Sexual Size and Shape Dimorphism Variation in Caesar's Lizard (Gallotia caesaris, Lacertidae) from Different Habitats Author(s): M. Molina-Borja, M. A. Rodríguez-Domínguez, C. González-Ortega, and M. L. Bohórquez-Alonso Source: Journal of Herpetology, 44(1):1-12. 2010. Published By: The Society for the Study of Amphibians and Reptiles DOI: 10.1670/08-266.1 URL: http://www.bioone.org/doi/full/10.1670/08-266.1 BioOne (www.bioone.org) is an electronic aggregator of bioscience research content, and the online home to over 160 journals and books published by not-for-profit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. Journal of Herpetology, Vol. 44, No. 1, pp. 1–12, 2010 Copyright 2010 Society for the Study of Amphibians and Reptiles Sexual Size and Shape Dimorphism Variation in Caesar’s Lizard (Gallotia caesaris, Lacertidae) from Different Habitats 1,2 3 3 M. MOLINA-BORJA, M. A. RODRI´GUEZ-DOMI´NGUEZ, C. GONZA´ LEZ-ORTEGA, AND 1 M. L. BOHO´ RQUEZ-ALONSO 1Laboratorio Etologı´a, Departamento Biologı´a Animal, Facultad Biologı´a, Universidad La Laguna, Tenerife, Canary Islands, Spain 3Centro Reproduccio´n e Investigacio´n del lagarto gigante de El Hierro, Frontera, El Hierro, Canary Islands, Spain ABSTRACT.—We compared sexual dimorphism of body and head traits from adult lizards of populations of Gallotia caesaris living in ecologically different habitats of El Hierro and La Gomera. Males had larger body sizes than females, and sexual size and shape dimorphisms were greater in a population from La Gomera than in three populations from El Hierro. Multivariate analyses of variance, using linear and shape-adjusted traits, showed that the populations differed significantly in body and head traits, with pileus (head) width, snout–vent length (SVL), and body mass the main traits contributing to the differences. Males had larger SVL, heads, and limbs than females in all populations, but SVL relative to a shape index (calculated as the geometric mean of several body parameters) was larger in females than in males. Moreover, shape-adjusted hind-limb lengths were significantly shorter in lizards from the more densely vegetated habitats than in those from the less vegetated ones. The magnitude of sexual dimorphism was larger for relative limb length and head depth in the populations with less vegetation than in those with more vegetation. Our data suggest that morphological differences between populations reflect local adaptation to habitat structure. Geographic variation in morphological, phys- demographic, or ontogenetic causes (Schoener iological, or behavioral traits may reflect adap- et al., 1982; Shine, 1990; Stamps et al., 1997; Le tation and evolutionary processes at the local Galliard et al., 2006) and may express itself to scale. A variety of organisms have been ana- different degrees in separate geographical loca- lyzed in this context (see Emerson and Arnold, tions (Madsen and Shine, 1993; Krause et al., 1989), and within reptiles, populations of 2003; Cox and John-Alder, 2007). several lizard species have been studied (Losos, Analyses of sexual dimorphism have com- 1990; McCoy et al., 1997; Butler and Losos, monly used linear measurements of the body, 2002). Variations in patterns of sexual dimor- head, or limbs (Cooper and Vitt, 1989; Hews, phism in body size (SBSD), for example, are 1990; Fairbairn, 1997; Lappin and Swinney, common and may include the following: (1) 1999). However, analyses of shape dimorphism males having larger snout–vent length (SVL) may provide very useful information and often than females (Carothers, 1984); (2) females reveal patterns that differ from those evident having larger SVL lengths than males (Fitch, from analyses of sexual dimorphism in linear 1978; Zamudio, 1998); or (3) no sexual body traits (Emerson, 1994; Bran˜ a, 1996; Butler and dimorphism (Schwarzkopf, 2005). Other body Losos, 2002). and head traits may also exhibit sexual dimor- Previous analyses have compared popula- phism (Cooper and Vitt, 1989). tions or species of Gallotia (Thorpe and Ba´ez, Sexual dimorphism may result from different 1987; Thorpe and Brown, 1991; Molina-Borja et selective forces acting separately on each sex al., 1997; Molina-Borja and Rodrı´guez-Domı´n- (Shine, 1989; Andersson and Vitt, 1990; Anders- guez, 2004). A phylogenetic analysis of variation son, 1994; Fairbairn, 1997). Thus, a higher in morphological traits in all Gallotia species competitive ability, important for male repro- showed that male to female SVL ratio (SBSD) ductive success, is often associated with larger did not change over evolutionary time in the ´ and