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Volume 27 (July 2017), 252-257 FULL PAPER Herpetological Journal Published by the British Sexual size dimorphism among populations of the Herpetological Society rose-bellied lizard Sceloporus variabilis (Squamata: Phrynosomatidae) from high and low elevations in Mexico Raciel Cruz-Elizalde1, Aurelio Ramírez-Bautista1 & Abraham Lozano2 1Laboratorio de Ecología de Poblaciones, Centro de Investigaciones Biológicas, Instituto de Ciencias Básicas e Ingeniería, Universidad Autónoma del Estado de Hidalgo, Km 4.5 carretera Pachuca-Tulancingo, 42184, Mineral de La Reforma, Hidalgo, México 2Instituto Politécnico Nacional, CIIDIR Unidad Durango, Sigma 119, Fraccionamiento 20 de Noviembre II, Durango, Durango 34220, México It is well known that geographic variation in morphological traits occurs among populations of lizard species. In this study, we analysed body size and sexual size dimorphism among four populations of the lizard Sceloporus variabilis from contrasting elevations. Males from all populations were larger than females in snout-vent length, head length, head width, tibia length, and forearm length. These findings are consistent with the hypothesis that sexual selection acts more strongly on males than on females. Females from higher elevations were larger in size than those found at lower elevations, which could be explained by an increased investment in body size to maximise reproductive success. We suggest that environmental (precipitation, temperature) and ecological (food, competition, predation) factors influence the expression of sexual dimorphism and morphological variation in S. variabilis. Key words: Sexual dimorphism, body size, populations, lizard, morphological characteristics INTRODUCTION Gekkonidae, Scincidae: Cox et al., 2009). Male-biased dimorphism is generally linked to sexual selection, range of ecogeographical rules governing the size of with large males being an advantage during male-male Amales and females have been developed to explain competition for territories and access to females, whereas geographic variation among species and populations female-biased dimorphism can be explained by higher (Cox et al., 2003; Schäuble, 2004). In amphibians and fecundity of larger females (Endler & Houde, 1995; Braña, fishes, females are generally the larger sex (Liao et al., 1996; Cox et al., 2009). Sexual size dimorphism in lizards 2013; Jonsson & Jonsson, 2015), while in mammals, can further arise from intraspecific niche divergence, birds, and reptiles, males tend to be larger (Kratochvíl enabling each sex to use different resources such as & Frynta, 2006). Sexual dimorphism can be observed food and microhabitats (Rand, 1967; Schoener, 1967; in a wide range of morphological traits, such as body Cox et al., 2003; Hierlihy et al., 2013). Size dimorphism size, head length and limbs length (Darwin, 1871; Polák is also influenced by the environment and is for example & Frynta, 2010), and can be related to environmental evidenced by oviparous species, for which females are gradients such as altitude and latitude, and the use and generally larger at higher latitudes or altitudes, leading to availability of resources such as microhabitats and food larger clutches with bigger eggs compared to females at (Madsen & Shine, 1993; Roitberg, 2007; Ramírez-Bautista lower latitudes or altitudes (Forsman & Shine, 1995; Du et al., 2014). In general terms, Bergmann´s rule predicts et al., 2005). that body size increases with latitude (Blackburn et al., Sexual-size dimorphism has been assessed in a range 1999), and Rensch´s rule establishes that sexual-size of lizard taxa (e.g. Braña, 1996; Ramírez-Bautista et al., dimorphism increases with latitude when males are the 2006; Cox et al., 2007; Aguilar-Moreno et al., 2010; larger sex, decreasing when females are larger (Abouheif Hierlihy et al., 2013), including comparisons between & Fairbairn, 1997). In reptiles such as lizards, Bergmann´s populations within species (Hernández-Salinas et al., rule has been tested in a large number of taxa, whereas 2010; Jin et al., 2013; Ramírez-Bautista et al., 2014). fewer case studies exist for Rensch´s rule (Angilletta et The genus Sceloporus (Phrynosomatidae) currently al., 2004; Cruz et al., 2005; Kratochvíl & Frynta, 2006; Cox comprises almost 100 species, occurring in a wide range et al., 2007). of habitats and largely being characterised by a marked Lizards can exhibit high variation in sexual size male-biased sexual-size dimorphism in line with male- dimorphism, which has been reported as male-biased male competition (Fitch, 1978; Ansell et al., 2014; Leaché (e.g., Tropiduridae, Teiidae: Brandt & Navas, 2013), et al., 2016). Differences in sexual size dimorphism female-biased (e.g., Pygopodidae, Diplodactylidae: