Effect of light and temperature upon gonad activity in the vole ( Microtus agrestis)

Abstract

The effects of artificial day length and ambient temperature upon growth and maintenance of activity of gonads of the vole ( Microtus agrestis ) have been investigated. Four experiments were of a factorial design enabling estimates to be made of separate and joint effects of light and temperature. Voles in three experiments were derived from a laboratory stock, while animals for a fourth had been trapped in the field. In all these experiments, day length exerted a statistically significant effect upon the growth of gonads or upon the maintenance of activity in them, such that long days (16 hours light per day) favored greater gonadal development or maintenance of a higher level of activity that short days (6 hours light per day). In three experiments, involving laboratory-bred voles, neither temperature nor interaction of light with temperature exerted a statistically significant effect upon gonadal growth or activity. However, temperature and light × temperature exerted a significant effect upon gonadal activity in the fourth experiment in which field animals had been used. Perhaps in selecting for high fertility in the laboratory stock, animals have become more independent of ambient temperature than are field animals. The experimental winter conditions interferred with gametogenesis and the growth and activity of interstitial cells. In a fifth experiment, no statistically significant difference in testis size could be found between laboratory-bred voles living in fixed short days and those kept in conditions of decreasing day length. However, histological differences suggest that decreasing day length may prove more effective than fixed reduced day length in preventing gonadal growth.