![]() The effects of torpor on male reproductive performance remain poorly understood. 17, 21, 22) where time spent at low body temperatures negatively influences milk production and foetal development 17, 22. In the large order of bats, the effects of torpor on reproduction have been studied almost exclusively in females (e.g. For example, testicle tissue becomes unresponsive to endocrine signals at low temperatures, and thus spermatogenesis proceeds at a slower pace 19, 20. A low metabolic rate down-regulates other physiological processes including those related to reproduction (e.g., 16, 17, 18). Torpor reduces energy expenditure, thus allowing conservation of fat reserves 13, which improves self-maintenance and survival during energetic bottlenecks 11, 14, 15. Torpor is characterized by controlled metabolic suppression and lower body temperature 11, 12. Bats especially, are prone to heat and water loss due to the large naked surface of their wing membranes and the poor insulation properties of their pelage 9, 10.īats commonly compensate for energetic constraints by using torpor. This demand is particularly high in small animals, including bats, as they have high metabolisms and lose heat rapidly due to their high surface to volume ratio 8. Yet, endothermy is energetically demanding 6, 7. For example, endogenous heat production buffers the effects of variation in ambient temperature on important biological functions and reduces dependence on weather. These mechanisms can be physiological (such as changes in metabolic rate, body temperature, or digestive function) or behavioural (including foraging behaviour, movement or roost choice) 3, 4, 5. Many animals possess mechanisms to cope with such environmental variation. Animals are often faced with unpredictable environments due to variation in environmental conditions, such as food availability or weather, which makes balancing their energy budget challenging 1, 2. Reproductive performance and survival are determined by fundamental energetic trade-offs. Our results show that not only low, but also constant high ambient temperatures are detrimental during seasonal sexual maturation and the trade-off between investing into self-maintenance and fitness is a finely tuned compromise. Interestingly, bats at constant high temperatures avoided deep torpor and matured faster than those at low temperatures, but sperm production was also slower than under natural conditions. Heavier bats were able to afford more intensive thermoregulation and consequently speed up maturation. This effect was partially buffered by higher body mass. We showed that long exposure to low ambient temperature shifts energy allocation away from sexual maturation to self-maintenance and results in a delay of sperm maturation by as much as an entire month. We used a unique experimental approach to test the consequences of extended low and high ambient temperatures on the trade-off in energy allocation to body mass maintenance, thermoregulation effort and seasonal sexual maturation in temperate zone male bats. Some temperate-zone species (heterotherms) regularly use torpor, which slows down their entire metabolism but also potentially delays reproduction, to compensate for this. Especially small endothermic mammals have high energy demands. ![]() The ability of animals to produce endogenous heat provides a buffer against environmental changes but also incurs high energetic costs.
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