Occurrence, distribution and bibliography of the medicinal leech Hirudo verbana Carena, 1820 (Hirudinea, Hirudinidae) in Sicily (Italy)

The occurrence of the medicinal leech Hirudo verbana in the inland waters of Sicily has been lately overlooked. In the present note, the occurrence and distribution of this species is reviewed based both on the review of the available literature data and field collecting. Although a noteworthy reduction in the distribution range of the species seems to have taken place in Sicily in the course of the XX century, Hirudo verbana was confirmed to be still present in several sites located both within and out of Natura2000 sites. The Sicilian populations of the species should be included in the frame of the monitoring activities established by the Article 17 of the EU Council Directive 92/43/EEC (“Habitats Directive”).


INTRODUCTION
Among the representatives of leech genera and families that have been historically used for medical purposes (Sket & Trontelj 2008, Elliott & Kutschera 2011, the true "medicinal leeches" belong to the Palearctic hirudinid genus Hirudo Linnaeus, 1758. This genus includes the highly divergent Hirudo nipponia Whitman, 1886 and a cluster of closely related species until recently lumped under the binomen Hirudo medicinalis Linnaeus, 1758, a species whose native range is in fact limited to central and northern Europe (Utevsky et al. 2010). Due to the impact of specimens' collecting for medical purposes and to a generalised degradation of the inhabited water bodies, the medicinal leeches are nowadays threatened throughout their distribution range (Utevsky et al. 2010). Following the taxonomical revisions carried out in recent times (e.g. Neubert & Nesemann 1999, Hechtel & Sawyer 2002, Trontelj & Utevsky 2005, 2012, Siddall et al. 2007, Utevsky et al. 2010, Saglam et al. 2016 In Italy, the occurrence of medicinal leeches is reported from the whole peninsula and its major islands (Minelli 1978, 1979, Ruffo & Stoch 2006, Minelli et al. 2016. In Sicily, the occurrence of Hirudo "medicinalis" was first reported between the XIX and the early XX century (Delle Chiaje 1823, Blanchard 1894, Dequal 1911, 1916) and, after a temporal hiatus of about one century when the species was not cited further for the island, findings of Hirudo verbana were reported for single sites at the beginning of the XXI century (Utevsky et al. 2010, Sorgi et al. 2011; see Table 2).
Since for some Italian regions only old records are available, and for other ones some recent records were overlooked, the presence of medicinal leeches has not been reported in the Italian guidelines for the monitoring of habitats and species included in the European "Habitats Directive" for Latium, Campania and Sicily, whereas for the rest of Peninsular Italy and Sardinia the occurrence of Hirudo verbana was confirmed (Minelli et al. 2016).
To date, only scarce data are available on the Sicilian leech fauna (Minelli 1978, 1979, Ruffo & Stoch 2005, Sorgi et al. 2011, and an exhaustive checklist of the taxa occurring on the island is missing. Accordingly, and in order to check the actual presence and distribution in Sicily of Hirudo verbana, which should be the object of monitoring for reporting under Article 17 of the "Habitats Directive", hirudinid leeches were actively searched throughout the territory, and all the available literature has been reviewed.

MATERIALS AND METHODS
A database of the available information about Sicilian Hirudinea was compiled based on an extensive literature search paying particular attention to the citations of species ascribed to the genus Hirudo. The services provided by Google Scholar (https://scholar.google.com/), PubMed (www.ncbi.nlm.nih.gov/pubmed/), and the "Biodiversity Heritage Library" (www.biodiversitylibrary.org/) were extensively used.
Lentic and lotic natural water bodies, both characterised by permanent and temporary hydroperiod, were surveyed throughout the Sicilian territory. Artificial water bodies such as agricultural ponds, dam reservoirs, and drinking trough for the cattle have also been included in the survey. Overall, more than 735 sites were sampled both on Sicilian mainland and in the circum-Sicilian archipelagos (F. Marrone, unpublished data). In each visited site, Hirudo specimens were actively searched for both visually and using a hand net. Moreover, in the larger water bodies, the possible presence of specimens was ascertained through the implementation of the methods described by Minelli et al. (2016). When present, leeches were photographed and voucher specimens were collected and stored in 90% ethanol in the collection of FM at the University of Palermo, Italy. The identification of the collected leeches was based on Neubert & Nesemann (1999), Trontelj & Utevsky (2005) and Kutschera (2012). Fig. 1 Location of the Hirudo verbana occurrence sites known to date. Black: XIX and XX century records; white: XXI century records, including the novel ones reported in present work. The numbers refer to the codes reported in Table 2.

