Acta Herpetologica 13(2): 147-154, 2018 ISSN 1827-9635 (print) © Firenze University Press ISSN 1827-9643 (online) www.fupress.com/ah DOI: 10.13128/Acta_Herpetol-21026 Age structures and growth parameters of the Levantine frog, Pelophylax bedriagae, at different localities in Denizli, Turkey Eyup Başkale*, Sevay Ayşe Ulubeli, Yakup Kaska Pamukkale University, Faculty of Arts and Sciences, Department of Biology, Kınıklı Campus 20100 Pamukkale Denizli, Turkey. *Cor- responding author. E-mail: eyupbaskale@gmail.com Submitted on: 2017, 26th July; revised on: 2018, 1st January; accepted on: 2018, 20th September Editor: Rocco Tiberti Abstract. Skeletochronology is a reliable tool for assessing several parameters in amphibian populations. We used skeletochronology to determine the age structure, growth rate, age at first reproduction, and longevity of Levantine frog Pelophylax bedriagae populations from different localities in Denizli, Turkey. All examined individuals (N = 161) exhibited Lines of Arrested Growth in the bone cross-sections. Age structure and age at first reproduction were similar among localities and sexes, while longevity and growth rates showed significant variation among localities. Obtained results were compared with literature data on age-related and grow parameters in Pelophylax bedriagae and cognate species. Keywords. Skeletochronology, Levantine frog, longevity, growth rate, sexual maturity. INTRODUCTION Turkish water frogs were long considered as a sin- gle species, and Pelophylax bedriagae and Pelophylax caralitanus were previously considered to be subspecies of Pelophylax ridibundus (Sinsch and Schneider, 1999). However, both subspecies have been raised to species level, based on morphometric, molecular and bioacoustic evidence (Schneider and Sinsch, 1999; Sinsch and Schnei- der, 1999; Jdeidi et al., 2001; Plötner et al., 2001; Akın et al., 2010a, 2010b). The Levantine frog is a highly oppor- tunistic amphibian, widely distributed in the eastern Mediterranean region, including several Greek islands close to the coast of Turkey (Papenfuss et al., 2009). In Turkey, it is present along the Aegean coast and the southern part of the Anatolian highlands, from sea level to 2100 m (Özeti and Yılmaz, 1994). It is highly aquat- ic and inhabits a wide variety of running and standing water habitats, e.g., puddles, shallow ponds, large lakes, large rivers, mountain streams. The Levantine frog has been listed in the Least Concern category of the IUCN Red List of Threatened Species because of its wide distri- bution and presumed large populations, but habitat loss and its commercial use as food could threaten natural populations (Papenfuss et al., 2009). The Levantine frog also spread outside its native range by means of sev- eral introductions (e.g., for aquaculture), threatening the genetic integrity of native water frogs (e.g., Plötner et al., 2015). The aim of the present study is to describe the age structure and individual growth patterns of Levantine frog populations from distinct areas of Turkey. We used skeletochronology for estimating the age of amphibians and studying age-related parameters in four frog popu- lations (e.g., mean longevity, growth rate, age at sexual maturity; Castanet et al., 1993; Smirina, 1994; Guarino et al., 1999, 2003; Esteban and Sanchiz, 2000). Skel- etochronology can be applied on amphibian phalanges, which can be sampled without animal culling and with- out affecting amphibian populations and endangered spe- cies (Smirina, 1994; Khonsue et al., 2000; Guarino and Erişmiş, 2008; Guarino et al., 2011; Bionda et al., 2015). 