Pulmonate slug evolution is reflected in the de novo genome of Arion vulgaris Moquin-Tandon, 1855

Stylommatophoran pulmonate land slugs and snails successfully completed the water-to-land transition from an aquatic ancestor and flourished on land. Of the 30,000 estimated species, very few genomes have so far been published. Here, we assembled and characterized a chromosome-level genome of the "Spanish" slug, Arion vulgaris Moquin-Tandon, 1855, a notorious pest land slug in Europe. Using this reference genome, we conclude that a whole-genome duplication event occurred approximately 93-109 Mya at the base of Stylommatophora and might have promoted land invasion and adaptive radiation. Comparative genomic analyses reveal that genes related to the development of kidney, blood vessels, muscle, and nervous systems had expanded in the last common ancestor of land pulmonates, likely an evolutionary response to the terrestrial challenges of gravity and water loss. Analyses of A. vulgaris gene families and positively selected genes show the slug has evolved a stronger ability to counteract the greater threats of external damage, radiation, and water loss lacking a protective shell. Furthermore, a recent burst of long interspersed elements in the genome of A. vulgaris might affect gene regulation and contribute to rapid phenotype changes in A. vulgaris, which might be conducive to its rapid adaptation and invasiveness.

Occurrence and abundance of invasive and native Arion slugs in three types of habitats in urban area of Wrocław (SW Poland)

Arion vulgaris and Arion rufus are two cryptic slug species whose ranges overlap in vast areas of Europe. In Poland, A. rufus is native; it reaches the eastern border of its range near Wrocław, while the invasive A. vulgaris was previously not recorded in this area. The study aimed to map the distribution of both species in the city of Wrocław and determine the size and abundance of their populations. Twenty-six sites were surveyed in 2019-2020. They represented three types of habitats: natural, semi-natural and anthropogenic. Because the investigated species are externally indistinguishable, their identification was based on the genital organs. Among 280 analysed specimens, 72% were identified as A. vulgaris, 23% as A. rufus and 5% were classified as hybrids. The hybrids and A. vulgaris were most abundant in semi-natural (83%) and anthropogenic habitats (95%), while A. rufus most often occurred in natural habitats (51%). Arion vulgaris occupied most of the sites (88.5%), and in 50%, it was collected alone. Arion rufus occurred in 46% of the sites (in 11.5% alone), and the hybrids were noted in 27%. In Wrocław A. vulgaris dominates in most sites, and its populations are much more abundant than those of A. rufus where the two species co-occur. This finding indicates that A. vulgaris, with its better adaptive skills and competitive abilities, may negatively impact the native species and, consequently, the latter’s displacement. Although the recorded frequency of hybridisation was very low (5%), it may also have an effect on the local extinction of A. rufus. Interspecific hybridisation is assumed to foster invasions, and climate change may further exacerbate displacement; therefore, they should continue to be monitored.

Detection of an invasive species Arion vulgaris Moquin-Tandon, 1855 (Mollusca: Gastropoda: Arionidae) in the Republic of North Ossetia-Alania

Arion vulgaris Moquin-Tandon is a serious agricultural pest. Its rapid spread started in the middle of the twentieth century. Currently, its range covers almost all of Western Europe and it is rapidly expanding to the east. A. vulgaris has been recorded in the Baltics, Ukraine, and central Russia; it is also found in the Faroe Islands. In 2009, it was discovered in Russia in the commercial greenhouses of Tver. Now it has spread in the suburbs and Moscow. On the 6th of August 2019, a population of this species was found in the arboretum of Vladikavkaz, North Ossetia which is the first record of A. vulgaris in the Caucasus. Description of the slug’s genitalia is given.

