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Edge effects result from the penetration to varying depths and intensities, of abiotic and biotic conditions from the surrounding non-forest matrix into the forest interior. Although 70% of the world's forests are within 1 km of a forest edge, making edge effects a dominant feature of most forest habitats, there are few empirical data on inter-site differences in edge responses in primates. We used spatially explicit capture-recapture (SECR) models to determine spatial patterns of density for two species of mouse lemurs (Microcebus murinus and Microcebus ravelobensis) in two forest landscapes in northwestern Madagascar. The goal of our study was to determine if mouse lemurs displayed spatially variable responses to edge effects. We trapped animals using Sherman live traps in the Mariarano Classified Forest (MCF) and in the Ambanjabe Forest Fragment Site (AFFS) site within Ankarafantsika National Park. We trapped 126 M. murinus and 79 M. ravelobensis at MCF and 78 M. murinus and 308 M. ravelobensis at AFFS. For M. murinus, our top model predicted a positive edge response, where density increased towards edge habitats. In M. ravelobensis, our top model predicted a negative edge response, where density was lower near the forest edges and increased towards the forest interior. At regional and landscape-specific scales, SECR models estimated different density patterns between M. murinus and M. ravelobensis as a result of variation in edge distance. The spatial variability of our results using SECR models indicate the importance of studying the population ecology of primates at varying scales that are appropriate to the processes of interest. Our results lend further support to the theory that some lemurs exhibit a form of ecological flexibility in their responses to forest loss, forest fragmentation, and associated edge effects., (© 2024 The Authors. American Journal of Primatology published by Wiley Periodicals LLC.)

The dwarf lemurs (Cheirogaleus spp.) of Madagascar are the only obligate hibernators among primates. Despite century-old field accounts of seasonal lethargy, and more recent evidence of hibernation in the western fat-tailed dwarf lemur (Cheirogaleus medius), inducing hibernation in captivity remained elusive for decades. This included the Duke Lemur Center (DLC), which maintains fat-tailed dwarf lemurs and has produced sporadic research on reproduction and metabolism. With cumulative knowledge from the field, a newly robust colony, and better infrastructure, we recently induced hibernation in DLC dwarf lemurs. We describe two follow-up experiments in subsequent years. First, we show that dwarf lemurs under stable cold conditions (13°C) with available food continued to eat daily, expressed shallower and shorter torpor bouts, and had a modified gut microbiome compared to peers without food. Second, we demonstrate that dwarf lemurs under fluctuating temperatures (12-30°C) can passively rewarm daily, which was associated with altered patterns of fat depletion and reduced oxidative stress. Despite the limitations of working with endangered primates, we highlight the promise of studying hibernation in captive dwarf lemurs. Follow-up studies on genomics and epigenetics, metabolism, and endocrinology could have relevance across multidisciplinary fields, from biomedicine to evolutionary biology, and conservation., (© 2024 The New York Academy of Sciences.)

Quaternary climatic changes have been invoked as important drivers of species diversification worldwide. However, the impact of such changes on vegetation and animal population dynamics in tropical regions remains debated. To overcome this uncertainty, we integrated high-resolution paleoenvironmental reconstructions from a sedimentary record covering the past 25,000 years with demographic inferences of a forest-dwelling primate species (Microcebus arnholdi), in northern Madagascar. Result comparisons suggest that climate changes through the African Humid Period (15.2 - 5.5 kyr) strongly affected the demographic dynamics of M. arnholdi. We further inferred a population decline in the last millennium which was likely shaped by the combination of climatic and anthropogenic impacts. Our findings demonstrate that population fluctuations in Malagasy wildlife were substantial prior to a significant human impact. This provides a critical knowledge of climatically driven, environmental and ecological changes in the past, which is essential to better understand the dynamics and resilience of current biodiversity., (© 2021. The Author(s).)

Madagascar is home to many threatened and endemic primate species, yet this island has seen dramatic declines in lemur habitat due to forest loss. This forest loss has resulted in an increasingly fragmented forest landscape, with fragments isolated from each other by grasslands (i.e., matrix). The grassland matrix is not entirely homogeneous containing matrix elements such as isolated trees and shrubs and linear features such as drainage lines. Because most lemurs are predominantly arboreal, they may preferentially use matrix elements to facilitate dispersal between fragments for access to mates or reduce feeding competition, allowing gene flow between fragments of habitat. Therefore, it is important to understand to what degree they use the matrix. We investigated matrix use in two mouse lemurs, the grey mouse lemur (Microcebus murinus) and the golden-brown mouse lemur (Microcebus ravelobensis) in a fragmented landscape in northwest Madagascar. We tested the predictions that: (1) lemurs use matrix less often than forest fragments, (2) if they use the matrix, then they will preferentially use matrix elements compared to grassland, and (3) M. murinus will disperse into the matrix further than M. ravelobensis. In 2011, we visually surveyed line transects in four areas containing matrix elements and four adjacent forest fragments during nocturnal walks. In 2017, we set up traplines in four areas of the matrix containing matrix elements, three areas that were grassland, and six traplines in adjacent fragments. We compared the relative abundance of mouse lemurs in matrix transects to fragmented forest transects, and the relative abundance of captured lemurs in matrix elements, grassland, and fragment traplines. We found that encounter rates of mouse lemurs did not significantly differ between the matrix and fragmented forest transects or traplines. Our sample size was too low to determine if the mean distance from the forest was greater for either Microcebus spp. Our study highlights that mouse lemurs do use matrix elements and there may be interspecific differences in use. Further research is needed to confirm species-specific matrix use, why mouse lemurs use matrix, and how much matrix elements facilitate movement for each species in fragmented landscapes., (© 2020 S. Karger AG, Basel.)

Predator odors such as urine and feces are known to elicit antipredator behaviors in prey including avoidance, fear, and curiosity. We measured how wild brown mouse lemurs (Microcebus rufus) responded to odors of mammalian, avian, and snake predators as well as nonpredator controls. The first experiment took place under controlled conditions in a laboratory where we recorded the occurrence of four behavioral categories (ignore, curiosity, alert, and fear) in response to a single odor. Subjects exhibited behavioral change significantly more often in response to the predator than to control stimuli, but did not distinguish between familiar and unfamiliar predators. Mammalian predator urine and feces were most likely to elicit behavioral change. The owl was the only predator to never elicit behavioral change, possibly because owls do not provide relevant odor cues. A second experiment employing live traps in the forest found that neither predator nor control odors affected the likelihood of capture. Due to their longevity, odors do not provide accurate information of spatial and temporal risk, and while mouse lemurs may have initially hesitated to enter a trap, in the absence of additional information about risk, they may have eventually ignored the stimuli. This study found that brown mouse lemurs are able to distinguish between predator and nonpredator odors, and that risk assessment may be affected by the experience, as well as predator and sensory stimulus quality., (© 2020 Wiley Periodicals LLC.)

