Acta Herpetologica 11(2): 111-118, 2016 ISSN 1827-9635 (print) © Firenze University Press ISSN 1827-9643 (online) www.fupress.com/ah DOI: 10.13128/Acta_Herpetol-18075 Effective thermoregulation in a newly established population of Podarcis siculus in Greece: a possible advantage for a successful invader Grigoris Kapsalas1, Ioanna Gavriilidi1, Chloe Adamopoulou2, Johannes Foufopoulos3, Panayiotis Pafilis1,* 1 Section of Zoology and Marine Biology, Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, GR-15784, Greece. *Corresponding author. E-mail: ppafil@biol.uoa.gr 2 Zoological Museum, Department of Biology, National and Kapodistrian University of Athens, Panepistimioupolis, GR-15784, Greece 3 School of Natural Resources and Environment, University of Michigan, Ann Arbor, MI 48109, USA Submitted on 2016, 3rd March; revised on 2016, 15th June; accepted on 2016, 21th June Editor: Daniele Pellitteri-Rosa Abstract. Temperature affects all aspects of reptilian biology. In order to colonize new habitats and support viable populations lizards have to successfully deal with their thermal environment. Podarcis siculus is a notorious example of a successful colonizer that has invaded numerous habitats outside its natural distribution range. Though certain features of its thermal biology have been assessed so far, the thermoregulatory abilities of the species remain poorly described. Here we investigated a recently discovered population in Greece and evaluated the effectiveness of ther- moregulation measuring three main thermal parameters: set-point range, operative and field body temperatures. The Greek P. siculus appear to be accurate, precise and effective thermoregulators achieving E = 0.96. This effective ther- moregulation may be used to explain, among other special characteristics, its spreading success. Keywords. Temperature, thermoregulation, invasive species, Italian wall lizard, Greece. INTRODUCTION Thermoregulation is crucial in ectotherms, shaping all features of their overall biology (Bartholomew, 1982). In small reptiles like lizards, thermoregulation is most times achieved behaviorally through appropriate move- ments between warmer and cooler microhabitat sites, shade and sun (Avery, 1982; Stevenson, 1985). System- atic research of reptilian thermal biology dates back to the mid-1940s (Cowles and Bogert, 1944). In 1976, Huey and Slatkin introduced a concise and detailed model to evaluate thermoregulation in ectotherms. This paradigm remained in use for the next two decades until Hertz and his partners (1993) fundamentally changed the way ther- moregulation was perceived and proposed a thorough research protocol to answer a question of paramount importance: how effectively do lizards thermoregulate? In order to answer this question, Hertz et al. (1993) took into account three main parameters: body tem- peratures (Tb, the temperature that animals achieve in the field), operative temperatures (Te, the temperature that a non-regulating animal would achieve in the field, measured with the use of models), and the species’ set- point range (Tset, the temperature that animals select in a laboratory setting in the absence of any ecological con- straints). Therefore Tb can be viewed as the result of the species’ mean Tset, which is considered a thermal uto- pia under ideal conditions (Sagonas et al., 2013a) and its interactions with a biotope’s Te. By considering these variables together, we are able to assess the effectiveness, accuracy and precision of thermoregulation of any given species (Hertz et al., 1993). The Italian Wall Lizard Podarcis siculus (Rafinesque- Schmaltz, 1810) (Sauria, Lacertidae) is definitely not any 112 Grigoris Kapsalas et alii given species. It is a small-bodied (snout-vent length, SVL, up to 90 mm; Corti and Lo Cascio, 2002), diur- nal, heliothermic lacertid that feeds mainly on terres- trial invertebrates (Corti, 2006), although its diet may include unusual food resources such as rodents, geckos and even conspecifics (Capula and Aloise, 2011; Grano et al., 2011), revealing a flexible and opportunistic feeder (Zuffi and Giannelli, 2013), as most lacertids are (Scali et al., 2015). A native lizard of the Italian peninsula and north Adriatic coasts, P. siculus has recently expanded its distribution in many other Mediterranean countries by establishing numerous new populations (Crnobrnja Isail- ovic et al., 2009). Its excellent dispersal abilities (Vigno- li et al., 2012) are underscored by the fact that it is the only Podarcis lizard that can be found in four continents: Europe, Asia, North