AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 3 522-R530, Copyright © 1991 by American Physiological Society
Thermoregulation, growth, and reproduction in Alaskan collared lemmings: role of short day and cold
H. A. Maier and D. D. Feist
Institute of Arctic Biology, University of Alaska Fairbanks 99775.
To assess factors controlling seasonal thermoregulatory and reproductive
changes, collared lemmings (Dicrostonyx groenlandicus) were exposed for 16
wk to long day (LD, 22 h light: 2 h dark) and warm (15 +/- 3 degrees C), LD
and cold (1 +/- 0.5 degrees C), short day (SD, 4 h light: 20 h dark) and
warm, SD and cold or acclimatized to outdoor winter conditions (OUT). Hair
length and color, body mass, and food intake were monitored weekly. Resting
metabolic rates (RMR) and nonshivering thermogenesis (NST) were estimated
several times by measuring oxygen consumption before and after
norepinephrine injections. Body composition and reproductive condition were
determined at the end of the experiment. SD and OUT groups had a 15.8%
lower (P less than 0.01) RMR at 7 degrees C than the LD groups. Lower
thermal conductance in SD and OUT animals appears due to molt to white
winter pelage, which occurred by week 3 in SD but not in LD groups. Neither
SD, cold, nor OUT altered NST or reproductive morphology. SD-exposed
lemmings showed 19.2% greater growth than those in LD, resulting primarily
from a 29.2 and 15.0% increase in lean and ash components, respectively.
Cold exposure increased food intake by 34.7%. Results suggest that the
pineal gland, which mediates SD effects, may influence molt and growth but
not NST or reproductive morphology.