Delimitation of cryptic species is increasingly based on genetic analyses but the integration of distributional, morphological, behavioral, and ecological data offers unique complementary insights into species diversification. We surveyed communities of nocturnal mouse lemurs (Microcebus spp.) in five different sites of northeastern Madagascar, measuring a variety of morphological parameters and assessing reproductive states for 123 individuals belonging to five different lineages. We documented two different non-sister lineages occurring in sympatry in two areas. In both cases, sympatric species pairs consisted of a locally restricted (M. macarthurii or M. sp. #3) and a more widespread lineage (M. mittermeieri or M. lehilahytsara). Estimated Extents of Occurrence (EOO) of these lineages differed remarkably with 560 and 1,500 km 2 versus 9,250 and 50,700 km 2 , respectively. Morphometric analyses distinguished unambiguously between sympatric species and detected more subtle but significant differences among sister lineages. Tail length and body size were most informative in this regard. Reproductive schedules were highly variable among lineages, most likely impacted by phylogenetic relatedness and environmental variables. While sympatric species pairs differed in their reproductive timing (M. sp. #3/M. lehilahytsara and M. macarthurii/M. mittermeieri), warmer lowland rainforests were associated with a less seasonal reproductive schedule for M. mittermeieri and M. lehilahytsara compared with populations occurring in montane forests. Distributional, morphological, and ecological data gathered in this study support the results of genomic species delimitation analyses conducted in a companion study, which identified one lineage, M. sp. #3, as meriting formal description as a new species. Consequently, a formal species description is included. Worryingly, our data also show that geographically restricted populations of M. sp. #3 and its sister species (M. macarthurii) are at high risk of local and perhaps permanent extinction from both deforestation and habitat fragmentation., (© 2020 The Authors. American Journal of Primatology published by Wiley Periodicals LLC.)

Studies on the impact of habitat loss on species occurrence consistently find that the amount of habitat (measured as patch area) is a major determinant of species occurrence at a patch-level. However, patch-level research may fail to detect important patterns and processes only observable at a landscape-level. A landscape-level approach that incorporates species-specific scale responses is needed to better understand what drives species occurrence. Our aim was to determine the landscape-level scale of effect of habitat amount on the occurrence of three species of nocturnal lemurs (Cheirogaleus medius, Microcebus murinus, and M. ravelobensis). We surveyed line transects to determine the occurrence of three lemur species within a fragmented landscape of deciduous dry forest and anthropogenic grassland in northwestern Madagascar. To determine the scale of effect of habitat loss on lemur occurrence, we compared logistic regression models of occurrence against habitat amount among eight different landscape scales using Akaike's Information Criterion values. We found differing scale responses among the lemurs in our study. Occurrence of C. medius responded to habitat amount at scales between 0.5-4 ha, M. murinus at scales between 1 and 4 ha and M. ravelobensis at scales between 0.125 and 4 ha. We suggest that the scale of effect for C. medius is mediated by their ability to hibernate. A relatively lower scale-response for Microcebus spp. likely reflect their omnivorous diet, small habitat requirements, and limited dispersal ability. Differences in scale responses between M. murinus and M. ravelobensis are likely a result of differing dispersal ability and responses to edge effects between these species. Our study is among the first on lemurs to show the value of a landscape-level approach when assessing the effects of habitat loss on species occurrence., (© 2020 Wiley Periodicals, Inc.)

Primate loud calls often encode information relating to species identity. A previous study of loud calls of fork-marked lemurs (genus Phaner) indicated differences among the calls of four populations that have been accorded species status on the grounds of morphology and biogeography: Phaner electromontis, P. parienti, P. furciferand P. pallescens. I made field recordings of two typical calls (kiu and kea) emitted by all four populations and conducted playback experiments in Kirindy Forest to investigate whether free-ranging P. pallescensindividuals could discriminate the loud calls of their own species from those of others. Individual response behaviour, social context and call type used in playback were analysed using a goodness-of-fit G test. The effect of specific call identity was significant, while the effects of context and call type were not. Individuals responded to P. pallescens calls by approaching the speaker, but not to the calls of other populations. P. pallescens individuals appear to be capable of distinguishing the loud calls of their conspecifics, but the fact that the habitat structure of the sites of recording and playback of P. pallescenscalls was similar sounds a note of caution. Future studies should repeat the experiments with the other populations of fork-marked lemurs., (© 2019 S. Karger AG, Basel.)

The nocturnal mouse and dwarf lemurs from Madagascar are known to express heterothermy. Whereas dwarf lemurs (Cheirogaleus) are obligate hibernators, mouse lemurs (Microcebus) can express a great range of heterothermic responses, including daily torpor, prolonged torpor or hibernation, depending on the species, population or individual. Although there is indirect evidence of heterothermy in a handful of mouse lemur species, direct physiological confirmation is currently limited to four: Microcebus berthae(dry forest), M. ravelobensis(dry forest), M. griseorufus(spiny forest), M. murinus(dry forest/littoral forest). We studied Goodman's mouse lemurs (M. lehilahytsara) at the high-altitude rain forest of Tsinjoarivo, central-eastern Madagascar. We captured a total of 45 mouse lemurs during pre- and post-torpor seasons. We recorded body mass and measured tail base circumference, which was used as proxy for fattening. Moreover, using telemetry, we obtained sporadic skin temperature data from a mouse lemur female between March and June. From June 9 to 16, we performed more intensive data sampling and thereby confirmed the expression of prolonged torpor in this female, when skin temperatures consistently displayed values below 25°C for more than 24 h. We documented 3 torpor bouts, 2 of which were interrupted by naturally occurring arousals. Torpor bout duration ranged from approximately 47 to maximally about 69 h. We found similarities between the Goodman's mouse lemur torpor profile and those known from other species, including the fact that only a portion of any mouse lemur population deposits fat stores and undergoes torpor in a given year. The variable expression of heterothermy in Goodman's mouse lemurs contrasts with obligatory hibernation displayed by two sympatric species of dwarf lemurs, suggesting cheirogaleids use a range of metabolic strategies to cope with seasonality and cold environments., (© 2020 S. Karger AG, Basel.)

It has been proposed that primates use advertisement calls exclusively to negotiate spacing, but the function of female calls has rarely been studied. Here, we investigated the function of male and female advertisement calls in the northern giant mouse lemur (Mirza zaza),a non-gregarious nocturnal primate from north-western Madagascar. We recorded advertisement calls and associated behaviours of 35 M. zaza individuals at the Duke University Lemur Center. We found that females of M. zazaexclusively use their advertisement calls to advertise oestrus. In contrast, male advertisement calls appeared to be used in a spacing context. These findings show that primates can use their advertisement calls for both spacing and mate attraction, and that the sexes may differ in how they use these calls. The novel find of females of M. zazaattracting mates with loud advertisement calls contrasts with many non-primate taxa, where acoustic mate attraction is usually a function of male advertisement calls, and with other primates, where females use visual and olfactory cues to attract males. The loud female advertisement calls of M. zaza likely ensure mating success during the short receptive phase in this non-gregariously foraging, nocturnal primate., (© 2019 S. Karger AG, Basel.)