Climate gradients, and patterns of biodiversity and biotic homogenization in urban residential yards

Residential yards constitute a substantive biodiverse greenspace within urban areas. This biodiversity results from a combination of native and non-native species and can contribute to biotic homogenization. Geographical climatic patterns affect the distribution of native species and may differently affect non-native species. In this study, we examined biodiversity and biotic homogenization patterns of yard-dwelling land snails across 12 towns in Oklahoma and Kansas (USA). The 3 x 4 array of towns incorporated a N-S winter temperature gradient (mean low January temperature range = -8.4 to 0.1°C) and an E-W annual rainfall gradient (annual rainfall range = 113.8 to 61.3 cm/yr). Ten yards per town were surveyed. We hypothesized that mild winter temperatures and greater annual rainfall would be associated with greater snail abundance and richness, and that the presence of non-native species would contribute to biotic homogenization. Non-native snails were present and often abundant in all towns. Snail communities varied with both rainfall and cold temperature. Contrary to our prediction, snail abundance was inversely related to annual rainfall–likely because drier conditions resulted in greater yard watering that both augmented rainfall and maintained moist conditions. Sørensen similarity between towns for the entire land snail community and for only non-native species both showed distance-decay patterns, with snail composition becoming less similar with increasing distance—patterns resulting from species turnover. The biotic homogenization index also showed a distance-related pattern, such that closer towns were more likely to have biotic homogenization whereas more distant towns tended to have biotic differentiation. These results support the concept that biotic homogenization is more likely regionally and that climatic changes over distance result in species turnover and can reduce spatially broad biotic homogenization.

Two new alien slugs, Krynickillus melanocephalus Kaleniczenko, 1851 and Tandonia kusceri (H. Wagner, 1931), are already widespread in Hungary

Two slug species (Krynickillus melanocephalus Kaleniczenko, 1851 and Tandonia kusceri (H. Wagner, 1931)) are reported from Hungary for the first time. Identification was supported by anatomical examination in both, and molecular data in the latter species. A citizen science survey applying a Realtime Social Networking Service (RSNS) method using Facebook posts revealed that both species are already widespread in Hungary, i.e. Krynickillus melanocephalus is reported from 14 and Tandonia kusceri from 25 sites. So far, we received no reports on any damage caused by these two slug species. Nevertheless, we treat them as potential horticultural pests requiring further attention.

A comprehensive phylogeographic study of Arion vulgaris Moquin-Tandon, 1855 (Gastropoda: Pulmonata: Arionidae) in Europe

Arion vulgaris Moquin-Tandon, 1855 is regarded as one of the 100 most invasive species in Europe. The native distribution range of this species is uncertain, but for many years, the Iberian Peninsula has been considered as the area of origin. However, recent studies indicate that A. vulgaris probably originated from France. We have investigated the genetic structure of 33 European populations (Poland, Norway, Germany, France, Denmark, Switzerland) of this slug, based on two molecular markers, mitochondrial cytochrome c oxidase subunit I (COI, mtDNA) and nuclear zinc finger (ZF, nDNA). Our investigation included published data from two previous studies, giving a total of 95 populations of A. vulgaris from 26 countries. This comprehensive dataset shows comparable haplotype diversity in Central, North and Western Europe, and significantly lower haplotype diversity in the East. All haplotypes observed in the East can be found in the other regions, and haplotype diversity is highest in the Central and Western region. Moreover, there is strong isolation by distance in Central and Western Europe, and only very little in the East. Furthermore, the number of unique haplotypes was highest in France. This pattern strongly suggests that A. vulgaris has originated from a region spanning from France to Western Germany; hence, the slug is probably alien/invasive in other parts of Europe, where it occurs. Our results indicate the necessity to cover as much of the distribution range of a species as possible before making conclusive assumptions about its origin and alien status.

Occurrence of canine and feline lungworms in Arion vulgaris in a park of Vienna: First report of autochthonous Angiostrongylus vasorum, Aelurostrongylus abstrusus and Troglostrongylus brevior in Austria

So far, neither the feline lungworms Aelurostrongylus abstrusus and Troglostrongylus brevior nor the canine lungworm Angiostrongylus vasorum was reported in wildlife or intermediate hosts from Austria. The slug Arion vulgaris represents an invasive species in Europe and serves as intermediate host for several lungworm species. This study aimed to analyse the occurrence of metastrongyloid lungworm larvae in slugs in Vienna, Austria. Therefore, 193 A. vulgaris were collected in the central Prater park in summer 2016. Specimens were artificially digested, analysed microscopically for lungworm larvae, and species were confirmed via PCR and sequencing. Out of 193, five slugs were positive to lungworms (2.6%), one for A. vasorum, two for A. abstrusus (genotypes A and B) and one for T. brevior, and one slug had a mixed infection of A. abstrusus and T. brevior larvae. The current study is the first evidence on the endemicity of these metastrongyloid lungworm species in Austria.