RESULTS
Based on the field survey, the occurrence of Hirudo specimens was observed in six new sites, mostly located on the Nebrodi mountain chain and neighbouring localities. Moreover, isolated populations occur in the Monti Sicani area and in the Monti di Montemaggiore (Fig.  1, Table 2). All the new occurrence sites are natural or semi-natural ponds characterized by clear waters and abundant macrophytes, usually located above 800 m a.s.l. (Table 2). With the single exception of the pond Urio Quattrocchi, where the non-native fishes Carassius auratus and Tinca tinca are present, no fish were observed in any other of the inhabited ponds. Based on the dorsal and ventral patterns of the observed specimens, and in accordance to Utvesky et al. (2010), all the studied Sicilian specimens fall within the colour variants described for the polymorphic Hirudo verbana (Kutschera 2012) and are thus here ascribed to this species.

DISCUSSION
Whilst Delle Chiaje (1823) reported the widespread presence of the species in Sicily ("habitat ubique in stagnis et paludibus utriusque Siciliae"), and Blanchard (1894) studied specimens collected in a natural pond, the early XX century records of "Hirudo medicinalis" in Sicily only refer to the neighbourhoods of large towns (Dequal 1911(Dequal , 1916, suggesting the presence of introduced or translocated "medicinal leeches" used by local human population for medical purposes. Conversely, all the XXI century records of Hirudo verbana (including the novel ones reported in present note) are pertaining to scarcely inhabited areas, where pastoralism is still actively performed. It is thus possible that some of the older reports were actually referring to non-native specimens of dubious identity and origin, although no sound evidences supporting this hypothesis are available. Conversely, the current presence of Hirudo verbana in sites located in natural areas suggests that these populations may be native to the island.
In spite of the known faunal affinities between the inland water fauna of Sicily and North Africa (e.g. Marrone et al. 2009, Stöck et al. 2015, no evidences of the presence of the closely related Ibero-Maghrebian Hirudo troctina in Sicily could be found. This species, although allegedly reported to occur in Sardinia (see discussion in : Minelli 1978), is not currently considered part of the Italian fauna (Ruffo & Stoch 2006).
Unfortunately, no quantitative data are available on the consistency of the Hirudo populations reported here, and the absence of previous data prevents us from carrying out an estimate of the distribution trends of the species on the island. However, in contrast with the widespread local diffusion of the species mentioned in the XIX century, all the currently known Sicilian Hirudo verbana populations occur within protected areas. This suggests a general disappearance of the species from the more urbanized and agriculturally managed areas, and its survival in "natural refuges" where both well-structured water bodies and traditional rearing of livestock are still present.
One of the novel sites of occurrence of H. verbana lies just out of the Special Area of Conservation, SAC (Zona Speciale di Conservazione, ZSC, in Italian) "Lago Gurrida e Sciare di S. Venera" (SAC ITA070019), and an update in the perimeter delimitation of the SAC itself should thus be considered (see Table  2). In order to prevent the further decline of the species, it is also desirable that, in good accordance with the Article 17 of the EU Council Directive 92/43/EEC ("Habitats Directive"), the status and trends of the existing Sicilian populations of the species are monitored on regular bases.