Molecular phylogeny of the lemur family cheirogaleidae (primates) based on mitochondrial DNA sequences

Conservation genomic analysis reveals ancient introgression and declining levels of genetic diversity in Madagascar's hibernating dwarf lemurs

Madagascar’s biodiversity is notoriously threatened by deforestation and climate change. Many of these organisms are rare, cryptic, and severely threatened, making population-level sampling unrealistic. Such is the case with Madagascar’s dwarf lemurs (genus Cheirogaleus), the only obligate hibernating primate. We here apply comparative genomic approaches to generate the first genome-wide estimates of genetic diversity within dwarf lemurs. We generate a reference genome for the fat-tailed dwarf lemur, Cheirogaleus medius, and use this resource to facilitate analyses of high-coverage (~30×) genome sequences for wild-caught individuals representing species: C. sp. cf. medius, C. major, C. crossleyi, and C. sibreei. This study represents the largest contribution to date of novel genomic resources for Madagascar’s lemurs. We find concordant phylogenetic relationships among the four lineages of Cheirogaleus across most of the genome, and yet detect a number of discordant genomic regions consistent with ancient admixture. We hypothesized that these regions could have resulted from adaptive introgression related to hibernation, indeed finding that genes associated with hibernation are present, though most significantly, that gene ontology categories relating to transcription are over-represented. We estimate levels of heterozygosity and find particularly low levels in an individual sampled from an isolated population of C. medius that we refer to as C. sp. cf. medius. Results are consistent with a recent decline in effective population size, which is evident across species. Our study highlights the power of comparative genomic analysis for identifying species and populations of conservation concern, as well as for illuminating possible mechanisms of adaptive phenotypic evolution.

The lemur revolution starts now: the genomic coming of age for a non-model organism

Morris Goodman was a revolutionary. Together with a mere handful of like-minded scientists, Morris established himself as a leader in the molecular phylogenetic revolution of the 1960s. The effects of this revolution are most evident in this journal, which he founded in 1992. Happily for lemur biologists, one of Morris Goodman's primary interests was in reconstructing the phylogeny of the primates, including the tooth-combed Lorisifomes of Africa and Asia, and the Lemuriformes of Madagascar (collectively referred to as the suborder Strepsirrhini). This paper traces the development of molecular phylogenetic and evolutionary genetic trends and methods over the 50-year expanse of Morris Goodman's career, particularly as they apply to our understanding of lemuriform phylogeny, biogeography, and biology. Notably, this perspective reveals that the lemuriform genome is sufficiently rich in phylogenetic signal such that the very earliest molecular phylogenetic studies - many of which were conducted by Goodman himself - have been validated by contemporary studies that have exploited advanced computational methods applied to phylogenomic scale data; studies that were beyond imagining in the earliest days of phylogeny reconstruction. Nonetheless, the frontier still beckons. New technologies for gathering and analyzing genomic data will allow investigators to build upon what can now be considered a nearly-known phylogeny of the Lemuriformes in order to ask innovative questions about the evolutionary mechanisms that generate and maintain the extraordinary breadth and depth of biological diversity within this remarkable clade of primates.

Concatenation and concordance in the reconstruction of mouse lemur phylogeny: an empirical demonstration of the effect of allele sampling in phylogenetics

The systematics and speciation literature is rich with discussion relating to the potential for gene tree/species tree discordance. Numerous mechanisms have been proposed to generate discordance, including differential selection, long-branch attraction, gene duplication, genetic introgression, and/or incomplete lineage sorting. For speciose clades in which divergence has occurred recently and rapidly, recovering the true species tree can be particularly problematic due to incomplete lineage sorting. Unfortunately, the availability of multilocus or "phylogenomic" data sets does not simply solve the problem, particularly when the data are analyzed with standard concatenation techniques. In our study, we conduct a phylogenetic study for a nearly complete species sample of the dwarf and mouse lemur clade, Cheirogaleidae. Mouse lemurs (genus, Microcebus) have been intensively studied over the past decade for reasons relating to their high level of cryptic species diversity, and although there has been emerging consensus regarding the evolutionary diversity contained within the genus, there is no agreement as to the inter-specific relationships within the group. We attempt to resolve cheirogaleid phylogeny, focusing especially on the mouse lemurs, by employing a large multilocus data set. We compare the results of Bayesian concordance methods with those of standard gene concatenation, finding that though concatenation yields the strongest results as measured by statistical support, these results are found to be highly misleading. By employing an approach where individual alleles are treated as operational taxonomic units, we show that phylogenetic results are substantially influenced by the selection of alleles in the concatenation process.

