Acta Herpetologica 11(2): 189-195, 2016 ISSN 1827-9635 (print) © Firenze University Press ISSN 1827-9643 (online) www.fupress.com/ah DOI: 10.13128/Acta_Herpetol-18616 Swimming performance and thermal resistance of juvenile and adult newts acclimated to different temperatures Hong-Liang Lu, Qiong Wu, Jun Geng, Wei Dang* Hangzhou Key Laboratory for Animal Adaptation and Evolution, School of Life and Environmental Sciences, Hangzhou Normal Uni- versity, Hangzhou 310036, Zhejiang, China. *Corresponding author. E-mail: dang.wei@hotmail.com Submitted on 2016, 11th July; revised on 2016, 20th October; accepted on 2016, 22nd October Editor: Rocco Tiberti Abstract. Thermal acclimatory adjustments of locomotor performance and thermal tolerance occur commonly in ecto- thermic animals. However, few studies have investigated ontogenetic differences in these acclimatory responses, and thus, their causes remain unclear. In this study, juvenile and adult Chinese fire-bellied newts (Cynops orientalis) were accli- mated to one of two temperatures (16 or 24 °C) for 4 weeks to examine ontogenetic differences in acclimation effect on burst swimming speed, and critical thermal minimum (CTMin) and maximum (CTMax). Swimming performance was thermally acclimated in both juvenile and adult C. orientalis. Adult newts had greater absolute swimming speeds than juveniles, which may simply result from their larger sizes. Cold acclimation enhanced low-temperature resistance, and warm acclimation enhanced high-temperature resistance in both juveniles and adults. Despite no ontogenetic difference in CTMin, adult newts had greater CTMax and acclimation response ratio than juveniles, indicating their greater abilities to withstand extreme high temperatures and manage rapid temperature shifts. Ontogenetic change in the thermal accli- matory responses of newts may be related to changes in the thermal environment they experience. Keywords. Salamandridae, ontogeny, thermal acclimatory response, swimming performance, thermal tolerance. INTRODUCTION Acclimation is the process that modulates the physi- ological and behavioural performance of organisms, allowing them to adjust to fluctuating environmental fac- tors such as temperature, humidity, and salinity (Lager- spetz, 2006). Thermal acclimation of physiological and behavioural traits has been widely investigated in vari- ous organisms and has been shown to vary considerably among different species (Angilletta et al., 2002; Lager- spetz and Vainio, 2006). Due to the potential impact on determining resilience to future climate change, the ther- mal acclimatory ability of ectothermic species has attract- ed increasing attention in recent years (Gvoždík, 2012; Sandblom et al., 2014; Seebacher et al., 2015). Locomotor performance and thermal tolerance are fitness-related traits, and may determine the survival of animals that are exposed to high predation pressures or extreme environmental temperatures (Arnold, 1983; Leroi et al., 1994; Willett, 2010). Consequently, the loco- motor performance and thermal tolerance of animals acclimated to various environmental conditions have frequently been assessed (Wilson et al., 2000; Gvoždík et al., 2007; Měráková and Gvoždík, 2009; Grigaltchik et al., 2012; Xu et al., 2015). Such acclimation effects also vary at different ontogenetic stages (Brooks and Sassaman, 1965; Menke and Claussen, 1982; Wilson and Frank- lin, 2000; Wilson et al., 2000). Previous studies on anu- ran species have showed that thermal acclimatory abil- ity on locomotor performance could easily be observed before metamorphosis, but was lost after metamorphosis, which was explained by an ontogenetic shift in the liv- ing environment (Wilson and Franklin, 2000; Wilson et al., 2000). Acclimatory ability on locomotor performance 190 Hong-Liang Lu et alii should be reduced when metamorphosed frogs migrate from thermally stable aquatic habitats to terrestrial habi- tats with large daily temperature fluctuations (Wilson and Franklin, 2000; Wilson et al., 2000). In most amphib- ian species, the critical thermal minimum (CTMin) and maximum (CTMax) generally increase with increasing acclimation temperatures (Floyd, 1983; Gvoždík et al., 2007; Shi et al., 2012), but sometimes warm-acclimated metamorphosing tadpoles do not necessarily have higher CTMax than those that are cold-acclimated (Cupp, 1980; Menke and Claussen, 1982). This might also be partly due to a shift in the thermal regime of a species (Cupp, 1980; Sherman, 1980; Menke and