Acta Herpetologica 11(2): 213-219, 2016 ISSN 1827-9635 (print) © Firenze University Press ISSN 1827-9643 (online) www.fupress.com/ah DOI: 10.13128/Acta_Herpetol-17821 On the feeding ecology of Pelophylax saharicus (Boulenger 1913) from Morocco Zaida Ortega1,*, Valentín Pérez-Mellado1, Pilar Navarro2, Javier Lluch2 1 Department of Animal Biology, University of Salamanca, Campus Miguel de Unamuno, 37007, Salamanca, Spain. *Corresponding author. Email: zaidaortega@usal.es 2 Department of Zoology, University of Valencia, C/ Doctor Moliner, 50, 46100, Burjassot, Valencia, Spain Submitted on 2016, 14th January; reviewed on 2016, 11th April; accepted on 2016, 7th May Editor: Sebastiano Salvidio Abstract. The Sahara frog is the most common amphibian found in North Africa. However, the knowledge of its nat- ural history is rather fragmentary. In the present work we studied the trophic ecology of Pelophylax saharicus at some areas of Morocco through the analysis of 130 gastric contents. We did not find any significant sexual dimorphism in body size of adult individuals. Consumed prey show similar sizes in both sexes, while bigger frogs normally eat larger prey. As in other Palearctic frogs, the diet is basically insectivorous, including terrestrial and aquatic prey. We found some differences in the diet of juveniles, with a higher proportion of flying prey, probably indicating a foraging strategy closer to ambush hunting. In the Atlas region, the high consumption of slow-moving terrestrial prey, as Gas- tropoda, stands out. Only in the Atlas region, the diet was similar to that described from other areas of North Africa, as Tunisia. Keywords. Trophic ecology, Ranidae, Green frogs, Morocco, Pelophylax saharicus. The Sahara frog, Pelophylax saharicus, inhabits a large portion of North Africa, from South Sahara to the Mediterranean coast, through the Atlas Mountains (Pas- teur and Bons, 1959; Amor et al., 2010), living at altitudes of more than 2600 m.a.s.l. Its distribution ranges from Morocco to Egypt, being the most common green frog of North Africa (Salvador, 1996; Amor et al., 2010). The species is strictly aquatic and is found both in natural and artificial permanent ponds, even when these are slightly eutrophized (Salvador, 1996). Pelophylax saharicus is currently considered a full species, following Bons and Géniez (1996) that sum- marized the discussion about the controversial status of Moroccan green frogs. Molecular studies support the specific status of P. saharicus (Plötner, 1998; Frost et al., 2006; Lymberakis et al., 2007; Lansari et al., 2015; Nicolas et al., 2015), ranging it as the sister group of Pelophylax perezi, apart from the other species of the genus. Both males and females reach the sexual maturity in the sec- ond year of life, and are able to live as much as six years (e.g. Oromi et al., 2011). Previous studies concluded that P. saharicus does not show sexual dimorphism in the size of adult animals (Esteban et al., 1999). In a preliminary study of feeding ecology of Palearc- tic frogs, Smith (1951) described the diet of Rana ridibunda ridibunda. Then, Lizana et al. (1989) com- pared the feeding ecology of P. perezi with other Iberian amphibians and with trophic availability at an area of the central Iberian Peninsula. Subsequent studies have addressed the feeding ecology of other Pelophylax species (Çiçek et al., 2006; Sas et al., 2009; Mollov et al., 2010; Paunović et al., 2010; Bogdan et al., 2012, 2013; Plitsi et al., in press). A recent study assesses the effect of temper- ature, density and food in the growth and metamorphosis of P. saharicus tadpoles (Bellakhal et al., 2014). Regarding its trophic ecology, some data have been published about 214 Zaida Ortega et alii P. saharicus in the oases of Kettana, in Tunisia (Hassine and Nouira, 2009). Here we present the first data about trophic ecology of the Sahara frog in Morocco. All samples used in this study came from Moroccan areas within the semi-arid Mediterranean zone of North Africa (Le Houéron, 1989). Frogs were captured during 1996 in three different areas of Morocco: (1) The Western Plateau, an area of subhumid to semiarid climate and two localities were sampled: El Borj and Zwiat Cheikh, (2) Rif Mountains and adjacent areas (this is the most humid area of Morocco with more than 600 mm of annual rain- fall), and (3) The Middle Atlas, with a climate of strong continental characteristics. Sample sizes were 9 males, 4 females and 5 juveniles for the Western Plateau, 26 males, 52 females and 6 juveniles for the Rif Mountains, and 11 males, 16 females and 1 juvenile for the Middle Atlas. Frogs were euthanized during the field work because they were captured to study helminthic parasites in the framework of a parasitological research (see Navarro and Lluch, 2006). Maturity and sex of the individuals were determined by direct examination of the gonads after dis- section. The analysis included 130 gastric contents. Prey items were identified to Family or Order level. Prey size was measured from intact items with a micrometric ocu- lar. Afterwards, absolute frequencies of each prey type and its percentage in the diet were calculated for each region, as well as the number of gastric contents in which such prey was present. We used Spearmann rank correlation and ANCOVA on prey size, with SVL (snout-vent length) as a covariate, to study the relation between body length of frogs and the size of consumed prey for each category (adult males, adult females, and juveniles). Then, we estimated and compared diet diversities using the approach proposed by Pallmann et al. (2012). Instead describing diet diversity through a given index as, for example, Simpson or Shan- non indices, we converted these “raw” indices into “true” diversities. That is, regarding different measures as spe- cial cases of Hill’s general definition of diversity measures (Hill, 1973). To study differences in diversity between males, females and juveniles, we performed two-tailed tests for integral Hill numbers of orders -1 ≤ q ≤ 3. This selection includes the transformed versions of the three following indices: the species richness index, Hsr (q = 0), the Shannon entropy index, Hsh (q → 1) and the Simpson concentration index, Hsi (q = 2). All comparisons among diversities of groups were made with Tukey-like contrasts employing a resampling procedure. We did 5000 boot- strap replications so as to obtain reliable p-values (West- fall and Young, 1993). Methods described here are imple- mented in R package “simboot” (Scherer and Pallmann, 2014) and are fully described in Pallmann et al. (2012). All calculations were done in R version 3.0.3 (R Core Team, 2014). Finally, in order to visualize differences in the composition of the diet of adults of both sexes and juveniles, we conducted a discriminant function analysis. Box’s M test of equality of covariance matrix was not sig- nificant, so data were suitable for discriminant analysis. Only two variables (Dictyoptera larvae and Dermaptera larvae) failed the tolerance test, so were excluded from the analysis, the rest of the variables (Table 3) were suit- able for analysis (tolerance test with P > 0.05). The diet of P. saharicus was mainly insectivorous and more varied in females than in males or juveniles. But, we did not find significant differences in the diversity values of males, females and juveniles (P > 0.05 in all pairwise comparisons, Table 2). Diptera were the most important prey item. The diet of juvenile individuals, principally dominated by Formicidae and other small Hymenoptera, was less diverse than that of adult males and females. We observed a high proportion of Hymenoptera in the diet of Western Plateau frogs, much higher than for Tunisian populations (Hassine and Nouira, 2009). This is principally due to the massive presence of this prey in five juvenile individuals, in which we found 95.58% (65 of 68 prey items) of all sampled Hymenoptera. In addi- tion, all adult individuals of P. saharicus from the Plateau ate proportionally more Hymenoptera than those from the Atlas or Rif regions, suggesting a greater availabil- ity of such prey at the Plateau. Alternatively, these differ- ences can be due