Taxonomic Revision of Mouse Lemurs (Microcebus) in the Western Portions of Madagascar

The genus Microcebus (mouse lemurs) are the smallest extant primates. Until recently, they were considered to comprise two different species: Microcebus murinus, confined largely to dry forests on the western portion of Madagascar, and M. rufus, occurring in humid forest formations of eastern Madagascar. Specimens and recent field observations document rufous individuals in the west. However, the current taxonomy is entangled due to a lack of comparative material to quantify intrapopulation and intraspecific morphological variation. On the basis of recently collected specimens of Microcebus from 12 localities in portions of western Madagascar, from Ankarana in the north to Beza Mahafaly in the south, we present a revision using external, cranial, and dental characters. We recognize seven species of Microcebus from western Madagascar. We name and describe 3 spp., resurrect a previously synonymized species, and amend diagnoses for Microcebus murinus (J. F. Miller, 1777), M. myoxinus Peters, 1852, and M. ravelobensis Zimmermann et al., 1998.     

Social System of <Emphasis Type="Italic">Microcebus berthae</Emphasis>, the World’s Smallest Primate

Our goal was to provide a first characterization of the social system of pygmy mouse lemurs (Microcebus berthae), the worlds smallest primate species. During a 4-mo field study of 12 females and 27 males, we combined capture-recapture and morphometric data with detailed behavioral observations of individually marked subjects and genetic paternity analyses of a population in Kirindy Forest, western Madagascar. We describe the social organization of Microcebus berthae as a solitary forager living in an individualized neighborhood system characterized by extensive intra- and intersexual home range overlap of adult individuals within a male-biased population. Male and female pygmy mouse lemurs inhabited home ranges (males: 4.9 ha; females: 2.5 ha) that are more than twice as large as those of sympatric Microcebus murinus. On average, pygmy mouse lemurs of both sexes spent about half of the days sleeping alone. Preliminary analysis of genetic population structure suggests female philopatry and male dispersal. Sleeping associations of variable composition that consisted not preferentially of close relatives and proximity during part of the nightly activity contributed together with regular social interactions to the maintenance of a social network. The spatial distribution pattern of adult males and females, the absence of sexual size dimorphism, relatively large male testicular volume and moderate female estrous synchrony suggest a promiscuous mating system with a high potential for scramble competition. In general, there are many similarities between the social system of Microcebus berthae and those of other Microcebus spp. However, striking differences with sympatric gray mouse lemurs (Microcebus murinus) in female home range size, dispersion and sleeping behavior indicate the existence of species-specific socioecological adaptations in closely related species occupying very similar ecological niches.     

Comparative Feeding Ecology of Sympatric <Emphasis Type="Italic">Microcebus berthae and M. murinus</Emphasis>

Most Malagasy primate communities harbor a diverse assemblage of omnivorous species. The mechanisms allowing the coexistence of closely related species are poorly understood, partly because only preliminary data on the feeding ecology of most species are available. We provide an exemplary feeding ecology data set to illuminate coexistence mechanisms between sympatric gray and Madame Berthe’s mouse lemurs (Microcebus murinus, M. berthae). We studied their feeding ecology in Kirindy Forest/CFPF, a highly seasonal dry deciduous forest in western Madagascar. Between August 2002 and December 2007, we regularly (re-)captured, marked, and radiotracked females of both species. A combination of direct behavioral observations and fecal analyses revealed that both Microcebus species used fruit, arthropods, gum, insect secretions, and small vertebrates as food sources. However, Microcebus berthae and M. murinus differed in both composition and seasonal variation of their diets. Whereas the diet of Microcebus murinus varied seasonally and was generally more diverse, M. berthae relied mainly on insect secretions supplemented by animal matter. The differences were also reflected in a very narrow feeding niche of Microcebus berthae and a comparatively broad feeding niche of M. murinus. Resource use patterns of Madame Berthe’s and more so of opportunistic gray mouse lemurs broadly followed resource availability within the strongly seasonal dry forest. Feeding niche overlap between the 2 sympatric species was high, indicating that food resource usage patterns did not reflect niche partitioning, but can instead be explained by constraints due to food availability.     

Genetic and morphological diversity of mouse lemurs (Microcebus spp.) in northern Madagascar: The discovery of a putative new species?

