Comparative thermal ecology of the high-altitude lizard Sceloporus grammicus on the eastern slope of the Iztaccihuatl Volcano, Puebla, Mexico

Abstract

We studied the thermal ecology of Sceloporus grammicus occurring in very different thermal environments at 3700 and 4400 m elevation on the Iztaccihuatl Volcano, Mexico. Despite differences in the thermal environment between study sites, individual lizards maintained similar active body temperatures (around 31.5"C). Similar body temperatures at the two study sites probably result in differences in the cost of the thermoregulatory behavior. Lizards at the high-altitude site, an open area with few predators or competitors, presumably incur a lower thermoregulatory cost than those at the low-altitude site, which has a considerable number of shaded spots and more predators and competitors. Lizards at the low-elevation site showed a greater resistance to high temperatures than those at the high-elevation site. Physiological acclimatization to higher environmental temperatures at low elevation is likely to explain the greater heat tolerance. Freezing tolerance, thermoregulatory behavior, and low energy requirements permit S. grammicus to survive at high altitudes.RCsumC : Nous avons etudie l'kcologie thermique de Sceloporus grammicus dans des milieux h regimes thermiques trks differents, a 3700 et 4400 m d'altitude, sur le volcan Iztaccihuatl au Mexique. En depit de differences de regime thermique aux deux endroits, les lezards actifs avaient des tempkratures semblables (d'environ 3 1,5 "C) . Ces temperatures semblables aux deux endroits resultent probablement de differences dans les coQts relies aux comportements thermoregulateurs. Le site de haute altitude, une zone ouverte oh le nombre de predateurs et de competituers est moins important, correspond probablement a une thermoregulation moins coQteuse que le site de basse altitude qui comporte un nombre considerable de zones ombragees, plus de predateurs et plus de competiteurs. Les lezards du site de basse altitude ont manifeste une plus grande resistance aux temperatures elevees que les lezards de haute altitude. Un phenomkne d'acclimatation physiologique h des temperatures ambiantes plus elevees h basse altitude explique probablement la plus grande tolerance h la chaleur. La tolerance au gel, le comportement thermoregulateur et les besoins energetiques reduits permettent h S. grammicus de survivre h haute altitude. [Traduit par la Redaction]

Distributional range, ecology, and mating system of the Cape mole-rat (Georychus capensis) family Bathyergidae

“…Similar patterns of smaller size-specific litters at higher altitudes relative to their lowland counterparts have been reported for populations of various lizard species (Waltner 1991;Mathies and Andrews 1995;Rohr 1997;Lemos-Espinal et al 1998). This phenomenon has been attributed to environmental conditions such as lower resource availability (Rohr 1997).…”

“…In addition, sperm competition (Merilä and Sheldon 1998;Jolly and Phillips-Conroy 2001;Preston et al 2002;SchulteHostedde and Millar 2004;Hettyey and Roberts 2006), scramble competition polygyny (Clutton-Brock 1989;Davies 1991), the temporal and spatial distribution of the sexes (Davies 1991;Reynolds 1996) and the operational sex ratio of a species (Greenwood 1980;Hettyey and Roberts 2006) are also influential in determining intraspecific variation in reproductive biology. Such intraspecific geographic variation has been demonstrated in litter size (Hill 1972;Waltner 1991;Mathies and Andrews 1995;Rohr 1997;Lemos-Espinal et al 1998) and testicular size (Merilä and Sheldon 1998;Hettyey et al 2005) due to various ecological and biological factors.…”

Demography of the lizard Sceloporus grammicus: exploring temporal variation in population dynamics

“…Mean adult size of females vary from 44.5 to 55.2 mm snout-vent length (SVL), whereas minimum size at maturity ranges from 34.0 to 44.1 mm SVL among populations (Martínez 1985;Méndez-de la Cruz 1988;Ramírez-Bautista et al 2004). Mean litter size also exhibits considerable intraspecific variation from 3.3 to 6.2 young (Ortega and Barbault 1984;Guillette and Bearce 1986;Lemos-Espinal et al 1998). Body growth rates are faster at relatively low elevations when compared with those observed in populations at relatively high elevations (Lemos-Espinal and Ballinger 1995;Ortega-Rubio et al 1999b;Zúñiga-Vega et al 2008).…”

Ecologia térmica do lagarto Sceloporus gadoviae (Squamata: Phrynosomatidae) em uma região semi-árida do sul de Puebla, México.

“…In contrast, Lemos-Espinal et al (1997a) did not find a significant difference in T b between males and females, but did find significant differences in the environmental temperatures at the site of capture of males and females. Within Sceloporus, males with higher mean T b s than in females have been reported for S. scalaris and S .mucronatus (Lemos-Espinal et al 1997b, Smith et al 1993, with lower mean T b in S. undulatus erythrocheilus (Gillis 1991) and no difference in mean T b between males and females in a number of other species (e.g., Vial 1984, Guyer and Linder 1985, Lemos-Espinal and Ballinger 1995, LemosEspinal et al 1997c, 2001, 2003. Possible explanations for the differences in mean T b between and within sexes may include habitat partitioning for basking, activity at different times, or behavior.…”