America and Africa (Arnold and Ovenden, 2002; Kolbe et al., 2013; Tok et al., 2015). As such, P. siculus has been widely used as a model organ- ism in numerous ecological, physiological, behavioral and phylogenetic studies (Fulgione et al., 2004; Podnar et al., 2005; Bonacci et al., 2008; Biaggini et al., 2009; Vervust et al., 2010; Raia et al., 2010). Several aspects of its thermal biology have been also studied (Avery, 1978; Ouboter, 1981; Van Damme et al., 1990; Tosini et al., 1992, 1996). However, its thermoregulation effectiveness (sensu Hertz et al., 1993) remains undetermined. In this study, we worked with a new, recently estab- lished population in Greece (Adamopoulou, 2015). We focused on the thermoregulatory capacity of P. siculus by measuring the three main thermal features, that is Tb, Te, and mean Tset. Furthermore, we compared the published data on set-point range temperatures from different sites within the species range. We hypothesized that since P. siculus is a highly successful colonizer capable of adapt- ing easily to new habitats, it should achieve effective ther- moregulation. MATERIALS AND METHODS The study site (Palaio Faliro) is located along the back side of a sandy beach in the Athens, Greece (37o55’9.38”N, 23o42’0.50”E). It is a heavily modified habitat planted with ole- anders, tamarisks and yuccas delimited by a crowded beach on the front and a highway avenue on the back. The only other reptile recorded on site was the Ocellated skink (Chalcides ocel- latus). The site represents the only known location of P. siculus in Greece (Adamopoulou, 2015), which probably originates from the Adriatic region (Silva-Rocha et al., 2014). In May 2015 we measured the operative temperatures of the site using 31 hollow, electroformed copper models that mimic the size, shape and reflectance of the species and were validated against live animals in the field (Bakken, 1992; Dzi- alowski, 2005). To simulate the heat capacity of the lizards, we added 2.5-3 ml of water into each model, both ends of which were sealed with plasticine, except for a narrow opening where the probe of a data-logger (HOBO U12 4-Channel External Data Logger - U12-008) was inserted (Diaz, 1997; Grbac and Bauwens, 2001). The models were placed on various spots on site so as to cover all types of microhabitats available to lizards (Huey, 1991). We recorded Te every 15 minutes for two consec- utive days (09:00-19:00). To ensure that the temperature responses between the cop- per models and the study animals were similar, we tested their cooling and heating rate (Lutterschmidt and Reinert, 2012). An adult male lizard and a copper model were placed side by side near a heating source (two 140 W lamps) for 45 minutes. Sub- sequently, the heating source was turned off and the subjects were left to cool down for 45 minutes, resulting in a total period of 90 minutes. During this period we recorded the temperature of the model and the lizard every five minutes with a Weber quick reading cloacal thermometer. A linear regression of Tb on Te suggested that there was a good fit between the model and the animal responses (regression statistics ± SE; slope = 1.305 ± 0.118, intercept = -7.290 ± 3.557, r2 = 0.928, P < 0.001). The body temperatures (Tb) of 30 individuals were meas- ured on site during the same dates that Tes were sampled. Liz- ards were caught by hand or noose from all occupied micro- habitats and their temperature was measured within 20 seconds using a quick-reading cloacal thermometer (T-4000, Miller & Weber, Inc., Queens, NY) to the nearest 0.1 °C. For every liz- ard caught we also measured SVL with digital calipers (Silver- line 380244, accurate to 0.01 mm) while sex was determined by inspection of the femoral pores. Finally, 11 adult males (since sampling took place within the reproductive period we tried to avoid the impact of sex on set-point range temperatures; Carneiro et al., 2015) were trans- ferred to the laboratory facilities of the Department of Biology at the University of Athens to measure Tset. The lizards were placed in a specially designed terrarium (100 x 25 x 25 cm) where a thermal gradient (10-60 °C) was achieved with the use of two incandescent heating lamps (100 W and 60 W) at one end and two ice bags on the opposite (Van Damme et al., 1991). Subsequently their body temperature was measured every 30 min for four consecutive hours (Castilla and Bauwens, 1991) using a quick-reading cloacal thermometer (T-4000, Miller & Weber, Inc., Queens, NY). We used the inter-quartile range of the body temperatures selected by lizards