Ballinger, R. E.

Lemos-Espinal, J. A.

Smith, Geoffrey R.

English

Denison University

Denison University Denison Digital Commons Denison Faculty Publications 2001 Sexual dimorphism and body temperatures of Sceloporus siniferus from Guerrero, Mexico J. A. Lemos-Espinal Geoffrey R. Smith R. E. Ballinger Follow this and additional works at: https://digitalcommons.denison.edu/facultypubs  Part of the Biology Commons Recommended Citation Lemos-Espinal, J. A., Smith, G. R., & Ballinger, R. E. (2001). Sexual dimorphism and body temperatures of Sceloporus siniferus from Guerrero, Mexico. Western North American Naturalist, 61(4), 498-500. This Article is brought to you for free and open access by Denison Digital Commons. It has been accepted for inclusion in Denison Faculty Publications by an authorized administrator of Denison Digital Commons. The biology of temperate North Americanlizards of the genus Sceloporus is relativelywell known. We know substantially less aboutthe majority of Mexican and Latin AmericanSceloporus species. Indeed, for too manyspecies we know only what has been pub-lished in the original descriptions. Recently,herpetologists have begun to recognize theimportance of studying the biology of tropicalreptiles (see Vitt and Zani 1996). In somecases studies on tropical species have obtainedresults counter to those obtained in temperatesystems that were sometimes thought to per-tain to all reptiles (e.g., Shine and Madsen1996). Thus, it is important to study the gen-eral biology and ecology of previously unstud-ied species, especially those from tropical orsubtropical regions. Such information hope-fully can serve as the basis of future syntheseson the biology of lizards. This note concernsthe sexual dimorphism and body temperatureof Sceloporus siniferus, a relatively unstudiedspecies from the seasonal semiarid tropics ofMéxico.The study population was located in a trop-ical deciduous forest located near the BahiaPapanoa (Km 161, Highway Mex 200 Acapulco-Zihuatanejo: 17°2′0.4″N, 101°3′0.0″W). Lizardswere collected by rubber band during May1996. We measured snout-vent length (SVL;to nearest mm) in the field. In addition, wetook body temperatures (Tb; nearest 0.1°C)with a quick-reading cloacal thermometerimmediately upon capture. We also measuredair temperature (Ta; shaded thermometer 1cm above substrate where individual firstobserved) and substrate temperature (Ts;shaded thermometer touching substrate whereindividual first observed). We also made vari-ous morphological measurements to analyzesexual dimorphism. We measured head width(HW; at the widest point), head length (HL;from anterior edge of ear to tip of snout), andfemur length (FL; from knee to middle ofpelvic region) using calipers.Mean SVL was 51.2 ± 0.8 mm (N = 56;range = 38–62 mm). For all morphometricvariables, the relationship with SVL was highlysignificant (all r2 > 0.80; P < 0.0001); thus, weused ANCOVA to analyze for sexual dimor-phism (on log-transformed data; after assump-tions checked).Males were larger on average than females(Table 1; df = 59, t = 4.37, P < 0.0001). Maleshad relatively wider heads than females (Fig.1; Table 1; ANCOVA with SVL as covariate:F1,58 = 7.6, P = 0.008). The interaction be-tween sex and the covariate was not significantand was not included in the final model.Males and females did not differ in the lengthof their heads after the effects of SVL wereremoved using ANCOVA (Table 1; ANCOVAwith SVL as covariate: F1,58 = 1.61, P = 0.21).The interaction between sex and the covariatewas not significant and was not included inthe final model. The length of a male’s femurwas, on average, the same as the length of afemale’s femur (Table 1; ANCOVA with SVLas covariate: F1,58 = 0.47, P = 0.50). The inter-action between sex and the covariate was notsignificant and was not included in the finalmodel.Western North American Naturalist 61(4), © 2001, pp. 498–500SEXUAL DIMORPHISM AND BODY TEMPERATURES OFSCELOPORUS SINIFERUS FROM GUERRERO, MÉXICOJulio A. Lemos-Espinal1, Geoffrey R. Smith2,4, and Royce E. Ballinger3Key words: lizards, sexual dimorphism, Sceloporus, México, thermal ecology.1Laboratorio de Ecologia, Unidad de Biología, Tecnología y Prototipos, Escuela Nacional de Estudios Profesionales Iztacala, Av. de los Barrios s/n, Los ReyesIztacala, Estado de México, 54090 México.2Department of Biology, William Jewell College, Liberty, MO 64068 USA.3School of Biological Sciences, University of Nebraska, Lincoln, NE 68588 USA.4Corresponding author. Present address: Department of Biology, Denison University, Granville, OH 43023 USA.498Mean Tb was 36.2 ± 0.3°C (N = 64; range27.6–39.4°C). Mean Ta was 30.4 ± 0.2°C (N =64; range 25.9–36.8°C), and mean Ts was 34.0± 0.7°C (N = 64; range 27.1–49.6°C). Bodytemperature was significantly influenced byboth Ta (N = 64, r2 = 0.42, P < 0.0001; Tb =13.10 + 0.76Ta) and Ts (N = 64, r2 = 0.28, P< 0.0001; Tb = 28.2 + 0.24Ts). Body temper-atures showed some diel fluctuations, as didTa and Ts (Fig. 2). Body size did not influenceTb (N = 56, r2 = 0.02, P = 0.36). Males andfemales had the same mean Tb (36.2°C;ANCOVA with Ta as covariate; F1,61 = 0.12, P= 0.72).Sceloporus