Claussen, 1982). How- ever, studies on ontogenetic differences in the thermal acclimation of locomotor performance and thermal tol- erance are still limited in amphibian species. Since the mechanisms underlying the ontogenetic change in ther- mal acclimatory response are still not completely under- stood, it is necessary to collect more extensive data. The Chinese fire-bellied newt, Cynops orientalis, is a small-sized (up to 80 mm snout-vent length, SVL) pri- marily aquatic newt that is widely distributed in central and eastern China, and can be commonly found in per- manent ponds, rice terraces, and ditches (Fei et al., 2006). C. orientalis individuals are predominantly aquatic, but occasionally migrate short distances across land to oth- er water bodies. Mating and oviposition occur between March and July when water temperature is between 15 and 23 °C (Yang and Shen, 1993). Although the histol- ogy, sexual behaviour, and breeding ecology of this spe- cies have been studied during the past decades (Yang and Shen, 1993; Sparreboom and Mouta Faria, 1997; Xie et al., 2012; Jin et al., 2016), none of these studies has focused on thermal physiological performance. Here, we acclimated juvenile and adult C. orientalis to two tem- peratures for 4 weeks to examine ontogenetic differences in thermal acclimatory performances. On the basis of results from previous studies on the thermal acclimatory responses of amphibian species, we predict the following: (1) the ability to thermally acclimate locomotor perfor- mance should not disappear, (2) and ability to withstand extreme temperatures should be enhanced from juvenile to adult stages in predominantly aquatic newts. MATERIALS AND METHODS All newts (16 metamorphosed juveniles and 24 adults) used in the present study were collected from Fuyang mountain- ous area (Hangzhou, Zhejiang, eastern China) in July 2015 and transferred to our laboratory at Hangzhou Normal University. Prior to thermal acclimation, animals were maintained in six 60 (L) × 50 (W) × 40 (H) cm3 aquaria (6−7 individuals per aquar- ium) with a water depth of 15 cm at 20 °C and on an L:D 12:12 photoperiod for 2 weeks. Each aquarium was provided with pieces of tiles and some aquatic plants that served as refuges. The newts were then randomly divided into two groups (8 juveniles and 12 adults in each group), each of which was assigned to one temperature treatment: 16 or 24 °C. These tem- peratures were chosen because they may approximate the range of optimal temperatures for newt activity in the field (Yang and Shen, 1993). Each group of animals was housed in five identi- cal aquaria (4 juveniles or 4 adults per aquarium) in one of two temperature-controlled rooms held at the experimental temperatures. Aquaria (photoperiod L:D 12:12) were placed on the same shelf to minimize water temperature difference among aquaria. Water temperature of each aquarium was con- firmed multiple times using a UT-325 electronic thermometer (Uni-trend Group, Shanghai, China), and it varied less than 1 °C. Newts were maintained at the designated temperatures for 4 weeks. Throughout the experiment, newts were fed with Tubifex worms or fish meat. All newts were measured for burst swimming perfor- mances at test temperatures of 16 and 24 °C, and allowed to rest for 48 h between trials. During the resting period, newts were maintained in their aquaria at corresponding acclima- tion temperature. To avoid possible test sequence effects, newts were randomly assigned to different test orders (different accli- mation and test temperatures). The test temperatures of newts were achieved by placing them into an incubator at the corre- sponding temperatures for approximately 1 h prior to each trial. Newts were placed into a racetrack (120 × 10 × 20 cm3) filled with water to a depth of 10 cm at the test temperature and then encouraged to swim by tapping the tails with a paintbrush. A Panasonic HDC-HS900 digital video camera (Panasonic Co., Japan) was positioned laterally to record the swimming perfor- mance of each newt. Each newt was tested twice with a mini- mum of 30 min rest between the trials. To minimise the pos- sible diel and photophasic effects, measurements on any given day started at 13:00 and ended within 3 h. All video-clips were examined using MGI VideoWave III software (MGI Software Co., Canada) for maximal speed over 25 cm. In the following text, speed was expressed as two metrics: absolute speed (cm/s) and relative speed (the ratio of absolute speed to SVL for each