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

Non-structural genes of novel lemur adenoviruses reveal codivergence of virus and host

Adenoviruses (AdVs) are important human and animal pathogens and are frequently used as vectors for gene therapy and vaccine delivery. Surprisingly, there are only scant data regarding primate AdV origin and evolution, especially in the most basal primate hosts. We detect and sequence AdVs from faeces of two Madagascan lemur species. Complete genome sequence analyses define a new AdV species with a particularly large gene encoding a protein of unknown function in the early gene region 3. Unexpectedly, the new AdV species is not most similar to human or other simian AdVs but to bat adenovirus C. Genome characterisation shows signals of virus-host codivergence in non-structural genes, which show lower diversity than structural genes. Outside a lemur species mixing zone, recombination less frequently separates structural genes, as in human adenovirus C. The evolutionary history of lemur AdVs likely involves both a host switch and codivergence with the lemur hosts.

RADseq data reveal a lack of admixture in a mouse lemur contact zone contrary to previous microsatellite results

Microsatellites have been a workhorse of evolutionary genetic studies for decades and are still commonly in use for estimating signatures of genetic diversity at the population and species level across a multitude of taxa. Yet, the very high mutation rate of these loci is a double-edged sword, conferring great sensitivity at shallow levels of analysis (e.g. paternity analysis) but yielding considerable uncertainty for deeper evolutionary comparisons. For the present study, we used reduced representation genome-wide data (restriction site-associated DNA sequencing (RADseq)) to test for patterns of interspecific hybridization previously characterized using microsatellite data in a contact zone between two closely related mouse lemur species in Madagascar (Microcebus murinus and Microcebus griseorufus). We revisit this system by examining populations in, near, and far from the contact zone, including many of the same individuals that had previously been identified as hybrids with microsatellite data. Surprisingly, we find no evidence for admixed nuclear ancestry. Instead, re-analyses of microsatellite data and simulations suggest that previously inferred hybrids were false positives and that the program NewHybrids can be particularly sensitive to erroneously inferring hybrid ancestry. Combined with results from coalescent-based analyses and evidence for local syntopic co-occurrence, we conclude that the two mouse lemur species are in fact completely reproductively isolated, thus providing a new understanding of the evolutionary rate whereby reproductive isolation can be achieved in a primate.

Differential habitat use by sympatric species of mouse lemurs across a mangrove–dry forest habitat gradient

Understanding the mechanisms by which similar species coexist in sympatry is a major driver of ecological research. Niche partitioning and ecological plasticity can facilitate spatial and habitat use overlap between generalist and specialist species. Mouse lemurs (Microcebus spp.) are a highly speciose group of small primates that are endemic to the forests of Madagascar. In northwestern Madagascar, the relatively widespread M. murinus occurs sympatrically with the microendemic M. ravelobensis. We investigated spatial distributions and densities of these two species across a mangrove–dry forest habitat gradient in Mariarano commune. We used capture-mark-recapture techniques and nocturnal line transect surveys along six transects during June and July 2017. Spatial capture-recapture and distance sampling models were used to estimate lemur densities across habitat types. The congeners displayed differential patterns of spatial distribution and densities. Microcebus murinus was found in similar densities across all habitat types, while M. ravelobensis was found at much higher densities in dry forests compared with mangroves. This suggests that the generalist M. murinus uses a wider array of habitats more evenly than the specialist M. ravelobensis. Our study provides empirical evidence of how cryptic lemur species differ in their habitat use and distribution across an environmental gradient and provides new insights into their ecology in an understudied habitat. Lemurs are one of the most threatened groups of mammals in the world, and understanding how these species are distributed across different forest types is crucial for planning and implementing conservation measures to protect lemur habitat.

Mouse Lemurs in an Assemblage of Cheirogaleid Primates in Menabe Central, Western Madagascar – Three Reasons to Coexist

