Acta Herpetologica 14(2): 141-145, 2019 ISSN 1827-9635 (print) © Firenze University Press ISSN 1827-9643 (online) www.fupress.com/ah DOI: 10.13128/a_h-7753 Variability in the dorsal pattern of the Sardinian grass snake (Natrix natrix cetti) with notes on its ecology Enrico Lunghi1,2,3,4,*, Simone Giachello5, Manuela Mulargia6, Pier Paolo Dore7, Roberto Cogoni8, Claudia Corti2 1 Institute of Zoology, Chinese Academy of Sciences, Beichen West Road 1, 100101, Beijing, China. *Corresponding author. Email: enri- co.arti@gmail.com 2 Museo di Storia Naturale dell’Università di Firenze, Sede “La Specola”, Via Romana 17, 50125 Firenze, Italia 3 Natural Oasis, Via di Galceti 141, 59100 Prato, Italia 4 Universität Trier Fachbereich VI Raum-und Umweltwissenschaften Biogeographie, Universitätsring 15, 54286 Trier, Germany 5 Dipartimento di Scienze e politiche ambientali, Università degli Studi di Milano, via Celoria 2, 20133 Milano, Italia 6 CEAS Santa Lucia Siniscola. Via Isalle 4, 08029 Siniscola, Italia 7 Gruppo Speleo Ambientale Sassari, Via Pigliaru, 3, 07100 Sassari, Italia 8 Unione Speleologica Cagliaritana, via Scarlatti, 11, 09045 Quartu Sant’Elena, Italia Submitted on: 2019, 4th July; revised on: 2019, 2nd September; accepted on: 2019, 17th September Editor: Marco Mangiacotti Abstract. The Sardinian grass snake (Natrix natrix cetti) is a Critically Endangered snake endemic to Sardinia (Italy), for which information is still scarce. In the present work, we report information obtained from 36 observations of N. n. cetti performed in different areas of the Island. Three different colorations were mainly observed and darker snakes were in general males and big adults; the only juvenile found showed a complete different dorsal colouration. Snakes were observed active during day-time and often far from the aquatic habitats. Keywords. Melanism, abundism, mimicry, predator avoidance, island. The Sardinian grass snake (Natrix natrix cetti) is a Critically Endangered snake endemic to Sardinia, for which we still have very limited information (European Reptile & Amphibians Specialist Group, 1996; Vanni and Cimmaruta, 2010). A recent phylogenetic analysis per- formed on the Natrix natrix complex grouped the Sardin- ian grass snake together with the Corsican subspecies (N. n. corsa) into a distinct genetic group, which was likely promoted by their isolation occurred during glaciations (Fritz et al., 2012; Kindler et al., 2013). According to the most recent phylogenetic study, the western grass snakes belong to a new clade called Natrix helvetica (Kindler et al., 2017); however, in this study no samples from Sardin- ia have been analysed. Its elusiveness could be one of the causes of the few data available on its distribution, ecol- ogy and biology (Lunghi et al., 2016; Lunghi et al., 2018; Vanni and Cimmaruta, 2010). It is known that N. n. cetti can exploit different environments, from dry rocky areas to wetlands, rivers and even caves, and that the species is relatively widespread on the Island (Capula et al., 1994; de Pous et al., 2012; Lanza 1986; Mulargia et al., 2018; Salvi and Bombi, 2010). However, the presence of the Viperine snake (Natrix maura), as potential competitor, seems to affect its distribution (Stefani 1983; Vanni and Cimmaruta 2010). Adults of N. n. cetti differ morphologically from the continental subspecies because of the lack of the typi- cal light “collar”, and the smaller size (Speybroeck et al., 2016; Vanni and Cimmaruta, 2010). Stefani (1983) reports for N. n. cetti a typical light greyish background 142 Enrico Lunghi et alii colour, a characteristic that should be of help in distin- guishing the Sardinian grass snake from the Corsican one, being the latter characterised by a dark greenish background. Recently, abundistic (i.e., dorsum character- ized by enlarged dark stripes) and melanotic (i.e., near- ly completely black coloration) individuals