Varying patterns of coexistence of two mouse lemur species (Microcebus ravelobensis and M. murinus) in a heterogeneous landscape

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.

Deep evolutionary roots of strepsirrhine primate labyrinthine morphology

The cavity system of the inner ear of mammals is a complex three-dimensional structure that houses the organs of equilibrium and hearing. Morphological variation of the inner ear across mammals reflects differences in locomotor behaviour and hearing performance, and the good preservation of this structure in many fossil specimens permits analogous inferences. However, it is less well known to what extent the morphology of the bony labyrinth conveys information about the evolutionary history of primate taxa. We studied this question in strepsirrhine primates with the aim to assess the potential and limitations of using the inner ear as a phylogenetic marker. Geometric morphometric analysis showed that the labyrinthine morphology of extant strepsirrhines contains a mixed locomotor, allometric and phylogenetic signal. Discriminant analysis at the family level confirmed that labyrinthine shape is a good taxonomic marker. Our results support the hypothesis that evolutionary change in labyrinthine morphology is adequately described with a random walk model, i.e. random phenotypic dispersal in morphospace. Under this hypothesis, average shapes calculated for each node of the phylogenetic tree give an estimate of inner ear shapes of the respective last common ancestors (LCAs), and this information can be used to infer character state polarity. The labyrinthine morphology of the fossil Adapinae is close to the inferred basal morphology of the strepsirrhines. The inner ear of Daubentonia, one of the most derived extant strepsirrhines, is autapomorphic in many respects, but also presents unique similarities with adapine labyrinths.

Molecular phylogeny and evolution of prosimians based on complete sequences of mitochondrial DNAs

Prosimians (tarsiers and strepsirrhini) represent the basal lineages in primates and have a close bearing on the origin of primates. Although major lineages among anthropoidea (humans, apes and monkeys) are well represented by complete mitochondrial DNA (mtDNA) sequence data, only one complete mtDNA sequence from a representative of each of the infraorders in prosimians has been described until quite recently, and therefore we newly determined complete mtDNA sequences from 5 lemurs, 4 lorises, one tarsier and one platyrrhini. These sequences were provided to phylogenetic analyses in combination with the sequences from the 15 primates species reported to the database. The position of tarsiers among primates could not be resolved by the maximum likelihood (ML) and neighbor-joining (NJ) analyses with several data sets. As to the position of tarsiers, any of the three alternative topologies (monophyly of haplorhini, monophyly of prosimians, and tarsiers being basal in primates) was not rejected at the significance level of 5%, neither at the nucleotide nor at the amino acid level. In addition, the significant variations of C and T compositions were observed across primates species. Furthermore, we used AGY data sets for phylogenetic analyses in order to remove the effect of different C/T composition bias across species. The analyses of AGY data sets provided a medium support for the monophyly of haplorhini, which might have been screened by the variation in base composition of mtDNA across species. To estimates the speciation dates within primates, we analyzed the amino acid sequences of mt-proteins with a Bayesian method of Thorne and Kishino. Divergence dates were estimated as follows for the crown groups: about 35.4 million years ago (mya) for lorisiformes, 55.3 mya for lemuriformes, 64.5 mya for strepsirrhini, 70.1 mya for haplorhini and 76.0 mya for primates. Furthermore, we reexamined the biogeographic scenarios which have been proposed for the origin of strepsirrhini (lemuriformes and lorisiformes) and for the dispersal of the lemuriformes and lorisiformes.

