Phenotypic variation in seasonal adjustments of testis size, body weight, and food intake in deer mice: role of pineal function and ambient temperature

Abstract

We investigated pineal function as well as reproductive and energetic characteristics in male deer mice (Peromyscus maniculatus) that differentially respond to short photoperiod with full, partial or no gonadal regression. In mice at both high (23 degrees C) and low temperature (1 degree C), these phenotypic differences in reproductive responses to short days were not reflected by differences in urinary excretion of 6-sulphatoxy-melatonin, the main metabolite of pineal melatonin. Neither duration nor amplitude or phase-angle of nocturnal peaks in 6-sulphatoxymelatonin significantly differed between reproductive phenotypes at either temperature. Differences in testis size were, however, associated with different energy requirements. In gonadally regressed males only, food intake and body weight were significantly (P < 0.01) reduced by up to 29% and 13% respectively. Chronic cold exposure (5 degrees C) had no effect on the proportion of males undergoing testicular regression under short days, but caused a general elevation in body weights among all mice (P < 0.05). Phenotypic differences in body weight and food intake were maintained in the cold. Together, these results suggest that within-population variation of reproductive responses in male deer mice is based on post-pineal differences in the regulation of gonadal function, and that phenotypic characteristics in reproductive and energetic responses to short days are largely unaffected by ambient temperature.

Temperature dependence of gonadal regression in Syrian hamsters exposed to short day lengths

“…A similar modulatory role of T a on photoperiodic responses has been documented in other photoperiodic rodents (7,25,(37)(38)(39). In Siberian hamsters, T a affects the photoperiodic response by altering neuroendocrine responsiveness to long melatonin signals (25).…”

Phenotypic differences in the GnRH neuronal system of deer mice Peromyscus maniculatus under a natural short photoperiod

“…1) (Glass, 1986;Korytko et al, 1995 (Hoffmann, 1979;Goldman and Darrow, 1983;Reiter, 1987). Recent evidence indicates that melatonin secretion (Ruf et al, 1997) and hypothalamic GnRH content …”

“…For members of the genus Peromyscus, gonadal regression confers several advantages, including increased abilities to tolerate cold ambient temperatures and to conserve energy in a winter environment (Blank and Ruf, 1992;Blank et al, 1994;Ruf et al, 1997). Collectively, these adjustments promote survival during harsh environmental conditions and reduce social interactions in the winter months that are associated with mating behaviour and territorial defence (Korytko and Vessey, 1991).…”

Short Photoperiods Impair Spatial Learning and Alter Hippocampal Dendritic Morphology in Adult Male White-Footed Mice (Peromyscus leucopus)

“…In nontropical environments, energy-conserving, adaptive adjustments occur among individuals in response to decreasing day lengths that are believed to promote survival during the harsh conditions of winter (Bronson, 1985). For example, short days decrease reproductive system size and function in white-footed mice (Peromyscus leucopus) (Whitaker, 1940;Ruf et al, 1997).…”