Tropical forests harbor extremely high levels of biological diversity and are quickly disappearing. Despite the increasingly recognized high rate of habitat loss, it is expected that new species will be discovered as more effort is put to document tropical biodiversity. Exploring under‐studied regions is particularly urgent if we consider the rapid changes in habitat due to anthropogenic activities. Madagascar is known for its extraordinary biological diversity and endemicity. It is also threatened by habitat loss and fragmentation. It holds more than 100 endemic primate species (lemurs). Among these, Microcebus (mouse lemurs) is one of the more diverse genera. We sampled mouse lemurs from several sites across northern Madagascar, including forests never sampled before. We obtained morphological data from 99 Microcebus individuals; we extracted DNA from tissue samples of 42 individuals and amplified two mitochondrial loci (cytb and cox2) commonly used for species identification. Our findings update the distribution of three species (Microcebus tavaratra, Microcebus arnholdi, and Microcebus mamiratra), including a major increase in the distribution area of M. arnholdi. We also report the discovery of a new Microcebus lineage genetically related to M. arnholdi. Several complementary approaches suggest that the newly identified Microcebus lineage might correspond to a new putative species, to be confirmed or rejected with additional data. In addition, morphological analyses showed (a) clear phenotypic differences between M. tavaratra and M. arnholdi, but no clear differences between the new Microcebus lineage and the sister species M. arnholdi; and (b) a significant correlation between climatic variables and morphology, suggesting a possible relationship between species identity, morphology, and environment. By integrating morphological, climatic, genetic, and spatial data of two northern Microcebus species, we show that the spatial distribution of forest‐dwelling species may be used as a proxy to reconstruct the past spatial changes in forest cover and vegetation type.     

Daily Torpor in Free-Ranging Gray Mouse Lemurs (Microcebus murinus) in Madagascar

I aimed to determine when and under which seasonal environmental conditions gray mouse lemurs (Microcebus murinus), a small nocturnal primate species endemic to Madagascar, utilize daily torpor. Using temperature-sensitive radio collars, I measured skin temperature (T _sk ) of free-ranging mouse lemurs under natural conditions. My results showed that male and female mouse lemurs in the wild enter torpor spontaneously over a wide range of ambient temperatures (T _a ) during the dry season, but not during the rainy season. Mouse lemurs that remained normothermic had significantly lower body masses (mean: 59.7 g) than individuals that used torpor (mean: 80.2 g). Skin temperatures dropped to 20.9°C and the mean torpor bout duration is 10.3 h. The use of torpor on a given night varied among individuals, whereas the propensity for torpor did not differ significantly between males and females. I found no evidence that T _a can be used to predict whether mouse lemurs will remain normothermic or enter torpor. It appears that the most reliable indicator for the occurrence of torpor in free-ranging Microcebus murinus is time of the year, i.e., photoperiod.     

Use of Vocal Fingerprinting for Specific Discrimination of Gray (Microcebus murinus) and Rufous Mouse Lemurs (Microcebus rufus)

Advertisement calls are often important noninvasive tools for discriminating cryptic species and for assessing specific diversity and speciation patterns in nature. We investigated the contribution of these calls to uncover specific diversity in nocturnal Malagasy lemurs. We compared sexual advertisement and predator advertisement calls of two mouse lemur species, western gray and eastern rufous mouse lemurs (Microcebus murinus and M. rufus, respectively) living in two contrasting habitats (dry deciduous vs. rain forest), and analyzed them statistically. Both species emitted several highly variable whistle calls in the context of predator-avoidance. Intrapopulation variation was high and overlapped interspecific variation. Sexual advertisement calls, given in the mating context, displayed a totally distinct, species-specific acoustic structure. Whereas gray mouse lemurs produced rapidly multifrequency modulated, long trill calls, rufous mouse lemurs gave slowly frequency-modulated short chirp calls. Our results suggest specific status for gray and rufous mouse lemurs and indicate the importance of predation and social needs in shaping vocal communication.     