individual, SVL/s). We used the dynamic method for determining the CTMin and CTMax of the newts (Kour and Hutchison, 1970; Lutter- schmidt and Hutchison, 1997). Trials were conducted in water baths between 10:00 and 15:00. The newts were cooled or heated from their acclimation temperatures at a rate of 0.3 °C min-1 until individuals lost righting response, and their body temperatures were measured by inserting the probe of an elec- tronic thermometer into the cloaca (Lutterschmidt and Hutch- ison, 1997; Xu et al., 2015). We ran tests at 1-week intervals to minimise possible interactions between CTMin and CTMax. The newts were maintained in their aquaria during the inter- vals between trials. The thermal resistance range (TRR) was calculated as the difference between CTMax and CTMin (van Berkum, 1988), and the acclimation response ratio (ARR) was calculated by dividing the tolerance change by the change in acclimation temperature (Claussen, 1977). 191Thermal acclimation in a Chinese fire-bellied newt We used Statistica 6.0 (StatSoft, Tulsa, USA) to analyse the data. Data were tested for normality using Kolmogorov- Smirnov tests, and for homogeneity of variances using Bartlett’s test. The primary analyses indicated that aquarium had no vis- ible effects on swimming performance (mixed model ANOVAs with aquarium as the random factor, all P > 0.532), so repeated- measure ANOVAs were used to determine whether ontogeny, acclimation temperature and test temperature affected swim- ming performance. Two-way ANOVAs were used to determine whether ontogeny and acclimation temperature affected CTMin and CTMax. RESULTS There were no differences between groups in the body sizes of juveniles (SVL: 39.9 ± 1.1 mm vs 41.5 ± 0.8 mm, t = 1.21, df = 14, P = 0.246; mass: 1.89 ± 0.09 g vs 1.84 ± 0.11 g, t = 0.35, df = 14, P = 0.731) or adults (SVL: 64.2 ± 1.4 mm vs 65.4 ± 0.7 mm, t = 0.73, df = 22, P = 0.470; mass: 6.48 ± 0.49 g vs 7.00 ± 0.35 g, t = 0.86, df = 22, P = 0.400) prior to the beginning of the experi- ment. The absolute swimming speed of C. orientalis was significantly affected by acclimation, test temperature, and ontogeny (Table 1, Fig. 1A, B). Overall, newts that acclimated and tested at high temperature swam faster than those acclimated and tested at low temperature. Moreover, adults swam faster than juveniles (Fig. 1A, B). The absolute speeds of newts were positively related to their SVLs (linear regression analysis, all P < 0.05). With regard to relative speed, the differences between acclima- tion temperatures and between test temperatures were still evident, but not between adult and juvenile individu- als (Table 1, Fig. 1C, D). The interaction between test temperature and acclimation temperature, and between ontogeny and acclimation temperature had no significant effects on relative speed of newts (Table 1). Both mean CTMin and CTMax of juvenile and adult newts significantly increased as acclimation tempera- ture increased (Table 2, Fig. 2A, B). Overall, the mean CTMax of adults was significantly higher than that of juveniles (Fig. 2B), but there was no significant difference in CTMin between adults and juveniles (Table 2, Fig. 2A). The effect of thermal acclimation on CTMax dif- fered significantly between adults and juveniles, but this effect on CTMin did not (Table 2). There was a signifi- cant increase in the CTMax of adults as acclimation tem- perature increased (t = 7.78, df = 22, P < 0.0001), but not in that of juveniles (t = 1.56, df = 14, P = 0.141) (Fig. 2B). Similarly, acclimation temperature significantly affected the TRR of newts (Table 2, Fig. 2C). The acclimation temperature effect differed between adult and juvenile individuals. The TRR of adults increased as acclimation Table 1. Results of repeated-measures ANOVAs on swimming performance variables (absolute and relative speed) measured for juvenile and adult Cynops orientalis acclimated to two different temperatures. Swimming performance Absolute speed Relative speed Acclimation temperature F1, 36 = 4.73, P = 0.036 F1, 36 = 6.27, P = 0.017 Test temperature F1, 36 = 7.96, P = 0.008 F1, 36 = 10.31, P = 0.003 Ontogeny F1, 36 = 13.43, P < 0.001 F1, 36 = 0.12, P = 0.726 Acclimation × test temperature interaction F1, 36 = 0.12, P = 0.730 F1, 36 = 0.13, P = 0.716 Acclimation temperature × ontogeny interaction F1, 36 = 0.22, P = 0.641 F1, 36 = 0.13, P = 0.720 Test temperature × ontogeny interaction F1, 36 = 0.61, P = 0.439 F1, 36 = 0.03, P = 0.853 Acclimation × test temperature × ontogeny interaction F1, 36 = 0.01, P = 0.905 F1, 36 = 0.02, P = 0.900 Juvenile Test temperature (oC) 16 24 R el at iv e sp ee d (S V L/ s) 0 1 2 3 4 5 6 16 24 A bs ol ut e sp ee d (c m /s ) 0 8 16 24 32 40 acclimated to 16oC acclimated to 24oC Adult A B C D 1 2 Fig. 1. Mean values (+SE) for swimming performance (absolute and relative swimming speed) of juvenile and adult Cynops orientalis acclimated to different temperatures. 