those on calcareous soils, and the younger recent woods are very different from the ancient woodlands. An analysis of historical cartographic material and aerial photographs shows that in the last few decades the area of recent woods has increased considerably at the expense of grasslands. Changes in species diversity in the woods during secondary succession and their successional convergence were examined and discussed. It was found that young and mature woods on sandy soils are more similar to each other than young and mature woods on calcareous soils. These differences are mainly related to the fact that many woodland herb species growing in rich, broadleaved ancient woods are unable to colonize recent woods since they have a limited colonization capacity.     

Woodland area,species turnover and the conservation of bird assemblages in lowland England

A study over 4 years into the number of breeding bird species and species turnover (extinctions and colonisations) in relation to area was conducted in 35 woodlands, set in an intensively farmed landscape, in north-east Essex, UK. A total of 46 species was recorded. The number of species breeding increased with woodland area; the slope of the species–area relationship did not differ between years. Habitat diversity was the only other measured variable to influence species richness. Absolute species turnover was independent of woodland area but relative turnover declined with increase in woodland area. The numbers of territories of nine species were determined. For four summer visitors the number of woods occupied increased as the overall populations increased but, for the other species, changes in overall population size led to changes in numbers in occupied woods. Chaffinch Fringilla coelebs and Song Thrush Turdus philomelos were more associated with woodland edges, Nightingale Luscinia megarhynchos, Garden Warbler Sylvia borin, Chiffchaff Phylloscopus collybita and Willow Warbler P. trochilus with interiors. Several species showed an inverse relationship between population density and woodland area. Collections of small woods hold similar species richness to single large woods. While the acquisition of large woods for conservation purposes should be a priority, the extension of smaller woods to a size of about 10 ha would be highly beneficial to both the species richness and population stability of regional woodland bird assemblages.