ISSN 1827-9635 (print) © Firenze University Press ISSN 1827-9643 (online) www.fupress.com/ah Acta Herpetologica 7(1): 29-39, 2012 Quantifying the intersexual and interspecific morphometric variation in two resembling sympatric lacertids: Iberolacerta horvathi and Podarcis muralis Anamarija Žagar1,2,*, Nadja Osojnik3, Miguel A. Carretero2, Al Vrezec4 1 University of Ljubljana, Biotechnical faculty, Department of Biology, Večna pot 111, SI-1000 Ljublja- na, Slovenia. *Corresponding author. E-mail: anamarija.zagar@gmail.com 2 CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Campus Agrário de Vairão, 4485-661 Vairão, Portugal 3 Cesta III/4, SI-3320 Velenje, Slovenia 4 National institute of Biology, Večna pot 111, SI-1000 Ljubljana, Slovenia Submitted on: 2011, July 10th; revised on 2011, October 20th; accepted on 2011, November 26th. Abstract. Podarcis muralis and Iberolacerta horvathi are sympatric, frequently syntop- ic, lacertids through the entire range of I. horvathi and very similar in their general body size and shape, as well as in most ecological traits. We morphologically com- pared adults from the area of sympatry using biometric measurements and performed analyses to investigate their sexual size and shape dimorphism. A total of 34 males and 24 females of I. horvathi, and 25 males and 23 females of P. muralis, all adult indi- viduals, were measured. Both species showed sexual size dimorphism with females being longer (snout-vent length, SVL) than males. After SVL correction (ANCOVA), head width, length and height and mass showed to be sexually dimorphic in both spe- cies. Males carry relatively wider, longer and higher heads and were heavier than con- specific females. I. horvathi heads were more flattened than those of P. muralis and P. muralis were heavier than I. horvathi. Both species displayed the same pattern of sexu- al dimorphism regarding body size, head size and shape not only in direction but also in magnitude. All results confirm that both species are very similar in studied biomet- ric characters and, together with their ecological similarities, these suggest in absence of other factors they are likely to interact when living together. Keywords. Biometric characters, sexual dimorphism, southern Slovenia, Podarcis muralis, Iberolacerta horvathi, Lacertidae INTRODUCTION The Common wall lizard (Podarcis muralis) and Horvath’s rock lizard (Iberolacerta horvathi) are sympatric and frequently syntopic lacertids through the entire range of I. 30 A. Žagar et al. horvathi (Tiedemann, 1997). The range of latter as known today extends from pre-alpine and alpine part of north eastern Italy, to north western Slovenia (Lapini et al., 2004; Ras- sati, 2010) and southern Austria (Cabela et al., 2007), and Dinaric Alps of central and southern Slovenia and Velebit in Croatia (De Luca, 1989; Krofel et al., 2009). Allotopic I. horvathi populations are only known from high elevations where P. muralis is absent; in the north of its distributional range above 900 m a.s.l. (e.g., Lapini et al., 1993; Cab- ela et al., 2007). Both species are said to be very similar in their general body size and shape, the average snout-vent length of adults being between 55-65 mm (e.g. De Luca, 1989; Aleksić and Ljubisavljević, 2001). Reproductively, I. horvathi is monoestrous while P. muralis may lay a second clutch when conditions are favourable (Lapini et al., 1993; Cap- ula et al., 1993). The dietary niches of both species are highly overlapping (De Luca, 1992; Richard and Lapini, 1993). In the area of sympatry both species start their activity period in March/April and go to hibernation in October/November, exhibiting the diurnal activ- ity pattern typical of lacertids in temperate zone (De Luca, 1992; Lapini et al., 1993). The overall habitat use of both species is also highly similar (Cabela et al., 2007). They most- ly occupy rocky habitats with sparse vegetation or open rocky screes in forests. On the microhabitat scale, some differences in slope and vegetation cover selection between spe- cies have been detected, I. horvathi tending to use more rocks and vertical surfaces than P. muralis (Arnold, 1987; Lapini et al., 1993; Cabela et al., 2007). Moreover, similarity in the overall appearance between both species has frequently led to misidentification in the past (e.g. Brelih, 1954; De Luca, 1989). To determine the species it is usually necessary to catch or make a close-up photograph of the individual to see the position of rostral and fronto- nasal scales that are frequently in contact in I. horvathi and separated in P. muralis (e.g. Arnold et al., 2007). Because of that, recent intensive studies discovered unknown popula- tions of I. horvathi in many parts of its range where the species had previously been misi- dentified as P. muralis or not recorded yet (Lapini et al., 2004; Žagar, 2008 a, b; Krofel et al., 2009; Cafuta, 2010; Rassati, 2010). Sexual dimorphism in size and shape occurs in most species of lacertids. Size (snout- vent length