Selected publications:

SCHMID, J. & GANZHORN, J.U. (1996): Resting metabolic rates of Lepilemur ruficaudatus.. American Journal of Primatologie 38:169-174.
SCHMID, J. (1998): Tree Holes used for Resting by the Grey Mouse Lemur (Microcebus murinus) in Madagascar: Insulation Capacities and Energetic Consequences. International Journal of Primatology 19:797-810.
SCHMID, J. & KAPPELER, P.M. (1998): Fluctuating sexual dimorphism and differential hibernation by sex in a primate, the gray mouse lemur (Microcebus murinus). Behavioral Ecology and Sociobiology 43:125-132.
SCHMID, J. (1999): Sex-specific differences in activity patterns and fattening in the gray mouse lemur (Microcebus murinus) in Madagascar. Journal of Mammalogy 80(3):749-757.
SCHMID, J. (2000): Conservation Planning in the Mantady-Zahamena Corridor, Madagascar: Rapid Assessment Program (RAP). In Isolated Vertebrate Communities in the Tropics. (Edited by Rheinwald G.), pp. 285-296. Bonn. Zool. Monogr. 46.
SCHMID, J. (2000): Daily torpor in the gray mouse lemur (Microcebus murinus) in Madagascar: Energetic consequences and biological significance. Oecologia 123:175-183.
SCHMID, J., RUFUS, T. & HELDMAIER, G. (2000): Metabolism and temperature regulation during daily torpor in the smallest primate, the pygmy mouse lemur (Microcebus myoxinus) in Madagascar. Journal of Comparative Physiology B 170: 59-68.
SCHMID, J. & Speakman, J. R. (2000): Daily energy expenditure of the grey mouse lemur (Microcebus murinus): a small primate that uses torpor. Journal of Comparative Physiology B 170:633-641.

Abstracts:

SCHMID, J. & GANZHORN, J.U. (1996): Resting metabolic rates of Lepilemur ruficaudatus.
Abstract: Seventeen sportive lemurs (Lepilemur ruficaudatus) were captured in a dry, deciduous forest in western Madagascar, and the resting metabolic rates were measured. According to the data, Lepilemur ruficaudatus has the lowest resting metabolic rate of any primate and any mammalian folivore recorded so far.

SCHMID, J. (1998): Tree Holes used for Resting by the Grey Mouse Lemur (Microcebus murinus) in Madagascar: Insulation Capacities and Energetic Consequences.
Abstract: The insulation capacity of tree holes used by grey mouse lemurs (Microcebus murinus) was studied in a primary dry deciduous forest in western Madagascar, during the cool dry season. Tree holes had an insulating effect and fluctuations of air temperatures were less extreme inside the holes than outside. The insulation capacity of the tree holes peaked between 0800 - 1100 h, when ambient temperatures ranged between 25 - 30°C. To compare between different tree holes, the mean difference between the internal temperature (Ti) and the external temperature (Te) was calculated for each tree hole. Thus, large differences indicate good insulation capacities. The mean difference of tree holes in living trees was significantly larger than of tree holes in dead trees, which shows that insulation in living trees is more effective. During the dry season, insulation capacity of tree holes in living trees decreased and were lowest in July, whereas the insulation capacity of holes in dead trees remained approximately constant. Physiological studies under natural temperature and light conditions in M. murinus revealed that daily torpor saves around 40% of the daily energy expenditure compared to normothermia. However, torpor can only be maintained up to the threshold body and ambient temperature of 28°C at which M. murinus have to terminate torpor actively. By occupying insulating tree holes, mouse lemurs may stay longer in torpor. This increase their daily energy savings by an extra 5%.

SCHMID, J. & KAPPELER, P.M. (1998): Fluctuating sexual dimorphism and differential hibernation by sex in a primate, the gray mouse lemur (Microcebus murinus).
Abstract: The aim of this study was to investigate reproductive strategies and their consequences in gray mouse lemurs (Microcebus murinus), small solitary nocturnal primates endemic to Madagascar. Previous reports of sexual dimorphism in favor of males and females, respectively, a high potential for sperm competition and pheromonal suppression of mating activity among captive males, led us to investigate mechanisms of intrasexual competition in a wild population. Based on 3 years of mark-recapture data, we demonstrate that sexual dimorphism in this species fluctuated annually as a result of independent changes in male and female body mass. Male body mass increased significantly prior to the short annual mating season. Because their testes increased by 100% in the same period and because their canines are not larger than those of females, we suggest that large male size may be advantageous in searching for estrous females and in enabling them to sustain periods of short-term torpor. In contrast, to reports from captive colonies, we found no evidence for two morphologically distinct classes of males. Finally, we also show that most adult males are active throughout the cool dry season that precedes the mating months. This is in contrast to other solitary hibernating mammals, where males typically emerge 1-2 weeks before females. Thus, this first extended field study of M. murinus clarified previous conflicting reports on sexual dimorphism and male reproductive strategies in this primitve primate by showing that their apparent deviation from predictions of sexual selection theory is brought about by specific environmental conditions which result in sex-specific life history tactics not previously described for mammals. A general conclusion is that sexual selection can operate more strongly on males without resulting in sexual dimorphism because of independent selection on the same traits in females.

