Partitioning of metabolizable energy intake in sucking altricial and precocial rodent pups

On heights and plains: How rodents from different habitats cope with three-dimensional environments?

Dwelling in a specific habitat requires adaptation to the habitat physical and biological properties in order to maximize fitness. Adaptations that are manifested in the organization of behavior in time and space reflect how the environment is perceived and utilized. Testing species from different habitats in the same laboratory environment can uncover the differences in their behavior and their adaptations to specific habitats. The question posed in this study is that of how two rodent species, one occupying flatlands (Tristram’s jird; Meriones tristrami) and the other occupying structured rocky habitats (common spiny mouse; Acomys dimidiatus), differ in the way that they explore the same three-dimensional laboratory environment. Individuals of these two species were introduced into an arena with a five-level ziggurat in the center, and their behavior was followed for 60 min. We found that both species preserved the typical spatiotemporal rodents’ behavior of establishing a home-base—a location that is a terminal from which they set out to explore the environment. However, the jirds, which live in flatlands, mainly travelled on the arena floor and the lower levels of the ziggurat; while, in contrast, the spiny mice, which live in rocky habitats and are used to climbing, mostly remained and travelled on the ziggurat, with some of them hardly descending to the arena floor. We suggest that the distinction in spatial behavior between the two species reflects their different motor abilities, different depth perception, and different umvelt (perceived world), in accordance with their different natural habitats.

Dietary fatty acids sex-specifically modulate guinea pig postnatal development via cortisol concentrations

Early ontogenetic periods and postnatal maturation in organisms are sex-specifically sensitive to hypothalamic-pituitary-adrenal (HPA)-axis activities, related glucocorticoid secretions, and their effects on energy balance and homeostasis. Dietary polyunsaturated (PUFAs) and saturated (SFAs) fatty acids potentially play a major role in this context because PUFAs positively affect HPA-axis functions and a shift towards SFAs may impair body homeostasis. Here we show that dietary PUFAs positively affect postnatal body mass gain and diminish negative glucocorticoid-effects on structural growth rates in male guinea pigs. In contrast, SFAs increased glucocorticoid concentrations, which positively affected testes size and testosterone concentrations in males, but limited their body mass gain and first year survival rate. No distinct diet-related effects were detectable on female growth rates. These results highlight the importance of PUFAs in balancing body homeostasis during male's juvenile development, which clearly derived from a sex-specific energetic advantage of dietary PUFA intakes compared to SFAs.

The physiological costs of reproduction in small mammals

Life-history trade-offs between components of fitness arise because reproduction entails both gains and costs. Costs of reproduction can be divided into ecological and physiological costs. The latter have been rarely studied yet are probably a dominant component of the effect. A deeper understanding of life-history evolution will only come about once these physiological costs are better understood. Physiological costs may be direct or indirect. Direct costs include the energy and nutrient demands of the reproductive event, and the morphological changes that are necessary to facilitate achieving these demands. Indirect costs may be optional 'compensatory costs' whereby the animal chooses to reduce investment in some other aspect of its physiology to maximize the input of resource to reproduction. Such costs may be distinguished from consequential costs that are an inescapable consequence of the reproductive event. In small mammals, the direct costs of reproduction involve increased energy, protein and calcium demands during pregnancy, but most particularly during lactation. Organ remodelling is necessary to achieve the high demands of lactation and involves growth of the alimentary tract and associated organs such as the liver and pancreas. Compensatory indirect costs include reductions in thermogenesis, immune function and physical activity. Obligatory consequential costs include hyperthermia, bone loss, disruption of sleep patterns and oxidative stress. This is unlikely to be a complete list. Our knowledge of these physiological costs is currently at best described as rudimentary. For some, we do not even know whether they are compensatory or obligatory. For almost all of them, we have no idea of exact mechanisms or how these costs translate into fitness trade-offs.