Acoustic divergence in the communication of cryptic species of nocturnal primates (Microcebus ssp.)

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.

Resource-aware taxon selection for maximizing phylogenetic diversity

Phylogenetic diversity (PD) is a useful metric for selecting taxa in a range of biological applications, for example, bioconservation and genomics, where the selection is usually constrained by the limited availability of resources. We formalize taxon selection as a conceptually simple optimization problem, aiming to maximize PD subject to resource constraints. This allows us to take into account the different amounts of resources required by the different taxa. Although this is a computationally difficult problem, we present a dynamic programming algorithm that solves it in pseudo-polynomial time. Our algorithm can also solve many instances of the Noah's Ark Problem, a more realistic formulation of taxon selection for biodiversity conservation that allows for taxon-specific extinction risks. These instances extend the set of problems for which solutions are available beyond previously known greedy-tractable cases. Finally, we discuss the relevance of our results to real-life scenarios.

Unexpected species diversity of Malagasy primates (Lepilemur spp.) in the same biogeographical zone: a morphological and molecular approach with the description of two new species

BACKGROUND

The lemurs of Madagascar provide an excellent mammalian radiation to explore mechanisms and processes favouring species diversity and evolution. Species diversity, in particular of nocturnal species, increased considerably during the last decade. However, the factors contributing to this high diversity are not well understood. We tested predictions derived from two existing biogeographic models by exploring the genetic and morphological divergence among populations of a widely distributed lemur genus, the sportive lemur (Lepilemur ssp.) along a 560 km long transect from western to northern Madagascar.

RESULTS

By using the phylogenetic analyses of mtDNA sequence data, molecular diagnostic sites and phenotypic morphometric traits, we uncovered two previously undetected species whose distributions contradict the two existing biogeographic models. Brief species descriptions are provided and a new biogeographic model is proposed (the "large river model").

CONCLUSION

According to the "large river model", large rivers in north and northwestern Madagascar acted as geographical barriers for gene flow and facilitated speciation events on a much smaller spatial scale than previously thought. Thereby, this study does not only show that species diversity in nocturnal Malagasy primates is continuously underestimated but aims to emphasize the need for conservation actions if those species with small ranges shall not face extinction in the near future.

Body size and scaling of the hands and feet of prosimian primates

The hands and feet of primates fulfill a variety of biological roles linked with food acquisition and positional behavior. Current explanations of shape differences in cheiridial morphology among prosimians are closely tied to body size differences. Although numerous studies have examined the relationships between body mass and limb morphology in prosimians, no scaling analysis has specifically considered hand and foot dimensions and intrinsic proportions. In this study, we present such an analysis for a sample of 270 skeletal specimens distributed over eight prosimian families. The degree of association between size and shape was assessed using nonparametric correlational techniques, while the relationship between each ray element length and body mass (from published data and a body mass surrogate) was tested for allometric scaling. Since tarsiers and strepsirrhines encompass many taxa of varying degrees of phylogenetic relatedness, effective degrees of freedom were calculated, and comparisons between families were performed to partially address the problem of statistical nonindependence and "phylogenetic inertia." Correlational analyses indicate negative allometry between relative phalangeal length (as reflected by phalangeal indices) and body mass, except for the pollex and hallux. Thus, as size increases, there is a significant decrease in the relative length of the digits when considering all prosimian taxa sampled. Regression analyses show that while the digital portion of the rays scales isometrically with body mass, the palmar/plantar portion of the rays often scales with positive allometry. Some but not all of these broadly interspecific allometric patterns remain statistically significant when effective degrees of freedom are taken into account. As is often the case in interspecific scaling, comparisons within families show different scaling trends in the cheiridia than those seen across families (i.e., lorisids, indriids, and lemurids exhibit rather different allometries). The interspecific pattern of positive allometry that appears to best characterize the metapodials of prosimians, especially those of the foot, parallels differences found in the morphology of the volar skin. Indeed, relatively longer metapodials appear to covary with flatter and more coalesced volar pads, which in turn slightly improve frictional force for animals that are at a comparative disadvantage while climbing because of their larger mass. Despite the essentially isometric relationship found between digit length and body mass across prosimians, examination of the residual variation reveals that tarsiers and Daubentonia possess, relative to their body sizes, remarkably long fingers. Such marked departures between body size and finger length observed in these particular primates are closely linked with specialized modes of prey acquisition and manipulation involving the hands.