and body mass) can be either male- or female-biased (e.g., Kaliontzopou- lou et al., 2007; Kratochvíl et al., 2003) and males in most species have bigger and wider heads and longer limbs (e.g. Herrel et al., 1996). Such sexual differentiation in lacertids is hypothesised to be derived from different selection pressures: males having bigger head proportions to have a firm grasp of a female’s trunk during copulation and females hav- ing longer trunks to hold the eggs (Kaliontzopoulou et al., 2007, 2008 a, b). In the case of P. muralis, instances of both male-biased (Strijbosch et al., 1980; Barbault and Mou, 1988; Braña and Ji, 2000; Allan et al., 2006; Bruner and Constantini, 2007; Gracceva et al., 2008; Aleksić et al., 2009) and female-biased (Gracceva et al., 2008; Kaliontzopoulou and Car- retero, unpublished) sexual dimorphism have been described. In contrast, for I. horvathi a single comparative study of sexual dimorphism published so far showed a female-biased sexual size dimorphism (De Luca, 1989) as described for some other species of this genus (e.g. for I. galani; Arribas et. al., 2006). The main aim of our study is to reveal morphometric (dis)similarity in two very resembling species of lacertids, P. muralis and I. horvathi living in the area of sympatry. In the past, most comparisons of size and shape of both species only referred to descrip- tive, often qualitative data and were not targeted to biometric characters in order to detect 31Morphometric variation in two sympatric lacertids possible subtle interspecific differences. We aimed to compare differences at intra- (inter- sexual) and interspecific level in order to evaluate morphological divergences of consid- ered sympatric lacertids. For the first time, we quantitatively investigate biometric charac- ters of these two species from a sympatric area in southern Slovenia. Intersexual differenc- es in size and shape in lacertids are a result of sexual selection rather than resulting from niche segregations (Carretero, 2004) and therefore we expect it exists in both species. MATERIAL AND METHODS Study area and individuals studied Lizards were captured at 19 localities in the sympatric area of P. muralis and I. hor- vathi in Kočevsko region, Southern Slovenia (45˚28’37’’N, 14˚48’34’’E) in spring and sum- mer periods between 2007 and 2010 (Fig. 1). The maximal distance between locations was 30 km that ensured similar environmental conditions. Climate was moderate continental and mountainous influenced by Mediterranean, inland and Atlantic ocean (Kordiš, 1993) with total annual precipitation of 1600 to 1800 mm and mean temperature in July 17.9 °C and in January -2.8 °C (Puncer, 1980). Typical habitats of both lacertid species in the region are natural or artificial rock cliffs with no or sparse vegetation and rocky outcrops on the forest edge (Žagar, 2008 a). Sampling sites were chosen to have similar microhabi- tat characteristics. All individuals caught were measured and photographed, and released afterwards on the same location. Sex was verified by inspection of colouration, cloacal region and femoral pores. Biometric characters To quantify intra- and interspecific differences we measured six biometric characters: snout vent length (SVL), head length (HL) from the tip of the snout to the posterior bor- der of the collar, pileus length (PL), head width (HW), head height (HH), and mass (M) (only for specimens caught in 2010, measuring scheme after Kaliontzopoulou et al., 2007). All linear measurements were taken to the closest 0.1 mm, using digital callipers and mass was measured to the closest 0.1 g, using scale with a hook type Pesola max. 30 g. Statistical analysis Variables were logarithmically transformed to meet the assumptions of normality and homogeneity of variances. Considering that sexual dimorphism either in size (SSD) or in shape (SShD) is common in lacertids (see Introduction) sex was taken into account in all analyses. Differences in SVL were tested through a two-way ANOVA with sex and species as factors. Differences for the other measurements were relativized to SVL by using a two- way ANCOVA design with sex and species as factors and SVL as covariate for size correc- tion. All statistical analyses have been done using Statistica 10 (STATSOFT, 2011). 