192 Hong-Liang Lu et alii temperature increased, but slightly decreased in juveniles (Table 2, Fig. 2C). The ARR values of CTMin and CTMax at acclimation temperatures between 16 and 24 °C were 0.08 and 0.07 for juveniles, and 0.12 and 0.26 for adults, respectively. DISCUSSION Our results showed that thermal acclimation signifi- cantly affected the locomotor performance of C. orientalis. Warm-acclimated newts appeared to have better locomo- tor performance than those that were cold-acclimated, which is not consistent with the beneficial acclimation hypothesis that predicts acclimation to a particular tem- perature should enhance an animal’s performance or fit- ness at that temperature (Leroi et al., 1994). The effect of thermal acclimation on locomotor performance has been shown to vary among different amphibian species. For example, constant temperature acclimation failed to affect aquatic and terrestrial locomotor performance in adult Ambystoma tigrinum nebulosum and Ichthyosaura alpestris (Else and Bennett, 1987; Šamajová and Gvoždík, 2010), or only had acclimatory capacity in terrestrial locomotion to warm temperatures in Triturus dobrogicus (Gvoždík et al., 2007), or in aquatic locomotion to cold temperatures in Eurycea guttolineata and Pseudotriton ruber (Mar- vin, 2003a, b). The fire-bellied newts living in permanent aquatic habitats in mountainous areas may experience limited temperature fluctuations at both juvenile and adult stages (Fei et al., 2006). Therefore, unlike those newts and salamanders that spend more than one-half of the year on land, such as A. tigrinum nebulosum and I. alpestris (Else and Bennett, 1987; Šamajová and Gvoždík, 2010), C. ori- entalis individuals do not lose the ability to acclimate their aquatic locomotor performance when they reach sexual maturity. This is consistent with our aforementioned pre- diction. In fact, the explanation proposed by Wilson and Franklin (2000) for the reduced acclimatory ability was based on the absence of thermal acclimatory responses of terrestrial locomotor performance rather than aquatic locomotor performance. Aquatic locomotor performance can still be thermally acclimated in adults of fully aquat- Table 2. Results of two-way ANOVAs on critical thermal minimum, critical thermal maximum, and thermal resistance range of juvenile and adult Cynops orientalis acclimated to two different temperatures. Critical thermal minimum Critical thermal maximum Thermal resistance range Acclimation temperature F1, 36 = 88.77, P < 0.0001 F1, 36 = 36.60, P < 0.0001 F1, 36 = 5.15, P = 0.029 Ontogeny F1, 36 = 0.27, P = 0.606 F1, 36 = 9.76, P = 0.004 F1, 36 = 11.64, P = 0.001 Acclimation temperature × ontogeny interaction F1, 36 = 3.07, P = 0.088 F1, 36 = 12.51, P = 0.002 F1, 36 = 8.35, P = 0.006 C ri tic al th er m al m ax im um (o C ) 35 36 37 38 39 Th er m al r es is ta nc e ra ng e (o C ) 34 35 36 37 38 Juvenile Adult C ri tic al th er m al m in im um (o C ) 0.0 0.5 1.0 1.5 2.0 acclimated to 16oC acclimated to 24oC A B C 1 2 Fig. 2. Mean values (+SE) for critical thermal minimum, critical thermal maximum, and thermal resistance range of juvenile and adult Cynops orientalis acclimated to different temperatures. 193Thermal acclimation in a Chinese fire-bellied newt ic or semi-aquatic species (Wilson et al., 2000; Marvin, 2003a, b; Gvoždík et al., 2007; Wu et al., 2013; Mineo and Schaeffer, 2014; Xu et al., 2015). Inconsistent with the results of previous studies on one species of Triturus newt and two species of Amby- stoma salamander (Shaffer et al., 1991; Wilson, 2005; Landberg and Azizi, 2010), adults swam faster than juve- niles in C. orientalis. This might simply result from larger body size at adulthood because there was no significant ontogenetic difference in relative speed. The reduced swimming performance in adult urodeles amphibians is interpreted as a consequence of changes in tail shape, rather than a negative size effect on performance (Land- berg and Azizi, 2010). The effect of ontogenetic change in tail shape on the swimming performance of C. orientalis should be