Lack of torpor in free-ranging southern lesser galagos, Galago moholi: ecological and physiological considerations

Studies investigating heterothermy under natural conditions are particularly scarce for tropical species. However, heterothermy patterns in tropical and subtropical environments often differ markedly from those observed in arctic and temperate species. The investigation of heterothermy in strepsirhine primates has focussed largely on the Malagasy cheirogaleids. In addition, a physiological verification of torpor occurrence in mainland strepsirhines is important with regard to arguments pertaining to the colonization of Madagascar by strepsirhine primates. We measured body temperatures of 11 free-ranging Galago moholi, between February 2002 and September 2003, for 3 consecutive months for each animal. No incidents of heterothermy were recorded throughout the study period. We considered how physiological and ecological aspects of G. moholi biology might have obviated the use of torpor. It was suggested that the breeding pattern observed in G. moholi prevented torpor use whilst increasing fecundity, and that the ecological costs of torpor far outweighed the energetic costs. This study highlights the need for more studies on free-ranging animals to elucidate the physiological, ecological and phylogenetic constraints and determinants of torpor use. Furthermore, if convincing arguments are to be made regarding the possible role of heterothermy in species dispersal, more data from free-ranging animals are needed.

A composite molecular phylogeny of living lemuroid primates

Lemuroid phylogeny is a source of lively debate among primatologists. Reconstructions based on morphological, physiological, behavioural and molecular data have yielded a diverse array of tree topologies with few nodes in common. In the last decade, molecular phylogenetic studies have grown in popularity, and a wide range of sequences has been brought to bear on the problem, but consensus has remained elusive. We present an analysis based on a composite molecular data set of approx. 6,400 bp assembled from the National Center for Biotechnology Information (NCBI) database, including both mitochondrial and nuclear genes, and diverse analytical methods. Our analysis consolidates some of the nodes that were insecure in previous reconstructions, but is still equivocal on the placement of some taxa. We conducted a similar analysis of a composite data set of approx. 3,600 bp to investigate the controversial relationships within the family Lemuridae. Here our analysis was more successful; only the position of Eulemur coronatus remained uncertain.

Incongruence between genetic and morphological diversity in Microcebus griseorufus of Beza Mahafaly

BACKGROUND

The past decade has seen a remarkable increase in the number of recognized mouse lemur species (genus Microcebus). As recently as 1994, only two species of mouse lemur were recognized according to the rules of zoological nomenclature. That number has now climbed to as many as fifteen proposed species. Indeed, increases in recognized species diversity have also characterized other nocturnal primates--galagos, sportive lemurs, and tarsiers. Presumably, the movement relates more to a previous lack of information than it does to any recent proclivity for taxonomic splitting. Due to their nocturnal habits, one can hypothesize that mouse lemurs will show only minimal variation in pelage coloration as such variation should be inconsequential for the purposes of mate and/or species recognition. Even so, current species descriptions for nocturnal strepsirrhines place a good deal of emphasis on relatively fine distinctions in pelage coloration.

RESULTS

Here, we report results from a multi-year study of mouse lemur populations from Beza Mahafaly in southern Madagascar. On the basis of morphological and pelage variation, we initially hypothesized the presence of up to three species of mouse lemurs occurring sympatrically at this locality, one of which appeared to be undescribed. Genetic analysis reveals definitively, however, that all three color morphs belong to a single recognized species, Microcebus griseorufus. Indeed, in some cases, the three color morphs can be characterized by identical mitochondrial haplotypes.

