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RESEARCH PRODUCT

Sex-specific variation in the onset of reproduction and reproductive trade-offs in a boreal small mammal

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In seasonal environments, the optimal onset of reproduction plays a major role in defining the reproductive success of an individual. Environmental cues, like day length, weather conditions, and food, regulate the initiation and termination of the breeding season. Besides the interspecific variation in response to environmental cues, it has been suggested that due to different selection pressures, females and males can have different responses to environmental stimuli. However, this phenomenon has gained relatively little consideration, and the physiological mechanism behind these differences is not well known. Here, we report how two different environmental cues, variability of temperature and nutritional conditions in spring, affect the onset of breeding in a boreal small rodent, the bank vole, Myodes glareolus. We exposed wild-trapped individuals to four different treatments manipulating temperature (stable vs. variable) and food quality (high vs. low protein content) over five weeks in the laboratory. We monitored body-mass development, food consumption, and initiation of breeding. We found sex-specific responses to temperature variability, as males achieved their breeding condition faster in variable temperature treatments, whereas female maturation was delayed. Food quality had no effect on the onset of breeding. To test for possible reproductive trade-offs caused by reproductive decisions made in early spring, the experiment was continued in large outdoor enclosures. There seemed to be no significant long-term effects on reproduction, but early summer survival was affected by climate conditions experienced in spring. Our results show clear sex differences in the response to environmental cues regulating the onset of reproduction in bank voles. Hence, our study suggests that when an organism experiences rapid environmental changes, as are occurring on a global scale, divergent cues may lead to a reproductive mismatch between the sexes. This could noticeably decrease the fitness of many seasonally breeding species.