Fat and Breeding Cycles in Two Montane Populations of Sceloporus occidentalis (Reptilia, Lacertilia, Iguanidae)

Changes in fat body weights, total body fat and reproductive activity were studied in Sceloporus occidentalis in the central Sierra Nevada, California at 1500m and 2200 m elevation. At 1500m adult females have a mean SVL of 72.0 to 75.5mm, and at 2200 m range in SVL from 75.0 to 77.5 mm. Emergence of adults begins eginin early April and is complete by the end of April at 1500 m; at 2200 m adults first appear in late May or early June, depending upon weather. Activity of adults lasts until the latter part of September at 1500 m but at 2200 m most adults have disappeared before the middle of September; at 1500 m adult activity lasts ca. 6 months and at 2200 m 4.5 months. Total body fat for males at the two elevations is nearly the same in the spring, and very low after reproduction; but males before hibernation at 1500 m have means of ca. 0.5-0.6 g total body fat and inguinal fat bodies of 0.4 g, and at 2200 m ca. 1.0 g total body fat and fat bodies of ca. 0.8 g. Total body fat of females at 1500 m is ca. 0.8-0.9 g before ovulation in the spring, 0.5 g after egg-laying (in July) and 0.8 g before hibernation; and at 2200m preovulatory total body fat is 1.4 g, after egg-laying 0.8 g, and 1.2+g before hibernation. Fat bodies of females fluctuate in approxi- mately the same manner as does total body fat, but individuals vary greatly in fat body size at any given time. Females' liver fat levels decline as ova develop: in early spring (when ova are 3-4 mm) livers have ca. 0.1 g fat at 1500 m and more than 0.6 g at 2200 m. Prior to egg-laying, mean liver fat (of females) is nearly undetectable at 1500 m and less than 0.1 g at 2200 m. Liver fat increases after egg-laying. Ovulation starts at 15 May (1500 m) and 30 May (2200 m); and egg-laying occurs from 18 June-19 July (1500 m) and 26 June-10 July (2200 m). Newly hatched young were first seen on 15 August (1500m) and 17 August (2200 m). Clutch size is 11.3 (?0.41) at 1500m and 13.4 (?+ 0.57) at 2200 m; the combined mean is 12.0 (? 0.35). A single clutch is laid annually; second clutches are probably very unusual. The difference in total body fat in early spring in females at 1500 m and 2200 m is nearly the same as the difference in fat content of an average clutch of eggs at 1500 m (11.3 eggs) and at 2200 m (13.4 eggs). It is suggested that the greater size of adult females at 2200 m is a means of accumulating more fat so as to lay larger clutches of eggs. It is also suggested that the major function of fat stores in females is the production of eggs. During hibernation, calculated fat loss at 1600 m was 0.018 KCal/gm body weight/month (males) and 0.006 KCal/gm body weight/month (females). At 2200 m the loss was 0.04 KCal (males) and 0.01 KCal (females). * * * Annual cycles of fat occur in many genera of lizards, and fat stores are believed to be associated with hibernation, seasonal wet-dry periods, and reproduction (egg production). Inasmuch as fat is energy-rich, cyclical occurrence may suggest degrees of adaptation to seasonal needs. It seems appropriate to explore differences within a species in different habitats, and between allied species in the same habitat. This account describes some aspects of fat cycles and reproduction in Sceloporus occidentalis at 1500 m and provides a basis for comparing this species with S. graciosus on the same ground (Jameson, 1974). We also present data on S.