PHENOTYPIC VARIATION IN SEASONAL ADJUSTMENTS OF TESTIS SIZE, BODY-WEIGHT, AND FOOD-INTAKE IN DEER MICE - ROLE OF PINEAL FUNCTION AND AMBIENT-TEMPERATURE

We investigated pineal function as well as reproductive and energetic characteristics in male deer mice (Peromyscus maniculatus) that differ entially respond to short photoperiod with full, partial or no gonadal regression. In mice at both high (23 degrees C) and low temperature ( 1 degrees C), these phenotypic differences in reproductive responses t o short days were not reflected by differences in urinary excretion of 6-sulphatoxymelatonin, the main metabolite of pineal melatonin. Neith er duration nor amplitude or phase-angle of nocturnal peaks in 6-sulph atoxymelatonin significantly differed between reproductive phenotypes at either temperature. Differences in testis size were, however, assoc iated with different energy requirements. In gonadally regressed males only, food intake and body weight were significantly (P < 0.01) reduc ed by up to 29% and 13% respectively. Chronic cold exposure (5 degrees C) had no effect on the proportion of males undergoing testicular reg ression under short days, but caused a general elevation in body weigh ts among all mice (P < 0.05). Phenotypic differences in body weight an d food intake were maintained in the cold. Together, these results sug gest that within-population variation of reproductive responses in mal e deer mice is based on post-pineal differences in the regulation of g onadal function, and that phenotypic characteristics in reproductive a nd energetic responses to short days are largely unaffected by ambient temperature.