Seasonal changes in general activity, body mass and reproduction of two small nocturnal primates: a comparison of the golden brown mouse lemur ( Microcebus ravelobensis) in Northwestern Madagascar and the brown mouse lemur ( Microcebus rufus) in Eastern Madagascar

To investigate for the first time the relationship between contrasting patterns of seasonal changes of the environment and activity, body mass and reproduction for small nocturnal primates in nature, we compared a population of golden brown mouse lemur (Microcebus ravelobensis) in a dry deciduous forest of northwestern Madagascar and of the brown mouse lemur (Microcebus rufus) in an evergreen rain forest of eastern Madagascar. Both species live under similar photoperiodic conditions. Golden brown mouse lemurs (GBML) were active during the whole period (May to December) irrespective of changing environmental conditions. In contrast, a part of the population of brown mouse lemurs (BML) showed prolonged seasonal torpor, related to body mass during periods of short day length and low ambient temperatures. Differences between species might be due to differences in ambient temperature and food supply. Body weight and tail thickness (adipose tissue reserve) did not show prominent differences between short and long photoperiods in GBML, whereas both differ significantly in BML, suggesting species-specific differences in the photoperiodically driven control of metabolism. Both species showed a seasonal reproduction. The rate of growth and size of the testes were similar and preceded estrous onset in both species suggesting a photoperiodic control of reproduction in males. The estrous onset in females occurred earlier in GBML than in BML. Estrous females were observed over at least 4 months in the former, but in only 1 month in the latter species. Intraspecific variation of estrous onset in GBML may be explained by body mass. Interspecific variation of female reproduction indicates species-specific differences in the control of reproduction. Thus, environmentally related differences in annual rhythms between closely related small nocturnal lemurs emerged that allow them to cope with contrasting patterns of seasonal changes in their habitats.     

Different Population Dynamics of Microcebus murinus in Primary and Secondary Deciduous Dry Forests of Madagascar

The goal of this study was to identify causes for lower population densities of mouse lemurs (Microcebus murinus) in secondary than in primary dry deciduous forests of western Madagascar. Variations in the abundance of Microcebus murinus are linked to the capacity to enter energy-saving torpor during the dry season. Under natural conditions in primary forest, Microcebus murinus can maintain daily torpor (and possibly hibernation) as long as body temperatures remain below 28°C. Females are more likely to hibernate than males, resulting in skewed sex ratios of captured Microcebus murinus in the primary forest. In the secondary forest the sex ratio of subjects captured during the dry season is more balanced than in primary forest, indicating that fewer females go into torpor in secondary than in primary forest. Secondary forests have fewer large standing or fallen trees that might provide holes as shelter for Microcebus murinus. Ambient temperatures are higher in secondary than in primary forests and higher outside than inside tree holes. These high ambient temperatures might hinder the ability of Microcebus murinus to maintain torpor for prolonged periods in secondary forests. Mouse lemurs from secondary forest have lower body mass than in primary forest. The year-to-year recapture rate is zero in secondary forest and thus significantly lower than in primary forest. This indicates that survival rates are lower in secondary than in primary forests. Thus, secondary forests may be of limited value as buffer zones or even corridors for mouse lemurs.     

Habitat Utilization of Three Sympatric Cheirogaleid Lemur Species in a Littoral Rain Forest of Southeastern Madagascar

I compared the habitat utilization in 3 sympatric species of Cheirogaleidae (Microcebus murinus [81 g], Cheirogaleus medius [183 g] and Cheirogaleus major [362 g]) in a littoral rain forest in southeastern Madagascar during 3 rainy seasons. Females of promiscuous Microcebus murinus had small home ranges and the males had large overlapping home ranges. Home ranges of family groups of monogamous Cheirogaleus medius and C. major overlapped extensively. Home ranges of all 3 species overlapped completely in the study area but home range sizes differed among species and correlate positively with body masses. Male Microcebus murinus slept in open vegetation (79%) and alone (71%), whereas female M. murinus and family group members of Cheirogaleus spp. preferred communal sleeping in tree holes. There are significant interspecific differences in the choice of sleeping sites: smaller lemurs chose smaller trees and used more sleeping sites than larger lemurs did. Species also differed significantly in the vertical dimension of forest utilization: Cheirogaleus major used the upper part of the trees, C. medius used the middle parts, and Microcebus murinus used the understory during nocturnal activities. The 3 species differed mainly in vertical habitat utilization and showed vertical stratification.     