stronger males (Stamps, 1983), but in Archipelago (Molina-Borja and Rodrıguez- ´ species where female reproductive output in- Domınguez, 2004). But geographical variation creases with body size, females are often larger of morphological traits and body shape, as well as relationships between them and ecological than males (Cooper and Vitt, 1989; Shine, 1989; characteristics, has not been analyzed for Olsson et al., 2002). However, sexual dimor- Gallotia caesaris. However, we predicted that phism may also be caused by ecological, the magnitude of SBSD could differ within each species because of differences in the degree of 2 Corresponding Author. E-mail: [email protected] sexual selection, natural selection, or ecological 2 M. MOLINA-BORJA ET AL. TABLE 1. Percentage of soil covered by different TABLE 2. Factor loadings of principal component plants and substrate types along transects in the sites analysis applied to the matrix of vegetation and of Gallotia caesaris sampling. Gcc: Gallotia caesaris substrate type coverage of the four habitats (see caesaris; Gcg: Gallotia caesaris gomerae. Table 1). Sargos Guinea Dehesa Tecina Sampling sites PC1 PC2 (Gcc) (Gcc) (Gcc) (Gcg) Los Sargos 0.625 0.258 Kleinia 4.0 2.8 30 0 Guinea 0.390 0.732 Euphorbia 0 3.7 27 0 Dehesa 0.434 20.781 Rumex 23.1 12.2 0 0 Tecina 20.835 0.129 Schizogine 0 0 10 0 % explained variance 35.69 30.73 Rubia 0 0 15 0 Artemisia 4.7 27.8 2 0 Cistus monspeliensis 00 40closely related to G. c. gomerae, and both may be Messerschmidia 0 1.3 0 0 descendent from an ancestral Gallotia galloti like Gramineans (small lizard. grasses) 10 515 We used pitfall traps baited with tomato and Stones 62.1 3.9 7 0 Sandy 4.1 0 0 0 banana pieces to capture animals in the local- Loamy 1.0 0 0 0 ities of Tecina (G. c. gomerae, southeast of La Lapilli 0 40.8 0 0 Gomera), and Guinea, Los Sargos and La Stone wall 0 7.5 0 24.5 Dehesa (G. c. caesaris, northwest and west of El Fallen dry leaves Hierro, respectively), during breeding seasons (banana) 0 0 0 60.5 (April to July) from 1999 to 2001. Lizard data were obtained at two different years only for the Guinea population. We pooled all data for this population because lizards were not resampled processes at a local scale. Therefore, the aim of (marked by toe-clipping), and we did not find the present work is to provide quantitative information on variation of SBSD and sexual significant between-year differences in their dimorphism of head and body traits for traits. populations of G. caesaris differing in the We used variation in coverage by different vegetative structure of their microhabitat. To plants and type of substratum as a measure of that end, we examined sexual dimorphism in habitat diversity for each population. Because four populations of G. caesaris, one of Gallotia adult Gallotia lizards are preferentially herbivo- caesaris gomerae and three of Gallotia caesaris rous (Valido and Nogales, 1994), the degree of caesaris, living in areas with varied ecological vegetative coverage also reflects food availabil- characteristics. Hypothesizing stronger selective ity. We calculated coverage as the percentage of pressures in habitats with fewer resources that the ground covered by each plant species and could have led to competitive advantage for by each substratum type (Table 1). To charac- larger males, we expected higher SBSD in the terize habitat differences in vegetation covering more severe habitats of G. caesaris. However, and substrate type, we performed a principal taking into account previous results for other component analysis (PCA) on the matrix of lizard species and habitats (e.g., Herrel et al., Table 1 (after arcsine-square-root transforma- 2001), and the differences in habitat structure tion of the data). between our study sites, we expected to find We present the number of collected males larger relative limb lengths in individuals of G. and females in each population in Table 2. We caesaris from the more open habitat (less considered individuals to be adults when their vegetation) of Los Sargos in comparison with body size exceeded the minimum body size at those from more closed (high vegetation densi- sexual maturity for each sex of each subspecies. ty) ones of La Dehesa and Guinea. This minimum body size corresponds to the smallest male having well-developed hemi- penes (62.0 and 77.1 mm SVL, respectively, for MATERIALS AND METHODS G. c. caesaris and G. c. gomerae) and the smallest Gallotia caesaris caesaris (from El Hierro Island) female (57.0 and 73.6 mm, respectively) having and G. c. gomerae (La Gomera) are small lizards developing eggs.