Biodiversity Data Journal :
Research Article
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Corresponding author: Ivailo Kanev Dedov (idedov@gmail.com)
Academic editor: Zoltán Fehér
Received: 14 Oct 2020 | Accepted: 27 Nov 2020 | Published: 03 Dec 2020
© 2020 Ivailo Dedov, Ulrich Schneppat, Heike Reise, Manh Quang Vu
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Dedov IK, Schneppat UE, Reise H, Quang Vu M (2020) First record of an agriolimacid slug in Southeast Asia – Deroceras laeve (O. F. Müller, 1774) (Gastropoda: Pulmonata) recently introduced to the Socialist Republic of Vietnam. Biodiversity Data Journal 8: e59644. https://doi.org/10.3897/BDJ.8.e59644
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Several individuals of the terrestrial slug Deroceras laeve were collected in 2018 in the Hoàng Liên Son mountain range of northern Vietnam. The three specimens which were investigated anatomically were aphallic or hemiphallic. A partial COI sequence verified the species identity. This is the first discovery of D. laeve and also of the slug family Agriolimacidae on the Indochinese Peninsula. The collecting site is situated near a cable-car station and below a tourist complex on Fansipan mountain, both of which had just been built by a Swiss-Austrian company between 2013 and 2016. This and the fact that the species had not been found elsewhere in the surrounding area, although searched for thoroughly, indicate that D. laeve is most probably a recent introduction, potentially with building material from Austria or Switzerland.
terrestrial slug, new introduction, COI, Gastropoda, Pulmonata, Agriolimacidae
Globalisation of trade and long-distance travelling have led to unintended introductions of alien species worldwide, of which some have become serious pests causing problems in agriculture and horticulture or for human health (
Location: Southeast Asia, Socialist Republic of Vietnam, Hoàng Liên Son Mountains range (the south-eastern extension of the Himalayan chain), Lao Cai Province, Municipality of Sa Pa, Hoàng Liên National Park, below Fansipan peak, northern-slope, 22.3054°N, 103.7751°E, 3020 m a.s.l.
Habitat: Open, stony area with some sparse weedy vegetation, not far from the cable-car station and near temple buildings, surrounded by forest (Fig.
Collection: All sites around the top of Fansipan mountain (if not inaccessible as a result of the steepness of the terrain or impenetrability of bamboo thickets) were searched intensively for gastropods by four zoologists (I. Dedov, N. Simov, R. Bekchiev and P. Beron) on 21.09.2018.
Eight specimens of D. laeve were found close to the temple and not far from the cable-car station on an area of just a few square metres. The slugs were found in the middle of the day (13:00–14:00 hrs), some active on the moist soil and some hidden under stones. The air temperature was approximately 15–20°C, with almost no wind and a cloudy sky. Deroceras laeve was found nowhere else, but several other, indigenous species, including semi-slugs (Helicarionidae), were collected elsewhere on Fansipan
Treatment of specimens: The slugs were killed and fixed on the evening of the collecting day, following the methods in
Some specimens were photographed alive before they were killed, using a digital camera Panasonic, Lumix DMC-TZ31.
All individuals are adult (judging by the visible and open genital pore: U. Schneppat, personal observation). Six specimens of the series are kept in the Mollusca collection of the Institute of Biodiversity and Ecosystem Research, Bulgarian Academy of Sciences, Sofia (Collection I. Dedov 40339/B–F and H), two specimens (ex Collection I. Dedov 40339/A and G) are stored in the collection of the Senckenberg Museum of Natural History Görlitz, Germany (p23737, p23738).
Morphological studies: Seven specimens, preserved in 75% ethanol, were measured using callipers, a metal ruler or with a calibrated eyepiece. Three specimens were dissected: 4039/B by U. Schneppat and p23737 and p23738 by H. Reise. The general dissection method followed
DNA sequencing: DNA was extracted from foot muscle tissue of specimen 40339/G (= SMNG p23738) following the method of
Colouration: (N = 8) All specimens in the preserved series are of the same general colouration, dark greyish-olive. The coloration of preserved specimens was still largely unchanged after six months in 75% ethanol (Fig.
The ommatophores are entirely black, and the black ommatophorean retractor muscle is well visible through the integument of head and neck. The lower pair of tentacles are uniform pale-grey. The area around the pneumostome is much paler than the mantle and with dark micro-dots along its outer margin. Pigmentation of the sole at first sight appears to be uniform pale grey, but the centre field is slightly lighter. In some specimens, at the outermost end of the lateral sole fields, there is a higher accumulation of dark pigment, and the tip of the sole appears almost black or at least dark-grey. The body mucus of all specimens observed was colourless, wateryand translucent.