CONCLUSION

Given these results, we conclude that investigators should always proceed with caution when using a single data source to identify novel species. A synthetic approach that combines morphological, genetic, geographic, and ecological data is most likely to reveal the true nature of species diversity.

The ever-increasing diversity in mouse lemurs: three new species in north and northwestern Madagascar

Mouse lemurs (Microcebus spp.) are the world's smallest primates and endemic to Madagascar. Several recent taxonomic revisions resulted in an extraordinary increase of recognized species. What still was considered as being two species at the beginning of the 20th century is currently recognized as 12 taxa. Based on fur coloration pattern, they can be divided into grayish and reddish forms. Two major models have been proposed to explain the extensive speciation events in the Malagasy fauna. The best known suggests that major rivers and mountains combine to act as effective barriers to gene flow and thereby facilitate allopatric speciation processes. A more recent model used an analysis of watersheds in the context of Quaternary climatic shifts to explain the process of explosive speciation on the island. We tested these two models by covering the areas between all major rivers (n=8) in northwestern and northern Madagascar. Mouse lemurs were systematically caught, sampled and morphometrically characterized in 25 sites (with 2-49 individuals per site and species). A complete phylogeny was constructed on the basis of the sequences of three mitochondrial loci (in total 1296 bp). The phylogenetic data revealed a previously unknown biodiversity with three new mouse lemur species among the reddish forms, each having a very small distribution, i.e., being restricted to only one Inter-River-System (IRS). Morphometric analyses underlined their distinctiveness and a brief formal species description is provided. In contrast to the reddish forms, grayish forms have a very low species diversity coupled with broad distributions that cover more than one IRS. These differences among the species are discussed as outcome of divergent colonization scenarios. Elements of both biogeographic models are combined in a new hypothesis that aims to explain the speciation process leading to the present distribution of mouse lemurs in Madagascar.

Molecular phylogeny and taxonomic revision of the sportive lemurs (Lepilemur, Primates)

BACKGROUND

The number of species within the Malagasy genus Lepilemur and their phylogenetic relationships is disputed and controversial. In order to establish their evolutionary relationships, a comparative cytogenetic and molecular study was performed. We sequenced the complete mitochondrial cytochrome b gene (1140 bp) from 68 individuals representing all eight sportive lemur species and most major populations, and compared the results with those obtained from cytogenetic studies derived from 99 specimens.

RESULTS

Interspecific genetic variation, diagnostic characters and significantly supported phylogenetic relationships were obtained from the mitochondrial sequence data and are in agreement with cytogenetic information. The results confirm the distinctiveness of Lepilemur ankaranensis, L. dorsalis, L. edwardsi, L. leucopus, L. microdon, L. mustelinus, L. ruficaudatus and L. septentrionalis on species level. Additionally, within L. ruficaudatus large genetic differences were observed among different geographic populations. L. dorsalis from Sahamalaza Peninsula and from the Ambanja/Nosy Be region are paraphyletic, with the latter forming a sister group to L. ankaranensis.

CONCLUSION

Our results support the classification of the eight major sportive lemur taxa as independent species. Moreover, our data indicate further cryptic speciation events within L. ruficaudatus and L. dorsalis. Based on molecular data we propose to recognize the sportive lemur populations from north of the Tsiribihina River, south of the Betsiboka River, and from the Sahamalaza Peninsula, as distinct species.