of N. n. cetti were observed (Lunghi et al., 2016), thus increasing the variability of the dorsal colouration known for this sub- species. Furthermore, as far as we know, no information exists on juveniles. Here we report observations of Natrix natrix cet- ti gathered during three years fieldwork. All captured snakes were measured, and information on dorsal pattern and habitat were recorded. The observation of one juve- nile is also reported. From 2016 to 2018, we conducted herpetological field observations focusing on Eastern and Southern Sardinia (see Table 1; coordinates are not reported for species safe- guard, see Lunghi et al., 2019). Repeated linear transects, based on VES (Visual Encounter Survey), were carried out. The surveys were performed by day (9 a.m. – 5 p.m.) throughout the year, but the most in spring (Jan-Mar = 9.1%; Apr-Jun = 70.6%; Jul-Sep = 14.4%; Oct-Dec = 5.9%; total surveys = 153). For each snake we recorded: local- ity, elevation and time of the observation, habitat typology and dorsal background colour pattern (greyish, greenish- brownish, melanotic) (Fig. 1). Captured snakes were measured (total length) and sexed. Total length was meas- ured photographing the snakes on a plasticised millimetre paper; snakes’ length was extrapolated using the program ImageJ. Sex was assessed combining visual inspection of the morphology of the snake (proportion of the head and tail) and number of sub-caudal scales (Vanni and Cim- maruta, 2010). Head pattern was used for individually snake recognition (Sacchi et al., 2016; Vaughan, 1999). A Generalized Linear Model (R software with nlme package; Pinheiro et al., 2016; R Development Core Team 2018) was used to assess whether snake coloration is related to sex, elevation, time of survey and total length (TL). We used colouration as dependent variable, while sex, TL, time of survey and elevation as independent variables; year and transect identity as random factors. To use col- Fig. 1. The four different dorsal colourations of Natrix natrix cetti reported in this study: A) greyish, B) greenish-brownish, C) black, D) the juvenile. (Photos A and B by M. Di Nicola; C by E. Lunghi; D by S. Giachello). 143Dorsal pattern in Sardinian grass snake ouration as dependent variable, we ascribed an ascending order to the different colourations, going from the light- est (greyish = 1) to the darkest (greenish = 2) (Table 1). In this analysis we excluded the juvenile, the single mel- anotic individual, and, for the individual captured twice (see below) only the first observation. In total we performed 153 surveys on 3 different are- as (Barega, no. of transects = 1, total surveys = 5; Mon- te Albo, no. of transects = 11, total surveys = 102; Sette Fratelli, no. of transects = 2, total surveys = 46) and we observed 19 Natrix natrix cetti; seventeen were adults. Most of the observations (17) were performed on the Sette Fratelli Mountain and only an adult female was cap- tured twice. The greenish-brownish (n = 12) coloration resulted to be the most common, followed by the grey- ish (n = 5) and the melanotic (n = 1) (Fig. 1A-C). The observed juvenile (TL = 22 cm) showed a complete dif- ferent dorsal colouration: the background colour was black, the stripes white and a white collar was also pre- sent (Fig. 1D). Snakes were observed at an elevation between 341 and 1029 m a.s.l. Two individuals were found in small temporary water bodies, one in a mine, while the others 15 in rocky areas sometimes even more than 1 km far from the nearest water body. Snakes’ coloration significantly correlated only with total length (F1,8 = 8.94, P = 0.017); the darker (greenish) coloration was most frequently observed in the longer snakes (Fig. 2). No significant effect was observed for other variables (sex, F1,8 = 2.00, P = 0.195; elevation, F1,8 = 2.90, P = 0.127; time of survey, F1,8 = 1.69, P = 0.229). During our study, a female with a wounded