investigated in future studies. The ability to withstand extreme temperatures may determine the survival of animals. The CTMin value for C. orientalis (0.5–1.5 °C) falls within the values reported for other fully aquatic or semi-aquatic urodeles (-1.9–3.9 °C for four Desmognathus, one Plethodon, and one Eurycea salamanders, Layne and Claussen, 1982a, b, 1987), where- as the CTMax for C. orientalis (36.2–38.3 °C) is similar to the values reported for most other urodeles, and is higher than those for some high-latitude or high-altitude species (Hutchison, 1961; Brooks and Sassaman, 1965; Sealander and West, 1969; Berkhouse and Fries, 1995; Gvoždík et al., 2007). Compared with anuran species, for C. orienta- lis, the CTMin (tadpoles: 7.4−8.9 °C for Fejervarya limno- charis, 8.7−11.7 °C for Microhyla ornata, Shi et al., 2012; but 0–1.6 °C for Rana catesbeiana, Menke and Claussen, 1982; adults: 2.1−5.1 °C for three Hyla treefrogs, Layne and Romano, 1985; 4.1−4.9 °C for Rhinella arenarum and Odontophrynus occidentalis, Sanabria et al., 2012, 2013) and CTMax (tadpoles: 37–43 °C, Cupp, 1980; Sherman, 1980; Navas et al., 2010; Shi et al., 2012; Simon et al. 2015; adults: 41.5–43.7 °C for two Hyla treefrogs, Blem et al., 1986; but 35.0–37.8 °C and 34.1–36.1 °C for R. arenarum and O. occidentalis, Sanabria et al., 2012, 2013) were low- er than those for most frog and toad species. Therefore, thermal tolerance varies among amphibian species, and is believed to be correlated with habitat and geographic dis- tribution (Hutchison, 1961). Moreover, adult C. orientalis had a greater CTMax than did juveniles, which was also found in other urodeles and anurans, such as E. nana, Notophthalmus viridescens, Bufo woodhousii fowleri, and Hoplobatrachus chinensis (Hutchison, 1961; Sherman, 1980; Berkhouse and Fries, 1995; Fan et al., 2012). As reported for other amphibian species (e.g., Brooks and Sassaman, 1965; Sealander and West, 1969; Menke and Claussen, 1982; Gvoždík et al., 2007; Shi et al., 2012), low-temperature resistance can be enhanced by cold acclimation, whereas high-temperature resistance can be enhanced by warm acclimation in C. orientalis. Warm- acclimated adult newts had a relatively wider TRR than those that were cold-acclimated, but this pattern was not observed in juveniles. Contrarily, the TRR of tad- poles decreased with increasing acclimation temperature (20, 25 and 30 °C) in two other anuran species, F. lim- nocharis and M. ornata (Shi et al., 2012). Although par- tially reflecting a difference in temperature treatment, the differential results from these studies may also reflect different optimal temperatures that enable animals to exhibit a high thermal resistance. Those thermal condi- tions resembling environmental temperatures in animals’ natural habitats may be propitious for enhancing their thermal resistance (Xu et al., 2015). The magnitude of the resistance response to thermal acclimation may reflect the ability to manage temperature shifts. It has been assumed that the species living in environments with large daily temperature variations should have a greater ability to withstand rapid temperature shifts than those living in thermally stable environments (Sandblom et al., 2014). Surprisingly, the ARR of CTMax for adult C. ori- entalis is greater than that of other semi-aquatic urodeles (0.02–0.17, Hutchison, 1961; Sealander and West, 1969; Gvoždík et al., 2007). Despite no significant ontogenetic difference in accli- mation effect on CTMin, the ARRs of critical thermal limits in adult C. orientalis appeared to be greater than those of juveniles. Combined with the greater CTMax and TRR, our results indicate that adult C. orientalis have greater abilities to withstand extreme high tempera- tures and manage rapid temperature shifts than juveniles do. This is consistent with our second prediction. Such ontogenetic shifts in thermal resistance may be related to  changes  in the  thermal environments experienced by active newts. Animals living in warmer and more ther- mally variable environments are believed to have greater resistance abilities than those living in cooler, less vari- able environments (Brooks and Sassaman, 1965; Berk- house and Fries, 1995). Adult C. orientalis can be active over a wider area, and occasionally migrate from aquatic environments to humid-land environments. 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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. 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