Molar scaling in strepsirrhine primates

We examined how maxillary molar dimensions change with body and skull size estimates among 54 species of living and subfossil strepsirrhine primates. Strepsirrhine maxillary molar areas tend to scale with negative allometry, or possibly isometry, relative to body mass. This observation supports several previous scaling analyses showing that primate molar areas scale at or slightly below geometric similarity relative to body mass. Strepsirrhine molar areas do not change relative to body mass(0.75), as predicted by the metabolic scaling hypothesis. Relative to basicranial length, maxillary molar areas tend to scale with positive allometry. Previous claims that primate molar areas scale with positive allometry relative to body mass appear to rest on the incorrect assumption that skull dimensions scale isometrically with body mass. We identified specific factors that help us to better understand these observed scaling patterns. Lorisiform and lemuriform maxillary molar scaling patterns did not differ significantly, suggesting that the two infraorders had little independent influence on strepsirrhine scaling patterns. Contrary to many previous studies of primate dental allometry, we found little evidence for significant differences in molar area scaling patterns among frugivorous, folivorous, and insectivorous groups. We were able to distinguish folivorous species from frugivorous and insectivorous taxa by comparing M1 lengths and widths. Folivores tend to have a mesiodistally elongated M1 for a given buccolingual M1 width when compared to the other two dietary groups. It has recently been shown that brain mass has a strong influence on primate dental eruption rates. We extended this comparison to relative maxillary molar sizes, but found that brain mass appears to have little influence on the size of strepsirrhine molars. Alternatively, we observed a strong correlation between the relative size of the facial skull and relative molar areas among strepsirrhines. We hypothesize that this association may be underlain by a partial sharing of the patterning of development between molar and facial skull elements.

Application of molecular cytogenetics for chromosomal evolution of the Lemuriformes (Prosimians)

R-banding chromosomal studies of 21 species of Lemuriformes allowed us to reconstruct the presumed ancestral karyotype of all the Lemuriformes except for Daubentoniidae and permitted the construction of their phylogenetic tree. Chromosome painting with fluorescently labeled heterologous DNA probes permitted comparative chromosome maps to be established. The Zoo-FISH method was used to reassess the karyotypes of 22 species or subspecies. While our results largely confirm the previous reconstruction of the ancestral karyotype, they resulted in a modification of the previously established phylogenetic tree. The Daubentoniidae emerged first followed by the divergence of the families Cheirogaleidae, Indriidae, Lepilemuridae and Lemuridae. Eight chromosome rearrangements occurred in all Lemuriformes except for Daubentoniidae in the common trunk. The present findings do not allow us to propose the occurrence of any rearrangement common to Daubentoniidae and other Lemuriformes, and probably other Prosimii. Conserved syntenies previously described in various mammalian orders were also conserved, while others were specific to the Lemuriformes.

Divergence dates for Malagasy lemurs estimated from multiple gene loci: geological and evolutionary context

The lemurs of Madagascar are a unique radiation of primates that show an extraordinary diversity of lifestyles, morphologies and behaviours. However, very little is known about the relative antiquity of lemuriform clades due to the lack of terrestrial fossils for the Tertiary of Madagascar. Here, we employ a Bayesian method to estimate divergence dates within the lemuriform radiation using several unlinked gene loci and multiple fossil calibrations outside the lemuriform clade. Two mitochondrial genes (cytochrome oxidase II and cytochrome b), two nuclear introns (transthyretin intron 1 and von Willebrand factor gene intron 11) and one nuclear exon (interphotoreceptor retinoid binding protein, exon 1) are used in separate and combined analyses. The genes differ in taxon sampling and evolutionary characteristics but produce congruent date estimates. Credibility intervals narrow considerably in combined analyses relative to separate analyses due to the increased amount of data. We also test the relative effects of multiple vs. single calibration points, finding that, when only single calibration points are employed, divergence dates are systematically underestimated. For the mitochondrial DNA data set, we investigate the effects of sampling density within the mouse lemur radiation (genus Microcebus). When only two representative species are included, estimated dates throughout the phylogeny are more recent than with the complete-species sample, with basal nodes less affected than recent nodes. The difference appears to be due to the manner in which priors on node ages are constructed in the two analyses. In nearly all analyses, the age of the lemuriform clade is estimated to be approximately 62-65 Ma, with initial radiation of mouse lemurs and true lemurs (genus Eulemur) occurring approximately 8-12 Ma. The antiquity of the mouse lemur radiation is surprising given the near uniform morphology among species. Moreover, the observation that mouse lemurs and true lemurs are of similar ages suggests discrepancies in rates of morphological, behavioural and physiological evolution in the two clades, particularly with regard to characteristics of sexual signalling. These differences appear to correlate with the nocturnal vs. diurnal lifestyles, respectively, of these two primate groups.

