Correcting misidentifications and first confirmation of the globally-invasive Physa acuta Draparnaud , 1805 ( Gastropoda : Physidae ) in Thailand and Laos

Introduced freshwater gastropods in the Indo-Burmese region may be under-documented owing to a lack of research attention. For the first time, we report on the widespread establishment of the globally invasive freshwater snail Physa acuta (Physidae) in Thailand and Laos, including decades old records that had previously been misidentified as Camptoceras jiraponi (Planorbidae). Occurrence of Physa acuta as hitchhikers among ornamental aquatic plants suggests that the ornamental trade was a likely introduction pathway of the species into Thailand. That a globally invasive species was able to spread unnoticed for such a long period of time highlights the need for countries like Thailand to focus research efforts on prevention and early detection of introduced species, in addition to increasing our understanding of native biodiversity.


Introduction
Almost 300 species of freshwater gastropods are found in Thailand (Brandt 1974;Nabhitabhata 2009), but in the monograph that is still considered the main authority on freshwater molluscs for Southeast Asia, Brandt (1974) only listed Amerianna carinata (H Adams, 1861) as being introduced.Four decades later, the most notorious invasive freshwater snails in Thailand are the South American Ampullariidae, Pomacea canaliculata (Lamarck, 1822) and Pomacea maculata Perry, 1810, which were the focus of intensive research in the 1990s because of the extensive damage they caused to rice fields (Keawjam and Upatham 1990;Halwart 1994;Chanyapate and Archavakom 1999;Cowie et al. 2017).Other than these species, only one freshwater snail, Gundlachia sp.(Planorbidae), has reportedly been introduced (Upatham et al. 1983).In contrast, Singapore, which is 700 times smaller than Thailand, has 25 species of non-native freshwater molluscs recorded (Tan et al. 2012;Ng 2016;Ng et al. 2014aNg et al. , 2014bNg et al. , 2015bNg et al. , 2016aNg et al. , 2016b)), with half of those species being found in the ornamental pet trade (Ng et al. 2016c).
Given that the ornamental pet trade is one of the probable sources of introduction of Pomacea spp.into Thailand (Chanyapate and Archavakom 1999), it would be unsurprising if other freshwater molluscs have been introduced via the same pathway, but have thus far remained undetected or misidentified.One species that may have been introduced into Malaysia and Singapore via the ornamental pet trade is Physa acuta Drapranaud, 1805, but it was misidentified as Physastra sumatrana (Martens, 1897) for many years (see Ng et al. 2015b).
The globally invasive Physa acuta originates from North America (Lydeard et al. 2016;Vinarski 2017).While there appears to be no published accounts of the species being established in Thailand to date, Physa acuta has previously been collected from tanks within a research facility in the capital city of Bangkok (Rico et al. 2014).In this article, we report for the first time that Physa acuta has established and spread throughout Thailand, and correct previous erroneous identifications of this species as Camptoceras jiraponi Hubendick, 1967, from specimens collected from Thailand and Laos.

Methods
Specimens deposited at the Chulalongkorn University Museum of Natural History (CUMZ), Mollusk Museum of the Faculty of Tropical Medicine, Mahidol University (TMMU), and the Department of Biology, Khon Kaen University (KKU) were examined (Supplementary material Table S1).The specimens were collected by hand or using nets in various freshwater habitats throughout Thailand and Laos for biodiversity surveys, regular monitoring of intermediate hosts of zoonotic parasites, or macro-invertebrate surveys for assessment of fresh waters between 2005 and 2017.Specimens were also collected from a bag of ornamental aquatic plants purchased from a market in Bangkok, Thailand.Identification of species was based on comparison with original descriptions, photographs of type material of Physa acuta and Camptoceras jiraponi (Draparnaud 1805;Hubendick 1967;Brandt 1974;Ng et al. 2015b), and descriptions of topotypic specimens of Physa acuta (Paraense and Pointier 2003).

Results
All sixty individuals from 13 lots were examined and identified as Physa acuta (Table S1).Four of the lots-one from Phang Nga province in southern Thailand, and three from Khammouane and Vientiane in Laos-were originally identified as Camptoceras jiraponi.The specimens were collected from eight provinces in Thailand and two provinces in Laos, and were found in natural (rivers), human-modified (paddy fields) and artificial (concrete pots or ponds and among ornamental aquatic plants) habitats (Figure 1).Specimens were also collected as hitchhikers on aquatic plants being sold in an ornamental pet trade shop in a market in Bangkok.All material examined had sinistral, ovate shells with smooth surfaces (Figure 2), and specimens that were collected in 2017 were observed to have mottled bodies within translucent shells when alive (Figure 2K).The examined shells ranged from 4-10 mm in height.