in the thermal gradi- ent (Hertz et al., 1993). To evaluate the effectiveness of thermoregulation we used the formula: Ε = 1 - (db − / de − ), where db − represents the mean deviation of field Tbs from mean Tset and de − provides a meas- ure of thermoregulation accuracy and the mean deviation of Tes from mean Tset, (Hertz et al., 1993). Mean db provides an index of the accuracy of thermoregulation whereas de − sketches out the thermal quality of the habitat. E may range from zero (perfect thermoconformers) to one (perfect thermoregulators). Complementary to the classical evaluation of the ther- moregulatory effectiveness (Hertz et al., 1993), we also employed an alternative approach that quantifies the extent of departure from perfect thermoconformity (Blouin-Demers and Weatherhead, 2001). In the latter, positive values of the differ- 113Thermoregulatory effectiveness of Podarcis siculus ence between de − and db − describe thermoregulation, zero repre- sents animals demonstrating perfect thermoconformity, and negative values describe animals avoiding habitats of high ther- mal quality. The magnitude of the difference (de − - db −) provides an index of the thermoregulatory effectiveness (Blouin-Demers and Weatherhead, 2001). RESULTS Our results (male SVL = 74.3 ± 3.5 mm, n = 9; female SVL = 65.3 ± 7.0 mm, n = 20; t-test, t = -3.650, df = 27, P = 0.001) corroborated the typical pattern of sexu- al body size differences according to which male P. siculus are larger than females (Henle and Klaver, 1986). Males did not differ from females in their Tb (t-test, t = 0.758, df = 28, P = 0.455) and achieved similar body temperatures in the field (mean Tb for males = 33.2, mean Tb for females = 32.6). The mean value for the pooled Tb data was 32.8°C (Table 1). The majority of Tb fell within the spectrum of mean Tset while the diel varia- tion of body temperatures was limited (Fig. 1). Operative temperatures ranged from 19.5 °C at 09:00 h (minimum) to 53.4 °C at 14:15 (maximum) and mean Te was 31.7 °C (Table 1, Fig. 1). Tset values ranged from 30.0°C to 37.0 °C (Table 1). Lizards achieved a mean set-point tempera- ture of 33.8 °C (Table 1). The mean deviation of Tb from mean Tset was 0.1 °C while the mean deviation of Te from mean Tset was 3.2 °C (Table 1). These values were used to estimate the effectiveness of thermoregulation (sensu Hertz et al., 1993), that was E = 0.96. This value indicates that P. siculus is an active thermoregulator, as expected from the closeness of body temperatures to mean Tset. The complementary approach we used (Blouin-Demers and Weatherhead, 2001), also revealed high thermoregu- latory effectiveness (de − - db − = 3.1) DISCUSSION This study provides a comprehensive analysis of the thermoregulation effectiveness of the Italian wall lizard. In line with our first hypothesis, P. siculus proved to be an effective thermoregulator and able to achieve body tem- peratures within mean Tset. Body temperatures that liz- ards achieve in the field vary considerably among differ- ent biotopes (Avery, 1978; Van Damme et al., 1990; Tosi- ni et al., 1992), in accordance with our second prediction. Operative temperatures at the study site revealed – at least during the study period – a benign habitat lack- ing extreme temperatures (Table 1). Nonetheless, the site offers the lizards the required thermal heterogeneity for behavioral thermoregulation. Mean de received a low val- ue (3.2), indicating the high thermal quality of the habi- tat. In other words, lizards can easily achieve body tem- peratures within mean Tset. Set-point range temperatures are critically important in reptiles as they determine the optimal overall perfor- mance of the animal (Clusella-Trullas et al., 2007). Many factors, such as season, sex, age, reproductive status, body size and habitat may affect Tset (Andrews et al., 1999; Car- Table 1. The thermal variables used in this study: operative tem- peratures (Te), body temperatures in the field (Tb), set-point range (Tset), deviation of Te from Tset (de) and deviation of Tb from Tset (db). Variable n Mean (°C) Range (°C) SD SE Te 31 31.7 19.5 – 53.4 7.10 0.22 de 31 3.2 0 – 16.4 3.30 0.10 Tb 30 32.8 26.8 – 35.8 1.94 0.35 db 30 0.1 0 – 3.2 0.59 0.11 Tset 11 33.8 30.0 – 37.0 2.25 0.30 Fig. 1. Distribution of the mean body temperature in the field (Tb) and the mean operative temperature (Te). The shaded area indicates the set-point range (Tset) measured in the laboratory. 