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.

A molecular approach to comparative phylogeography of extant Malagasy lemurs

The lemurs of Madagascar provide an excellent model for exploring evolutionary diversification. This study investigates genetic divergence among most extant lemur taxa in relation to potential geographical boundaries to gene flow. For this purpose, approximately 2,400 bp of mitochondrial DNA (part of the COIII gene; ND3, ND4L, and ND4 genes; and five tRNAs) were sequenced in a total of 131 lemurs from 5 families, 12 genera, 25 species, and 18 subspecies to reconstruct phylogenetic relationships among them. The comprehensive range of taxa makes this a particularly suitable molecular data set to examine lemur evolution. Those data clearly reveal that the Betsiboka River acts as an isolating barrier between populations of lemurs in north-western Madagascar. The Tsiribihina River similarly serves as a barrier to gene flow between northern and southern populations of lemurs in central western Madagascar, whereas the Mahavavy River does not seem to lead to genetic isolation of lemur populations. Several discrepancies among molecular data, current taxonomy, and geographic distribution along the western coast emerged. Examination of geographical distribution of the taxa concerned in comparison with distribution boundaries of other lemur taxa in that region yielded explanations for these inconsistencies. Eulemur fulvus and Eulemur mongoz are the only lemur taxa that also occur outside Madagascar, on the Comoro Islands. Genetic data show no significant differentiation between Malagasy and Comorian populations of these species, supporting the interpretation that both were introduced only recently to the Comoro Islands.

Social organization of the golden brown mouse lemur (Microcebus ravelobensis)

Our study provides the first data on the social organization of the golden brown mouse lemur, a nocturnal primate discovered in northwestern Madagascar in 1994. The study was carried out in two 6-month field periods during the dry season, covering time before and during the mating season. The spatial and temporal distributions of the sexes in the population were investigated by mark/recapture and radiotelemetry. Focal observations and the determination of sleeping associations provided further insights into the sociality of this solitary forager. High intra- and intersexual home-range overlaps occurred throughout the study. In general, individuals of both sexes had spatial access to more than one conspecific of the same and the opposite sex. We found no indication for spatial monopolization of females by certain males. These results suggest a dispersed multimale/multifemale system with a promiscuous mating pattern. Individuals showed temporal stability in their home range locations and interacted regularly with conspecifics. Five sleeping groups were identified during the study period: one female group and four mixed-sex groups. Even though sleeping sites were changed frequently, sleeping-group compositions remained stable over time. Thermoregulatory constraints are the most likely explanation for sleeping-group composition with members of both sexes in this species. Mixed-sex sleeping groups can be described as the basic social unit within this dispersed multimale/multifemale society.

Molecular systematics and biogeography of the Neotropical monkey genus, Alouatta

We take advantage of the broad distribution of howler monkeys from Mexico to Argentina to provide a historical biogeographical analysis on a regional scale that encompasses the entire Neotropics. The phylogenetic relationships among 9 of the 10 recognized Alouatta species were inferred using three mitochondrial and two nuclear genes. The nuclear gene regions provided no phylogenetic resolution among howler monkey species, and were characterized by very low levels of sequence divergence between Alouatta and the Ateles outgroup. The mtDNA genes, on the other hand, produced a well-resolved phylogeny, which indicated that the earliest split among howler monkeys separated cis- and trans-Andean clades. Eight monophyletic mtDNA haplotype clades were identified, representing six named species in South America, including Alouatta seniculus, Alouatta sara, Alouatta macconelli, Alouatta caraya, Alouatta belzebul, and Alouatta guariba, and two in Mesoamerica, Alouatta pigra and Alouatta palliata. Molecular clock-based estimates of branching times indicated that contemporary howler monkey species originated in the late Miocene and Pliocene, not the Pleistocene. The causes of Alouatta diversification were more difficult to pin down, although we posit that the initial cis-, trans-Andean split in the genus was caused by the late Miocene completion of the northern Andes. Riverine barriers to dispersal and putative forest refuges can neither be discounted nor distinguished as causes of speciation in many cases, and one, the other or both have likely played a role in the diversification of South American howler monkeys. Finally, we estimated the separation of Mesoamerican A. pigra and A. palliata at 3Ma, which corresponds to the completion date of the Panama Isthmus promoting a role for this earth history event in the speciation of Central American howler monkeys.