among Sceloporus species can be attributed to habitat Read, 1999; Cox et al., 2009), and absent (e.g., Anguidae, differences, variation in predation pressure, and lack of Correspondence: Aurelio Ramirez Bautista ([email protected]) 252 Sexual–size dimorphism among populations of Sceloporus variabilis territoriality or interspecific competition (Wiens, 1999; 2001), and can also be reflected in differential head length, head width, forearm length and tibia length between the sexes (Ramirez-Bautista & Pavón, 2009; Ramírez-Bautista et al., 2013). Sceloporus variabilis shows a wide geographic distribution across tropical and temperate regions (Mendoza-Quijano et al., 1998), but little is presently known about morphological variation between and among populations. Previous evidence from local studies suggests a male-biased sexual-size dimorphism (Benabib, 1994; Ramírez-Bautista et al., 2006), but data from different environments are as yet lacking. Thus, the aim of the present study is to quantify body size and sexual-size dimorphism in four populations S. variabilis from different elevations (see also Ramírez-Bautista et al., 2011). Figure 1. Populations at high (Cerro Azul, Veracruz; Metztitlán, Hidalgo) and low elevations (Atlapexco, MATERIAL AND METHODS Hidalgo; Alvarado, Veracruz) of S. variabilis analysed in this study. Specimens were obtained from the Colección Nacional de Anfibios y Reptiles (CNAR) del Instituto de Biología, and Colección del Museo de Zoología, Facultad de Ciencias Males were considered as adults if they had enlarged (MZFC), both at the Universidad Nacional Autónoma testes and convoluted epididymides consistent with de México (UNAM). Additional data were obtained sperm production. Adult females were defined by from a database held by the Laboratorio de Ecología de having vitellogenic follicles in ovaries, or eggs in oviducts Poblaciones of the Universidad Autónoma del Estado de (following Goldberg & Lowe, 1966). We measured snout- Hidalgo. The populations at high elevation were located vent length (SVL: measured to the nearest ± 0.01 mm), at Cerro Azul, Veracruz (97° 44´N, 21° 11´O; 1, 100 m head length (HL: ± 0.01 mm; distance from the anterior a.s.l., Table 1, Fig. 1) and Metztitlán, Hidalgo (98° 55´N, tip of the rostral scale to the posterior margin of the left 20° 38´O; WGS84; 1, 000 m a.s.l., Table 1, Fig. 1). The ear), head width (HW: ± 0.01 mm; maximum width of the low elevation localities were at Atlapexco, Hidalgo (98° head, measured as the distance between the posterior 20´N, 21° 01´O; 140 m a.s.l., Table 1, Fig. 1) and Alvarado, margin of the left and right ears), tibia length (TL: ± 0.01 Veracruz (95° 46´N, 18° 47´O; 50 m a.s.l., Table 1, Fig. 1; mm), and forearm length (FL: ± 0.01 mm; measured from INEGI, 2009). the knee (TL) or elbow (FL) to the pad of the foot) in all All specimens were collected between 1986 and 2014. specimens examined. In the absence of statistical variation in morphological For statistical analyses on sexual-size dimorphism, characteristics between years within populations (P > we used a multivariate analysis of variance (MANOVA) 0.05 in all cases, detailed data not shown), the samples to identify differences in body size (SVL) and other of all years were pooled for each population. Sample morphological characteristics as a function of population sizes were 55 specimens (Cerro Azul; 20 females and 35 origin (Zar, 1999). A Generalized Discriminant Function males), 116 (Metztitlán; 23 females and 93 males), 47 Analysis (GDFA) was performed at the sex and population (Atlapexco; 25 females and 22 males), and 355 (Alvarado; level to test for differences between sexes and among 131 females and 224 males). populations. Significant variables identified by GDFA were compared between sexes and among populations by univariate Kruskall-Wallis or U Mann-Whitney tests. Table 1. Environmental parameters for each of the A correlation analysis was conducted to determine the four localities sampled for sexual-size dimorphism of relationship between morphological traits and elevation. S. variabilis. Statistical analyses and post-hoc comparisons were performed when necessary using Statistica version 7.0, Populations and means were presented ± 1 SE (Zar, 1999). Environmental Cerro Azul, Metztitlán, Atlapexco, Alvarado, characteristic Veracruz Hidalgo Hidalgo Veracruz Elevation (m) 1100 1000 140 50 RESULTS Vegetation type Secondary Xeric scrub Tropical Evergreen vegetation/ rain forest forest A MANOVA including all traits showed statistically Coniferous significant differences between sexes (Wilk´s λ = 0.704, forest F1, 565 = 47.15, P < 0.001), among populations (Wilk´s λ Average annual 1600 700 2000 3435- = 0.582, F3, 565 = 22.37, P < 0.001), and in the interaction precipitation 6435 of