114 Grigoris Kapsalas et alii retero et al., 2005; Carretero, 2008; Veríssimo and Carret- ero, 2009; Sagonas et al., 2013 a, b). The mean Tset for P. siculus was 1°C lower than the only other value report- ed in literature (Avery 1978) and falls within the upper percentile of the thermal range of other Podarcis species (Table 2). To the best of our knowledge there are three pub- lished studies that present data on the set-point range and body temperatures of P. siculus (Avery, 1978; Van Damme et al., 1990; Tosini et al., 1992). The Greek popu- lation achieved higher Tbs in the field than lizards in Pisa (32.04 °C, Tosini et al., 1992) but lower compared to the populations from Tuscany (35.16 °C, Avery, 1978) and Corsica (33.89 °C, Van Damme et al., 1990). In regard to set-point range temperatures the mean Tset in the Italian population is approximately 1 °C higher (34.79 °C, Avery, 1978) than the one estimated in the present study. An interesting finding was that Tbs did not vary con- siderably during the day, contrary to other Podarcis liz- ards (e.g., Adamopoulou and Valakos, 2005; Sagonas et al., 2013a), a feature that was also reported by previous studies (Van Damme et al., 1990; Tosini et al., 1992). The limited range of Tbs is an indication of high precision in thermoregulation (Hertz et al., 1993). As predicted by the low de − that was mentioned above, an impressive 93% of all Tbs fell within the measured range of mean Tset. This corresponded to a very low mean db (0.1), which sug- gests high thermoregulation accuracy (Hertz et al., 1993). Thus, P. siculus appears to be not only a precise ther- moregulator (Van Damme et al., 1990; Tosini et al., 1992) but also an accurate one. The index of thermoregulation effectiveness took a high value (E = 0.96), which is among the highest that have been reported so far, not only for Podarcis lizards (Table 2) but among all lacertids. When animals are unable to thermoregulate, E will approach zero, whereas when they can successfully regulate their body tempera- ture, E will be close to one (Herzt et al., 1993). According to our results, P. siculus, at least in the study ecosystem, is actively thermoregulating with great success. This is directly related to the small deviation of Tbs from mean Tset. At this point we have to stress out that the evalua- tion of E was based on mean Tset that was calculated from exclusively male individuals and also that a limited num- ber of Tbs were obtained in a short period of time. In order to invade new ecosystems and establish via- ble populations, animals have to fullfill certain require- ments (Kolar and Lodge, 2001). Ectotherms need to fur- thermore meet additional thermal demands: they have to adapt swiftly to the environmental temperatures of the new biotope while, at the same time, perform close to optimal levels (Kraus, 2009). Thermal specialists, which achieve optimal performance in a narrow range of tem- peratures, are less apt to invade new habitats than ther- mal generalists (Angilletta et al., 2003; Angilletta, 2009). The Italian wall lizard is a successful colonizer thanks to the quick acclimatization and adaptability to the environ- mental conditions of the new “home” and to the numer- ous ways of dispersal (Deichsel et al., 2010; Valdeón et al., 2010; Silva-Rocha et al., 2012, 2014). Our findings suggest that P. siculus is able to effectively, accurately and precisely regulate its body temperature. Thanks to this Table 2. Studies on mean set-point range (Tset) and effectiveness of thermoregulation (E) in Podarcis lizards. Species Location E Tset Reference P. siculus Athens, Greece 0.96 33.8 This study P. liolepis Columbretes Island, Spain 0.95 34.2 Bauwens et al., 1996 P. milensis Milos Island, Greece 0.95 33.4 Adamopoulou and Valakos, 2005 P. lilfordi Menorca Island, Spain 0.88 35 Ortega et al., 2014 P. gaigeae Skyros Island, Greece 0.87 33.7 Sagonas et al., 2013a P. levendis Pori Island, Greece 0.84 33.9 Lymberakis et al., 2015 P. muralis Cres, Croatia 0.81 31.9 Grbac and Bauwens, 2001 P. peloponnesiacus Peloponnese, Greece 0.76 34 Pafilis, 2003 P. erhardii Andros Island, Greece 0.66 35.1 Pafilis, 2003 P. melisellensis Cres, Croatia 0.63 33.5 Grbac and Bauwens, 2001 P. tiliguerta Corsica, France 35.47 Van Damme et al., 1990 P. bocagei Spain 35.15 Bauwens et al., 1995 P. tauricus Peloponnese, Greece 33.8 Pafilis, 2003 P. vaucheri Ketama, Morocco 33.43 Verissimo and Carretero, 2009 P. hispanicus Bellaterra, Spain 33.07 Carretero et al., 2006 P. hispanicus Galera, Spain 31.65 Carretero, 2012 115Thermoregulatory effectiveness of Podarcis siculus effective thermoregulation, it may overcome the thermal challenges of new environments. As P. siculus