Reproduction is a fundamental trait in the life history of any species and contributes to species diversity and evolution. Here, we aim to review the barely known variation in reproductive patterns of the smallest-bodied primate radiation, the Malagasy mouse lemurs, focusing on twelve species of four phylogenetic clades. We present a new reproductive field dataset collected between May and November 1996-2016 for nine species (Microcebus murinus, M. myoxinus, M. ravelobensis, M. bongolavensis, M. danfossi, M. sambiranensis, M. margothmarshae, M. mamiratra, and M. lehilahytsara) and add published field information on three additional species. In the majority of species, the estrus of females was recorded in the period of long days (day length longer than 12 hr), whereas male testes size increased about one to three months prior to this. Reproductive schedules varied considerably between the four clades. Sympatric species-pairs of different clades differed in the timing of female and male reproduction, suggesting strong phylogenetic constraints. Populations of the same species in a different ecological setting varied in the onset of reproduction, suggesting substantial environmental plasticity. Warm temperatures and rainfall throughout the year may allow for less expressed reproductive seasonality. Our results suggest that an interplay between phylogenetic relatedness, ambient temperature (as a proxy for thermo regulatory constraints), and rainfall (as a proxy for food availability), may best explain this variation. Findings further point to a more complex control of mouse lemur reproduction than previously described and illuminate phylogenetic constraints and adaptive potentials in behavioral reaction norms of a species-rich primate radiation., (© 2018 Wiley Periodicals, Inc.)

The critically endangered Claire's mouse lemur, only found in the evergreen rain forest of the National Park Lokobe (LNP) and a few lowland evergreen rain forest fragments of northern Madagascar, was described recently. The present study provides the first quantified information on vocal acoustics of calls, sound associated behavioral context, acoustic niche, and vocal activity of this species. We recorded vocal and social behavior of six male-female and six male-male dyads in a standardized social-encounter paradigm in June and July 2016 at the LNP, Nosy Bé island. Over six successive nights per dyad, we audio recorded and observed behaviors for 3 hr at the beginning of the activity period. Based on the visual inspection of spectrograms and standardized multiparametric sound analysis, we identified seven different call types. Call types can be discriminated based on a combination of harmonicity, fundamental frequency variation, call duration, and degree of tonality. Acoustic features of tonal call types showed that for communication, mouse lemurs use the cryptic, high frequency/ultrasonic frequency niche. Two call types, the Tsak and the Grunt call, were emitted most frequently. Significant differences in vocal activity of the Tsak call were found between male-female and male-male dyads, linked primarily to agonistic conflicts. Dominant mouse lemurs vocalized more than subdominant ones, suggesting that signaling may present an honest indicator of fitness. A comparison of our findings of the Claire's mouse lemur with published findings of five bioacoustically studied mouse lemur species points to the notion that a complex interplay between ecology, predation pressure, and phylogenetic relatedness may shape the evolution of acoustic divergence between species in this smallest-bodied primate radiation. Thus, comparative bioacoustic studies, using standardized procedures, are promising to unravel the role of vocalization for primate species diversity and evolution and for identifying candidates for vocalization-based non-invasive monitoring for conservation purposes., (© 2018 Wiley Periodicals, Inc.)

Objectives: Testis size is an indirect indicator of a species' mating system, along with sexual size and canine dimorphism, existence and usage of mating and advertisement calls as well as the spatial distribution of males and females ready to mate in solitary species. Upon its recent discovery, the northern giant mouse lemur Mirza zaza was suggested to have a polygynandrous mating system and to exhibit seasonal breeding. We tested these predictions in a field study in Sahamalaza National Park, NW Madagascar., Materials and Methods: We caught 12 M. zaza, before and during the suggested mating period and obtained standard field morphometric measurements, including testes size., Results: We show that M. zaza has the highest relative testis volume among primates, indicating strong sperm competition and polygynandrous mating. In addition, based on inferred age of captured animals, observed mating behavior, a female caught in met-estrus and data from captivity, we suggest M. zaza to be one of the few lemurs that breed aseasonally., Discussion: Future field work on this endangered species is required to illuminate the causes and consequences of intense promiscuity and aseasonal breeding despite strong habitat seasonality, which distinguish M. zaza from most other nocturnal lemurs., (© 2015 Wiley Periodicals, Inc.)

Background: Spatio-temporal distribution patterns of species in response to natural and anthropogenic drivers provide insight into the ecological processes that determine community composition. We investigated determinants of ecological structure in a species assemblage of 4 closely related primate species of the family Cheirogaleidae (Microcebus berthae, Microcebus murinus, Cheirogaleus medius, Mirza coquereli) in western Madagascar by extensive line transect surveys across spatial and temporal heterogeneities with the specific goal of elucidating the mechanisms stabilizing competitive coexistence of the two mouse lemur species (Microcebus spp.)., Results: Interspecific competition between the mouse lemurs was indicated by negative spatial associations in degraded habitat and by habitat partitioning along anthropogenic disturbance gradients during dry seasons with resource scarcity. In non-degraded habitat, intraguild predator M. coquereli, but not C. medius, was negatively associated with M. murinus on the population level, whereas its regional distribution overlapped spatially with that of M. berthae. The species' interspecific distribution pattern across spatial and temporal heterogeneities corresponded to predictions for agent-mediated coexistence and thus confirmed M. coquereli's stabilizing impact on the coexistence of mouse lemurs., Conclusions: Interspecific interactions contribute to ecological structure in this cheirogaleid assemblage and determinants vary across spatio-temporal heterogeneities. Coexistence of Microcebus spp. is stabilized by an agent-mediated spatial storage effect: M. coquereli creates refuges from competition for M. berthae in intact habitat, whereas anthropogenic environments provide M. murinus with an escape from resource competition and intraguild predation. Species persistence in the assemblage therefore depends on the conservation of habitat content and context that stabilizing mechanisms rely on. Our large-scale population level approach did not allow for considering all potential functional and stochastic drivers of ecological structure, a key limitation that accounts for the large proportion of unexplained variance in our models.

The reddish-gray mouse lemur (Microcebus griseorufus) is one of only a few small mammals inhabiting the spiny forest of southwestern Madagascar. In this study we investigated the physiological adjustments which allow these small primates to persist under the challenging climatic conditions of their habitat. To this end we measured energy expenditure (metabolic rate) and body temperature of 24 naturally acclimatized mouse lemurs, kept in outdoor enclosures, during different seasons (summer, winter, and the transition period between the two seasons). Mouse lemurs displayed two main physiological strategies to compensate seasonal and diurnal fluctuations of ambient temperature. On the one hand, individuals entered hypometabolism with decreasing ambient temperature (T a) during the transition period and winter, enabling them to save up to 21 % energy per day (92 % per hour) compared with the normal resting metabolic rate at comparable T a. On the other hand, euthermic mouse lemurs also showed physiological adjustments to seasonality when resting: the lower critical temperature of the thermoneutral zone decreased from summer to winter by 7.5 °C, which allowed mouse lemurs to keep energy demands constant despite colder T as during winter. In addition, the basal metabolic rate was substantially lowered prior to the winter period, which facilitated accumulation of fat reserves. The combination of physiological modifications during euthermia in addition to hypometabolism, which can be individually adjusted according to external parameters and respective body condition, is important as it allows M. griseorufus to cope with the environmental variability of an energetically challenging habitat.

