The Slugs of Britain and Ireland: Undetected and Undescribed Species Increase a Well-Studied, Economically Important Fauna by More Than 20%

Abstract

The slugs of Britain and Ireland form a well-studied fauna of economic importance. They include many widespread European species that are introduced elsewhere (at least half of the 36 currently recorded British species are established in North America, for example). To test the contention that the British and Irish fauna consists of 36 species, and to verify the identity of each, a species delimitation study was conducted based on a geographically wide survey. Comparisons between mitochondrial DNA (COI, 16S), nuclear DNA (ITS-1) and morphology were investigated with reference to interspecific hybridisation. Species delimitation of the fauna produced a primary species hypothesis of 47 putative species. This was refined to a secondary species hypothesis of 44 species by integration with morphological and other data. Thirty six of these correspond to the known fauna (two species in Arion subgenus Carinarion were scarcely distinct and Arion (Mesarion) subfuscus consisted of two near-cryptic species). However, by the same criteria a further eight previously undetected species (22% of the fauna) are established in Britain and/or Ireland. Although overlooked, none are strictly morphologically cryptic, and some appear previously undescribed. Most of the additional species are probably accidentally introduced, and several are already widespread in Britain and Ireland (and thus perhaps elsewhere). At least three may be plant pests. Some evidence was found for interspecific hybridisation among the large Arion species (although not involving A. flagellus) and more unexpectedly in species pairs in Deroceras (Agriolimacidae) and Limacus (Limacidae). In the latter groups, introgression appears to have occurred in one direction only, with recently-invading lineages becoming common at the expense of long-established or native ones. The results show how even a well-studied, macroscopic fauna can be vulnerable to cryptic and undetected invasions and changes.

Towards the unravelling of the slug <i>A. ater–A. rufus</i> complex (Gastropoda Arionidae): new genetic approaches

“…1), showing three genetic lineages in addition to the outgroups (A. iratii and A. subfuscus): one with A. vulgaris, another comprising the sequences of A. ater and the last one including the sequences of A. rufus. The results obtained from these analyses confirm previous results, suggesting that both A. ater and A. rufus are independent evolutionary clades (Pfenninger et al, 2014;Rowson et al, 2014;Zemanova et al, 2016). Moreover, the large genetic distances between them ( Table 2) also imply that these independent clades are not very recent, strongly supporting the idea that both clades identify different species and not subspecies or morphotypes, and confirm that morphological variability within each of the species (in all cases specimens were taken from several different distant geographical areas) is actually reflecting the existence of such subspecies and morphotypes.…”

“…Hagnell et al, 2003) and introgression has occurred between them (e.g. Hatteland et al, 2015;Noble and Jones, 1996;Rowson et al, 2014). This problem probably comes from their very similar external morphology and their distinct internal morphology, as well as life history and ecological traits (Blattmann et al, 2013).…”

“…For example, A. ater is in general black coloured and A. rufus is orange, while another species of the genus (A. vulgaris) is brown; thus specimens of dark brown can be misidentified (Roth et al, 2012), although the morphology of their genitalia separates clearly these species (Hatteland et al, 2015). Genetically, their phylogenetic relationships were initially not clear and they were even proposed to be eco-types (Quinteiro et al, 2005), but more recently it has been suggested that A. ater and A. rufus are probably independent monophyletic clades (Rowson et al, 2014). But the fact remains that they belong to different phylogenetic clades and does not establish that they are actually different species.…”

Terrestrial molluscs of the Province of Newfoundland and Labrador, Canada. Part 1: Boettgerillidae

“…1) (Rowson et al 2014). Unlike in milacid slugs (which share a prominent keel running from mantle to tail; see Fig.…”

First records of the terrestrial slug Arion ater s. l. (Linnaeus, 1758) (Pulmonata: Arionidae) from Turkey

“…As an inhabitant of synanthropic habitats, it has also been spread by human activities, partly even by deliberate introduction (wiktoR 1973(wiktoR , von PRoscHwitz 1997(wiktoR , wiese 2014. The eastern margin of its natural range is not clear, but it is assumed to lie somewhere in western Poland (wiktoR 1973, Welter-sChultes 2012, Rowson 2017. There are also isolated populations in Eastern Europe such as in Latvia (rudZīte et al 2010) and Russia (likHaRev & wiktoR 1980), indicating earlier introductions (Rowson 2017).…”