to a different foraging behaviour in dif- ferent areas. According to our results, there is no sexual dimorphism in adult individuals of P. saharicus (see also Esteban et al., 1996; Meddeb et al., 2007). SVL of juveniles was 51.00 ± 2.00 mm (mean ± SE, n = 8). We did not find significant differences in body size of adult males and females of P. saharicus (one-way ANOVA of log-transformed data, F = 0.304, P = 0.583, homogeneous variances, Levene test, P = 0.90; SVL of adult males, mean = 88.43 ± 4.96 mm, range = 48-97 mm, n = 44; adult females, mean = 92.51 ± 4.40 mm, range = 48-223, n = 74), even if females were slightly larger than males. We measured 803 prey items (mean = 5.26 ± 0.18 mm, range = 0.5-70 mm). We found a signifi- cant correlation between frog body size (SVL) and prey size (Spearmann Rank correlation, Rs = 0.510, P < 0.001, n = 803). This correlation was also maintained within adult individuals (Rs = 0.399, P < 0.001, n = 695; mean = 5.68 ± 0.20 mm, range = 0.5-70 mm). According to this result, we analysed the prey size in both genders employ- ing the SVL as the covariate. Adult females ate prey of significantly larger size than adult males (ANCOVA anal- ysis, F = 4.816, P = 0.029, with no significant differences in regression slopes, F = 1.055, P = 0.305; mean = 5.04 215Feeding ecology of Pelophylax saharicus ± 0.24, n = 268 for adult males, and mean = 6.08 ± 0.29 mm, n = 427 for adult females). For the discriminant analysis, the correlations between the variables and the two discriminant axes are provided in Table 3. The discriminant function is able to correctly classify the 64.5% of individuals as adult males, adult females or juveniles according to their diet, so the goodness of fit is acceptable. Differences in the diet of Table 1. Data from the analysis of 130 stomach contents of Pelophylax saharicus. Fi is the absolute frequency of each type of prey item group in the sample, % Fi the relative frequency of the group in the sample, P is the presence of each group (i.e. the number of stomach contents in which the group appears), and % P the percentage of the presence of the item in the sample. Group Total Juveniles Adult males Adult females Fi % Fi P % P Fi % Fi P % P Fi % Fi P % P Fi % Fi P % P Gastropoda 48 5 21 16.2 2 1.74 2 18.18 9 2.90 6 13.64 37 6.93 13 17.57 Araneae 21 2.18 17 13.1 0 0 0 0 13 4.19 11 25 8 1.50 6 8.11 Acarina 2 0.21 1 0.8 2 1.74 1 9.09 0 0 0 0 0 0 0 0 Ostracoda 5 0.52 2 1.5 0 0 0 0 0 0 0 0 5 0.94 2 2.70 Isopoda 7 0.73 6 4.6 0 0 0 0 1 0.32 1 2.27 6 1.12 5 6.76 Crustacea 1 0.1 1 0.8 0 0 0 0 1 0.32 1 2.27 0 0 0 0 Diplopoda 1 0.1 1 0.8 0 0 0 0 1 0.32 1 2.27 0 0 0 0 Chilopoda 6 0.62 3 2.3 0 0 0 0 0 0 1 2.27 5 0.94 2 2.70 Diplura larvae 1 0.1 1 0.8 1 0.87 1 9.09 1 0.32 0 0 0 0 0 0 Thysanura 2 0.21 2 1.5 0 0 0 0 1 0.32 1 2.27 1 0.19 1 1.35 Odonata 1 0.1 1 0.8 0 0 0 0 1 0.32 1 2.27 0 0 0 0 Ephemeroptera 9 0.94 1 0.8 0 0 0 0 9 2.90 1 2.27 0 0 0 0 Plecoptera 4 0.41 4 3.1 0 0 0 0 1 0.32 1 2.27 3 0.56 3 4.05 Plecoptera larvae 6 0.62 4 2.3 0 0 0 0 2 0.64 2 4.54 4 0.75 2 2.70 Orthoptera 28 2.92 21 16.2 0 0 0 0 5 1.61 5 11.36 23 4.31 16 21.62 Orthoptera larvae 1 0.1 1 0.8 0 0 0 0 1 0.32 1 2.27 0 0 0 0 Dictyoptera 16 1.66 5 3.8 2 1.74 1 9.09 2 0.64 2 5.54 12 2.25 2 2.70 Dictyoptera larvae 1 0.1 1 0.8 0 0 0 0 1 0.32 1 2.27 0 0 0 0 Dermaptera 4 0.41 4 3.1 0 0 0 0 1 0.32 1 2.27 3 0.56 3 4.05 Dermaptera larvae 1 0.1 1 0.8 0 0 0 0 1 0.32 1 2.27 0 0 0 0 Phasmida 7 0.73 1 0.8 0 0 0 0 0 0 0 0 7 1.31 1 1.35 Embioptera 1 0.1 1 0.8 0 0 0 0 0 0 0 0 1 0.19 1 1.35 Thysanoptera 4 0.41 4 3.1 2 1.74 2 18.18 0 0 0 0 2 0.37 2 2.70 Homoptera 28 2.92 25 19.2 1 0.87 1 9.09 12 3.87 12 27.27 15 2.81 12 16.22 Homoptera larvae 3 0.31 3 2.3 0 0 0 0 2 0.64 2 4.54 1 0.19 1 1.35 Heteroptera 45 4.69 29 22.3 2 1.74 2 18.18 20 6.45 12 27.27 23 4.31 15 20.27 Heteroptera larvae 1 0.1 1 0.8 0 0 0 0 1 0.32 1 2.27 0 0 0 0 Diptera 245 25.52 87 66.9 18 15.65 7 63.64 97 31.29 33 75 129 24.16 47 63.51 Diptera larvae 19 1.98 14 10.8 1 0.87 1 9.09 5 1.61 4 9.09 13 2.43 9 12.16 Trichoptera larvae 1 0.1 1 0.8 0 0 0 0 0 0 0 0 1 0.19 1 1.35 Lepidoptera 9 0.94 7 