There is some urgency in the necessity to incorporate physiological data into mechanistic, trait-based, demographic climate change models. Physiological responses at the individual level provide the mechanistic link between environmental changes and individual performances and hence population dynamics. Here we consider the causal relationship between ambient temperature (Ta) and metabolic rate (MR), namely, the Arrhenius effect, which is directly affected by global warming through increases in average global air temperatures and the increase in the frequency and intensity of extreme climate events. We measured and collated data for several small, free-ranging tropical arboreal mammals and evaluated their vulnerability to Arrhenius effects and putative heat stress associated with climate change. Skin temperatures (Tskin) were obtained from free-ranging tarsiers (Tarsius syrichta) on Bohol Island, Philippines. Core body temperature (Tb) was obtained from the greater hedgehog tenrec (Setifer setosus) and the gray brown mouse lemur (Microcebus ravelobensis) from Ankarafantsika, Madagascar. Tskin for another mouse lemur, Microcebus griseorufus, was obtained from the literature. All four species showed evidence of hyperthermia during the daytime rest phase in the form of either Tskin or Tb that was higher than the normothermic Tb during the nighttime active phase. Potentially, tropical arboreal mammals with the lowest MRs and Tb, such as tarsiers, are the most vulnerable to sustained heat stress because their Tb is already close to Ta. Climate change may involve increases in MRs due to Arrhenius effects, especially during the rest phase or during torpor and hibernation. The most likely outcome of increased Arrhenius effects with climate change will be an increase in energy expenditure at the expense of other critical functions such as reproduction or growth and will thus affect fitness. However, we propose that these hypothetical Arrhenius costs can be, and in some species probably are, offset by the use of hyperthermic daily torpor, that is, hypometabolism at high Ta.

Edge effects are an inevitable and important consequence of forest loss and fragmentation. These effects include changes in species biology and biogeography. Here we examine variations in body mass and morphometrics for 2 sympatric species of mouse lemurs (Microcebus murinus and M. ravelobensis) between edge and interior habitats in the dry deciduous forest at Ankarafantsika National Park. Between May and August 2012, we conducted mark-recapture experiments on mouse lemurs trapped along edge and interior forest transects within continuous forest adjacent to a large savannah. Of the 34 M. murinus captured during our study, 82% (n = 28) were trapped in interior habitats. Conversely, 72% (n = 47) of M. ravelobensis were captured in edge habitats. We found that mean body mass of M. murinus and M. ravelobensis did not differ between edge and interior habitats. However, female M. ravelobensis weighed significantly more in edge habitats (56.09 ± 1.74 g) than in interior habitats (48.14 ± 4.44 g). Our study provides some of the first evidence of sex differences in edge responses for a primate species., (© 2015 S. Karger AG, Basel.)

A thorough knowledge of biological variation in extant primates is imperative for interpreting variation, and for delineating species in primate biology and paleobiology. This is especially the case given the recent, rapid taxonomic expansion in many primate groups, notably among small-bodied nocturnal forms. Here we present data on dental, cranial, and pelage variation in a single-locality museum sample of mouse lemurs from Amboasary, Madagascar. To interpret these data, we include comparative information from other museum samples, and from a newly collected mouse lemur skeletal sample from the Beza Mahafaly Special Reserve (BMSR), Madagascar. We scored forty dental traits (n = 126) and three pelage variants (n = 19), and collected 21 cranial/dental measures. Most dental traits exhibit variable frequencies, with some only rarely present. Individual dental variants include misshapen and supernumerary teeth. All Amboasary pelage specimens display a "reversed V" on the cap, and a distinct dorsal median stripe on the back. All but two displayed the dominant gray-brown pelage coloration typical of Microcebus griseorufus. Cranial and dental metric variability are each quite low, and craniometric variation does not illustrate heteroscedasticity. To assess whether this sample represents a single species, we compared dental and pelage variation to a documented, single-species M. griseorufus sample from BMSR. As at Amboasary, BMSR mouse lemurs display limited odontometric variation and wide variation in non-metric dental traits. In contrast, BMSR mouse lemurs display diverse pelage, despite reported genetic homogeneity. Ranges of dental and pelage variation at BMSR and Amboasary overlap. Thus, we conclude that the Amboasary mouse lemurs represent a single species - most likely (in the absence of genetic data to the contrary) M. griseorufus, and we reject their previous allocation to Microcebus murinus. Patterns of variation in the Amboasary sample provide a comparative template for recognizing the degree of variation manifested in a single primate population, and by implication, they provide minimum values for this species' intraspecific variation. Finally, discordance between different biological systems in our mouse lemur samples illustrates the need to examine multiple systems when conducting taxonomic analyses among living or fossil primates., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Not only can teeth provide clues about diet, but they also can be indicators of habitat quality. Conspecific groups living in different habitats with different kinds of foods may exhibit different rates of dental attrition because their teeth are less well adapted to some foods than to others. Ecological disequilibrium describes the situation in which animals live in habitats to which they are relatively poorly adapted. We test whether dental senescence, the wear-related decrease in dental functionality that is associated with decreased survival of infants born to older Propithecus edwardsi females, can be explained by ecological disequilibrium. Specifically, we compare the rates of dental wear in sifaka groups living in nearby habitats that differ in the degree of anthropogenically induced disturbance. We hypothesize that sifakas living in disturbed areas have an unusual rate of tooth wear compared to those living in a more pristine area, and that dental senescence is a consequence of an atypically high wear rate in a degraded habitat. To test whether habitat quality affects tooth wear more generally, we compare rates of use-wear in two subsets of Microcebus rufus living in either relatively undisturbed or disturbed habitats. Contrary to our predictions, we did not detect different rates of tooth wear in disturbed versus undisturbed habitats for either species and consider that reproductively detrimental dental senescence in P. edwardsi females is unlikely to be a pathological consequence of ecological disequilibrium., (Copyright © 2012 Wiley Periodicals, Inc.)

Very little information is known of the recently described Microcebus tavaratra and Lepilemur milanoii in the Daraina region, a restricted area in far northern Madagascar. Since their forest habitat is highly fragmented and expected to undergo significant changes in the future, rapid surveys are essential to determine conservation priorities. Using both distance sampling and capture-recapture methods, we estimated population densities in two forest fragments. Our results are the first known density and population size estimates for both nocturnal species. In parallel, we compare density results from four different approaches, which are widely used to estimate lemur densities and population sizes throughout Madagascar. Four approaches (King, Kelker, Muller and Buckland) are based on transect surveys and distance sampling, and they differ from each other by the way the effective strip width is estimated. The fifth method relies on a capture-mark-recapture (CMR) approach. Overall, we found that the King method produced density estimates that were significantly higher than other methods, suggesting that it generates overestimates and hence overly optimistic estimates of population sizes in endangered species. The other three distance sampling methods provided similar estimates. These estimates were similar to those obtained with the CMR approach when enough recapture data were available. Given that Microcebus species are often trapped for genetic or behavioral studies, our results suggest that existing data can be used to provide estimates of population density for that species across Madagascar., (© 2012 Wiley Periodicals, Inc.)

