Snails as Taxis for a Large Yeast Biodiversity

Yeasts are unicellular fungi that harbour a large biodiversity of thousands of species, of which particularly ascomycetous yeasts are instrumental to human food and beverage production. There is already a large body of evidence showing that insects play an important role for yeast ecology, for their dispersal to new habitats and for breeding and overwintering opportunities. Here, we sought to investigate a potential role of the terrestrial snails Cepaea hortensis and C. nemoralis, which in Europe are often found in association with human settlements and gardens, in yeast ecology. Surprisingly, even in a relatively limited culture-dependent sampling size of over 150 isolates, we found a variety of yeast genera, including species frequently isolated from grape must such as Hanseniaspora, Metschnikowia, Meyerozyma and Pichia in snail excrements. We typed the isolates using standard ITS-PCR-sequencing, sequenced the genomes of three non-conventional yeasts H. uvarum, Meyerozyma guilliermondii and P. kudriavzevii and characterized the fermentation performance of these three strains in grape must highlighting their potential to contribute to novel beverage fermentations. Aggravatingly, however, we also retrieved several human fungal pathogen isolates from snail excrements belonging to the Candida clade, namely Ca. glabrata and Ca. lusitaniae. Overall, our results indicate that diverse yeasts can utilise snails as taxis for dispersal. This courier service may be largely non-selective and thus depend on the diet available to the snails.

A century after introduction: variability in Cepaea hortensis (Müller, 1774) in Sibiu, central Romania

The polymorphic land snail Cepaea hortensis was introduced to the city of Sibiu, central Romania, in the first decade of the 20th century and has spread widely across the city. A total of 97 locations were examined in 2017 across the city to determine the habitat preferences and variation in shell size, shape, colour and banding polymorphism of C. hortensis, and to relate these to the same features in the likely source population from Mannheim, Germany, and the first established population in Sibiu. We found that C. hortensis was largely restricted to sites with some woody vegetation cover and showed a marked preference for abandoned and overgrown private gardens. Mean adult shell size in present-day populations was almost always smaller than in both the presumed population of origin from Germany and the first recorded population from Sibiu. Populations showed a wide range of variation in frequencies of shell colours and banding morphs. This variation was not related to habitat or cover, and there was no evident geographical structure in the patterns. Comparisons with a smaller-scale sampling in 2004/5 showed that some populations had gone extinct, some remained stable and in some morph frequencies had changed drastically, but in no consistent direction. These results are similar to those obtained for the related species C. nemoralis in comparable circumstances, but differ from those obtained from regions where C. hortensis is long established and where habitats have been stable. The patterns we observed most likely reflect the effect of passive dispersal by humans, genetic drift and founder effects.

A comparative analysis of the camera eyes of gastropod pulmonate mollusks Cepaea nemoralis (Linnaeus, 1758) and Cepaea hortensis (Müller, 1774) (Stylommatophora, Helicidae)

A comparative analysis of the camera eyes of gastropod pulmonate molluscs Cepaea nemoralis and Cepaea hortensis was carried out on the basis of original and published data. It was demonstrated that the eyeballs and their main components in C. nemoralis and C. hortensis have more similarities in morphological and optical properties than in anatomical parameters.