Dwarf Lemur Cheirogaleus Medius Research Articles

Hibernation in a primate: does sleep occur?

During hibernation, critical physiological processes are downregulated and thermogenically induced arousals are presumably needed periodically to fulfil those physiological demands. Among the processes incompatible with a hypome tabolic state is sleep. However, one hibernating primate, the dwarf lemur Cheirogaleus medius, experiences rapid eye movement (REM)-like states during hibernation, whenever passively reaching temperatures above 30°C, as occurs when it hibernates in poorly insulated tree hollows under tropical conditions. Here, we report electroencephalographic (EEG) recordings, temperature data and metabolic rates from two related species (C. crossleyi and C. sibreei), inhabiting high-altitude rainforests and hibernating underground, conditions that mirror, to some extent, those experienced by temperate hibernators. We compared the physiology of hibernation and spontaneous arousals in these animals to C. medius, as well as the much more distantly related non-primate hibernators, such as Arctic, golden-mantled and European ground squirrels. We observed a number of commonalities with non-primate temperate hibernators including: (i) monotonous ultra-low voltage EEG during torpor bouts in these relatively cold-weather hibernators, (ii) the absence of sleep during torpor bouts, (iii) the occurrence of spontaneous arousals out of torpor, during which sleep regularly occurred, (iv) relatively high early EEG non-REM during the arousal, and (v) a gradual transition to the torpid EEG state from non-REM sleep. Unlike C. medius, our study species did not display sleep-like states during torpor bouts, but instead exclusively exhibited them during arousals. During these short euthermic periods, non-REM as well as REM sleep-like stages were observed. Differences observed between these two species and their close relative, C. medius, for which data have been published, presumably reflect differences in hibernaculum temperature.

Striking longevity in a hibernating lemur

AbstractBody mass correlates with life span across mammals; larger species tend to live longer than small ones. There are, however, exceptions to this pattern. One metabolic strategy that has been linked to increased longevity is hibernation; that is, small‐bodied hibernating mammals live longer than expected based on their size alone. Hibernation may be beneficial in seasonal and unpredictable habitats because individuals can reduce metabolic rates to conserve energy in times of resource scarcity. On the downside, the extended periods of dormancy hibernating mammals undergo afford them fewer reproductive opportunities per year compared with their similarly sized non‐hibernating relatives. One strategy to compensate for a reduced reproductive rate is to extend reproductive life span. Increased longevity may also be expected if hibernators possess cellular machinery resilient to metabolic stress, which is generally associated with aging. Here we present data on life span and other life‐history variables for four small‐bodied strepsirrhine primates: (1) the fat‐tailed dwarf lemur Cheirogaleus medius, a hibernator; (2) the gray mouse lemur Microcebus murinus, a closely related species, which opportunistically expresses torpor and/or hibernation; (3) the Northern giant mouse lemur Mirza zaza another closely related species, which does not hibernate, but may employ daily torpor; (4) the bushbaby Galago moholi, a non‐lemur, non‐hibernating strepsirrhine that employs torpor only as an emergency response to harsh conditions. We analyzed newly compiled captive data from the developing Duke Lemur Center Database, and report that dwarf lemurs live significantly longer, reproduce longer and show later incidences of both morphologic and reproductive senescence than the other species analyzed. That these correlations hold in captive populations with no predation indicates that intrinsic biologic effects must play some role.

Topographical localization of lipofuscin pigment in the brain of the aged fat‐tailed dwarf lemur Cheirogaleus Medius and grey lesser mouse lemur Microcebus Murinus: Comparison to iron localization

Topographical localization of lipofuscin pigment in the brain of the aged fat‐tailed dwarf lemur Cheirogaleus Medius and grey lesser mouse lemur Microcebus Murinus: Comparison to iron localization

Monogamy as a Rule Rather than Exception in Nocturnal Lemurs: the Case of the Fat‐tailed Dwarf Lemur, Cheirogaleus medius

According to present hypotheses on the evolution of life history traits and social systems in Malagasy lemurs, nocturnality and infant parking are associated with a solitary lifestyle and a polygynous mating system. However, theoretically extreme seasonality of reproduction could limit the number of females that can be monopolized by a given male and thus hinder the evolution of polygyny. The aim of this ongoing study is to test these contrasting expectations by looking at the social and mating system of the fat‐tailed dwarf lemur Cheirogaleus medius. This species hibernates for up to 7 mo, so that time for breeding and raising offspring is extremely limited.A mark‐recapture study in western Madagascar was combined with observations and radio‐tracking of 36 individuals during the rainy seasons from 1995 to 1998. According to these data, fat‐tailed dwarf lemurs live in permanent sleeping groups consisting of a male and a female (n = 8) or one male and two females (n = 1). One or two offspring from the previous year were frequently observed to sleep together with an adult pair. Members of each sleeping group were the exclusive users of their nest holes and home ranges. During the birth season, males and females took turns at baby‐sitting their offspring. Females without paternal help were unable to raise their offspring successfully. Since females did not exhibit oestrus synchrony, the ultimate selective factor favouring pair‐living could be obligate paternal investment. The results, together with the lack of sexual size dimorphism and relatively small testis size, suggest that the fat‐tailed dwarf lemur lives in family groups with a monogamous mating system. A review of the mating systems of nocturnal lemurs shows that monogamy appears to be the rule rather the exception.

Topographical localization of iron in brains of the aged fat‐tailed dwarf lemur Cheirogaleus medius and gray lesser mouse lemur Microcebus murinus

Iron deposits in the human brain are characteristic of normal aging but have also been implicated in various neurodegenerative diseases. Among nonhuman primates, strepsirhines are of particular interest because hemosiderosis has been consistently observed in captive aged animals. In particular, the cheirogaleids, because of their small size, rapid maturity, fecundity, and relatively short life expectancy, are a useful model system for the study of normal and pathological cerebral aging. This study was therefore undertaken to explore iron localization in the brain of aged cheirogaleids (mouse and dwarf lemurs) with histochemistry and magnetic resonance microscopy. Results obtained with both techniques were comparable. There was no difference between old animals in the two species. The young animals (3 years old) showed no iron deposits. In the old animals (8–15 years old), iron pigments were mainly localized in the globus pallidus, the substantia nigra, the neocortical and cerebellar white matter, and anterior forebrain structures, including the nucleus basalis of Meynert. This distribution agrees with previous findings in monkeys and humans. In addition, we observed iron in the thalamus of these aged nonhuman primates. Microscopic NMR images clearly reveal many features seen with the histochemical procedure, and magnetic resonance microscopy is a powerful method for visualizing age-related changes in brain iron. Am. J. Primatol. 45:291–299, 1998. © 1998 Wiley-Liss, Inc.