The factors that limit the distribution of the highly diverse lemur fauna of Madagascar are still debated. We visited an understudied region of eastern Madagascar, a lowland rainforest site (Sahafina, 29-230 m a.s.l.) close to the Mantadia National Park, in order to conduct a survey and collect further distributional data on mouse lemurs. We captured, measured, photographed, and sampled mouse lemurs from the Sahafina forest, performed standard phylogenetic methods based on three mitochondrial DNA genes, and conducted morphometric comparisons in order to clarify their phylogenetic position and taxonomic status. The mouse lemurs from the Sahafina forest could not be assigned to any of the known mouse lemur species and were highly divergent in all molecular analyses from all previously described species. Since they also differed morphometrically from their sister species and from their geographic neighbors, we propose species status and include a species description at the end. This study suggests that M. lehilahytsara may be the first highland specialist among all mouse lemurs. The distribution of the newly described mouse lemur is not fully known, but seems to be rather restricted and highly fragmented, which raises serious conservation concerns.

The massive energetic costs entailed by reproduction in most mammalian females may increase the vulnerability of reproductive success to food shortage. Unexpected events of unfavorable climatic conditions are expected to rise in frequency and intensity as climate changes. The extent to which physiological flexibility allows organisms to maintain reproductive output constant despite energetic bottlenecks has been poorly investigated. In mammals, reproductive resilience is predicted to be maximal during early stages of reproduction, due to the moderate energetic costs of ovulation and gestation relative to lactation. We experimentally tested the consequences of chronic-moderate and short-acute food shortages on the reproductive output of a small seasonally breeding primate, the grey mouse lemur (Microcebus murinus) under thermo-neutral conditions. These two food treatments were respectively designed to simulate the energetic constraints imposed by a lean year (40% caloric restriction over eight months) or by a sudden, severe climatic event occurring shortly before reproduction (80% caloric restriction over a month). Grey mouse lemurs evolved under the harsh, unpredictable climate of the dry forest of Madagascar and should thus display great potential for physiological adjustments to energetic bottlenecks. We assessed the resilience of the early stages of reproduction (mating success, fertility, and gestation) to these contrasted food treatments, and on the later stages (lactation and offspring growth) in response to the chronic food shortage only. Food deprived mouse lemurs managed to maintain constant most reproductive parameters, including oestrus timing, estrogenization level at oestrus, mating success, litter size, and litter mass as well as their overall number of surviving offspring at weaning. However, offspring growth was delayed in food restricted mothers. These results suggest that heterothermic, fattening-prone mammals display important reproductive resilience to energetic bottlenecks. More generally, species living in variable and unpredictable habitats may have evolved a flexible reproductive physiology that helps buffer environmental fluctuations.

Although primates have remarkable olfactory capabilities, their ability for olfactory predator recognition is still understudied. We investigated this cognitive ability in wild gray and golden-brown mouse lemurs (Microcebus murinus and M. ravelobensis) that were confronted with four different olfactory stimuli, derived from two Malagasy predators (fossa and barn owl) and two local nonpredator species (brown lemur and sifaka). The predator response was tested (1) in a systematic cage setup and (2) in a two-way choice experiment with two Sherman traps on platforms in the forest (stimulus trap vs. nonstimulus trap). For part 1, the study animals were housed in cages during habituation and 5 days of experiments. One stimulus was tested per night and was presented underneath a drinking bottle. The changes in the time spent close to the stimulus and the drinking time at the bottle were used as indicators of predator recognition. A timidity score was established by classifying the strength of the antipredator response during the experiment. The study animals spent significantly less time drinking and less time in the stimulus area when confronted with fossa odor compared with the other stimuli. The timidity score was significantly higher during the fossa stimulus compared with the nonpredator and the control stimuli. The two-way choice experiments revealed a complete avoidance of the fossa odor, which was not found with the other stimuli. Thus, wild mouse lemurs showed clear signs of olfactory predator recognition in the case of the fossa in both experiments, but no signs of avoidance to the other presented stimuli. The lack of owl avoidance may be explained by less or no aversive metabolites in the owl stimulus or by lower significance for olfactory recognition of aerial predators. Furthermore, the results showed slight differences between the two mouse lemur species that may be linked to differences in their ecology., (© 2011 Wiley-Liss, Inc.)

The small-bodied nocturnal mouse lemurs (genus Microcebus) occupy a variety of habitats in Madagascar. Gray (M. murinus) and brown (M. rufus) mouse lemurs have been widely studied both in the wild and captivity. Whereas captive studies revealed an endogenous regulation of reproduction entrained by photoperiod, field studies have suggested that reproductive activation could be affected by additional climatic, physical, or social conditions. I collected data on wild brown mouse lemur females at Ranomafana between 2004 and 2008 to determine: 1) the timing of estrus and estrous periodicities across multiple seasons, and 2) whether additional factors such as body mass, age, or rainfall are correlated with onset of reproduction. In mouse lemur females at Ranomafana, the first seasonal estrus occurs 3-4 weeks after the vernal equinox. I report ~1 month's intra-population variation in the timing of estrus and inter-annual estrous intervals with periodicities of ~365 days. There were significant differences between the onset of reproduction across years. Estrous onset was uncorrelated with body mass, but there was an apparent age effect. There was a significant negative correlation between August rainfall and onset of reproduction when 2004 data were removed from the analysis. Results from this study are consistent with the notion that timing of estrus is photoperiod-dependent. As in captivity, intra-population variation in estrous onset is ~4 weeks in length. In the wild, variation in estrous onset and polyestry (multiple reproductive opportunities per year) appear to be favored under the highly unpredictable conditions of Madagascar's environments. In the wild, variation in estrous onset and polyestry (multiple reproductive opportunities per year) appear to be favored under the highly unpredictable conditions of Madagascar's environments., (Copyright © 2011 Wiley-Liss, Inc.)

Interspecific competition has been suggested to influence the biogeographic distribution patterns of species. A high competitive potential could entail species-specific advantages during resource acquisition that could translate into a higher potential for range expansion. We investigated whether differences in the competitive potential of the morphologically similar and partially sympatric gray mouse lemur (Microcebus murinus) and golden-brown mouse lemur (Microcebus ravelobensis) may help to explain differences in their geographic range sizes. We carried out encounter experiments with 14 pairs of captured female mouse lemurs of both species. The experimental dyads were tested in a two-cage arrangement, with individuals being separated from each other outside the experiments. Two days of habituation and four subsequent days of 1-h encounter experiments were conducted, before releasing the animals again in the wild. In general, the M. murinus individuals won significantly more conflicts than their partners. In eight of 14 tested pairs, there was a significant species bias in winning conflicts, and in 87.5% of these dyads, M. murinus was the "dyad winner". A high competitive potential did not depend on body mass. Furthermore, "dyad winners" spent more time feeding (P < 0.05) and were less spatially restricted than "dyad losers". To conclude, our results suggest that the widely distributed M. murinus may indeed have a higher competitive potential than the regional endemic M. ravelobensis, which may, among other possible factors, have enabled this species to expand geographically, despite the presence of other competing congeners., (Copyright © 2011 Wiley-Liss, Inc.)

