Social, but Not Photoperiodic, Influences on Reproductive Function in Male Peromyscus aztecus 1

Abstract

Nontropical rodents rely on environmental factors to restrict breeding to a specific time of the year. Among these factors, photoperiod appears to be the primary environmental cue used for predicting optimal breeding conditions. The purpose of the present study was to characterize reproductive function, as well as photoperiodic and social responsiveness in male Peromyscus aztecus, which occupy low-latitude, high-altitude habitats. In experiment 1, adult male P. aztecus were individually housed in either long (16L:8D) or short days (8L:16D) for 10 wk. Short-day mice did not differ from long-day mice on any reproductive or nonreproductive parameter. Comparisons to related Peromyscus species suggested that relative reproductive organ size and function were reduced in both long- and short-day males. Because ad libitum food and water were available, we reasoned that males in both photoperiodic conditions lacked social stimuli. To test this hypothesis, adult male P. aztecus were housed in long days either individually or with a female conspecific in experiment 2. Mice housed with females had significantly larger relative paired testes and epididymal masses, and higher testicular sperm counts and serum testosterone levels compared to those of individually housed mice. Taken together, these results suggest that social factors may play a more prominent role than photoperiod in stimulating reproductive development in laboratory-housed P. aztecus. These results are consistent with the results found for other low-latitude rodent species and suggest that P. aztecus uses a flexible rather than obligatory breeding strategy.

Social and photoperiod effects on reproduction in five species of Peromyscus

“…Consistent with previous observations (Demas and Nelson, 1998), P. aztecus did not show reproductive suppression in short days. P. eremicus also did not exhibit reproductive suppression in short days, similar to closely related Peromyscus californicus (Nelson et al, 1995).…”

“…A previous study reported that components of male P. aztecus reproduction did not respond to photoperiod, but that males increased testes mass and T when housed with an intact female for 8 days (Demas and Nelson, 1998). In our study, male P. aztecus did not respond to photoperiod and did not show significant responses to social housing.…”

“…In general, species that inhabit tropical climates have expanded breeding seasons compared to closely related species that live in temperate climates. Several studies have observed that short days do not inhibit reproduction in tropical rodents (Demas and Nelson, 1998;Heideman and Bronson, 1990;Nunes et al, 2002), although this outcome does not necessarily reflect an inability to detect slight changes in photoperiod in these species (Hau et al, 1998). In the tropics, photoperiod may be a less informative predictor of impending climate, so other cues may be more useful for timing reproductive activity.…”

“…For example, male Peromyscus aztecus failed to reduce testes mass when housed in short days (8L: 16D), but males that were housed with a female in long day lengths had larger testes and epididymides than singly housed males (Demas and Nelson, 1998). Male Siberian hamsters (Phodopus sungorus) housed with a female did not undergo testicular regression in short days (Hegstrom and Breedlove, 1999).…”

Social environment modulates photoperiodic immune and reproductive responses in adult male white-footed mice(Peromyscus leucopus)

“…It has been hypothesized that the energetic savings attained by seasonal suspension of reproduction liberates energy for immune function, thereby enhancing immune responses in short-day animals (7). Although additional environmental cues (e.g., temperature, food availability, precipitation, and social cues) have also been studied separately or in conjunction with photoperiod manipulation (8,10,20,28), photoperiod generally appears to be the most influential cue for seasonal adaptations.…”