eye was captured twice, the first on May 2016 and the second in April 2017; in both occasions this female was active at about the same time (16:41 and 16:21 respectively). This individual was recaptured almost 90 m far from the site of first encounter (difference in altitude 98 m). The Sardinian grass snake is one of the least studied Italian species. Elusiveness, rather than its potential rarity, could be the reasons for the few existing studies on this species (Vanni and Cimmaruta, 2010); indeed, although being made of just 19 records, our dataset is one of the richest available. The dorsal coloration of Natrix natrix cetti seems to be more variable than previously reported; indeed, most of our observations highlighted the high frequency of the greenish-brownish coloration, a charac- teristic that should be typical of the Corsican grass snake (Stefani, 1983). Because of our dataset paucity, we cannot provide any assumptions on the causes supporting the high pat- tern differentiation observed in this subspecies (but see also Lunghi et al., 2016). Further studies are needed to assess whether factors are influencing the observed vari- Table 1. Data of the captured individuals of Natrix natrix cetti: sex, total length (TL), dorsal background colour (1 = greyish, 2 = greenish- brownish, 3 = melanotic), elevation (m a.s.l.), time at which snakes were observed (24h), province, year, transect identity and the mountain complex. *individuals captured twice. Sex TL (cm) Colour Elevation Time Province Year Transect Mountain Female 65.7 2 341 16:15 Carbonia-Iglesias 2017 Barega1 Barega Female 44 1 474 14:32 Cagliari 2017 Cagliari3 Sette Fratelli Female 72.1 2 515 10:30 Cagliari 2016 Cagliari2 Sette Fratelli Female 74 1 534 10:08 Cagliari 2018 Cagliari2 Sette Fratelli Female 53.1 1 535 11:10 Cagliari 2017 Cagliari2 Sette Fratelli Female 62.3 2 539 12:00 Cagliari 2017 Cagliari2 Sette Fratelli Female 61.8 2 541 14:01 Cagliari 2017 Cagliari2 Sette Fratelli Male 54.3 2 633 11:02 Cagliari 2017 Cagliari2 Sette Fratelli Female 59 2 634 10:36 Cagliari 2017 Cagliari2 Sette Fratelli *Female 63 2 638 16:21 Cagliari 2017 Cagliari2 Sette Fratelli Female 57.9 2 670 15:45 Cagliari 2016 Cagliari2 Sette Fratelli Male 64.7 2 689 14:05 Cagliari 2017 Cagliari2 Sette Fratelli Male 60.1 3 706 13:45 Cagliari 2016 Cagliari2 Sette Fratelli Female 58.8 2 730 16:42 Cagliari 2016 Cagliari2 Sette Fratelli *Female 63 2 736 16:40 Cagliari 2016 Cagliari2 Sette Fratelli Female 63 1 792 15:58 Cagliari 2018 Cagliari2 Sette Fratelli Male 46.4 2 830 15:50 Cagliari 2017 Cagliari2 Sette Fratelli Female 59.8 2 863 13:20 Cagliari 2017 Cagliari3 Sette Fratelli Male 55.5 1 1029 14:45 Nuoro 2018 M_albo3 Monte Albo 144 Enrico Lunghi et alii ability and, if darker coloration may be beneficial for snakes’ longevity (Castella et al., 2013; Clusella Trullas et al., 2007; Fulgione et al., 2015; Stevens et al., 2009; Zuffi 2008). The juvenile highlighted ontogenetic variability in dorsal coloration in N. n. cetti. Our study agrees with Stefani (1983) and Lanza (1986) considering N. n. cetti not strictly related to water bodies. This likely allows the snake to exploit further hab- itats, increasing prey availability and lowering competi- tion with Natrix maura (Lunghi et al., 2018; Stefani, 1983; Vanni and Cimmaruta, 2010). Our study was carrried out in day-time (see also Lanza, 1986) but we cannot exclude nocturnal activity as reported by Capula et al. (1994). ACKNOWLEDGMENTS The study was authorised by the Italian Minis- try of Environment (n. 68754/T-A31 of 28/11/2016) and by Regione Autonoma della Sardegna (n° 9112 of 04/05/2017). REFERENCES Capula, M., Rugiero, L., Luiselli, L. (1994): Ecological observations on the Sardinian grass snake, Natrix natrix cetti. Amphibia-Reptilia 15: 221-227. Castella, B., Golay, J., Monney, J.-C., Golay, P., Mebert, K., Dubey, S. 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