Physidae (Mollusca: Gastropoda) of western and central European range - morphological diversification and ecological features

Background: This is the first comparative study on Physidae identified in west and central Europe range. A thorough exploration of morphology supported by ecological features and distribution of European Physidae species are presented within this study. In the context of the lack of research on detailed morphology features on Physidae species we deeply analysed taxonomical features of snails which are being identified more and more frequently in the last years in the territory of the west and central Europe. Scanning electron microscopy (SEM) methods were used to elucidate the external morphology of freshwater snails (Mollusca: Gastropoda: Physidae), that occur in the area of western and central part of Europe. We compared the external morphology of their shells and found important differences between the species. Results: Morphological analysis are benefited in revealing variations of Physide shells. We found intraspecific similarities within Physidae, which are the most evident in the overall structure of shells and the height of the spires. Many interspecific differences in morphology in the apex structure and spires were found. From our results, we can infer that the shells P. fontinalis and A. hypnorum had the lowest amount of variability between particular individuals. The most characteristic features and differences of representatives of Physidae are presented and discussed. This is especially important in Physa gyrina and a worldwide invader Physa acuta identification which is shape-wise not easy to distinguish.Conclusions: The implications of our study are new identification key along with the ecological characteristic of physid species and the assessment of their current range in Europe. Our data demonstrate similarities within Physidae, which are the most evident in the overall structure of shells, and the height of the spires, apex structure, and spires were found between analysed species and provide further evidence of the importance of morphological features as an identification driver.

Experience and relatedness influence mating interactions in a simultaneously hermaphroditic snail, Physa gyrina

The means by which animals assess potential mates is an important issue in studies of reproductive systems. I tested whether an individual’s previous experiences and the relatedness of mates affected mating behavior in a simultaneous hermaphrodite snail, Physa gyrina. Previous work with this species showed reduced reproductive success resulting from both strong outbreeding and inbreeding. Thus, I predicted that individuals should prefer partners of intermediate relatedness. During activity trials, snails moved longer distances when exposed to chemical cues from conspecifics of lesser relatedness. Furthermore, during mating interactions, behavioral responses to relatedness varied with gender-role: male-role behaviors did not vary across relatedness treatments, while snails paired with either closely related or highly dissimilar partners increased their female-role resistance behaviors as interactions escalated. Experiences with their current partner also affected behavioral dynamics. Familiar pairs had fewer matings and longer latency times until a mating occurred than unfamiliar pairs. Snails acting in the female role also exhibited higher resistance rates in familiar pairs than in unfamiliar pairs. Previous, brief exposure to chemical cues in a non-mating context also influenced behavior during a subsequent mating interaction. Snails that were previously exposed to chemical cues from unfamiliar individuals tended to be more likely to occupy the male role following an encounter, and had significantly lower copulation frequencies and higher female-role resistance rates (i.e. were choosier) than those previously exposed to cues from familiar individuals. Overall, the results show that: 1) relatedness, past exposure to conspecific chemical cues, and experience with a current partner all influence mating behaviors in these snails; and 2) in these simultaneous hermaphrodites, an individual’s responses depend on whether it is occupying the male or female role.

Microhabitat differences surrounding a pond affects the distribution of trematode parasites among a pulmonate snail community

Anthropogenic disturbance associated with clear-cutting and changing the environmental landscape can lead to distinct microhabitat structure surrounding aquatic habitats. The transmission dynamics of trematode parasites in their snail first intermediate hosts were examined to determine if these alterations affect trematode parasite distribution. This was accomplished by examining 2,771 pulmonate snails belonging to two species (Physa gyrina and Lymnaea columella) over a three month period in a pond surrounded by distinct microhabitats as a result of anthropogenic changes to the environmental landscape. Trematode parasite distribution in the snail first intermediate hosts was largely tied to the microhabitat preference of their vertebrate definitive hosts. Autogenic species were found further away from the center of the open microhabitat and allogenic parasites were closer to the centralized point, most likely as a result of habitat preference by their frog and waterfowl definitive hosts, respectively. Additionally, there was increased parasitism in the molluscan hosts at the edges of the wooded environments due to habitat overlap of autogenic and allogenic species hosts, indicating that microhabitat structure can have profound effects on parasite distribution.

Molecular phylogenetics of central Canadian Physidae (Pulmonata: Basommatophora)

The phylogenetic relationships of four nominal south-central Canadian freshwater physids ( Physa (sensu lato) skinneri Taylor, 1954, Physa integra (Haldeman, 1841), Physa gyrina (Say, 1821), and the endemic Physa winnipegensis Pip, 2004) were studied by analyses of combined partial sequences coding for mitochondrial 16S and cytochrome c oxidase (COI) genes. Maximum parsimony and neighbour joining analyses, as well as comparisons with published sequences, supported four major clades of physids, of which three are represented in central Canada. Physa skinneri and P. integra were placed within the Physa fontinalis (L., 1758) and Physa acuta Draparnaud, 1805 clades, respectively. Physa winnipegensis formed a distinct branch within the P. acuta group. An additional, previously unreported and unclassified, morph within the P. acuta group was identified from Lake Winnipeg.

Grazer–collector facilitation hypothesis supported by laboratory but not field experiments

Grazing invertebrates in streams feed by harvesting algal cells from surfaces, and in doing so release fine particulate organic matter (FPOM). The "grazer–collector facilitation hypothesis" holds that FPOM production by grazers facilitates growth and (or) survival of FPOM-collecting invertebrates. We tested for grazer–collector facilitation in laboratory and field experiments. In recirculating flumes in the laboratory, we tested for facilitation of the collector Hydropsyche slossonae by the grazers Physa gyrina, Glossosoma intermedium, and Baetis tricaudatus. All three grazers increased FPOM levels in flume water, but only Physa facilitated Hydropsyche growth. In the field, we manipulated Physa and Glossosoma densities to test for facilitation (at a local scale) of natural collector assemblages in an eastern Iowa stream. We did not detect facilitation of any collector by either grazer in the field, despite high power to detect such interactions. We suspect that grazer–collector facilitation was not observed in the field because (unlike in our laboratory flumes) field FPOM levels are often high and extremely variable in time and space and because organic particles can arise from sources other than grazer activity (= grazer-independent processing). Therefore, at local scales, collectors may not be significantly limited by the supply of grazer-derived FPOM.