LIGHT-INTENSITY AND REPRODUCTION IN WILD AND DOMESTIC HOUSE MICE

Wild caught house mice [Mus musculus] and laboratory raised CF-1 stocks each were bred under low light intensities. The 1st litters of these 2 stocks were paired as adults in constant darkness, or on a 14L[light]:10D[dark] cycle with the light phase maintained at either 10-20 lux or at > 1000 lux. Reproduction over a 75 day period was normal for both stocks in constant darkness. Productivity, particularly litter size, was markedly depressed in wild Mus at > 1000 lux but was unaffected by lighting condition in the domestic stock. Normal animal room lighting will evidently depress productivity in wild Mus. Selection against this response must have occurred during domestication. Seasonal breeding in wild Mus, where it occurs, is apparently not photoperiodically-induced. This species can breed well in the absence of any light cycle.