Anette Baur

Sperm allocation in the simultaneously hermaphroditic land snail Arianta arbustorum

To test the idea that individuals of the simultaneously hermaphroditic land snail Arianta arbustorum can control the number of spermatozoa in their spermatophores, we investigated whether they differentially release sperm to virgin or nonvirgin partners with respect to the potential risk of sperm competition in a given mating. The number of sperm transferred ranged from 802 620 to 3 968 800 (X= 2 185 100; N=91), but was related neither to the mating history of the partner nor to copulation duration. This indicates that individuals of A. arbustorum are not able to adjust sperm expenditure to the mating history of the partner. Furthermore, the number of sperm transferred was correlated neither with the size of the donor nor with the size of the recipient. It has been proposed that the sexual conflict between the two genders in simultaneous hermaphrodites could be resolved by gamete trading. Theory predicts that sperm trading should occur in hermaphrodites in which the female role controls fertilization, for example in gastropods with a gametolytic gland and/or sperm storage such as A. arbustorum. To see whether sperm trading occurs, we also examined whether individuals of A. arbustorum adjust the number of sperm they release to the number they receive from their mating partner. There was a high degree of reciprocity in spermatophore transfer: in 45 of the 46 mating pairs investigated both partners delivered a spermatophore that contained spermatozoa. The numbers of sperm transferred by the two mating partners were not correlated, however. This indicates that sperm trading does not occur in this simultaneously hermaphroditic land snail. Copyright 1998 The Association for the Study of Animal Behaviour.

Differential herbivore damage to calcicolous lichens by snails

Abstract Abstract: 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 clienta, 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. Aspicilia calcarea, Tephromela atra and Verrucaria nigrescens were preferred by all snail species except Chondrina clienta . 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 discussed.

Herbivory on calcicolous lichens: different food preferences and growth rates in two co-existing land snails

A total of 32 calcicolous lichen species, one alga and one bryophyte were recorded on a limestone wall in the grassland Great Alvar on the Baltic island of Öland, Sweden. Fourteen (41%) of these 34 species and free-living cyanobacteria showed herbivore damage, most probably due to grazing by the land snails Chondrina clienta and Balea perversa which inhabited the limestone wall. Three laboratory experiments were conducted to examine the food preferences of individuals of C. clienta and B. perversa collected at this site and to evaluate any association between their preference and the net food quality of the lichens to the snails. Chondrina clienta and B. perversa exhibited food preferences, which differed significantly between species. Within species, variation in food choice was similar among individuals. This indicates that snail populations may be composed of polyphagous individuals with similar food preferences. Different lichen species were of different net food quality to the snails as indicated by growth rate differences. In both snail species the most preferred lichen species of the choice experiment caused the largest weight increase in juveniles, viz. Caloplaca flavovirescens for C. clienta and Aspicilia calcarea for B. perversa. This suggest that the snail species studied differ in their abilities to deal with secondary compounds and physical characteristics of certain lichens or that they can utilize the energy and nutrients of these lichens to a different extent. It is suggested that differential food preferences might reduce the intensity of interspecific competition for resources (lichens) between C. clienta and B. perversa.

Climatic Warming Due to Thermal Radiation from an Urban Area as Possible Cause for the Local Extinction of a Land Snail

A field survey revealed that the land snail Arianta arbustorum had become extinct at 16 (55.2%) out of 29 localities in the surroundings of Basel (Switzerland) between 1908 and 1991. Habitat destruction by urban development was the reason for extinction of eight local snail populations. However, A. arbustorum also became extinct at eight localities, which were covered by vegetation suitable for the species and which still supported abundant populations of other helicid snail species including Cepaea nemoralis (all of them recorded in 1906-8). Localities where A. arbustorum persisted and localities where it went extinct did not differ in exposure, inclination, percentage of woody plant cover, height of ground vegetation, distance to the nearest water body and number of other helicid snail species present. In this paper we provide evidence that local climatic warming due to increased thermal radiation from built-up areas might be a cause for the local extinction of A.arbustorum

Sequestration of lichen compounds by three species of terrestrial snails

Three species of lichen-grazing snails,Balea perversa, Chondria clienta, andHelicigona lapicida, all from the Swedish island of Öland, were found to sequester lichen compounds when feeding on the crustous lichen speciesAspicila calcarea, Caloplaca flavovirescens, Lecanora muralis, Physcia adscendens, Tephromela atra, andXanthoria parietina. The lichen compounds detected in the soft bodies of the snail species analyzed included the anthraquinone parietin, the depside atranorin, as well as a presumable degradation product of the latter. Other lichen compounds such as (+)-usnic acid or α-collatolic acid were not found in the soft bodies but were only detected in the feces, suggesting selective uptake of lichen compounds by the snails. In individuals ofC. clienta initially fed on the lichenX. parietina, the amount of sequestered parietin decreased over time on a parietin-free diet but was still detectable in the soft bodies after 28 days. In the ovoviviparous land snail,B. perversa, sequestered parietin was transferred from the mother to the eggs in the reproductive tract.

