THE EFFECT OF HIBERNATION POSITION ON WINTER SURVIVAL OF THE ROCK-DWELLING LAND SNAILS CHONDRINA CLIENTA AND BALEA PERVERSA ON ÖLAND, SWEDEN

The effect of hibernation position on winter survival was examined for four years in the rock-dwelling land snails Chondrina chenta and Balea perversa inhabiting exposed stone walls on the Baltic island of Öland, Sweden. Individuals of both species hibernated either singly or aggregated in groups, attached to the lower surface of horizontally arranged pieces of limestone. B. perversa hibernated more frequently in aggregations than did C. clienta, and in both species adults occurred more frequently in aggregations than did juveniles. For both age classes of C. clienta in winter 1987/88 and for juveniles of B. perversa in 1988/89, individuals that hibernated in large aggregations had a higher survival rate than individuals hibernating singly or in small aggregations. No differential survival with respect to hibernation position was found in the winter of 1986/87 when the lowest temperatures were recorded (minimum temperature -16.4°C). During this extremely cold winter mean survival rates of 33.9% were recorded for C. clienta and 73.3% for B. perversa. The succeeding three winters were mild, with mean survival rates of 83.2% in C. clienta and 91.1% in B. perversa. In both species adults had a higher survival rate than juveniles. After a period of extreme cold (-16°C) survival of C. clienta inhabiting a snow-covered pile of stones was significantly higher than that of conspecifics on a snow-free stone wall, suggesting that snow cover has an insulating effec

Differential herbivore damage to calcicolous lichens by snails

A laboratory experiment was conducted to determine the damage caused by snail grazing to 35 calcicolous lichen species and cyanobacteria from the Baltic island of Oland, Sweden. Individuals of four species of land snails (Balea perversa, Chondrina cliema, Clausilia bidentata and Helicigona lapicida) were allowed to graze on identified lichen species growing on pieces of limestone. Snail grazing on thalli and ascocarps was classified into four categories ranging from no damage to completely eaten. In general, some lichen species were heavily grazed, whereas others were only slightly damaged or not injured. Aspiciha calcarea, Tephromela atra and Verrucaria nigrescens were preferred by all snail species except Chondrina cliema. In general, lichen thalli that were not immersed in the calcareous rock and cyanobacteria were preferred, whereas ascocarps were avoided by one of the snail species (C. clienta). Immersed perithecia with a carbonized outer layer were avoided by all snail species except C. bidentata. Possibilities of chemical and mechanical defence properties in calcicolous lichens are discusse

Partial precopulatory isolation between two geographically distant populations of the land snail Arianta arbustorum (L.)

Different mechanisms of reproductive isolation were examined in the simultaneously hermaphroditic land snail Arianta arbustorum. Snails from two geographically isolated populations in the Swiss Alps were allowed to copulate with both a homotypic (individual from the same population) and a heterotypic (individual from the other population) partner (in half of the pairs in reversed order). Control snails mated twice with a homotypic partner. In the first mating, successful copulations occurred in a lower frequency in heterotypic pairs (55.6%) than in homotypic pairs (82.9%). Heterotypic pairs that eventually copulated showed more breaks during courtship than homotypic pairs. However, neither the number of eggs produced nor their hatching success was influenced by the type of mating partner. In the second mating, the sequence of different partners had an effect on the proportion of successful copulations in snails from one geographical population. Snails that copulated first with a homotypic partner remated more frequently with a homotypic partner than snails that copulated first with a heterotypic partner. Paternity analyses of progeny of snails that mated twice indicate no influence of the origin of the mating partner. The proportion of hatchlings sired by the second mate (P2) averaged 0.39, indicating a slight first-mate advantage. However, highly skewed paternity patterns were found in the progeny of 44.4% of the double-mated snails. Genetic analyses also revealed a low frequency of self-fertilization (3.7%). These findings indicate the presence of partial precopulatory isolation between two distant snail populations, although reproductive compatibility is still maintaine

Testing a typology system of running waters for conservation planning in Hungary

Landscape and site classifications are increasingly being used in conservation planning and biodiversity management. We examined the utility of a simple typology system for predicting the conservation value of running-water sites in Hungary using aquatic invertebrates. Aquatic invertebrates (444 species) were collected by kick and sweep sampling technique, in a few cases also with a net, at 317 running-water sites covering the entire area of Hungary. On the basis of three criteria (naturalness, altitude and size of catchment area) we obtained a typology scheme distinguishing five running-water types: artificial lowland stream, natural highland river, natural highland stream, natural lowland river and natural lowland stream. We expressed the conservation value of each site using the numbers of native species, unique native species, red-list species, protected species and alien species. Furthermore, the conservation value of each river type was expressed by a measure of beta diversity. Our results show that any interpretation of the effect of a single criterion might be misleading. Consequently, the use of the whole typology system is recommended. The study revealed that all stream types are valuable to a certain extent because they maintain distinct biological communities. We found that the conservation value of artificial watercourses is comparable to that of natural running-water sites. We identified that natural lowland rivers and artificial lowland streams are the ones mostly exposed to species invasions. These findings are essential in maintaining and protecting conservation values of any freshwater ecosystem, and may contribute to management decisions on running waters in Hungar

Among- and within-population variation in sperm quality in the simultaneously hermaphroditic land snail Arianta arbustorum

Sperm competition models on the evolution of sperm size assume associations with another sperm quality trait, sperm longevity. Sperm length can also provide an indication of possible mechanisms affecting motility and thus fertilization success. Despite their importance, however, detailed mechanisms of sperm competition at the gamete level are poorly understood. In simultaneously hermaphroditic land snails, sperm traits and cryptic female choice are assumed to be crucial in determining fertilization success. We examined the variation in sperm length and number among individuals from four natural populations of the land snail Arianta arbustorum, a species with multiple mating and long-term sperm storage. We also assessed variation in velocity, motility and longevity of sperm in snails from two of the four populations. Independent of shell size, sperm length differed among populations and, to a minor extent, even among individuals within populations. Mean sperm length of a snail was not correlated with the number of sperm delivered in a spermatophore. The mean sperm velocity (=VCL) did not differ between snails from two populations. However, VCL varied among snails. Percentage motility and longevity of sperm differed between snails from the two populations. No correlations were found between length, velocity, percentage motility and longevity of sperm. To conclude, individual snails differed in sperm quality, and this variation may partly explain the differential fertilization success between A. arbustorum snails. Moreover, our findings did not support the positive association between sperm length and longevity assumed by sperm competition models for internally fertilizing specie