An empirical estimate of the generation time of mouse lemurs

The generation time of organisms drives the rate of change in populations and across evolutionary times. In long‐lived species, generation time should also account for overlapping generations, and the average age of parents has been proposed as a best approximation under these conditions. This study uses this definition to estimate the generation time of a widely studied small primate, Microcebus murinus, based on parentage data generated for a free‐living population over a 6‐year period in northwestern Madagascar. The average age of parents was calculated separately for mothers and fathers of three different offspring cohorts that differed in the degree of demographic uncertainty. In addition, adult survival rates were calculated for males and females based on long‐term capture data from the same population to estimate the possible upper limits of generation time. Adult survival was low with only 44% of adult females and 38% of adult males being recaptured at the beginning of their second breeding season. The average age of mothers was 1.56–1.91 years, pointing toward a 2‐year female generation time due to the high proportion of 1‐year old mothers in all three cohorts. Female generation time estimates were fairly stable across the three offspring cohorts. In contrast, the average age of fathers differed by more than 1 year from the first to the third offspring cohort (1.71–2.83 years) pointing toward a 3‐year generation time, but also suggesting a higher degree of demographic uncertainty in the early years of the study. For future modeling purposes, we, therefore, propose to use the average, 2.5 years, of male and female values as new estimate for the generation time of mouse lemurs.     

臭鼠的种群年龄结构研究

１９８６年１月至１９９３年１２月,作者在浙江萧山围垦农区采用体重法将臭　种群分为５个年龄组。雄体：Ⅰ．幼年组（体重≤３０８）、Ⅱ．亚成年组（体重＞３０９,≤４０ｇ）、Ⅲ．成年１组（体重＞４０ｇ,≤５２ｇ）、Ⅳ．成年ＩＩ组（体重＞５２８,≤６４８）、Ⅴ．老年组（体重＞６４ｇ）;雌体：幼年组（体重≤２４ｇ）,Ⅱ．亚成年组（体重＞２４ｇ;≤３６ｇ）．Ⅲ．成年Ⅰ组（体重＞３６９,≤４６ｇ）,Ⅳ．成年Ⅱ组（体重＞４６８,≤５４ｇ）,Ⅴ．老年组（体重＞５４ｇ）。各年龄组的繁殖特性存在差异。种群以成年Ⅰ组为主,但其种群的年龄结构存在有性别差异,雄性种群以成年Ⅰ组、成年Ⅱ组和老年组为主,雌性种群以亚成年组和成年Ⅰ组为主。种群的年龄结构存在季节性变化。在室内,雄性在春季和冬季以成年Ⅱ组为主,夏季和秋季以老年组为主;在室外春季、秋季和冬季均以成年Ⅰ组为主,夏季则以成年Ⅱ组为主。室内雌性在各季节均以成年Ⅰ组为主,而在室外春季和冬季以亚成年组为主,夏季和秋季以成年Ⅰ组为主。其种群年龄结构存在有年变化。     

Serotonergic ligand binding in aging brain of experimental animals

Although the use of aging expeimental animals for studying serotonergic neuronal changes is limited because of species differences, cholinergic neuronal deterioration does appear to be a feature common to mammalian aging brains. In the present study, a recently introduced experimental animal, Suncus murinus (house musk shrew, an insectivore classified as being at the stem of the mammalian phylogenic tree) which in certain physiological characteristics is more closely related to the primate than is the rat, was used as an experimental animal model for serotonergic neuronal deterioration in aging brain. We examined the changes in binding to the membrane fraction of aging brain cortex of the experimental animals Suncus and Fischer rat of the serotonergic ligands, 5-HT, imipramine, and 8-OH-DPAT. Morphological study of the brain stem including the Nucleus raphae by immunohistochemical staining demonstrated that in Suncus all the serotonergic ligands had decreasing affinity to the membrane of aging brain; binding of 8-OH-DPAT and imipramine decreased to a greater extent than that of 5-HT. In contrast, the aging rat brain showed no appreciable change in the binding of serotonergic ligands.     