32 A. Žagar et al. RESULTS A total of 34 males and 24 females of I. horvathi, and 25 males and 23 females of P. muralis, all adult individuals, were measured (Tab. 1). Both species showed sexual size dimorphism with females being longer (SVL) than males, but no interspecific differenc- es either in SVL or in sexual dimorphism were found (Tab. 1 and 2). After size correc- tion (ANCOVA), only PL did not show to be dependent on sex, but HW, HL, HH and M proved to be sexually dimorphic in both species (Tab. 2). In fact, males of both spe- cies had relatively wider, longer and higher heads and were heavier than the conspecif- ic females (Tab. 1). Moreover, for both sexes, I. horvathi heads were more flattened than those of P. muralis and P. muralis were heavier than I. horvathi but no interspecific differ- ences were found for the remaining variables (Tab. 2). DISCUSSION Our results comparing body size, head size and head shape of adult P. muralis and I. horvathi form the area of sympatry, indicated both sexual dimorphism and (limited) interspecific variation which were independent one from another. We have also confirmed that species were similar to each other in their external appearance. Considering each sex   Fig. 1. Locations of the sampling sites (A) of Common wall lizards (Podarcis muralis, numbers 1, 2, 7-9, 16 and 19) and Horvath’s rock lizards (Iberolacerta horvathi, numbers 3-6, 10-15, 17 and 18) and the loca- tion of the study area in Slovenia (B) with distributions of both species (P. muralis in grey and I. horvathi in black stripes). 33Morphometric variation in two sympatric lacertids separately, there were no significant differences in body size and some head dimensions between the species, except for the head height (see Tab. 2). However, I. horvathi’s heads tended to be more flattened, whereas the heads of P. muralis have a higher arc. Flatness of I. horvathi heads has been reported already before and is a trait that is often used in general description of this species (e.g. Radovanović, 1951; Mršić, 1997; Arnold and Ove- Table 1. Descriptive statistics of biometric characters for two species of lacertids, Podarcis muralis and Iberolacerta horvathi, from southern Slovenia. For each variable next values are given: Mean±SD, Min- max and n (numbers of individuals). Legend: SVL – snout-vent length, HH – head height, PL – pileus length, HL – head length, HW – head width and M – mass. Variable Iberolacerta horvathi Podarcis muralis Males Females Males Females SVL 53.46±3.90 43.7-60.0 34 58.30±4.27 48.2-65.9 24 54.71±4.62 41.9-62.8 25 58.85±3.36 50.1-64.6 23 HH 6.37±0.38 5.7-7.0 19 6.19±0.38 5.5-6.9 23 6.96±0.88 4.5-8.5 25 6.87±0.66 5.3-8.2 23 PL 13.29±1.73 10.7-21.4 33 12.57±0.80 10.5-13.8 24 14.14±1.00 11.9-15.6 25 13.24±0.80 11.5-14.8 23 HL 19.72±1.55 16.7-23.0 34 18.83±1.32 16.1-21.4 24 20.10±1.48 17.1-22.5 25 18.82±1.58 13.3-21.3 23 HW 8.96±0.91 7.0-10.5 33 8.71±0.71 6.9-9.8 24 9.14±0.81 7.0-11.0 25 8.43±0.39 7.6-9.2 23 M 4.25±0.58 2.8-5.3 19 4.01±0.83 2.5-5.5 23 4.26±1.11 1.5-6.3 25 4.55±0.90 2.5-5.5 23 Table 2. Results of AN(C)OVA comparisons for species and sex (variables are SVL corrected, except SVL) for two species of lacertids, Podarcis muralis and Iberolacerta horvathi, from southern Slovenia. Legend: SVL – snout-vent length, HH – head height, PL – pileus length, HL – head length, HW – head width and M – mass. Variable Denominator Species Sex Species*sex df F df p F df p F df p SVL 105 1.20 1 0.2730 30.0 1 <0.0001* 0.20 1 0.6939 HH 89 35.00 1 <0.0001* 15.83 1 0.0001* 0.01 1 0.9173 PL 104 0.0006 1 0.9813 2.29 1 0.1337 1.23 1 0.2705 HL 105 0.04 1 0.8390 64.06 1 < 0.0001* 0.31 1 0.5759 HW 104 1.73 1 0.1911 67.33 1 <0.0001* 3.30 1 0.0723 M 89 5.45 1 0.0220* 25.79 1 <0.0001* 2.43 1 0.1225 34 A. Žagar et al. den, 2002, Cabela et al., 2007; Lapini et al., 1993, 2004). Flat head was also described as a general trait for all species of genera Iberolacerta (Arnold et al., 2007). Most of the spe- cies from genera Podarcis and Iberolacerta use crevices as escape sites and their body and heads are moderately to very depressed (Arnold and Oveden, 2002). Both species also displayed the same pattern of sexual dimorphism regarding body size, head size and shape not only in direction but also in magnitude. Females had long- er snout-vent lengths whereas males carried relatively bigger heads in all dimensions but length. In the family Lacertidae, considerable lability in the direction of sexual size dimorphism have been found both between (reviewed in Cox et al., 2007) and within species where either males or females are bigger depending on the population (Roitberg and Smirina, 2006 a, b; Roitberg, 2007) in response to geographic variations in the rela- tive contributions of sexual, fecundity and natural selection forces (Kaliontzopoulou et al., 2010 a, b). Across populations of lacertids, size (snout-vent length and body mass) was described to be either male-biased with males having larger body sizes (Vogrin, 2005; Kaliontzopoulou et al., 2007; Brecko et al., 2008; Kaliontzopoulou et al., 2008 a; Aleksić et al., 2009), or female-biased with females having larger size dimensions on account of a longer trunk (Kratochvíl et al., 2003; Liu et al., 2008). More specifically in the case of P. muralis, the direction of the sexual size dimorphism observed in our study (females longer than males) was not always found. Namely, in some populations no significant dif- ference in snout-vent length between adults of the two sexes was observed (Barbault and Mou, 1988; Strijbosch et al., 1980; Allan et al., 2006) whereas in others even there was the opposite trend, males being longer than females (Gracceva et al., 2008), than showed here. The results from this study