SCHMID, J. (1999): Sex-specific differences in activity patterns and fattening in the gray mouse lemur (Microcebus murinus) in Madagascar.
Abstract: The gray mouse lemur (Microcebus murinus) is a small, nocturnal primate endemic to Madagascar and has evolved specific activity patterns to survive the dry season, a period of low food availability and low ambient temperatures. These patterns are sex-specific. I determined seasonal fluctuations of body mass and tail circumference in M. murinus under natural conditions in a dry deciduous forest of western Madagascar in 1994--1995. I compared those variables were among individuals during different activity patterns. Based on mark-recapture and monitoring of sleeping sites, 73.1% of adult females but only 18.9% of adult males remained inactive for the several weeks to 4--5 months throughout the cool dry season. Inactive females stored fat before the onset of the inactive phase and lost 31.7% of their mass during the dry winter, but inactive males hardly stored fat, and their body mass did not change between onset and end of the period of inactivity. Duration of inactivity was significantly longer for females than males, due to earlier emergence of males. At the end of inactivity and activity periods, respectively, body masses and tail circumferences did not differ between inactive and active males and females. Thus, M. murinus has evolved two different strategies to survive the cool dry season: being generally active but combined with daily torpor of <24 h, and remaining inactive for days to several weeks, which might be associated with prolonged bouts of torpor.

SCHMID, J. (2000): Conservation Planning in the Mantady-Zahamena Corridor, Madagascar: Rapid Assessment Program (RAP).
Abstract: Conservation International (CI) conducted a Rapid Assessment Program (RAP) of the biodiversity of the humid forest within the Mantady-Zahamena corridor in Madagascar. The RAP methodology is designed to quickly provide information needed to catalyze conservation activity and improve regional and national biodiversity protection. The Mantady-Zahamena corridor links the protected areas of the Parc National (PN) de Mantady and the Réserve Naturelle Intégrale (RNI) de Zahamena. This region is of particular interest and importance since not only does it comprise of primary and secondary lowland rainforest as well as moist montane forest, but it also connects two protected areas in the north and south. Survey work was divided into two expeditions (expedition 1: November 7 - December 14, 1998; expedition 2: January 15 - 28, 1999). Four camps were placed in different classified forests, and one site was placed in PN de Mantady. At each site, presence and relative abundance of lemur species were estimated using the line transect method. A total of eleven lemur species (four diurnal, two cathemeral, and five nocturnal species) were found in the corridor, including the Aye-Aye, Daubentonia madagascariensis. Forest clearance and settlement in the entire corridor are the major threats and might explain relatively low densities and absence of certain lemur species like Propithecus diadema diadema (Site 1) and Varecia variegata variegata (Site 1 and 5). Exceptional biodiversity cannot be maintained in areas where genetic exchange is impossible due to geographic isolation and disconnection of forest blocks. The most urgent and actually basic need is to stop forest fragmentation and habitat destruction, with exceptionally high conservation priorities on remaining lowland forests.

SCHMID, J. (2000): Daily torpor in the gray mouse lemur (Microcebus murinus) in Madagascar: Energetic consequences and biological significance.
Abstract: Patterns and energetic consequences of spontaneous daily torpor were measured in the gray mouse lemur (Microcebus murinus) under natural conditions of ambient temperature and photoperiod in a dry deciduous forest in western Madagascar. Over a period of two consecutive dry seasons, oxygen consumption (VO2) and body temperature (Tb) were measured on ten individuals kept in outdoor enclosures. In all animals, spontaneous daily torpor occurred on a daily basis with torpor bouts lasting from 3.6 to 17.6 hours, with a mean torpor bout duration of 9.3 hours. On average, body temperatures in torpor were 17.3 ± 4.9 °C with a recorded minimum value of 7.8 °C. Torpor was not restricted to the mouse lemurs´ diurnal resting phase, and entries occurred throughout the night and arousals mainly around midday, which coincides with the daily ambient temperature maximum. Arousal from torpor was a two-phase process with a first passive, exogenous heating where the Tb of animals increased from the torpor Tb minimum to a mean value of 27.1 °C before the second, endogenous heat production commenced to further raise the Tb to normothermic values. Metabolic rate during torpor (28.6 ± 13.2 ml O2 * h-1) was significantly reduced by ca. 76 % compared to resting metabolic rate (132.6 ± 50.5 ml O2 * h-1). On average for all M. murinus individuals measured, hypometabolism during daily torpor reduced daily energy expenditure by ca. 38 %. In conclusion, all these energy conserving mechanisms with passive exogenous heating during arousal from torpor, low minimum torpor Tbs, extended torpor bouts into the activity phase of the nocturnal mouse lemurs, comprise an important and highly adapted mechanism to minimize energetic costs as a response to the unfavorable environmental conditions and may play a crucial role for individual fitness.

