Blank, James L. and Ruf, Thomas. 1991. Effect of Reproductive Function on Cold Tolerance in Deer Mice. 22 p.
Submitted to: American Journal of Physiology; Regulatory, Integrative and Comparative Physiology: Thermoregulatory responses were evaluated in male deer mice (Peromyscus maniculatus nebrascensis) after exposure to inhibitory photoperiod and either warm or cold ambient temperature (Ta). Deer mice were chosen for this study because males exhibit differential reproductive responses to short daylength (SD); this difference has a genetic basis and both genotypes are found within natural breeding populations. Deer mice undergoing SD-induced gonadal regression improved their cold limit to - 32.9°C after exposure to SD/warm Ta and to -47.4°C after SD/cold Ta exposure, relative to LD/warm Ta controls (-17.4°C). In contrast, deer mice maintaining reproductive function despite SD-exposure, improved cold limit to -27.2° only after exposure to SD/cold Ta exposure, relative to controls (-16.3°C). Maximum NE-induced nonshivering thermogenesis and NST capacity did not vary with the reproductive state indicating differences in cold tolerance were not due to capacity of brown adipose tissue to produce heat. Comparison between genotypes of heat production during cold tolerance tests indicated that greater cold tolerance among mice exhibiting SD-induced gonadal regression can be accounted for by 1) lower rates of heat loss and 2) greater improvement of heat production. These findings suggest a functional relationship between reproductive function and seasonal thermoregulartory adjustments and indicate a significant cost to breeding during winter months.