Body: (N = 7) Animals with very thin and delicate integument. Total body length of preserved specimens 16–18 mm; mantle length 7.0–9.0 mm (43–50% of the total length); keel very inconspicuous and its length highly variable 1.7–5.0 mm. The tail gradually tapers towards the end, with no truncation and not laterally flattened.
Anatomy: (N = 3) Penis: completely missing and not even a small vestigial bump found in specimens 40339/A and 40339/B; specimen 40339/G is hemiphallic with a tiny vestigial penis. Musculus retractor penis: completely missing and no remains found at the usual position at the inner body wall. Vas deferens: completely missing in specimen 40339/G, but in specimens 40339/A & B there is a vestigial duct at the proximal end of the free oviduct (Fig.
Deroceras laeve, Collection I. Dedov no. 40339/B, genital tract preparation. Abbreviations: ag = albumen gland, at = atrium, bc = bursa copulatrix, fo = free oviduct, hd = hermaphroditic duct, hg = hermaphroditic gland (gonad), so = sperm-oviduct, vvd = vestigial vas deferens. Photograph R. Heim.
Vestigial shell (40339-B): length 3.58 mm, width 2.49 mm. Very flat and straight with almost no cavity ventrally, a little whitish, but almost translucent and without a ventrally thickening calcium-carbonate layer. Periostracum completely colourless, shiny and only visible as a narrow seam at the left and right edge of the shell. Apex almost in the centre of the anterior edge and not very pronounced. Five very regular growth-lines clearly visible all around the shell (Fig.
Genetics: We sequenced a 644 bp fragment of the COI gene (GenBank number MT941435). Deroceras laeve sequences in GenBank show much variation, but this sequence fully matches one from Massachusetts (GenBank AF239733.1) and also an individual from the Costa Brava, Spain (GenBank number MT941436; collection number SMNG p24032). Another haplotype only one base pair different has been found in Gloucestershire, England (KF894311.1) and Ontario, Canada (MG422202.1). Evidently, the Vietnamese specimen has a widely distributed haplotype, so this does not reliably indicate a likely source population.
The record of a small population of Deroceras laeve in northern Vietnam is the first from the Indochinese Peninsula and thereby fills a gap in its range within SE Asia. There are a few other species of this genus which have been spread widely by human activity, such as D. reticulatum which has, like D. laeve, an almost worldwide distribution (
Populations in the tropics are believed to have been introduced. While D. laeve seems widespread in tropical America (e.g. Mexico:
The new locality in Northern Vietnam is on a south-eastern outpost of the Himalayan foothills and only about 400 km south of the nearest records in China (
The area of Hoang Lien National Park (29,845 ha in Lao Cai Province, including Sapa town and Fansipan peak at 3143 m a.s.l.) is the site of intersection of two sub-regions of subtropical and tropical high mountains. The year there is divided into two seasons: summer = rainy season from May to October (very wet, with heavy rains) and winter = dry season from November to April. The usual temperature in the summer months is 18–20ºC; in the winter months 10–12ºC. The temperature maximum of the area, measured in April in the lowlands, is 33ºC, the temperature minimum -3ºC. The average annual rainfall is 2,759 mm, with a recorded maximum of 3,484 mm, but rainfall depends on topography and season. About 80–85% of the total annual precipitation falls in summer, mainly June and July, while there is only 50–100 mm rain per month during winter. Humidity is relatively stable with 85–90% during most of the year. It may reach up to 97% and decrease to 65–70% during April. Fog and hoar frost appear often and at all times of the year, especially in winter. On average, there are ca. 160 foggy days per year and six average days with frost (
The study was supported by the Institute of Ecology and Works Protection, Hanoi, Vietnam and by Projects “Research on ecologically sustainable development model on the coastal area of Mekong Delta”, Code Number: 10/2017/HĐ.ĐTĐL.CN.CNN. Thanks go to Regula Cornu, Chur, Switzerland, for assistance in the laboratory, collection and cataloguing and to René Heim, Luzern, Switzerland, for photographing specimen 40339/B for figures 3 and 4, for further support when studying the specimens in his laboratory and for ongoing constructive discussions and preparing the stack photographs. Bettina Schlitt (SMNG) isolated and sequenced the DNA of specimen 40339/G. John M.C. Hutchinson provided valuable comments and advice, analysed the COI data and improved the English. Authors would like to thank two reviewers, Ben Rowson and Ágnes Turóci, for their helpful remarks.