SCHMID, J., RUFUS, T. & HELDMAIER, G. (2000): Metabolism and temperature regulation during daily torpor in the smallest primate, the pygmy mouse lemur (Microcebus myoxinus) in Madagascar.
Abstract: Thermoregulation, energetics and patterns of torpor in the pygmy mouse lemur, Microcebus myoxinus, were investigated under natural conditions of photoperiod and temperature in the Kirindy/CFPF Forest in western Madagascar. M. myoxinus entered torpor spontaneously during the cool dry season when food availability was low. Torpor only occurred on a daily basis and torpor bout duration was on average 9.6 h, and ranged from 4.6 h to 19.2 h. Metabolic rates (MRs) during torpor were reduced to about 86% of the normothermic value. Minimum body temperature (Tb) during daily torpor was 6.8 °C at an ambient temperature (Ta) of 6.3°C. Entry into torpor occurred randomly between 20:00 and 06:20 hours, whereas arousals from torpor were clustered around 13:00 hours within a narrow time window of less than 4 h. Arousal from torpor was a two-step process with a first passive climb of Tb to a mean of 27°C, carried by the daily increase of Ta when oxygen consumption (VO2) remained more-or-less constant, followed by a second active increase of VO2 to further raise the Tb to normothermic values. In conclusion, daily Tb rhythms in M. myoxinus further reduce the energetic costs of daily torpor seen in other species: 1) they extend to unusually low Tbs and consequently low MRs in torpor, and 2) they employ passive warming to reduce the energetic costs of arousal. Thus, these energy conserving adaptations may represent an important energetic aid to the pygmy mouse lemur and help to promote their individual fitness.

SCHMID, J. & Speakman, J. R. (2000): Daily energy expenditure of the grey mouse lemur (Microcebus murinus): a small primate that uses torpor.
Abstract: We aimed to investigate the pattern of utilisation of torpor and its impact on energy budgets in free-living grey mouse lemurs (Microcebus murinus), a small nocturnal primate endemic to Madagascar. We measured daily energy expenditure (DEE) and water turnover using doubly labelled water, and we used temperature sensitive radio collars to measure skin temperature (Tsk) and home range. Our results showed that male and female mouse lemurs in the wild enter torpor spontaneously over a wide range of ambient temperatures (Ta) during the dry season, but not during the rainy season. Mouse lemurs remained torpid between 1.7 - 8.9 h with a daily mean of 3.4 h, and their Tsks fell to a minimum of 18.8 °C. Mean home ranges of mouse lemurs which remained normothermic were similar in the rainy and dry season. During the dry season, mean home range of mouse lemurs showing daily torpor was significantly smaller than that of animals remaining normothermic. The DEE of M. murinus remaining normothermic in the rainy season (122 ± 65.4 kJ d-1) was about the same of that of normothermic mouse lemurs in the dry season (115.5 ± 27.3 kJ d-1). During the dry season, the mean DEE of M. murinus that utilised daily torpor was 103.4 kJ ± 32.7 kJ d-1 which is not significantly different from the mean DEE of animals remaining normothermic. We found that DEE of mouse lemurs using daily torpor was significantly correlated with the mean temperature difference between Tsk and Ta (r2 = 0.37) and with torpor bout length (r2 = 0.46), while none of these factors explained significant amounts of variation in the DEE of the mouse lemurs remaining normothermic. The mean water flux rate of mouse lemurs using daily torpor (13.0 ± 4.1 ml d-1) was significantly lower than that of mouse lemurs remaining normothermic (19.4 ± 3.8 ml d-1), suggesting the lemurs conserve water by entering torpor. Thus, this first study on the energy budget of free-ranging M. murnius demonstrates that torpor may not only reflect its impact on the daily energy demands, but involve wider adaptive implications such as water requirements.

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