Intra- and interspecific influences on age at first reproduction and fecundity in the land snail Balea perversa

The influences of conspecific density and of presence of a competitor (the land snail Chondrina clienta) on both age at first reproduction and reproductive output in the rock-dwelling land snail Balea perversa were evaluated in a laboratory experiment. Since adult size of B. perversa decreases with increasing density of conspecfics, fecundity was also examined for size-dependence. Age at first reproduction of B. perversa was positively correlated with time to complete shell growth. Both increased with density of conspecifics, indicating intraspecific competition. By contrast, the presence of C. clienta did not influence the age at first reproduction of B. perversa. However, both fecundity (number of young produced per adult snail during the experiment) and reproductive rate (number of young produced per 100 days of adult life) in B. perversa were negatively affected by increased density of conspecifics and by the presence of C. clienta, indicating intra-and interspecific influences. No relationship was found between shell size of B. perversa and number of young produced. This suggests that the reduced fecundity of B. perversa was caused by conditions experienced during adulthood rather than by the smaller adult size as a result of growth under crowded conditions.

Effect of courtship and repeated copulation on egg production in the simultaneously hermaphroditic land snail Arianta arbustorum

Summary An experiment was conducted to examine whether extended courtship display (a major component of mating behaviour) or repeated copulation in the course of a reproductive season stimulates egg production in the simultaneously hermaphroditic land snail Arianta arbustorum. Repeated copulation was found to increase the number of eggs produced while courtship display did not appear to affect egg production. However, repeated copulation neither accelerated the onset of egg laying nor increased the hatching success of eggs. These results suggest that reciprocal intromission and/or receipt of a spermato-phore, but not the long-lasting courtship behaviour, stimulates egg production in A. arbustorum.

Intensified grazing affects endemic plant and gastropod diversity in alpine grasslands of the Southern Carpathian mountains (Romania)

Alpine grasslands in the Southern Carpathian Mts, Romania, harbour an extraordinarily high diversity of plants and invertebrates, including Carpathic endemics. In the past decades, intensive sheep grazing has caused a dramatic decrease in biodiversity and even led to eroded soils at many places in the Carpathians. Because of limited food resources, sheep are increasingly forced to graze on steep slopes, which were formerly not grazed by livestock and are considered as local biodiversity hotspots. We examined species richness, abundance and number of endemic vascular plants and terrestrial gastropods on steep slopes that were either grazed by sheep or ungrazed by livestock in two areas of the Southern Carpathians. On calcareous soils in the Bucegi Mts, a total of 177 vascular plant and 19 gastropod species were recorded. Twelve plant species (6.8%) and three gastropod species (15.8%) were endemic to the Carpathians. Grazed sites had lower plant and gastropod species richness than ungrazed sites. Furthermore, grazed sites harboured fewer gastropod species endemic to the Carpathians than ungrazed sites. On acid soils in the Fagaras Mts, a total of 96 vascular plant and nine gastropod species were found. In this mountain area, however, grazed and ungrazed sites did not differ in species richness, abundance and number of endemic plant and gastropod species. Our findings confirm the high biodiversity of grasslands on steep slopes in the Southern Carpathian Mts and caution against increasing grazing pressure in these refuges for relic plants and gastropods as well as for other invertebrates.

Seasonal variation in size and nutrient content of eggs of the land snail Arianta arbustorum

Summary Variation in size and nutrient content of eggs deposited in successive batches is a life-history aspect that has received little attention. We examined the size and nutrient content of eggs laid in successive batches by the land snail Arianta arbustorum. Snails from three populations (a lowland, a subalpine and an alpine locality in Switzerland) differed in number of batches produced, clutch size, egg size and nutrient concentration and energy content of eggs. This was partly due to differences in shell size, since reproductive characters of A. arbustorum scale with shell size. In the first batch snails from the lowland and subalpine population laid eggs that had a higher protein concentration (28.1%) than snails from the alpine population (25.6%). Similarly, eggs from the first batch did not differ in carbon concentration in the lowland and subalpine population, whereas eggs from the alpine population had a lower concentration. Clutch size tended to decrease in successive egg batches in all popul...

Chemical variation within and between individuals of the lichenized ascomycete Tephromela atra

Abstract HPLC-analysis was used to determine the concentrations of the lichen compounds alectoronic acid (depsidon), α-collatolic acid (depsidon) and atranorin (depsid) in the lichenized ascomycete Tephromela atra (syn. Lecanon atra ) (Hudson) Hafeliner from limestone walls on the Baltic island of Oland, Sweden. In 24 individuals of T. atra sampled on a stone wall, the pre-reproductive and reproductive tissue did not differ in the concentrations of alectoronic acid, collatolic acid and atranorin. The concentrations of the three lichen compounds were inter-correlated in the reproductive tissue, but not in the pre-reproductive tissue. Single individuals of T. atra ranged in area covered from 10.1 to 147.4 cm 2 (mean: 38.5 cm 2 ; N =24); 38.6% of this area was pre-reproductive tissue. However, the concentrations of the three lichen compounds were correlated neither with the total area covered by the lichen nor with the percentage of pre-reproductive tissue. This suggests that the concentrations of the lichen compounds do not change with increasing size (age) of the lichen. Analysis of specimens of T. atra from eight localities revealed a significant variation in lichen compounds (range between localities: alectoronic acid 0.60–3.26 μg/mg lichen dry weight (DW); collatolic acid 2.14–11.59 μg/mg lichen DW; atranorin 0.58–4.16 μg/mg lichen DW). The level of grazing observed in the lichens differed significantly among localities. However, no correlations between the concentrations of the three lichen compounds and the grazing damage to the lichens were found.