Origins,Diversity and Relationships of Lemurs

I review new evidence on origins and adaptive radiation of Malagasy lemurs, a remarkably diverse group containing 13% of living primate species. The number of recognized lemur species has increased significantly, partly due to research revealing specific subdivisions within known populations but mainly because of discovery of new populations through fieldwork. Some species feared to be extinct have also been rediscovered. Specific numbers have increased particularly in small-bodied, cryptic genera for which continued research will surely reveal even more species.Adaptative radiation of lemurs has been essentially confined to Madagascar. The high density of lemur species on that island, associated with very small geographical ranges, has major implications both for their evolutionary divergence and for conservation. Reconstructions of phylogenetic relationships among primates have been considerably enhanced by DNA sequence data. Sufficient data are now available from both nuclear and mitochondrial sequences to examine relationships among and within the major groups of living primates. Most studies have confirmed that lemurs constitute a monophyletic sister-group of the lorisiform clade and all exclude a specific relationship between cheirogaleids and lorisiforms repeatedly inferred from morphological evidence. However, some analyses indicate that the aye-aye may have branched away before the divergence between other lemurs and lorisiforms. DNA sequence analyses have also yielded a broad consensus for relationships between Eulemur, Hapalemur, Lemur and Varecia: Varecia branched away first, while Lemur is more closely related to Hapalemur than to Eulemur. As debate about phylogenetic relationships among lemurs and other primates seems to have been settled in favor of lemur monophyly (possibly excluding the aye-aye), only a single invasion of Madagascar is required; but it must still be explained how ancestral lemurs could have migrated there at an appropriate time. Separation between Madagascar and Africa was apparently complete by about 120 Ma, too far in the past for direct overland migration. A recent hypothesis suggested that uplifted land in the Mozambique Channel assisted colonization of Madagascar 26-45 Ma, seemingly agreeing with an estimated date of about 40 Ma for divergence of lemurs from other primates. However, mounting evidence suggests that divergence occurred significantly earlier. Because the earliest known fossil representatives of several modern orders of placental mammals (including primates) are dated no earlier than the early Tertiary, it is widely accepted that their divergence took place after the Cretaceous/Tertiary mass extinction. Yet the known fossil record can only yield minimum divergence times; if sampling is poor and/or biased there may be a considerable discrepancy between minimum and actual dates. There is, for example, virtually no known fossil record for lemurs in Madagascar and the earliest known representatives are subfossil lemurs, so in this case a direct reading of the fossil record would indicate that the lemurs first originated just a few thousand years ago! Examination of underestimation of times of origin because of poor sampling in the fossil record has confirmed previous suggestions that primates originated considerably earlier than generally believed. Several recent phylogenetic reconstructions based on DNA sequence data and using calibration dates derived from groups other than primates provide independent support for this inference. Overall, it now seems that primates originated at around 90 Ma rather than the 55 Ma indicated by direct reading of the known fossil record. Hence, colonization of Madagascar by lemurs would have taken place at about 80 Ma, double the date usually accepted, and should be interpreted in terms of contemporary continental relationships.     

MtDNA reveals strong genetic differentiation among geographically isolated populations of the golden brown mouse lemur, <Emphasis Type="Italic">Microcebus ravelobensis</Emphasis>

Microcebus ravelobensis is an endangered nocturnal primate endemic to northwestern Madagascar. This part of the island is subject to extensive human intervention leading to massive habitat destruction and fragmentation. We investigated the degree of genetic differentiation among remaining populations using mitochondrial control region sequences (479–482 bases). Nine populations were sampled from the hypothesized geographic range. The region is composed of three inter-river systems (IRSs). Samples were collected in three areas of continuous forests (CFs) and six isolated forest fragments (IFFs) of different sizes. We identified 27 haplotypes in 114 animals, with CFs and IFFs harbouring 5–6 and 1–3 haplotypes, respectively. All IFFs were significantly differentiated from each other with high Φ_ST values and sets of unique haplotypes. The rivers constitute significant dispersal barriers with over 82% of the molecular variation being attributed to the divergence among the IRSs. The data suggest a deep and so far unknown split within the rufous mouse lemurs of northwestern Madagascar. The limited data base and the lack of ecological and morphological data do not allow definite taxonomic classification at this stage. However, the results clearly indicate that M. ravelobensis consists of three evolutionary significant units, possibly cryptic species, which warrant urgent and separate conservation efforts.     

