High altitude adaptation and anaerobiosis in sceloporine lizards.

1. The duration of maximal activity and the intensity of anaerobic metabolismwere measured in lowland Sceloporus occidentalis at low (200 ft) and high (10,150 ft) elevations and compared to those of resident S. occidentalis and S. graciosus at high altitude. 2. The duration of maximal activity is independent of altitude: all groups of S. occidentalis had the same stamina, regardless of the altitude of experimentation or prior residence. 3. The amount of lactate formed during activity is also independent of altitude or prior residence. 4. No indications of altitude adaptation were found in these species. It is hypothesized that the basically anaerobic activity patterns of small lizards constitute a preadaptation to colonization of high altitudes. INTRODUCTION Increased stamina could result from either greater MAMMALS and birds inhabiting high altitudes demonstrate a suite of compensatory physiological adjustments facilitating the acquisition of oxygen. Such hematological adaptations as greater hematocrit, oxygen capacity and oxygen affinity are commonly associated with the lower levels of environmental oxygen available to highland animals. Similar adaptations have yet to be demonstrated unequivocally in reptiles from high altitudes. A compensatory increment in hematological parameters has been reported in some reptiles exposed naturally or artificially to high altitude (Richter, 1933; Hadley & Burns, 1968; Vinegar & Hillyard, 1972; Weathers & McGrath, 1972). Other investigators, often examining the same species, have not found such compensation (Sokolov, 1941; Altland & Parker, 1955; Dawson & Poulson, 1962; Pough, 1969; Weathers & White, 1972). A higher rate of resting oxygen consumption ( + 3 M 5 per cent) has been reported in highland vs. lowland forms of sceloporine lizards (Bartlett, 1970). The significance, indeed the adaptive value, of such an increased metabolic rate is unknown. At present, we can only conclude that adaptations to sustain aerobiosis at high altitudes, if they exist at all, are not as widespread or as well developed in reptiles as in the homwthermic groups. Even if hematological adaptations promoting aerobic or greater anaerobic capabilities. Evidence has accumulated that many lowland reptiles during maximal activity are largely dependent upon and tolerant of anaerobic metabolism (Moberly, 1968a, b; Bennett & Licht, 1972; Bennett & Dawson, 1972; Gatten, 1973). Lactic acid production provides most of the energy generation during rapid activity. The dynamics of lactate production have not been examined in reptiles resident at high altitude or in lowland animals during hypoxia. These experiments were undertaken to determine whether there is any difference in activity performance in low and high altitude reptiles and whether the patterns of anaerobic metabolism are similar in these forms. Lizards of the genus Sceloporus in the western United States present an excellent altitudinal series for comparative studies. Sceloporus occidentalis, the western fence lizard, occupies an altitudinal range from sea level to over 9000 ft in the mountains of California. A sympatric species, S. graciosus, is more commonly found at high elevations than is S. occidentalis and it ranges even higher (10,000+ ft) (Stebbins, 1954). We measured maximal activity and anaerobic metabolism in lowland S. occidentalis in the lowlands and transported a lowland group to high altitude. Here the experiments were repeated along with those on resident populations of S. occidentalis and S. graciosus. increased aerobiosis do exist in highland reptiles, MATERIALS AND METHODS whether they impart more stamina under oxygen stress, e.g. during activity, has never been examined. Lowland Scelo~o~ia occidentalis (mean wt.9 12.0 g) It is unknown whether highland animals perform were collected near Naps, Naps County, California (elevation approximately 1000 ft). Highland S. occibetter in hypoxic situations than do lowland forms. dentalis (16.2 g) and S. graciosus (5.8 g) were collected at 8000-9000ft in the White Mountains, Inyo County, * Present address: School of Biological Sciences, California. Experimentation was performed at the University of California, Irvine, California 92664. University of California, Berkeley (elevation 230 ft), for 106 ALBERT F. BEN NET^ AND JOHN RUBEN lowland determinations and at Crooked Creek Laboratory, White Mountain Research Station of the University of California (elevation 10,150 ft). Animals were utilized 24-48 hr after capture. Lowland S. occidentalis were exposed to highland conditions for less than 24 hr before experimentation. Lowland animals were measured in both the lowlands and highlands; highland animals were measured only in the highlands. All experiments were carried out in June during the normal season of activity. Anaerobic metabolism during maximal activity was measured according to the method of Bennett & Licht (1972). Lizards were weighed and placed overnight in the dark at 35OC, a temperature within the activity range of both species (Brattstrom, 1965). The following morning, some animals were removed and exercised for 30 sec, 90 sec or 5 min, and others were left unstimulated as