148 Eyup Başkale et alii MATERIAL AND METHODS Study sites The field study was conducted during the 2015-2017 breed- ing seasons at four distinct localities at different altitudes in Denizli, Turkey. Süleymanlı Lake, Buldan, Denizli province, Turkey (38°03’N, 28°46’E; 1163 m a.s.l.) is a natural lake which covers 0.5 km2 and attains a maximum depth of 2 m. The lake is sur- rounded by coniferous tree (red pine Pinus brutia), willow trees (Salix alba) and reeds (Phragmites australis). The water surface is covered by aquatic vegetation (i.e., Myriophyllum spicatum). Vali Recep Yazıcıoğlu Dam, Denizli, Turkey (37°46’N, 29°07’ E; 328 m a.s.l) is a reservoir located in the city centre of Denizli. It is fed by underground water and by the Gökpınar creek. This reservoir covers approximately 2 km2 and is sur- rounded by sparsely distributed trees such as Salix alba and Juniperus sp. Aquatic vegetation is absent, but some vegetation patches are present in the littoral zone. Acıgöl Lake, Denizli, Turkey (37°47’N, 29°51’E; 839 m a.s.l.) is included in a natural wetland surrounded by agricul- tural land. The lake covers approximately 47 km2 but it reaches approximately 100 km² if the surrounding wetlands are includ- ed. The littoral area and the water surface are covered by aquat- ic vegetation. Ornaz Valley, Denizli province, Turkey (37°46’N, 28°58’E; 834 m a.s.l.) is crossed by a slow-flowing stream, which starts at Karcı Mountain and continues to Başkarcı. Along the river, there are many ponds that form natural amphibian breeding areas rich in aquatic and riparian vegetation. Field studies and morphometric measurements The Levantine frogs were captured by 2-3 people with a dip net or by hand after sunset using flashlights. Snout-Vent Length (SVL) was measured with a dial calliper (accuracy: 0.02 mm) and body mass (W) with a precision balance (accuracy: 0.1 g). Sex was determined based on secondary sexual characteristics of males, i.e. presence of metatarsal tubercules on the first finger of the front feet and vocal sac. The Sexual Dimorphism Index (SDI) was calculated as SDI = [(mean length of the larger sex / mean length of the smaller sex) - 1] according to the method of Lovich and Gibbons (1992). We collected bone samples only from breeding individuals, i.e. calling males, females responding to the males, and already paired individuals. We assumed that the age at first reproduction (Age at Maturity: AM) is the lowest age recorded among the breeding individuals. The longest digit of the hind foot was cut off, fixed in 70% ethanol, and then processed according to the routine skele- tochronological procedure (e.g., Castanet et al., 1993; Castanet and Smirina 1990; Smirina 1994). Following tissue removal, the bones were washed in running water for 12-14 hours, decalci- fied for 3-5 hours in 5% nitric acid and then placed in distilled water overnight. The bones were dehydrated using graded eth- anol series and then cleared in xylene, before embedding in paraffin. Using a rotary microtome, we obtained 16-µm-thick cross-sections from the central region of the diaphysis. Bone sections were stained with haematoxylin and eosin and analysed under a light microscope. The age of the frog was determined by two of the authors who independently counted the number of Lines of Arrested Growth (LAGs) present in each of the bone sections. With regard to first LAG resorption, we distinguished between “completely resorbed” (the first LAG was not observa- ble in bone cross-section), “partially resorbed” (only some parts of the first LAG were visible in bone cross-section), and “not resorbed” (the first LAG well visible in bone cross-section). Statistical analyses Length and weight data were normally distributed (Kol- mogorov–Smirnov D test, all P > 0.05), thus allowing compar- isons using parametric tests. We used a t-test for independent samples to compare the lengths and weights of male and female frogs. Length–weight relationships were estimated separately for each sex and locality. Growth rate was estimated according to the von Bertalanffy equation (von Bertalanffy, 1938): SVLt = SVLmax - (SVLmax - SVLmet)e-k(t-tmet) [1] where SVLt is the average body length at age t; SVLmax is the asymptotic maximum body length; SVLmet is the body length at metamorphosis that was calculated on newly metamorphosed individuals at the end of the summer (fixed to mean 26.3±3.22 mm); k is the