settles new populations, there is strong evidence that it competes with native lacertids. Downes and Bauwens (2002) found that P. siculus is more aggres- sive and dominant than Podarcis melisellensis and occu- pies better thermal microhabitats. In laboratory experi- ments, P. siculus was also more aggressive and eventually suppressed activity levels in Podarcis tiliguerta (Vanhooy- donck et al., 2000). Furthermore, P. siculus hybridizes with other endemic Podarcis lizards (Capula, 1993; Cap- ula, 2002; Capula et al., 2002). The above considerations highlight the risk that P. siculus posses for autochthonous species, above all for Greece, which is home to seven endemic lacertids (Valakos et al., 2008). Since P. siculus has become established in Athens, it is only matter of time before it invades places that host endemic lizards (e.g., Peloponnese, Milos, Skyros, Crete). To eliminate the danger of further dispersal and the concomitant nega- tive effects, the investigated Athens population of P. sicu- lus needs to be exterminated. The Hellenic Herpetologi- cal Society inaugurated an eradication project in spring 2015. More than 150 individuals have been captured so far indicating that the initially estimated 50-60 animals (Adamopoulou, 2015) have multiplied to a much larger actual population in only a couple of years. This study, in spite of sampling flaws in field and lab temperature measurements, paves the way for delineating the particular features of ectotherms, which, like P. sicu- lus, rapidly expand their distribution. Further research that will assess the thermoregulation pattern of P. siculus in diverse habitats throughout its range is badly required. Effectiveness of thermoregulation and mean Tset should be the focal points. Thereby it will be clarified whether the successful dispersal of the species is due to a stand- ardized, conservative thermal pattern (the “static” view, Bogert, 1949) or just a response to environmental factors (the “labile” view, Huey, 1982). If E will receive equally high values and mean Tset will be similar to the studied population, then P. siculus will be indeed an effective thermoregulator with a conservative thermal physiology. Our results are the first step to this end. ACKNOWLEDGEMENTS We are grateful to Natalia Gourgouliani, Ana Pereira, Kostantina Mitsi and Stratos Kafentzis for their valuable help with fieldwork. All work was conducted with per- mission from the Hellenic Ministry for Environment and Energy (permit code 61ΣΜ465ΦΘΗ-ΕΣ6).  REFERENCES Adamopoulou, C. (2015): First record of Podarcis siculus (Rafinesque-Schmaltz, 1810) from Greece. Herpeto- zoa 27: 187-188. Adamopoulou, C., Valakos, E.D. 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Acta Herpetologica Vol. 11, n. 2 - December 2016 Firenze University Press Predator-prey interactions between a recent invader, the Chinese sleeper (Perccottus glenii) and the European pond turtle (Emys orbicularis): a case study from Lithuania Vytautas Rakauskas1,*, Rūta Masiulytė1, Alma Pikūnienė2 Effective thermoregulation in a newly established population of Podarcis siculus in Greece: a possible advantage for a successful invader Grigoris Kapsalas1, Ioanna Gavriilidi1, Chloe Adamopoulou2, Johannes Foufopoulos3, Panayiotis Pafilis1,* The unexpectedly dull tadpole of Madagascar’s largest frog, Mantidactylus guttulatus Arne Schulze1,*, Roger-Daniel Randrianiaina2,3, Bina Perl3, Frank Glaw4, Miguel Vences3 Thermal ecology of Podarcis siculus (Rafinesque-Schmalz, 1810) in Menorca (Balearic Islands, Spain) Zaida Ortega*, Abraham Mencía, Valentín Pérez-Mellado Growth, longevity and age at maturity in the European whip snakes, Hierophis viridiflavus and H. carbonarius Sara Fornasiero1, Xavier Bonnet2, Federica Dendi1, Marco A.L. Zuffi1,* Redescription of Cyrtodactylus fumosus (Müller, 1895) (Reptilia: Squamata: Gekkonidae), with a revised identification key to the bent-toed geckos of Sulawesi Sven Mecke1,*,§, Lukas Hartmann1,2,§, Felix Mader3, Max Kieckbusch1, Hinrich Kaiser4 The castaway: characteristic islet features affect the ecology of the most isolated European lizard Petros Lymberakis1, Efstratios D. 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Platt1, Dennis J. Miller2, Thomas R. Rainwater3,*, Jennifer L. Smith4 Heavy traffic, low mortality - tram tracks as terrestrial habitat of newts Mikołaj Kaczmarski*, Jan M. Kaczmarek Book Review: Sutherland, W.J., Dicks, L.V., Ockendon, N., Smith, R.K. (Eds). What works in conservation. Open Book Publishers, Cambridge, UK. http://dx.doi.org/10.11647/OBP.0060 Sebastiano Salvidio