Distribution and Morphological Variation of Microcebus spp. Along an Environmental Gradient in Southeastern Madagascar

The lemurs of Madagascar are known for their extraordinary levels of speciation. However, the mechanisms and environmental conditions that led to this diversity remain obscure. We used 3 species of Microcebus (M. griseorufus, M. murinus, M. rufus) occurring along an environmental gradient as a model to investigate 1) how the different species are distributed in relation to variation in environmental conditions and ecotones; 2) whether or not the morphology of a given species varies in relation to environmental conditions; and 3) whether or not there is evidence for morphological character displacement to reduce congeneric competition in sympatry vs. allopatry. The 3 species of Microcebus show clear associations with specific habitat types. Distributions overlap at ecotones. Nevertheless, the ecotone between dry spiny and gallery forest represents a species boundary between Microcebus griseorufus and M. murinus while the ecotone between dry spiny forest and evergreen humid forest represents the species boundary between M. murinus and M. rufus. Different ambient conditions are not reflected in changes in body measurements of Microcebus murinus living in different vegetation formations. There is no indication for character displacement in sympatry vs. allopatry. Thus, differences in body mass or other morphological characteristics do not contribute to species separation between Microcebus griseorufus and M. murinus. The results confirm the importance of ecotones as species boundaries as a condition postulated for the radiation of lemur and other species on Madagascar. They also demonstrate different habitat affinities of seemingly very similar lemur species and thus illustrate our very limited understanding of the actual selection pressures, adaptations of lemurs to their environments, and their possible response to interspecific competition.     

Reproductive Schedules of Female <Emphasis Type="Italic">Microcebus rufus</Emphasis> at Ranomafana National Park,Madagascar

I examined the reproductive status of female brown mouse lemurs (Microcebus rufus) from October 2005 to early January, 2006 at Ranomafana National Park, an eastern rain forest in Madagascar. I employed intensive capture/mark/recapture techniques to track individual changes in vaginal morphology and body mass and collected vaginal smears for individuals with open vaginas. I observed moderate estrous synchrony (vaginal openings between October 11 and November 18), with clusters of females showing strong estrous synchrony (6 of 15 on or around October 15, and 3 of 15 on or around October 25). My findings weakly support the proximity hypothesis—that closer females will enter estrus simultaneously—and offer virtually no support for the notion that body mass influences the timing of estrus in brown mouse lemurs. Females gave birth during the second and third weeks of December. Two females showing signs of abortion or perinatal death of offspring also showed renewed vaginal swelling in late December, suggesting that some form of polyestry, i.e., as reproductive compensation for infant loss, exists at Ranomafana. I discuss the implications of the data, in conjunction with other evidence of polyestry in wild mouse lemurs, in light of data on patterns of seasonality at Ranomafana and other sites. More data are needed to determine the frequency and pattern of polyestry in Microcebus rufus.     

Tree Holes Used for Resting by Gray Mouse Lemurs (Microcebus murinus) in Madagascar: Insulation Capacities and Energetic Consequences

I studied the insulation capacity of tree holes used by gray mouse lemurs (Microcebus murinus) 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 them. The insulation capacity of the tree holes peaked between 0800 and 1100 hr, when ambient temperatures ranged between 25 and 30°C. To compare tree holes, I calculated the mean difference between the internal temperature )(T_i ) and the external temperature (T_e ) for each tree hole. Thus large differences indicate good insulation capacities. The mean difference of tree holes in living trees was significantly larger than that of tree holes in dead trees, which shows that insulation in living trees is more effective. During the dry season, the insulation capacity of tree holes in living trees decreased and was lowest in July, whereas the insulation capacity of holes in dead trees remained approximately constant. Physiological studies under natural temperature and light condition in Microcebus murinus reveal that daily torpor saves around 40% of the daily energy expenditure compared to normothermia. However, torpor can be maintained only up to the threshold body and ambient temperature of 28°C, whereat Microcebus murinus have to terminate torpor actively. By occupying insulating tree holes, mouse lemurs may stay longer in torpor, which increases their daily energy savings by an extra 5%.     

Isolation of new microsatellite markers and application in four species of mouse lemurs (Microcebus sp.)