body growth rate coefficient (year-1); tmet is age at metamorphosis (0.3 years). The parameters SVLmax and k and their asymptotic confidence intervals (CI) were estimated by nonlinear regression. All statistical analyses were conducted using SPSS ver. 20.0 (SPSS 2011). RESULTS A total of 161 individuals (80♂, 81♀) were exam- ined. SVL and body mass were significantly higher in females than in males (Table 1), but not among the sam- pling localities (females: F3,77 = 3.324, P > 0.05; males: F3,76 = 2.326, P > 0.05). Consistently the sexual dimorphism index was equal to 0.13 for all studied populations, i.e. female Levantine frogs are larger and heavier than males. All the examined bones sampled from adult frogs had well-defined LAGs with visible layers (Fig. 1). The first LAG was partially resorbed in 22.3% of females and 19.2% of males and completely resorbed in 8.8% females and 6.4% males. The age structure of the Levantine frogs from the different sampling sites is summarized in Table 1. The average age varied between 4.6 and 6.5 years among the populations, most individuals were between 4-8 years, and a few individuals reached a maximum age of 12 years (Fig. 2). The age of males and females did not show significant differences (Table 1). The sex-specific age structure did not differ significantly among localities 149Levantine frog age structure and growth parameters (females: F3,77 = 2.406, P > 0.05 and males: F3,76 = 2.351, P > 0.05). The age at first reproduction was two years in all localities and in both sexes. The asymptotic SVL (SVLmax) was estimated as 88.1±1.68 mm (CI = 85.08- 91.58) for males and 91.5±1.57 mm (CI = 88.62-94.58) for females, while growth coefficient (k) was estimated as 0.239 ± 0.0761 (CI = 0.196-0.255) and 0.346 ± 0.0924 (CI = 0.3145-0.7162) respectively (Fig. 3). DISCUSSION Our findings showed that counting LAGs on the pha- langes of P. bedriagae was relatively simple because the growth arrest was clear during the winter and the degree of endosteal resorption was low. We did not observe dou- ble LAGs in any sample. The lack of double lines, which indicate a double annual growth cycle (e.g., due to aes- tivation period; Guarino and Erişmiş, 2008), or partly resorbed LAGs, suggests that these frogs experience an uninterrupted and regular annual bone growth cycle. As observed in other cognate species, female Levan- tine frogs grow larger than males (Sinsch and Schnei- der, 1999; Erişmiş, 2005; Erişmiş and Chinsamy, 2010; Çiçek et al., 2011; Erişmiş, 2011; Gül et al., 2011; Table 2). Many amphibians show sexual size dimorphism, and females are larger than males in 90% of anuran species (Shine, 1979). Sexual size dimorphism can be explained in terms of differences in the age structure between the sexes in breeding populations (Monnet and Cher- ry 2002), or by adaptive differences in the grow rates Table 1. Student t tests comparisons of mean Snout-Vent Length (SVL), body mass and age in male and female Levantine frogs from four localities in Denizli, Turkey. Location Parameters Gender N Min Max Mean Std. Error Mean t df Sig. Vali Recep Yazıcıoğlu Dam SVL (mm) Female 30 51.0 86.0 71.20 1.726 3.242 50 0.002** Male 22 43.6 72.3 63.01 1.774 Body mass (g) Female 30 12.9 71.3 38.59 2.751 4.001 50 0.001** Male 22 11.6 34.5 24.49 1.679 Age Female 30 2 9 5.20 0.334 1.198 50 0.237 Male 22 2 9 4.59 0.382 Süleymanlı Lake SVL (mm) Female 24 57.0 104.9 76.63 2.194 3.079 47 0.003** Male 25 45.0 84.2 68.01 1.760 Body mass (g) Female 24 12.6 94.4 46.05 3.710 2.354 47 0.023* Male 25 11.6 75.9 35.29 3.075 Age Female 24 2 12 6.46 0.474 0.025 47 0.981 Male 25 2 11 6.44 0.575 Acıgöl Lake SVL (mm) Female 15 45.0 90 71.93 2.872 2.511 30 0.018* Male 17 44.8 80.7 63.09 2.127 Body mass (g) Female 15 11.3 84.4 37.59 4.540 1.971 30 0.058 Male 17 8.7 60.4 26.98 3.095 Age Female 15 2 9 5.13 2.232 -0.648 30 0.522 Male 17 2 9 5.59 1.734 Ornaz Valley SVL (mm) Female 14 50.4 103.0 81.14 4.635 2.168 26 0.039* Male 14 50.0 96.0 69.49 2.718 Body mass (g) Female 14 32.4 94.5 67.39 5.462 4.011 26 0.000** Male 14 24.3 74.3 41.36 3.504 Age Female 14 2 12 7.21 0.903 1.596 26 0.122 Male 14 2 11 5.50 0.571 Pooled localities SVL (mm) Female 81 45.0 104.7 74.31 1.337 5.027 159 0.000** Male 80 43.6 94.0 65.78 1.040 Body mass (g) Female 81 11.3 94.4 45.33 2.243 4.889 159 0.000** Male 80 8.7 75.9 31.92 1.568 Age Female 81 2 12 5.79 0.264 0.375 159 0.708 Male 80 2 12 5.65 0.265 *P< 0.05, **P < 0.01. 