corroborate that interpopulation variability in sexual size dimorphism is very high in P. muralis. On the other hand, comparing data for I. horvathi with the only extensive morphomet- ric study previously carried out for this species, our study show similar trends: females were significantly larger in snout-vent length than males (De Luca, 1989). However, in the study of De Luca (1989), data of females and males from two populations were pooled together which posed doubts on the reliability of the results since inter-population variation in lac- ertids is known to be high and snout-vent length tends to be sexually dimorphic in lacertid lizards (i.e. Kaliontzopoulou et al, 2010 a, b). Hence, it is crucial to size-adjust other mor- phological traits before comparing them (Kratochvíl et al., 2003). More populations of I. horvathi, as well as of P. muralis, should be studied in the future to recognize if different pat- terns of sexual size and shape dimorphisms are exhibited in different populations. Regarding the sexual shape dimorphism, there were head shape differences in both species with males having relatively wider and higher (but not longer) heads. For I. hor- vathi, Bischoff (1984) and De Luca (1989) already suggested a similar pattern. Likewise, mostly all morphometric studies of P. muralis populations also found the same trend, e.g. males having larger heads adjusted to snout-vent length than females (Gracceva et al., 2008) or males having larger jaw sizes and larger heads than females (Aleksić et al., 2009). The direction of sexual shape dimorphism in the head robustness is common to whole family Lacertidae in which males have wider and bigger relative head measurements and also longer limbs (Herrel et al., 1996; Kratochvíl et al., 2003; Bruner et al., 2005; Vogrin, 2005; Kaliontzopoulou et al., 2007; Kaliontzopoulou et al., 2008 a; Ljubisavljević et al., 2008; Aleksić et al., 2009). Although the direction in shape sex dimorphism is common, its magnitude is highly variable between species (Verwaijen et al., 2002; Kaliontzopoulou 35Morphometric variation in two sympatric lacertids et al., 2007; Ljubisavljević et al., 2008), but even though, in our case almost no differences in the amount of sexual shape dimorphism were detected between both species living in the area of sympatry. Actually, the analysis revealed that sexual dimorphism was in gener- al higher (significant differences in all but one biometric characters) than species variation (significant differences only in head height and relative body mass, Tab. 2). Summarizing, the lacertids P. muralis and I. horvathi show remarkable similarities not only in general size and shape (and in colouration; De Luca, 1989; Arnold and Oveden, 2002), but also in their sexual dimorphism patterns. Our study comparison of inter- and intraspecific sexual dimorphism patterns form localities in the sympatric area confirmed that P. muralis and I. horvathi are very similar. Together with their ecological similarities these facts suggest that, in absence of other factors, they are likely to be in interaction when living together. With our analysis we could not yet identify what type of interspe- cific interaction is present between both species, but most probably acts as interference which is commonly found in predator guilds (e.g. Carothers and Jaksić, 1984; Robinson and Terborgh, 1995; Linnell and Strand, 2000), and even in lacertids (Downes and Bau- wens, 2002, 2004). In this perspective, results suggest potential for competition between species since interspecific effects in sympatric populations were not expressed in mor- phological, i.e. coevolved divergences. Perhaps such effects are expressed in other pheno- typic or ecological adaptations, e.g. spatial segregation or resource partitioning (Tokeshi, 1999) that need to be investigated in the future. Thus, biometric comparisons could pro- vide a first evaluation of competitive potential between lacertids of similar size belong- ing to the same predator guild (Valverde, 1967). If interspecific size differences are smaller than intraspecific, i.e. sexual dimorphism, this might suggest species to be potential com- petitors. On the other hand, equal or larger interspecific size differences could indicate already coevolved niche differentiation and consequently lower competition potential, i.e. “ghost of competition” pattern (Begon et al., 2006). Multipopulation comparison of sexual dimorphism and morphological divergence between both species in allopatry and sympa- try should be carried out to test the hypotheses of character displacement and relaxation of interspecific competition (Butler et al., 2007). ACKNOWLEDGEMENTS Collecting permits were provided by Agency for environment (Ministry for environment and space, Slovenia). We would like to thank Lara Kastelic, Martin Kavšček, Bia Rakar, Teo Delić, Tea Romih, Polona Raspor, Darja Osojnik and Alja Kastelic, who helped during sampling campaigns. 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