We report the development of 13 new microsatellite markers for mouse lemurs (Microcebus sp.). Two markers were isolated from the fat tailed dwarf lemur (Cheirogaleus medius) and 11 from the grey mouse lemur (Microcebus murinus). A total of 561 individuals from four different species of mouse lemurs was genotyped with the newly developed markers. All markers showed Mendelian inheritance in 21 families of mouse lemurs. All markers show polymorphism in several species of mouse lemurs and seven amplified in C. medius. Among these new markers are the first 10 published for M. berthae and the first 11 for M. griseorufus.     

Sensory Basis of Food Detection in Wild <Emphasis Type="BoldItalic">Microcebus murinus</Emphasis>

Very little is known about how nocturnal primates find their food. Here we studied the sensory basis of food perception in wild-caught gray mouse lemurs (Microcebus murinus) in Madagascar. Mouse lemurs feed primarily on fruit and arthropods. We established a set of behavioral experiments to assess food detection in wild-born, field-experienced mouse lemurs in short-term captivity. Specifically, we investigated whether they use visual, auditory, and motion cues to find and to localize prey arthropods and further whether olfactory cues are sufficient for finding fruit. Visual cues from motionless arthropod dummies were not sufficient to allow reliable detection of prey in choice experiments, nor did they trigger prey capture behavior when presented on the feeding platform. In contrast, visual motion cues from moving prey dummies attracted their attention. Behavioral observations and experiments with live and recorded insect rustling sounds indicated that the lemurs make use of prey-generated acoustic cues for foraging. Both visual motion cues and acoustic prey stimuli on their own were sufficient to trigger approach and capture behavior in the mouse lemurs. For the detection of fruit, choice experiments showed that olfactory information was sufficient for mouse lemurs to find a piece of banana. Our study provides the first experimental data on the sensory ecology of food detection in mouse lemurs. Further research is necessary to address the role of sensory ecology for food selection and possibly for niche differentiation between sympatric Microcebus species.     

Multiple nuclear loci reveal patterns of incomplete lineage sorting and complex species history within western mouse lemurs (Microcebus)

Mouse lemurs (genus Microcebus) are nocturnal primates endemic to the island of Madagascar. Until recently, they were classified as two species, one from eastern and one from western Madagascar. Previously published analyses of morphometric and mitochondrial DNA data show strong support for the recognition of more than eight species, however. Here, we test the eight-species hypothesis with DNA data derived from four independently segregating nuclear loci. We find many areas of congruence between the mitochondrial and nuclear data, but incomplete lineage sorting and low mutation rates limit the phylogenetic resolution of the nuclear data. Even so, the nuclear loci unanimously find evidence for three deeply diverged lineages within the mouse lemur radiation: one that is congruent with the mtDNA "southern clade", another that is congruent with the mtDNA "northern clade", and one monospecific branch comprised of the species Microcebus ravelobensis. The latter result in particular emphasizes the need for careful biological study of this species.     

The lack of female dominance in golden‐brown mouse lemurs suggests alternative routes in lemur social evolution

Female dominance is a well‐known trait of lemurs, although it has not been reported from all species and is still often unexplored, especially in the nocturnal species. We examined the intersexual dominance relationships in Microcebus ravelobensis, a congener of M. murinus who is well known for its female dominance. Given the many similarities in biology, it was predicted that M. ravelobensis should also possess female dominance. Seventeen unfamiliar male–female pairs were formed with animals captured in northwestern Madagascar and kept in a two‐cage setting (one cage for each animal) for up to 1 week. Four encounter experiments were conducted with each pair. In contrast to the expectations, females were not consistently dominant over their male partners. Only 3 of 17 dyads developed a clear agonistic asymmetry, among which were two cases of male dominance and only one case of female dominance. Because body mass differences did not explain the findings, various other possible explanations are discussed. It is suggested that food may not be the driving factor of female dominance in mouse lemurs. Instead, it is hypothesized that species‐specific differences in the quality of sleeping sites (i.e., tree holes) and in social grouping patterns may better explain why some mouse lemur species have female dominance, whereas others like the golden‐brown mouse lemur do not. It is concluded thatthese arguments and hypotheses may even hold true for other solitary foragers and may thereby lead to a better understanding of the variable social evolution in lemurs and primates in general. Am J Phys Anthropol, 2013. © 2012 Wiley Periodicals, Inc.