臭鼩染色体的研究

本文采用骨髓染色体制片法,对捕自我国浙江萧山市的臭鼩进行了组型、G-带、C-带和核仁组织区银染的观察分析。结果表明,我国臭鼩染色体数目为2n=40,组型为8(m)+2(sm)+10(st)+18(t),性染色体为,(?):X(m或sm),Y(m或sm);♀:XX(m或sm)。G-带较为丰富,每一对染色体都有其特定的带型,较易于辨别与配对。在C-带方前,4对中间着丝粒染色体与5对亚端着丝粒染色体均具有不同程度的着丝粒带,1对亚中着丝粒染色体与9对端着丝粒染色体缺乏C-带物质,性染色体具丰富的远端带及中间带.银染的结果显示,第5、12和13对染色体具银染物质。     

Effect of Aging on Circadian Activity in Gray Mouse Lemurs

Microcebus murinus s a very photoperiod-dependent primate with a potentially extended longevity (13 years). Reduction of artificial seasonal cycles allows acceleration of the aging process. Under these conditions, age is defined according to the number of seasonal cycles. We conducted experiments in order to assess the effects of aging upon (1) the main parameters (period: duration: ) of the circadian activity–rest rhythm; and (2) the plasticity of the response to light, which is the main entraining factor of the internal clock. We studied the evolution of and through two types of experiments: a transverse one comparing 36 males of various ages (1–13 seasonal cycles) and a longitudinal one following 2 pairs of males from the same litter (one from each pair was maintained under natural cycle while the other was submitted to a shortened cycle) over 54 months. Results from transverse experiments demonstrated no statistical difference in and with age except in 4 senescent (>10 cycles) subjects in which these two parameters were decreased. Longitudinal experiments confirmed this tendency. The plasticity of responses to light, resynchronization after a shift of the day–night cycle, or shift of activity onset after presentation of a light pulse at various circadian times was unaffected by aging. Taken together, the data demonstrate that the parameters of the circadian activity–rest rhythm remain stable over a long span of life and/or that light remains a powerful entraining parameter even in very old individuals.     

First evidence for relocation of stationary food resources during foraging in a strepsirhine primate (Microcebus murinus)

Field observations suggest that the diet of the Malagasy gray mouse lemur consists not only of non-stationary animal prey (invertebrates or small vertebrates), but also of stationary food resources such as gum or homopteran larvae secretions (HLS). We studied the foraging behavior of five mouse lemurs radiotelemetrically, each during six consecutive nights in the dry season, to explore to which extent they use these food resources and whether there is evidence for their relocation. We found that animals used all three different food categories. Mouse lemurs fed on gums and spent 68.5% (range 20.1-99.7%) of their feeding time eating this item. They were observed eating HLS in 8.4% (range 0-71.5%) of the feeding time and consuming small animals in 8.4% (range 0.3-26%) of their feeding time. The animals relocated stationary feeding sites significantly more frequently than non-stationary ones. They revisited the relocated stationary food sites about five times over the six nights. Furthermore, departure directions when leaving the sleeping site at dusk were not randomly distributed but showed a preferred orientation. Altogether, we provided first evidence for the relocation of stationary food resources in nature and thereby for the potential significance of spatial memory during foraging in a strepsirhine primate.     

Dynamics of Estrous Synchrony in Captive Gray Mouse Lemurs (Microcebus murinus)

Estrous synchrony in seasonal breeders can in principle be based on and shaped by environmental, internal, and/or social cues. We analyzed the dynamics of estrous synchrony for the first time in a seasonal, nocturnal primate species, the gray mouse lemur (Microcebus murinus). We compared successive estrous cycles and different levels of spatial proximity over two reproductive seasons in a captive population in order to identify possible social influences on estrous synchrony. The females exhibited a marked estrous synchrony at the beginning of each reproductive season, but we found no indication of a process of socially induced synchronization among them. Females housed in the same cage/room were not more strongly synchronized than females housed in different cages/rooms. Moreover, cycles desynchronized from the first to the second estrus of the season. Estrous cycle length did not depend on age, parity, or social housing conditions, but instead mainly on the individuality of the lemurs. This individuality, shown for the first time in a nocturnal primate species, is likely to be based on an endogenous rhythm with a genetic basis. We discuss possible social advantages, e.g., communal rearing, and disadvantages, e.g., mate choice and female-female competition, of estrous synchrony for nocturnal primates living in a dispersed individualized social network, and propose that a moderate flexibility within the individual cycle lengths probably enables the females to compromise between the different socioecological pressures.     

Relevance of Studbook Data to the Successful Captive Management of Grey Mouse Lemurs

This paper illustrates the importance of a well-managed studbook to the long-term captive management of an exotic species: Microcebus murinus. Analysis of the studbook provides an insight into the genetic diversity and demographic stability of the registered population. It also yields invaluable data on patterns of fertility and mortality occurring under the prevalent management conditions. This information is equally relevant to research and to captive management. I established a European studbook for the grey mouse lemur in 1994. It contains data on individuals in zoos and research establishments. Analyses of the data do not bode well for future of the European mouse lemur population. Although the number of individuals would seem to be sufficient to form a sound basis for future management, the population has inadequate genetic variability. Furthermore, inbreeding also seems to have had a negative impact on the reproductive output of the population. Thus, immediate action needs to be taken if a viable mouse lemur population is to be maintained in Europe.