Genital morphology differentiates three subspecies of the terrestrial slug Arion ater (Linnæus, 1758) s.l. and reveals a continuum of intermediates with the invasive A. vulgaris Moquin-Tandon, 1855

Abstract

The terrestrial slug Arion vulgaris Moquin-Tandon (= A. lusitanicus auct. non Mabille) is an important agricultural pest that has invaded much of Europe. Previous work has demonstrated hybridisation with A. ater (Linnaeus) s.l. We describe the genital anatomy of morphological intermediates found in eastern Saxony (Germany), comparing them with the parent species. We recommend a standard method of genital dissection and consider a set of five genital characters. The intermediates demonstrate the homology of the ligula-bearing organs of the two species; the ancestral position of the ligula in the dilated part of the oviduct has moved to the upper atrium in A. ater s.l. Furthermore we differentiate three morphotypes of A. ater s.l. in eastern Saxony, associated with different mitochondrial DNA sequences. One is A. ater ater, previously unrecognised from this part of Germany and the Czech Republic. The two other morphotypes correspond to the predominantly British and the Continental subspecies previously recognised on genetic and morphological grounds. We designate as the lectotype of Limax rufus Linnaeus, 1758 a non-surviving specimen from Almondbury, England, described by Lister; thus the predominantly British subspecies becomes A. ater rufus. The appropriate name for the Continental form is A. ater ruber (Garsault, 1764).

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

“…Very detailed genetic studies using microsatellites also confirmed many cases of hybridisation (Hutchinson et al 2021), although only ca. 4% of the population had anatomies identified as hybrids (Reise et al 2020). Our results based on anatomical identification revealed a small proportion of hybrids (5%), which partly may be due to poor sampling on a few sites; however, genetic data indicate that hybridisation is not rare (Hatteland et al 2015, Zemanova et al 2017.…”

“…5). In general, all specimens which did not fit into the pure species were determined as potential hybrids, similar to other studies (Reise et al 2020, Hutchinson et al 2021. It was difficult to decide whether the ligula-bearing part should be called atrium or oviduct for the intermediate forms.…”

“…Some researchers claim it is conspecific with A. rufus, but it is usually considered a separate subspecies. This question has been extensively reviewed by Reise et al (2020), who, based on a thorough morphological investigation and COI mtDNA, recognise three subspecies i.e. A. ater ater (Linnaeus, 1758), A. ater rufus (Linnaeus, 1758) and A. ater ruber (Garsault, 1764).…”

“…A. ater ater (Linnaeus, 1758), A. ater rufus (Linnaeus, 1758) and A. ater ruber (Garsault, 1764). Here, we consistently use the name Arion rufus (Linnaeus, 1758), probably corresponding to A. ater ruber in this area (Reise et al 2020). Monitoring the distribution of A. vulgaris is especially problematic when A. ater, A. rufus and A. vulgaris co-occur in the same habitat.…”

“…In 2001-2007 the slug spread rapidly in the south (voivodeships: małopolskie, śląskie, podkarpackie) and other regions of the country (voivodeships: łódzkie, mazowieckie, pomorskie, warmińsko-mazurskie and wielkopolskie) (Kozłowski 2008). Its occurrence in the western part of dolnośląskie voivodeship (= Lower Silesia) was also noted (Dreijers et al 2013, Reise et al 2020, Hutchinson et al 2021, but there were no data from Wrocław, the largest city of this region, where A. rufus is native; its natural eastern border of distribution runs near Wrocław (Wiktor 2004, Kozłowski 2012.…”