Discussion
For the first time, we confirm the establishment and spread of the globally-invasive Physa acuta in Thailand and Laos based on museum material.Physa acuta has a long history of introduction outside its native range in North America, and may have been introduced to Europe as early as the 1700s (Lydeard et al. 2016;Vinarski 2017).The species and its congeners have been introduced to most of Southeast Asia: Malaysia (Ali 1993;Hill et al. 1997;Ng et al. 2017), Indonesia (Mienis 2005), Myanmar (Win et al. 2011), Vietnam (Bousset et al. 2013;Do 2015), Singapore (Ng et al. 2015b) and Brunei (Ng et al. 2015a).The original introduction of Physa acuta was probably much earlier, but based on examined material we can confirm that the species has been established in Thailand in a northeastern province since 2001, in northern and southern provinces since 2005, and in Vientiane in Laos for almost thirty years.All these specimens were initially identified as Camptoceras jiraponi (Table S1).Camptoceras jiraponi also has a sinistral shell but differs from Physa acuta in that it has a more inflated body whorl, shorter spire, more impressed suture and periostracal hairs (Figure 3, also see Hubendick 1967: p. 168; Brandt 1974: Plate 16, Figure 1).The type locality of Camptoceras jiraponi is Thonburi (Hubendick 1967), within the wider Bangkok metropolitan area (Thailand), and Brandt (1974) recorded only one other locality in Thailand in the southern province of Nakhon Si Thammarat.Camptoceras jiraponi is assessed as Least Concern by the IUCN, and is assumed to have a widespread distribution in Thailand (Simonis 2012).Based on available material from two published studies, we identified specimens of Physa acuta, which were previously recognised as Camptoceras jiraponi (Sri-Aroon et al. 2006, 2015).No specimens that could be identified as Camptoceras jiraponi were collected from the field, nor found in the collections that were examined.It is, therefore, important to re-examine existing specimens from Thailand that have previously been identified as Camptoceras jiraponi, in order to update the status of the species.
While we have confirmed the presence of established populations of Physa acuta in Thailand and Laos, the introduction pathway remains uncertain.The global invasion of Physa acuta has been attributed to the ornamental pet trade (Duggan 2010;Bousset et al. 2013;Vinarski 2017).Given our discovery of Physa acuta as a hitchhiker among aquatic plants being sold for ornamental purposes in a Bangkok market, the ornamental trade is a likely source of the species in Thailand.Physa acuta may have subsequently spread via connected waterways or attachment to mammals and water birds (Bousset et al. 2013;van Leeuwen et al. 2013).Besides investigating introduction pathways to prevent and better manage future invasions, it is also important to examine the impact of Physa acuta in native habitats.In invaded ranges elsewhere, Physa acuta is known to be biologically superior to indigenous snails and has the potential to negatively impact native communities (Brackenbury and Appleton 1991;Zukowski and Walker 2009).In Thailand and Laos, Physa acuta may be competing with native species like Bithynidae, Lymnaeidae or Planorbidae.However, the ecology of these native freshwater snails is poorly known (Köhler et al. 2012).
It is perplexing, especially in the case of Thailand, that a globally invasive species was introduced and became widespread without being detected for an undetermined, but probably lengthy, period of time.Molecular methods are increasingly being used to resolve the identity and systematics of native molluscs in Thailand (e.g., Tongkerd et al. 2004;Kulsantiwong et al. 2013;Kongim et al. 2015), and should also be applied to monitor and confirm the presence of introduced species, which may be superficially similar to native species (Ng et al. 2015b(Ng et al. , 2016b) ) or which display high plasticity (Gustafson et al. 2014).The effectiveness and cost of managing invasive species increases with the elapsed time since their introduction, and the case of Physa acuta, therefore, highlights the need for countries like Thailand to focus research efforts on the prevention and early detection of introduced species (Simberloff et al. 2013), in addition to increasing our understanding of native biodiversity.

Figure 2 .
Figure 2. Physa acuta from Thailand and Laos, and the ornamental trade.Thailand: A. Nong Khai province, B. Phang-Nga province, C. Chiang Mai province, D. Phetchabun province, E. Nakhon Phanom province, F. Suphanburi province, G. Phitsanulok province and H. Nakhon Sawan province.Laos: I. Vientiane province and J. Khammouane province.K. Hitchhiker among aquatic plants sold in an ornamental pet shop in Bangkok, Thailand.Scale bar = 1 mm.Photographs by Ting Hui Ng and Phirapol Chusongsang.