siniferus are sexually dimorphicin both body size and head width, but not inhead length or length of femur. Males werelarger and had wider heads than females. Sev-eral other Sceloporus species are sexuallydimorphic, with males larger than females;however, not all Sceloporus species are sexu-ally dimorphic (Fitch 1978). Male-biased sex-ual dimorphism in head size is relatively com-mon in lizards (e.g., Vitt and Cooper 1985,Perez-Mellado and de la Riva 1993, Smith etal. 1997). We do not have enough informationto determine the cause of sexual dimorphismin S. siniferus (i.e., whether it is due to sexualselection or niche diversification; see Shine1989). However, the widespread occurrence ofsexual dimorphism in Sceloporus suggests itmay have a historical origin in the genus.The mean Tb of S. siniferus in this studywas 36.2°C, which places it among specieshaving the highest mean Tb reported in thegenus Sceloporus. Mean Tb ranges from 28.9°Cin S. variabilis (Benabib and Congdon 1992) to37.5°C in S. horridus (Lemos-Espinal et al.1997b; see Lemos-Espinal et al. 1997c for areview). Environmental temperatures appearto play a relatively large role in determiningthe Tb of individual S. siniferus, as evidencedby the relatively large r2 value for Tb on Taregression, and the diel variation in Tb. Maleand female S. siniferus did not have signifi-cantly different mean Tb, a situation that hasbeen observed in other studies on MexicanSceloporus (e.g., S. grammicus, Lemos-Espinaland Ballinger 1995; S. gadovae, Lemos-Espinalet al. 1997c; S. ochoteranae, Lemos-Espinal etal. 1997a). Such a lack of difference in Tbbetween males and females may suggest thatin these species males and females behavesimilarly, such as using similar microhabitatsor being active at the same time. Further workcomparing the microhabitat use and activity ofmales and females in species with sexual Tbdifferences with those without sexual Tb dif-ferences would be useful.2001] NOTES 499TABLE 1. Measurements (mm) of SVL and measure-ments (mm) of head width, head length, and femur lengthcorrected for SVL of male (N = 36) and female (N = 25)Sceloporus siniferus from Guerrero, México. Least squaresmeans are given ± 1sx–.Male FemaleSVL 52.8 ± 0.9 47.1 ± 0.8Head width 10.13 ± 0.09 9.73 ± 0.11Head length 11.54 ± 0.09 11.36 ± 0.11Femur length 14.56 ± 0.12 14.70 ± 0.14Fig. 1. The relationship between head width and SVLfor male (closed circles; upper regression line) and female(open circles; lower regression line) Sceloporus siniferusfrom Guerrero, México.Fig. 2. Diel variation in body temperature (closed cir-cles), air temperature (open circles), and substrate tem-perature (closed triangles) in Sceloporus siniferus fromGuerrero, México. Means are given ± 1sx–.We thank W.E. Cooper, Jr., and an anony-mous reviewer for their comments on themanuscript.LITERATURE CITEDBENABIB, M., AND J.D. CONGDON. 1992. Metabolic andwater-flux rates of free-ranging tropical lizards Scelo-porus variabilis. Physiological Zoology 65:788–802.FITCH, H.S. 1978. Sexual size differences in the genusSceloporus. University of Kansas Science Bulletin51:441–461.LEMOS-ESPINAL, J.A., AND R.E. BALLINGER. 1995. Com-parative thermal ecology of the high-altitude lizardSceloporus grammicus on the eastern slope of theIztaccihuatl Volcano, Puebla, México. Canadian Jour-nal of Zoology 73:2184–2191.LEMOS-ESPINAL, J.A., G.R. SMITH, AND R.E. BALLINGER.1997a. Body temperatures of Sceloporus ochoteranaefrom two populations in Guerrero, México. Herpeto-logical Journal 7:74–76.______. 1997b. Observations on the body temperaturesand natural history of some Mexican reptiles. Bul-letin of the Maryland Herpetological Society 33:159–164.______. 1997c. Thermal ecology of the lizard, Sceloporusgadoviae, in an arid tropical scrub forest. Journal ofArid Environments 35:311–319.PEREZ-MELLADO, V., AND I. DE LA RIVA. 1993. Sexual sizedimorphism and ecology: the case of a tropical lizard,Tropidurus melanopleurus (Sauria: Tropiduridae).Copeia 1993:969–976.SHINE, R. 1989. Ecological causes for the evolution of sex-ual dimorphism: a review of the evidence. QuarterlyReview of Biology 64:419–461.SHINE, R., AND T. MADSEN. 1996. Is thermoregulationunimportant for most reptiles? an example using waterpythons (Liasis fuscus) in tropical Australia. Physio-logical Zoology 69:252–259.SMITH, G.R., J.A. LEMOS-ESPINAL, AND R.E. BALLINGER.1997. Sexual dimorphism in two species of knob-scaled lizards (genus Xenosaurus) from México. Her-petologica 53:200–205.VITT, L.J., AND W.E. COOPER, JR. 1985. The evolution ofsexual dimorphism in the skink Eumeces laticeps: anexample of sexual selection. Canadian Journal ofZoology 63:995–1002.VITT, L.J., AND P.A. ZANI. 1996. Ecology of the lizardAmeiva festiva (Teiidae) in southeastern Nicaragua.Journal of Herpetology 30:110–117.Received 24 January 2000Accepted 6 June 2000500 WESTERN NORTH AMERICAN NATURALIST [Volume 61

Sexual dimorphism and body temperatures of Sceloporus siniferus from Guerrero, Mexico

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Sexual dimorphism and body temperatures of Sceloporus siniferus from Guerrero, Mexico

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