150 Eyup Başkale et alii between sexes (as observed in P. bedriagae; present study). Indeed, larger females are able to produce more and larger eggs (Crump, 1974; Crump and Kaplan, 1979; Berven, 1988; Kupfer et al., 2004; Haddad and Prado, 2005; Gunzburger, 2006) and males may prefer larger females (Dittrich et al., 2018). Body size parameters were comparable with previ- ous studies performed on other populations of Levantine frog (Çiçek et al., 2011) and on cognate species, such as P. ridibundus (Kyriakopoulou-Sklavounou et al., 2008; Gül et al., 2011; Erişmiş, 2011; Ashkavandi et al., 2012) and P. caralitanus (Erişmiş and Chinsamy, 2010; Başkale et al., 2017; Erişmiş, 2018) (Table 2). The age composition of amphibian populations may depend on several genetic and environmental factors, e.g., climate, trophic resourc- es, habitat quality, and interspecific interactions (Miaud et al., 2001; Morrison and Hero, 2003; Üzüm et al., 2011; Gümüş Özcan and Üzüm, 2015). Although our sampling habitats were quite different in terms of altitude, surface area, and habitat quality, all the studied populations had a similar age structure. However, different age structures can be retrieved in literature. Çiçek et al. (2011) and İsmail and Çiçek (2017) determined that the mean age of a Levantine frog population from Sülüklü Lake, Manisa, Turkey was much lower than what we observed (Table 2), possibly due to anthropogenic pressures. Similarly, also the age structure of the other cognate species may present high degrees of variation (Table 2). Compared to the pre- sent study (max longevity = 12 years), Çiçek et al. (2011) and İsmail and Çiçek (2017) found a lower longevity in P. bedriagae possibly due to anthropogenic stressors. Con- sidering cognate species, the maximum ages can reach 11 years (range = 5-11 years) and age at maturity ranged from 1-4 years in different parts of their range (Table 2). Fig. 3. Von Bertalanffy growth curve (age-length relationship) for Levantine frogs from different localities in Denizli, Turkey.Fig. 1. Phalangeal cross-sections (16 μm thick) of Levantine frog. The white arrows show LAGs in the periosteal bone: (A) Male: 4 LAGs with 65 mm SVL, (B) Female, 6 LAGs with 79.5 mm SVL. EB = Endosteal bone, PB= Periosteal bone, MC =Marrow cavity, RL=Resorption line. Fig. 2. Age distribution of four Levantine frog reproductive popula- tions from different localities in Denizli, Turkey. 151Levantine frog age structure and growth parameters Local climatic conditions can determine the activity period of amphibians and can be a key factor control- ling the activity and reproductive periods and popula- tion parameters in temperate species of anurans (Stebbins Table 2. Body size and grow parameters in P. bedriagae and cognate species: a comparison with existing literature. AM: age at sexual matu- rity; k: von Bertalanffy growth coefficient. Species Locality Sex N Mean SVL (mm) Max SVL (mm) Mean age (years) Max age (years) AM (years) k References P. bedriagae Vali Recep Yazıcıoğlu Dam, Denizli, Turkey M 30 63.01 80.17 4.59 9 2 0.18 Present study F 22 71.20 83.75 5.20 9 2 0.27 Süleymanlı Lake, Denizli, Turkey M 24 68.01 73.80 6.44 11 2 0.37 F 25 76.63 82.67 6.46 12 2 0.22 Acıgöl Lake, Denizli, Turkey M 15 63.09 70.04 5.59 9 2 0.37 F 17 71.93 80.79 5.13 9 2 0.24 Ornaz Valley, Denizli, Turkey M 14 69.49 78.64 5.9 12 2 0.19 F 14 81.14 96.41 6.8 12 2 0.33 Pooled localities M 80 65.78 88.1 5.65 12 2 0.24 F 81 74.31 91.5 5.79 12 2 0.35 Sülüklü Lake Manisa, Turkey M 14 56.1 73.2 2.5 4 2 0.30 Çiçek et al., 2011 F 22 64.5 92.4 2.95 5 2 M 51 59.80 