Reproduction, Seasonal Changes in Body Weight, Fat Deposition, Spleen and Adrenal Gland Weight of the Golden-Mantled Ground Squirrel, Spermophilus lateralis lateralis, (Sciuridae) in the Laramie Mountains, Wyoming

Abstract

Annual reproductive cycles, and seasonal changes in body weight, fat deposition, spleen and adrenal gland weights of 86 goldenmantled ground squirrels (Spermophilus lateralis lateralis) from the Laramie Mountains of southeastern Wyoming (elev. ca. 8500 ft) were investigated from June, 1967 to September, 1968. Males were first collected in late March, females in mid-April. Adult above-ground activity terminated by early September. Testes were at maximum weights and lengths in March and minimum in August. Mature sperm were present in testes tubules during March, April, and May. Testes were scrotal shortly after emergence from hibernation in April and became abdominal in early June. Breeding took place in late April and early May. Parturition occurred approximately a month later. The mean number of embryos was 5.4 -?+ 0.7 (N=8); of placental scars was 5.9 + 1.4 (N=24); of young born in the laboratory was 4.3 4 0.6 (N=3). Mean litter size determined from embryo counts, placental scar counts and young born in captivity was 5.6 + 1.3 (N=35). Embryo resorption was found in 12.5% of pregnant females. Mean monthly body weights of females exceeded those of males except during April and August. The heaviest female weighed 283 g while the heaviest male weighed 266 g. All animals possessed reserve retroperitoneal fat at the time of emergence from hibernation. By June measurable fat reserves had been depleted. New retroperitoneal fat accumulation commenced in August. No definite differences were apparent between the sexes concerning splenic hypertrophy. Adrenal gland weights were relatively stable during June and July and decreased in August. 1 Present address: Department of Zoology, Arizona State University, Tempe. 2 Present address: Department of Biology, Wisconsin State University, Medford.