Photoperiodic Regulation of Reproductive Development in White-footed Mice (Peromyscus leucopus)

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Abstract
Male and female Peromyscus leucopus were raised from birth either in long days (14L:10D) or short days (10L:14D). Testicular development was accelerated in long-day compared with short-day animals at all time points sampled between 45-100 days of age. Complete spermatogenesis was first manifested by the majority of long-day mice at 60 days of age and by short-day animals at 140 days of age. Similar results were obtained for indices of female reproductive activity. It is suggested that short daylengths prevalent during late summer and autumn delay maturation of the reproductive system of mice born late in the breeding season. The eventual escape from short-day inhibition permits development of the reproductive apparatus in overwintering juveniles so that breeding can occur at the outset of favorable spring conditions.