We investigated whether or not habitat structure contributes to the separation of two sister species of lemurs and their hybrids. For this, we studied Microcebus murinus and M. griseorufus along a continuous vegetation gradient where populations of the two species occur in sympatry or in allopatry. In allopatry, the two species are generalists without any sign of microhabitat selectivity. In sympatry, both species differed significantly and discriminated against certain habitat structures: M. murinus was found in microhabitats with larger trees than average while M. griseorufus utilized microhabitats with smaller trees. Hybrids between the two species did not show any significant discrimination for or against microhabitat structure and did not differ in their habitat utilization from either parent species. Both species can go into torpor and hibernation. M. griseorufus is seen more frequently during the cool dry season than M. murinus. We assume that M. murinus goes into extended torpor or hibernation more frequently than M. griseorufus. We interpret the different occurrence of large-sized trees in microhabitats of M. murinus as a prerequisite for M. murinus to be able to spend extended periods of time in tree holes that are isolated and allow hibernation at reduced temperature levels., (Copyright © 2012 S. Karger AG, Basel.)

The nocturnal dwarf lemurs of Madagascar (genus Cheirogaleus) are the only primates known to be obligate hibernators. Although the physiology of hibernation has been studied widely in the western, small-bodied species, Cheirogaleus medius, no direct evidence of hibernation, i.e., body temperature recordings, has been reported for any of the three recognized eastern dwarf lemur species. We present skin temperature data collected by external collar transmitters from two eastern dwarf lemur individuals (Cheirogaleus crossleyi) captured in the high-altitude forest of Tsinjoarivo, central-eastern Madagascar. Our study species is larger in body size than western dwarf lemurs and inhabits much colder environments. We present the first evidence of hibernation in an eastern dwarf lemur species, and we compare the results with data available for the western species. Although the hibernation period is shorter in dwarf lemurs from Tsinjoarivo, minimum body temperatures are lower than those reported for C. medius. Both individuals at Tsinjoarivo showed limited passive and extended deep hibernation during which they did not track ambient temperature as observed in most western dwarf lemurs. Because ambient temperatures at Tsinjoarivo never exceed 30°C, dwarf lemurs have to experience arousals to maintain homeostasis during periods of hibernation. We show that large dwarf lemurs (>400 g) are capable of undergoing deep hibernation and suggest that cold, high-altitude forests may render hibernation highly advantageous during periods of food scarcity. This study has implications for understanding the physiology of hibernation in small-bodied lemurs.

The relationships between resource distribution, type of competition, and consequences for social organization have been formalized in the socioecological model (SEM) which predicts that ecological factors are the main determinants of female distribution. We tested this basic prediction in two solitary primates (Microcebus berthae and M. murinus) which differ in female association patterns. Using stable nitrogen and carbon isotope data of hair samples and food sources we quantified inter-specific differences in diet. delta(13)C in M. berthae reflected a diet composed mainly of insect secretions. Higher within-species as well as seasonal variation in delta(13)C of M. murinus indicated a wider trophic niche including plant and animal source food. Constantly elevated delta(15)N in M. murinus most likely reflected extended torpor during the lean season. This energy-saving strategy together with a wider, more opportunistic feeding niche might reduce female competition in this species, facilitating smaller female ranges, and a higher association potential. In contrast, delta(15)N fluctuated seasonally in M. berthae, most likely indicating varying amounts of arthropod food in the diet. Intense scramble competition over small and seasonally limited resources might lead to female spatial avoidance and a reduced association potential in M. berthae. Thus, differences in female association patterns between these two solitary foragers are due to different types of competition and overall intensities of intra-specific competition., (2009 Wiley-Liss, Inc.)

The use of leaf nests has been documented in several mouse lemur species over the last few decades, including the golden-brown mouse lemur. Nest construction, however, has only rarely been observed and detailed descriptions of this process are lacking so far. We aim to determine the relative importance of leaf nests as shelters for the golden-brown mouse lemur, and to test predictions concerning the role of thermoregulation, safety (i.e., protection of infants), and of interspecific competition with the sympatric gray mouse lemurs in regulating nest use. Finally, we intend to clarify whether and how Microcebus ravelobensis constructs the nests, and we provide physical descriptions of seven leaf nests. Nocturnal focal observations were carried out from May 2007 to January 2008 on 18 females, and sleeping sites were regularly monitored during a six-month period. Data were collected from two study sites, one with exclusive presence of M. ravelobensis, and one with co-existence of the two mouse lemur species. Sixty-five out of 379 identified daily sleeping sites were leaf nests. These represented a total of 35 different leaf nests, used by 15 out of 18 females. The relative leaf nest use differed between sites during five out of six months, but without a consistent pattern. Interspecific competition can therefore not explain leaf nest use. Leaf nest use differed seasonally and may be partly explained by thermoregulatory advantages in the site with lower minimum temperatures. Nest use was furthermore higher than expected in both sites during the rearing season that indicates the role of nests in infant protection. For the first time, we could confirm that golden-brown mouse lemurs build leaf nests themselves. Nest building lasted between 46 and 68 min, which shows that this task is time consuming and therefore probably costly., ((c) 2009 Wiley-Liss, Inc.)

The coexistence of closely related species is not easily understood on the basis of ecological theories. This study investigates the extent of coexistence of two congeneric species of Microcebus murinus (MUR) and M. ravelobensis (RAV) in northwestern Madagascar. Their presence and local relative population densities were determined by capturing and nocturnal transect counts and compared at 22 study sites in the Ankarafantsika National Park. All sites were characterized with regard to their altitude, access to surface water, and 19 structural vegetation characteristics. RAV and MUR were not equally distributed over this regional scale. RAV occurred in more sites and at higher maximum densities than MUR. The relative population densities of both species were significantly and negatively correlated with each other. Whereas the relative population densities of MUR increased with altitude and were highest in dry habitats far from surface water, the relative population densities of RAV generally decreased with altitude and were highest in low altitude habitats close to surface water. The results of the vegetation characteristics also reflect these general trends. The divergent pattern of local and regional coexistence of these two species is discussed and can be best explained either by the existence of a spatially heterogeneous competitive environment or by independent evolutionary pathways in different historic environments., (Copyright 2009 Wiley-Liss, Inc.)