Ecological communities are structured by interactions between coexisting species that mutually influence their distribution and abundance. Ecologically similar species are expected to exclude one another from suitable habitat, so the coexistence of two mouse lemur species in an assemblage of several closely related cheirogaleid primates in the central Menabe region of Madagascar requires explanation. We assessed the occurrence of Madame Berthe’s mouse lemurs (Microcebus berthae) and Gray mouse lemurs (Microcebus murinus), and of two larger cheirogaleids, Coquerel’s giant mouse lemur (Mirza coquereli) and the western fat-tailed dwarf lemur (Cheirogaleus medius), by nocturnal line transect walks between 2003 and 2007. We explored interspecific interactions for four different scenarios with varying resource availability (degraded and non-degraded habitat in the wet and dry season), both on the regional spatial scale and on a finer local (transect) scale. We tested whether the interspecific distribution of mouse lemur individuals indicates interspecific competition and whether their regional coexistence might be stabilized by interactions with M. coquereli or C. medius. We developed the “Inter-Species Index of Attraction” (ISIA) to quantify the observed interspecific interactions within transects and determined if these were significantly different from a null model generated by a combination of randomization and bootstrapping to control for intraspecific aggregation. For the two mouse lemurs, interspecific spatial exclusion was most pronounced during the resource-poor dry season, consistent with the hypothesis of feeding competition. Seasonally varying distribution patterns indicated resource tracking in a spatio-temporally heterogeneous environment. The interspecific distribution of individuals suggested that the larger cheirogaleids benefit M. berthae at the expense of the more abundant M. murinus: spatial associations of both, M. coquereli and C. medius, with M. murinus were negative in most scenarios and across spatial scales, but neutral or even positive with M. berthae. Thus, our study revealed that coexistence among ecologically similar heterospecifics can rely on complex density-mediated interspecific processes varying with habitat quality and season. With regard to the stability of animal assemblages, this insight has major implications for biodiversity conservation.

First experimental evidence for olfactory species discrimination in two nocturnal primate species (Microcebus lehilahytsara and M. murinus)

Olfactory communication is highly important for nocturnal mammals, especially for solitary foragers, but knowledge is still limited for nocturnal primates. Mouse lemurs (Microcebus spp.) are nocturnal solitary foragers with a dispersed lifestyle and frequently use chemo-sensory signalling behaviour for governing social interactions. Different mouse lemur species can co-occur in a given forest but it is unknown whether olfaction is involved in species recognition. We first screened 24 captive mouse lemurs (9 M. murinus, 15 M. lehilahytsara) for their olfactory learning potential in an experimental arena and then tested the species discrimination ability with urine odour in an operant conditioning paradigm in four individuals. The majority of the screened animals (75%) did not pass the screening criteria within a 2-week test period. However, all four final test animals, two M. murinus and two M. lehilahytsara, were successfully trained in a 5-step-conditioning process to reliably discriminate conspecific from heterospecific urine odour (requiring an overall median of 293 trials). Findings complement previous studies on the role of acoustic signalling and suggest that olfaction may be an important additional mechanism for species discrimination.

Morphometric signals of population decline in diademed sifakas occupying degraded rainforest habitat in Madagascar

Anthropogenic habitat change can have varied impacts on primates, including both negative and positive outcomes. Even when behavioural shifts are seen, they may reflect decreased health, or simply behavioural flexibility; understanding this distinction is important for conservation efforts. This study examines habitat-related variation in adult and immature morphometrics among diademed sifakas (Propithecus diadema). We collected morphometric data from sifakas at Tsinjoarivo, Madagascar (19 years, 188 captures, 113 individuals). Captures spanned 12 groups, five within continuous forest ("CONT"), and seven in degraded fragments ("FRAG") where sifakas have lower nutritional intakes. Few consistent differences were found between CONT and FRAG groups. However, using home range quality as a covariate rather than a CONT/FRAG dichotomy revealed a threshold: the two FRAG groups in the lowest-quality habitat showed low adult mass and condition (wasting), and low immature mass and length (stunting). Though less-disturbed fragments apparently provide viable habitat, we suggest the sifakas in the most challenging habitats cannot evolve fast enough to keep up with such rapid habitat change. We suggest other long-lived organisms will show similar morphometric "warning signs" (wasting in adults, stunting in immatures); selected morphometric variables can thus be useful at gauging vulnerability of populations in the face of anthropogenic change.

Range Extension and Behavioural Observations of the Recently Described Sheth's Dwarf Lemur (Cheirogaleus shethi)

Sheth's dwarf lemur, Cheirogaleus shethi, is a small, recently discovered nocturnal primate endemic to northern Madagascar. Unlike many other nocturnal lemurs, C. shethi lives sympatrically with morphologically similar species of its cryptic genus, making it difficult for biologists to determine its population density and distribution. Here, we present new data and observations of this species. During a series of rapid biodiversity assessments in the SAVA region of north-eastern Madagascar, we observed C. shethi in 10 different sites, 9 of which were not previously known to harbour C. shethi populations. More significantly, 2 of these sites, in Analamanara, were situated approximately 20 km south of the previously known southern extremity of this species' distribution. This represents a large increase in the previously limited geographic range of this species. Moreover, our relatively high encounter rates at these sites suggest that C. shethi population densities may be high. We also observed C. shethi in human-altered (e.g., vanilla plantations) and non-forest, savannah environments, suggesting that this species can tolerate disturbed habitats. Our findings therefore provide important additional information on the distribution of C. shethi populations and highlight the necessity of further study for the conservation of this species.