120 3.45 7 2 0.22 İsmail and Çiçek, 2017 F 76 59.78 137 4.33 9 2 0.36 P. ridibundus Yıldızlı Stream, Trabzon, Turkey M 38 64.58 3.90 7 3-4 Yılmaz et al., 2005 F 11 76.64 3.72 6 3-4 Lake Vistonis, Lagos, Greece M 52 69.03 93.4 2.96 5 1 0.57 Kyriakopoulou-Sklavounou et al., 2008 F 56 82.38 107.5 3.73 5 1 0.54 Milicz Ponds Reserve, Stawno, Polland M 32 72.2 90 3.7 6 2 0.76 Socha and Maria, 2010 F 38 79.8 102.3 4.4 7 3 0.59 Artvin (Borçka, Lake Karagöl), Turkey M 20 72.96 5.15 8 2 Gül et al., 2011 F 25 63.49 4.20 7 2 Dörtyol, Hatay, Turkey M 20 64.70 5.50 11 4 F 19 76.74 5.58 7 3 Verkhne-Tagil Reservoir, Tagil and Vogulka rivers, Middle Urals. M - - - - - - - Ivanova et al., 2011 F 92.8 116 5.4 9 2 The Reftinskii Reservoir Reft River, Middle Urals. M - - - - - - - F 26 112.9 132 4.4 8 2 The north of Lorestan Province, central Zagros, Iran M 26 71.14 6.43 11 3 Ashkavandi et al., 2012 F 14 74.05 4.5 7 3 P. caralitanus Beysehir Lake, Turkey M 38 75.56 109 5.01 9 3-4 0.18 Erişmiş and Chinsamy 2010 F 51 92.05 126.24 6.01 10 3-4 0.16 M 96 90.41 111.35 5.63 9 3 Erişmiş, 2018 F 73 98.29 126.50 6.33 10 3 Karamık Lake, Turkey M 66 82.33 99.48 4.86 7 3 F 76 88.36 111.63 5.30 8 3 Işıklı Lake, Turkey M 49 73.06 93.68 3.69 6 2 F 47 82.54 106.72 4.80 8 2 Eğirdir Lake, Turkey M 90 86.44 110.12 5.42 8 3 F 97 94.52 120.28 6.21 10 3 152 Eyup Başkale et alii and Cohen, 1995; Kyriakopoulou-Sklavounou, 2000). For example, the Bergmann’s rule (Bergmann, 1847) indicates that the individuals living in a cold climate tend to be larger than individuals inhabiting warmer climates (i.e. Miaud et al., 2001; Khonsue et al., 2001; but see Ashton (2002) for several exceptions to this general role). Alti- tude variation causes steep environmental gradients at small geographic scale (e.g., temperature and humidity), but altitude had limited effects on the parameters of our study populations. Erişmiş (2018) observed that the P. caralitanus from the Lake District of Anatolia exposed to warmer temperatures had longer growth seasons, but smaller growth rates. Our results may depend on an unu- sually weak link between local climatic conditions and altitude. Alternatively, they could indicate that P. bedria- gae could have stable population parameters across its range, e.g., Gokhelashvili and Tarkhnishvili (1994) stated that P. ridibundus (formerly known as Rana ridibunda) from Georgia showed a constant age of maturation (after two hibernations) as a species-specific trait not depend- ing on local environmental factors. Our calculated grow rate in the present study is simi- lar to literature values for P. bedriagae (e.g., 0.30; Çiçek et al., 2011) and is lower than the values reported for most European Pelophylax species (Table 2). Previous stud- ies on P. ridibundus have shown significant correlations between SVL and age for both sexes (Yılmaz et al., 2005; Kyriakopoulou-Sklavounou et al., 2008) as commonly reported for the genus Pelophylax (Erişmiş et al., 2009; Esteban et al., 1996, 1999). In the present study, we found that the growth coefficients were higher in females than in males, and that the growth curves reached a plateau at an age of 3-4 years. In addition, the sizes at the same ages were highly variable among individuals, so that the size ranges of different age classes overlapped. These results show that body size is not an accurate indicator of the age of P. bedriagae, as already observed for other amphib- ians (Halliday and Verrell, 1988). ACKNOWLEDGEMENTS The permissions for field work, handling the frogs and laboratory studies were issued by the Animal Eth- ics Committee of Pamukkale University (Protocol No: PAUHDEK-2012/033), the Ministry of Forestry and Water Affairs, the General Directorate of Nature Con- servation and Natural Parks and the Turkish Ministry of Food, Agriculture and Livestock. We would like to thank to Pamukkale University Scientific Research Projects Unit – BAP (2012FBE029) for their support during this study. 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