The spiny forest of southwestern Madagascar is the driest and most unpredictable region of the island. It is characterized by a pronounced seasonality with high fluctuations in ambient temperature, low availability of food, and a lack of water during the cool dry season and, additionally, by changes in environmental conditions between years. One of the few mammalian species that manages to inhabit this challenging habitat is the reddish-gray mouse lemur (Microcebus griseorufus). The aim of our study was to determine whether this small primate uses continuous hibernation as an energy saving strategy, and if so, to characterize its physiological properties. We measured skin temperature of 16 free-ranging individuals continuously over 3 months during the cool dry season using collar temperature data loggers. Prolonged hibernation was found in three mouse lemurs and was not sex dependent (one male, two females). Skin temperature of hibernating individuals tracked ambient temperature passively with a minimum skin temperature of 6.5 degrees C and fluctuated strongly each day (up to 20 degrees C), depending on the insulation capacity of the hibernacula. Individuals remained in continuous hibernation even at an ambient temperature of 37 degrees C. The animals hibernated continuously during the dry season, and hibernation bouts were only interrupted by short spontaneous arousals. The study emphasizes that hibernation is an important measure to counter environmental challenge for more tropical species than previously thought, including primates. It furthermore provides evidence that tropical hibernation is functionally similar among tropical species.

Studies on reproductive endocrinology in wild primate populations have greatly increased in the last decades owing to the development of noninvasive techniques that can be applied under field conditions. However, small-bodied nocturnal species are not well represented on the long list of primates surveyed in the wild, and reproductive inferences regarding these animals in their natural habitats have not benefited from direct observations of hormonal changes. We collected fecal samples from female brown mouse lemurs (Microcebus rufus) in a southeastern rainforest of Madagascar in order to determine whether or not fecally excreted steroid levels show a consistent pattern of change during the reproductive season and are a useful complement to reproductive observations in wild-trapped individuals. Initial data show variation in reproductive hormone levels before and after estrus and estimated day of parturition. Elevated levels of excreted estradiol (E(2)) were observed around the time of estrus, whereas high levels of fecal progesterone (P) were seen during later stages of pregnancy and around parturition. A more complete picture of reproductive profiles in female mouse lemurs, and how they may change over the life span, can be obtained if hormone analyses are used to supplement field observations.

In this field study, the energetic properties of tropical hibernation were investigated by measuring oxygen consumption and body temperature of the Malagasy primate Cheirogaleus medius in their natural hibernacula. These lemurs use tree holes with extremely varying insulation capacities as hibernacula. In poorly insulated tree holes, tree hole temperature and body temperature fluctuated strongly each day (between 12.8 and 34.4 degrees C). The metabolic rate under these conditions also showed large daily fluctuations between about 29.0 ml O(2)/h and 97.9 ml O(2)/h in parallel with changes in body temperature. In well insulated tree holes in very large trees on the other hand, tree hole temperature and body temperature remained relatively constant at about 25 degrees C. Lemurs hibernating in these tree holes showed a more constant metabolic rate at an intermediate level, but hibernation was interrupted by repeated arousals with peak metabolic rates up to 350 ml O(2)/h. The occurrence of these spontaneous arousals proved that the ability for thermoregulation persists during hibernation. Arousals were energetically costly, but much less so than in temperate and arctic hibernators. Despite the decisive influence of tree hole properties on the pattern of body temperature and metabolic rate during hibernation, the choice of the hibernaculum does not seem to be of energetic importance. The overall energetic savings by tropical hibernation amounted to about 70% as compared to the active season (31.5 vs. 114.3 kJ/d). Therefore, tropical hibernation in C. medius is an effective, well-regulated adaptive response to survive unfavourable seasons.

Hybrid zones in ecotones can be useful model systems for the study of evolutionary processes that shape the distribution and discreteness of species. Such studies could be important for an improved understanding of the complex biogeography of Madagascar, which is renowned for its outstanding degree of small-scale endemism. Certain forest remnants in central Madagascar indicate that transitional corridors across the island could have connected microendemics in different forest types in the past. Evolutionary processes in such corridors are difficult to study because most of these corridors have disappeared due to deforestation in central Madagascar. We studied a hybrid zone in one of the few remaining ecotonal corridors between dry and humid forests in Madagascar, which connects two species of mouse lemurs, Microcebus griseorufus in dry spiny forest and Microcebus murinus in humid littoral forest. We sampled 162 mouse lemurs at nine sites across this boundary. Morphometric analyses revealed intermediate morphotypes of many individuals in transitional habitat. Bayesian clustering of microsatellite genotypes and assignment tests yielded evidence for a mixed ancestry of mouse lemurs in the ecotone, where we also observed significant linkage disequilibria and heterozygote deficiency. In contrast to these observations, mitochondrial haplotypes displayed a sharply delimited boundary at the eastern edge of spiny forest, which was noncoincident with the signals from microsatellite data. Among several alternative scenarios, we propose asymmetric nuclear introgression due to male-biased dispersal, divergent environmental selection, and an expansion of dry spiny forest in the course of aridification as a probable explanation of our observations.

In this study we describe tree hole characteristics and use by the hairy-eared dwarf lemur (Allocebus trichotis) to determine habitat needs, potential functions of tree holes and sleeping group composition. We radio-tracked 6 adult individuals between April and November 2007 in the Analamazaotra Special Reserve. Tree holes were 1-9 m high (median: 7 m), in living trees measuring 26-54 cm in diameter at breast height (median: 32 cm), and could be a limiting resource. Each individual used 4 or 5 tree holes and had high nest fidelity. Animals most often slept socially in mixed-sex groups of 2-6 individuals and occasionally shared a tree hole with white-tailed tree rats (Brachytarsomys albicauda). We identified two sleeping groups: one composed of 2 adult males, 2 adult females and 2 juveniles; one composed of at least 2 adult females and 2 juveniles. Although tree holes were generally group exclusive, some intergroup sleeping was observed. Tree holes could have antipredator and thermoregulatory functions. Further research into sleeping hole availability, nest use and the degree of niche separation or competition between sympatric Cheirogaleidae and other tree hole users (e.g. endemic rodents) is needed to assess better the conservation needs of these species., (Copyright 2009 S. Karger AG, Basel.)

Understanding the co-occurrence of ecologically similar species remains a puzzling issue in community ecology. The species-rich mouse lemurs (Microcebus spec.) are distributed over nearly all remaining forest areas of Madagascar with a high variability in species distribution patterns. Locally, many congeneric species pairs seem to co-occur, but only little detailed information on spatial patterns is available. Here, we present the results of an intensive capture-mark-recapture study of sympatric Microcebus berthae and M. murinus populations that revealed small-scale mutual spatial exclusion. Nearest neighbour analysis indicated a spatial aggregation in Microcebus murinus but not in M. berthae. Although the diet of both species differed in proportions of food categories, they used the same food sources and had high feeding niche overlap. Also, forest structure related to the spatial distribution of main food sources did not explain spatial segregation because parts used by each species exclusively did not differ in density of trees, dead wood and lianas. We propose that life history trade-offs that result in species aggregation and a relative increase in the strength of intra-specific over inter-specific competition best explain the observed pattern of co-occurrence of ecologically similar congeneric Microcebus species.