5.4 0 0 0 0 5 1.61 4 9.09 4 0.75 3 4.05 Lepidoptera larvae 1 0.1 1 0.8 0 0 0 0 0 0 0 0 1 0.19 1 1.35 Coleoptera 149 15.52 65 50 6 5.22 3 27.27 50 16.13 23 52.27 93 17.42 39 52.70 Coleoptera larvae 29 3.02 11 8.5 6 5.22 3 27.27 2 0.64 2 4.54 21 3.93 6 8.11 Hymenoptera 155 16.14 55 42.3 68 59.13 8 72.73 27 8.71 17 38.64 60 11.24 30 40.54 Formicidae 74 7.71 42 32.3 2 1.74 2 18.18 30 9.68 15 34.09 42 7.86 25 33.78 Undet. Arthropoda 5 0.52 5 3.8 0 0 0 0 1 0.32 1 2.27 4 0.75 4 5.40 Undet. Larvae 18 1.87 14 10.8 2 1.74 2 18.18 7 2.26 6 13.64 9 1.68 6 8.11 Birds 1 0.1 1 0.8 0 0 0 0 0 0 0 0 1 0.19 1 1.35 Total 960 130 115 11 310 44 534 74 216 Zaida Ortega et alii males, females and juveniles are plotted in Figure 1. On one hand, the discriminant axes 1 somewhat divides diet of males (negative values) from diet of females (positive values), and it is mainly positively correlated with the presence of Formicidae and Coleoptera, and negatively correlated with the presence of Hymenoptera, larvae of Diplura, Acarina and Tysanoptera (Fig. 1, Table 3). On the other hand, the discriminant axes 2 divides the diet of juveniles (negative values) from the diet of adults (positive values), and it is mainly positively correlated with the presence of Orthoptera, Gastropoda, larvae of Isopoda, Ostracoda and larvae of Coleoptera, among others, and mainly negatively correlated with the pres- ence of Araneae, Ephemenoptera, larvae of Orthoptera larvae, Diplopoda, larvae of Dermaptera, or larvae of Dictyoptera, among others (Fig. 1, Table 3). Regarding the area of study, we did not detect with the discrimi- nant analysis any clear pattern in the composition of the diet (Fig. 2). The diet of juvenile individuals is clearly different, being less diverse than the diet of adults (Table 2). Young frogs use to hunt smaller prey than adults, mainly small Hymenoptera. Hirai and Matsui (1999) found a signifi- cant correlation between SVL and prey size of Pelophylax nigromaculatus, as we observed in P. saharicus, suggesting that individuals of green frogs tend to eat larger prey as they grow. Table 2. Simpson’s diversity values of the diet of males, females and juveniles of P. saharicus and p-values from pairwise comparisons of Hill’s numbers (see more details in the text) Adult males Adult females Juveniles diversity values 0.8521 ± 1.80 x 10-4 0.8818 ± 5.51 x 10-5 0.6273 ± 2.19 x 10-3 Hill’s numbers males-females females-juveniles juveniles-males q = 0 0.8398 0.9134 0.6960 q = 1 0.7928 0.7014 0.4258 q = 2 0.8300 0.7280 0.4742 Fig. 1. Values of each dimension selected in the discriminant func- tion analysis of the diet of Pelophylax saharicus are plotted for each studied frog. Individuals are marked regarding age and sex in order to visualize the age and sex differences in the trophic ecology of the Sahara frog. Fig. 2. Values of each dimension selected in the discriminant func- tion analysis of the diet of Pelophylax saharicus are plotted for each studied frog. Individuals are marked regarding the area of study: the Western Plateau, the Rif Mountains, and the Middle Atlas. 217Feeding ecology of Pelophylax saharicus Pelophylax saharicus has a similar feeding ecology composition that its sister taxon, P. perezi, from the Ibe- rian Peninsula (Lizana et al., 1989), and other species of the genus, as P. ridibundus (Çiçek et al., 2006; Mollov et al., 2010). Diptera predominates as the main prey item of adult individuals of both species, followed in abun- dance by Coleoptera prey (aquatic species mostly) and Hymenoptera, often Formicidae. The diet of P. saharicus in Morocco has some differences with the diet of other species of Pelophylax, as P. kurtmuelleri in Greece, which actively selects arachnids over other types of prey (Plitsi et al., in press). Nonetheless, we lack data about availabil- ity of prey in the habitat of Sahara frogs, which limits our results. Thus, our results about the differences in the diet of sexes and ages should be taken with caution, since it is possible that the electability of each type of prey would be similar to their availability in the environment. There- fore, future