Maintaining microendemic primate species along an environmental gradient - parasites as drivers for species differentiation

Understanding the drivers of species adaptations to changing environments on the one hand and the limits for hybridization on the other hand is among the hottest questions in evolutionary biology. Parasites represent one of the major selective forces driving host evolution and at least those with free-living stages are at the same time dependent on the ecological conditions of their host's habitat. Local immunological adaptations of host species to varying parasite pressure are therefore expected and might represent the genetic basis for ecological speciation and the maintenance of recently diverged species. Madagascar provides one of the rare examples where two partially sympatric primate species (Microcebus griseorufus, M. murinus) and their hybrids, as well as an allopatric species (M. cf rufus) live in close proximity along a very steep environmental gradient ranging from southern dry spiny bush to gallery forest to evergreen eastern humid rain forest, thus mimicking the situation encountered during extensions and retreats of vegetation formations under changing climatic conditions. This system was used to study parasite infection and immune gene (MHC) adaptations to varying parasite pressure that might provide selective advantages to pure species over hybrids. Parasite burdens increased with increasing humidity. M. griseorufus, M. murinus, and their hybrids but not M. rufus shared the same MHC alleles, indicating either retention of ancestral polymorphism or recent gene flow. The hybrids had much higher prevalence of intestinal parasites than either of the parent species living under identical environmental conditions. The different representation of parasites can indicate a handicap for hybrids that maintains species identities.

Multilocus coalescent analyses reveal the demographic history and speciation patterns of mouse lemur sister species

Background

Debate continues as to whether allopatric speciation or peripatric speciation through a founder effect is the predominant force driving evolution in vertebrates. The mouse lemurs of Madagascar are a system in which evolution has generated a large number of species over a relatively recent time frame. Here, we examine speciation patterns in a pair of sister species of mouse lemur, Microcebus murinus and M. griseorufus. These two species have ranges that are disparately proportioned in size, with M. murinus showing a much more extensive range that marginally overlaps that of M. griseorufus. Given that these two species are sister taxa, the asymmetric but overlapping geographic ranges are consistent with a model of peripatric speciation. To test this hypothesis, we analyze DNA sequence data from four molecular markers using coalescent methods. If the peripatric speciation model is supported, we predict substantially greater genetic diversity in M. murinus, relative to M. griseorufus. Further, we expect a larger effective population size in M. murinus and in the common ancestor of the two species than in M. griseorufus, with a concomitant decrease in gene tree/species tree incongruence in the latter and weak signs of demographic expansion in M. murinus.

Results

Our results reject a model of peripatric divergence. Coalescent effective population size estimates were similar for both extant species and larger than that estimated for their most recent common ancestor. Gene tree results show similar levels of incomplete lineage sorting within species with respect to the species tree, and locus-specific estimates of genetic diversity are concordant for both species. Multilocus demographic analyses suggest range expansions for M. murinus, with this species also experiencing more recent population declines over the past 160 thousand years.

Conclusions

Results suggest that speciation occurred in allopatry from a common ancestor narrowly distributed throughout southwest Madagascar, with subsequent range expansion for M. murinus. Population decline in M. murinus is likely related to patterns of climate change in Madagascar throughout the Pleistocene, potentially exacerbated by continual anthropogenic perturbation. Genome-level data are needed to quantify the role of niche specialization and adaptation in shaping the current ranges of these species.

New postcranial elements for the earliest Eocene fossil primate Teilhardina belgica

Teilhardina belgica is one of the most primitive fossil primates known to date and the earliest haplorhine with associated postcranials, making it relevant to a reconstruction of the ancestral primate morphotype. Here we describe newly discovered postcranial elements of T. belgica. It is a small primate with an estimated body mass between 30 and 60 g, similar to the size of a mouse lemur. Its hindlimb anatomy suggests frequent and forceful leaping with excellent foot mobility and grasping capabilities. It can now be established that this taxon exhibits critical primate postcranial synapomorphies such as a grasping hallux, a tall knee, and nailed digits. This anatomical pattern and behavioral profile is similar to what has been inferred before for other omomyids and adapiforms. The most unusual feature of T. belgica is its elongated middle phalanges (most likely manual phalanges), suggesting that this early primate had very long fingers similar to those of living tarsiers.

Habitat separation of sympatric Microcebus spp. in the dry spiny forest of south-eastern Madagascar

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.