Background: A central question in evolutionary biology is how cryptic species maintain species cohesiveness in an area of sympatry. The coexistence of sympatrically living cryptic species requires the evolution of species-specific signalling and recognition systems. In nocturnal, dispersed living species, specific vocalisations have been suggested to act as an ideal premating isolation mechanism. We studied the structure and perception of male advertisement calls of three nocturnal, dispersed living mouse lemur species, the grey mouse lemur (Microcebus murinus), the golden brown mouse lemur (M. ravelobensis) and the Goodman's mouse lemur (M. lehilahytsara). The first two species occur sympatrically, the latter lives allopatrically to them., Results: A multi-parameter sound analysis revealed prominent differences in the frequency contour and in the duration of advertisement calls. To test whether mouse lemurs respond specifically to calls of the different species, we conducted a playback experiment with M. murinus from the field using advertisement calls and alarm whistle calls of all three species. Individuals responded significantly stronger to conspecific than to heterospecific advertisement calls but there were no differences in response behaviour towards statistically similar whistle calls of the three species. Furthermore, sympatric calls evoked weaker interest than allopatric advertisement calls., Conclusion: Our results provide the first evidence for a specific relevance of social calls for speciation in cryptic primates. They furthermore support that specific differences in signalling and recognition systems represent an efficient premating isolation mechanism contributing to species cohesiveness in sympatrically living species.

Predator mobbing is a widespread phenomenon in many taxa but the evolution of cooperative mobbing as an adaptive behavior is still subject to debate. Here, we report evidence for cooperative predator defense in a nocturnal solitarily foraging primate, the gray mouse lemur (Microcebus murinus). Several mouse lemurs mobbed a snake that held a non-related male conspecific until he could escape. Evolutionary hypotheses to explain cooperative mobbing include (1) by-product mutualism, when individuals defend others in the process of defending themselves; (2) reciprocity, where animals achieve a higher fitness when helping each other than when they do not cooperate; and (3) kin selection where animals help each other only if they share genes by common descent. Owing to the solitary activity of this species, reciprocity seems to be least likely to explain our observations. By-product mutualism cannot be ruled out entirely but, if costs of snake mobbing are relatively low, the available detailed socio-genetic information indicates that kin selection, rather than any of the other proposed mechanisms, is the primary evolutionary force behind the observed cooperative rescue.

The mechanisms and temporal aspects of mate choice according to genetic constitution are still puzzling. Recent studies indicate that fitness is positively related to diversity in immune genes (MHC). Both sexes should therefore choose mates of high genetic quality and/or compatibility. However, studies addressing the role of MHC diversity in pre- and post-copulatory mate choice decisions in wild-living animals are few. We investigated the impact of MHC constitution and of neutral microsatellite variability on pre- and post-copulatory mate choice in both sexes in a wild population of a promiscuous primate, the grey mouse lemur (Microcebus murinus). There was no support for pre-copulatory male or female mate choice, but our data indicate post-copulatory mate choice that is associated with genetic constitution. Fathers had a higher number of MHC supertypes different from those of the mother than randomly assigned males. Fathers also had a higher amino acid distance to the females' MHC as well as a higher total number of MHC supertypes and a higher degree of microsatellite heterozygosity than randomly assigned males. Female cryptic choice may be the underlying mechanism that operates towards an optimization of the genetic constitution of offspring. This is the first study that provides support for the importance of the MHC constitution in post-copulatory mate choice in non-human primates.

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.

Parental care should evolve only if fitness benefits exceed fitness costs. In Cheirogaleus medius, a small nocturnal lemur of western Madagascar, we found the peculiar situation of considerable parental care by both sexes, combined with an extremely high rate of extra-pair young (EPY). In this paper, we try to elucidate the costs and benefits of parental care in C. medius, and we discuss hypotheses as to why males might actively participate in raising young, especially with regard to the high rate of EPY. The study was carried out in the dry deciduous forest of western Madagascar between 1996 and 2001. The most important components of parental care in C. medius are babysitting and guarding of the young. Observational data suggest that thermoregulatory demands during the first days after birth and defence from predators may be the driving factors selecting for this infant care behaviour. The reproducing individuals of both sexes incur considerable energetic costs by this behaviour, resulting in reduced fat stores and body condition in comparison to non-reproducing individuals. The reason why males also care for EPY remains elusive. We propose that males might not be able to detect individual relatedness and that they would jeopardise the survival of their own young if they gave no parental care. Alternatively, they might gain advantages other than direct fitness from raising EPY, for example if caring behaviour increases their chances in further reproduction, or if EPY are fathered by close kin.

We investigated the sleeping site ecology of two sympatric mouse lemur species (Microcebus murinus and M. ravelobensis) in northwestern Madagascar during the second half of the dry season with respect to the type, quality, and usage pattern of the sleeping sites, as well as to social sleeping habits and response to potential threats. The type and quality of the sleeping sites differed between the two species. M. murinus used protected wooden shelters (tree holes) more frequently than M. ravelobensis, and M. ravelobensis used a broader variety of less protected sites (e.g., branches, lianas, and leaves) than M. murinus. Whereas male M. murinus usually slept alone, and female M. murinus mostly slept in groups, both sexes of M. ravelobensis slept in mixed-sex sleeping groups. M. murinus relied on crypsis in their sleeping sites, whereas M. ravelobensis regularly showed a flight response to the approach of an observer. This behavioral difference could indicate an adaptation to a higher predation risk in less protected sleeping sites. Whereas female M. murinus showed a high site fidelity, male M. murinus and both sexes of M. ravelobensis frequently changed their sleeping sites, which may also be interpreted as an antipredator strategy. The results are discussed with respect to three possible ecological explanations: interspecies competition, restricted resource availability, and niche differentiation. The latter is the most likely explanation for these interspecific differences., (Copyright 2003 Wiley-Liss, Inc.)

Body weight is an important attribute of any animal and influences its biology in many ways. In the case of the fat-tailed dwarf lemur (Cheirogaleus medius), this is of special interest because animals of this species store fat to survive extended torpor phases during the austral winter and, as a result, show extreme seasonal variation in body weight. In this paper, I present field data from a 20-month study at the Forestry Station of Ampijoroa in northwestern Madagascar on body weights of repeatedly trapped individuals combined with trapping results to investigate the general biology and notably the social life of C. medius. The most remarkable physical characteristic of wild C. medius is a dramatic weight-loss in males in September following emergence from torpor. Trapping results showed that adult males emerge from torpor earlier than females and offspring, even though food is still scarce. Early emergence from torpor puts males at an energetic disadvantage and confers no advantage in terms of access to females. Observation data from nightly follows indicate that males patrol their home range, probably to guarantee its integrity for the coming active season and to secure the food supply for their families. The high energetic costs of this strategy is argued to represent a form of paternal investment. Body weight data of repeatedly captured individuals showed that they may reach adult size and sexual maturity at 2 years of age but are not socially mature before the age of 3 years. The data presented may serve as a guide for keeping C. medius at a suitable weight in captivity.