Gender markedly modulates behavioral thermoregulation in a non-human primate species, the mouse lemur (Microcebus murinus)

The Torpid State: Recent Advances in Metabolic Adaptations and Protective Mechanisms†

Torpor and hibernation are powerful strategies enabling animals to survive periods of low resource availability. The state of torpor results from an active and drastic reduction of an individual's metabolic rate (MR) associated with a relatively pronounced decrease in body temperature. To date, several forms of torpor have been described in all three mammalian subclasses, i.e., monotremes, marsupials, and placentals, as well as in a few avian orders. This review highlights some of the characteristics, from the whole organism down to cellular and molecular aspects, associated with the torpor phenotype. The first part of this review focuses on the specific metabolic adaptations of torpor, as it is used by many species from temperate zones. This notably includes the endocrine changes involved in fat- and food-storing hibernating species, explaining biomedical implications of MR depression. We further compare adaptive mechanisms occurring in opportunistic vs. seasonal heterotherms, such as tropical and sub-tropical species. Such comparisons bring new insights into the metabolic origins of hibernation among tropical species, including resistance mechanisms to oxidative stress. The second section of this review emphasizes the mechanisms enabling heterotherms to protect their key organs against potential threats, such as reactive oxygen species, associated with the torpid state. We notably address the mechanisms of cellular rehabilitation and protection during torpor and hibernation, with an emphasis on the brain, a central organ requiring protection during torpor and recovery. Also, a special focus is given to the role of an ubiquitous and readily-diffusing molecule, hydrogen sulfide (H2S), in protecting against ischemia-reperfusion damage in various organs over the torpor-arousal cycle and during the torpid state. We conclude that (i) the flexibility of torpor use as an adaptive strategy enables different heterothermic species to substantially suppress their energy needs during periods of severely reduced food availability, (ii) the torpor phenotype implies marked metabolic adaptations from the whole organism down to cellular and molecular levels, and (iii) the torpid state is associated with highly efficient rehabilitation and protective mechanisms ensuring the continuity of proper bodily functions. Comparison of mechanisms in monotremes and marsupials is warranted for understanding the origin and evolution of mammalian torpor.

Survival is reduced when endogenous period deviates from 24 h in a non-human primate, supporting the circadian resonance theory

Circadian rhythms are ubiquitous attributes across living organisms and allow the coordination of internal biological functions with optimal phases of the environment, suggesting a significant adaptive advantage. The endogenous period called tau lies close to 24 h and is thought to be implicated in individuals' fitness: according to the circadian resonance theory, fitness is reduced when tau gets far from 24 h. In this study, we measured the endogenous period of 142 mouse lemurs (Microcebus murinus), and analyzed how it is related to their survival. We found different effects according to sex and season. No impact of tau on mortality was found in females. However, in males, the deviation of tau from 24 h substantially correlates with an increase in mortality, particularly during the inactive season (winter). These results, comparable to other observations in mice or drosophila, show that captive gray mouse lemurs enjoy better fitness when their circadian period closely matches the environmental periodicity. In addition to their deep implications in health and aging research, these results raise further ecological and evolutionary issues regarding the relationships between fitness and circadian clock.

Contributions of Nonhuman Primates to Research on Aging

Aging is the biological process of declining physiologic function associated with increasing mortality rate during advancing age. Humans and higher nonhuman primates exhibit unusually longer average life spans as compared with mammals of similar body mass. Furthermore, the population of humans worldwide is growing older as a result of improvements in public health, social services, and health care systems. Comparative studies among a wide range of organisms that include nonhuman primates contribute greatly to our understanding about the basic mechanisms of aging. Based on their genetic and physiologic relatedness to humans, nonhuman primates are especially important for better understanding processes of aging unique to primates, as well as for testing intervention strategies to improve healthy aging and to treat diseases and disabilities in older people. Rhesus and cynomolgus macaques are the predominant monkeys used in studies on aging, but research with lower nonhuman primate species is increasing. One of the priority topics of research about aging in nonhuman primates involves neurologic changes associated with cognitive decline and neurodegenerative diseases. Additional areas of research include osteoporosis, reproductive decline, caloric restriction, and their mimetics, as well as immune senescence and chronic inflammation that affect vaccine efficacy and resistance to infections and cancer. The purpose of this review is to highlight the findings from nonhuman primate research that contribute to our understanding about aging and health span in humans.

When to initiate torpor use? Food availability times the transition to winter phenotype in a tropical heterotherm

Timing of winter phenotype expression determines individual chances of survival until the next reproductive season. Environmental cues triggering this seasonal phenotypic transition have rarely been investigated, although they play a central role in the compensation of climatic fluctuations via plastic phenotypic adjustments. Initiation of winter daily torpor use-a widespread energy-saving phenotype-could be primarily timed according to anticipatory seasonal cues (anticipatory cues hypothesis), or flexibly fine-tuned according to actual energy availability (food shortage hypothesis). We conducted a food supplementation experiment on wild heterothermic primates (grey mouse lemurs, Microcebus murinus) at the transition to the food-limited dry season, i.e. the austral winter. As expected under the food shortage hypothesis, food-supplemented individuals postponed the seasonal transition to normal torpor use by 1-2 month(s), spent four times less torpid, and exhibited minimal skin temperature 6 °C higher than control animals. This study provides the first in situ experimental evidence that food availability, rather than abiotic cues, times the launching of torpor use. Fine-tuning of the timing of seasonal phenotypic transitions according to actual food shortage should provide heterotherms with a flexible adaptive mechanism to survive unexpected environmental fluctuations.

[Is the biological clock central to the aging process? Studies in a non-human primate]

The ability of organisms to adapt to their environment during aging is altered. Age-related disorders in Human include disturbances of biological rhythms, especially sleep-wake rhythms alterations, and perturbations of body temperature and hormone secretion. The alteration of biological rhythms with age leads to major health consequences, particularly due to the alteration of sleep-wake rhythms that causes a strong alteration of the general condition. The study of these changes is therefore a major health issue and requires the use of appropriate animal models such as the grey mouse lemur (Microcebus murinus), a small Madagascar primate with very pronounced biological rhythms.

Bats of a gender flock together: sexual segregation in a subtropical bat

Competition has long been assumed to be a major driver in regulating ecological communities. Intra-specific competition is considered to be maximal as members of the same species use the same ecological niches in a similar way. Many species of animals exhibit great physiological, behavioral, and morphological differences between sexes (sexual dimorphism). Here we report an extreme geographical segregation between the sexes in the greater mouse-tailed bat (Rhinopoma microphyllum). To gain insight into the driving mechanisms of sexual segregation outside the mating season, we collected and integrated environmental, behavioral, physiological, and spatial information. We found that both sexes choose roosts with similar characteristics and the same food type, but use different habitats for different durations. Males forage around cliffs at higher and cooler elevations while females forage in lowlands around a river delta. We suggest that it is their different physiological and social needs, and not competition, that drives sexual segregation in this species.

The grey mouse lemur: a non-human primate model for ageing studies

The use of non-human primate models is required to understand the ageing process and evaluate new therapies against age-associated pathologies. The present article summarizes all the contributions of the grey mouse lemur Microcebus murinus, a small nocturnal prosimian primate, to the understanding of the mechanisms of ageing. Results from studies of both healthy and pathological ageing research on the grey mouse lemur demonstrated that this animal is a unique model to study age-dependent changes in endocrine systems, biological rhythms, thermoregulation, sensorial, cerebral and cognitive functions.