Phylogenetic relationships between Hapalemur species and subspecies based on mitochondrial DNA sequences

BACKGROUND

Phylogenetic relationships of the genus Hapalemur remains controversial, particularly within the Hapalemur griseus species group. In order to obtain more information on the taxonomic status within this genus, and particularly in the cytogenetic distinct subspecies group of Hapalemur griseus, 357 bp sequence of cytochrome b and 438 bp of 12S mitochondrial DNAs were analyzed on a sample of animals captured in areas extending from the north to the south-east of Madagascar. This sample covers all cytogenetically defined types recognized of the genus Hapalemur.

RESULTS

Phylogenetic trees and distances analyses demonstrate a first emergence of Hapalemur simus followed by H. aureus which is the sister clade of the H. griseus subspecies. Hapalemur griseus is composed of 4 subspecies separated into two clades. The first contains H. g. griseus, H. g. alaotrensis and H. g. occidentalis. The second consists of H. g. meridionalis. A new chromosomal polymorphic variant from the region of Ranomafana, H. griseus ssp, has been analysed and was found in both clades.

CONCLUSIONS

Our results support the raising of H. g. meridionalis to the specific rank H. meridionalis, while neither cytogenetic nor molecular evidences support the raising of H. g. alaotrensis to a species rank despite its morphological characteristics. The new cytotype H. g. ssp which has been previously characterized by cytogenetic studies contains animals clustering either with the group of Hapalemur griseus griseus or with that of Hapalemur meridionalis. This suggests the existence of an ancestral polymorphism or an introgression of mitochondrial DNA between subspecies.

A fossil lemur from the Oligocene of Pakistan

In the absence of a comprehensive fossil record, the origin and early evolution of Malagasy lemurs have been subject to much uncertainty. We report here the discovery of a strepsirrhine fossil with strong cheirogaleid lemur affinities, Bugtilemur mathesoni gen. et sp. nov., from early Oligocene deposits of the Bugti Hills (Balochistan, Pakistan). Bugtilemur represents the earliest record of Lemuriformes, which hence appear to have already diversified outside of Madagascar at least 30 million years ago. This fossil clearly enhances the critical role of the Indian subcontinent in the early diversification of lemurs and constrains paleobiogeographic models of strepsirrhine lemur evolution.

Colony specificity in a social call of mouse lemurs (Microcebus ssp.)

Nocturnal primate species are often difficult to discriminate by gross visual bodily characteristics. This is also true for the world's smallest primate taxon, the Malagasy mouse lemurs. Recent findings imply that this taxon contains sibling species that can be diagnosed noninvasively by their species-specific advertisement call. We used comparative bioacoustics in order to explore variation of this call type and to assess species status of three European colonies. Acoustic variation was compared within and between colonies as well as with known species-specific differences. It was further related to morphological and genetic variations to investigate in how far it covaries with them. Results show that acoustic and genetic differences revealed by random amplified polymorphic DNA (RAPD) fingerprinting separated colonies reliably, but were on a different level than known species-specific differences. A Mantel test showed that acoustic differences were weakly correlated to genetic, but not to morphological differences. Our study is the first to reveal that both acoustic signaling and genetics clearly establish the species status for nocturnal primate populations. It also suggests that acoustic traits change at a more obvious and rapid pace than morphology in isolated populations, and may be used as an indication of conditions that may favor the evolution of subspecies.