Effect of Geographical Origin on the Photoperiodic Control of Reproduction in the White-Footed Mouse, Peromyscus leucopus

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Abstract
Summer wild-caught Peromyscus leucopus from Maine (ME), Connecticut (CT), and Georgia (GA) were exposed to a short day photoperiod (9L:15D) for 12 weeks, the last 6 of which were at 13°C. All of the mice from ME and CT exhibited reproductive regression after this time while mice from GA remained reproductively competent. Laboratory-reared mice from CT, Virginia (VA) and GA were subjected to the same treatment. CT mice underwent gonadal regression as judged by pronounced decreases in testicular weight, testicular index, spermatogenic index, and seminal vesicle weight in males and reproductive tract weight and follicular index in females. In contrast, values for these parameters in the VA and GA mice indicated reproductive maintenance. When exposed to natural fluctuations in photoperiod and temperature in CT between September and December, GA mice remained reproductively competent. Under the same environmental conditions, five of six CT male mice and all of the CT female mice underwent gonadal regression during October and early November. These data indicate that, in P. leucopus, there is considerable intraspecific variability for photoperiodic regulation of seasonal reproduction. Photoperiod-induced regression is more extensive in northern populations.