research in the diet of P. saharicus frogs, including the availability of prey in their habitats and sea- sonal comparisons would be useful to get deeper knowl- edge about the ecology of the species. Furthermore, the diet of P. kurtmuelleri frogs is high- ly influenced by their habitat (Plitsi et al., in press), and the diets of P. ridibundus and P. esculenta are also influ- enced by seasonality (Sas et al., 2009; Mollov et al., 2010) and weather conditions (Bogdan et al., 2012). Thus, we cannot exclude that P. saharicus could also employ a vari- able foraging strategy. Lizana et al. (1989) observed that the females of the Iberian green frog ate significantly larger prey than adult males, as we observed in P. saharicus. The ingestion of larger prey by females and their more diverse diet could be the reason of the slightly bigger parasite load of this sex. In this sense, and working with the same frogs, Nav- arro and Lluch (2006) found that females showed more diverse helminth infracommunities, even if differences with males were not statistically significant. The inclu- sion of a large amount of flying prey in the diet reinforces the hypothesis that P. saharicus is a sit-and-wait forager. Gastropoda were only important in the Rif sample, with a similar proportion as the reported for the Tunisian stud- ied population (Hassine and Nouira, 2009). In P. ridibun- da of Turkey no differences of diet regarding sex were found (Çiçek et al., 2006). The consumption of Formicidae is not higher in P. saharicus than in P. perezi of the Iberian Peninsula, and it is consistent with the diet of the Tunisian population (Hassine and Nouira, 2009). The consumption of ants and other prey groups could be due to a foraging behaviour near the water or at more terrestrial habitats. In fact, many rivers and natural ponds of Morocco scarcely have river- side edges, forcing the individuals to stand close to water shore. Sas et al. (2009) found that P. esculenta of Romania changes the proportion of aquatic and terrestrial preys along the year activity period, which, although unknown yet, would be also possible for P. saharicus of Morocco. Table 3. Pooled values of within-groups correlations between the discriminating variables (the prey items) and the standardized canonical discriminant functions (the two discriminant axes). Dis- criminating variables are ordered by absolute size of correlation within the discriminant axes 1. Group Discriminant axes 1 Discriminant axes 2 Hymenoptera -0.481* -0.019 Diplura larvae -0.302* -0.043 Acarina -0.302* -0.043 Thysanoptera -0.281* 0.087 Formicidae 0.119* -0.059 Coleoptera 0.088* 0.052 Plecoptera larvae 0.050* 0.030 Araneae 0.144 -0.319* Orthoptera 0.109 0.280* Gastropoda 0.049 0.211* Ephemenoptera 0.041 -0.200* Orthoptera larvae 0.041 -0.200* Diplopoda 0.041 -0.200* Dermaptera larvaea 0.041 -0.200* Dictyoptera larvaea 0.041 -0.200* Crustacea 0.041 -0.200* Odonata 0.041 -0.200* Heteroptera larvae 0.041 -0.200* Isopoda larvae 0.061 0.188* Ostracoda 0.032 0.174* Homoptera larvae 0.061 -0.159* Lepidoptera 0.084 -0.140* Coleoptera larvae -0.084 0.140* Diptera 0.049 -0.139* Undet. Arthropoda 0.060 0.137* Lepidoptera larvae 0.023 0.125* Embioptera 0.023 0.125* Trichoptera larvae 0.023 0.125* Phasmida 0.023 0.125* Bird 0.023 0.125* Diptera larvae 0.076 -0.119* Diplura larvae 0.040 0.110* Chilopoda 0.037 0.101* Homoptera 0.093 -0.095* Dictyoptera -0.020 0.090* Plecoptera 0.055 0.089* Dermaptera 0.055 0.089* Undet. Larvae -0.018 -0.069* Thysanura 0.045 -0.052* * Largest absolute correlation between each variable and any discri- minant function a This variable not used in the analysis. 218 Zaida Ortega et alii ACKNOWLEDGEMENTS Mohamed El Ayadi helped during field work in Morocco. Angélica Hernández-González and María Mar- quínez helped during laboratory work. Field work was possible thanks to collecting permits (“Ordres de Mis- sion”) issued by Morrocan Government to Faculté des Sciences de l’Université Abdelmalek Essaadi. 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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