Urs Thalmann

Origin and evolution of primate social organisation: a reconstruction

The evolution and origin of primate social organisation has attracted the attention of many researchers, and a solitary pattern, believed to be present in most nocturnal prosimians, has been generally considered as the most primitive system. Nocturnal prosimians are in fact mostly seen alone during their nightly activities and therefore termed’ solitary foragers’, but that does not mean that they are not social. Moreover, designating their social organisation as’ solitary’, implies that their way of life is uniform in all species. It has, however, emerged over the last decades that all of them exhibit not only some kind of social network but also that those networks differ among species. There is a need to classify these social networks in the same manner as with group‐living (gregarious) animals if we wish to link up the different forms of primate social organisation with ecological, morphological or phylogenetic variables. In this review, we establish a basic classification based on spatial relations and sociality in order to describe and cope properly with the social organisation patterns of the different species of nocturnal prosimians and other mammals that do not forage in cohesive groups. In attempting to trace the ancestral pattern of primate social organisation, the Malagasy mouse and dwarf lemurs and the Afro‐Asian bushbabies and lorises are of special interest because they are thought to approach the ancestral conditions most closely. These species have generally been believed to exhibit a dispersed harem system as their pattern of social organisation (‘dispersed’ means that individuals forage solitarily but exhibit a social network). Therefore, the ancestral pattern of primate social organisation was inferred to be a dispersed harem. In fact, new field data on cheirogaleids combined with a review of patterns of social organisation in strepsirhines (lemurs, bushbabies and lorises) revealed that they exhibit either dispersed multi‐male systems or dispersed monogamy rather than a dispersed harem system. Therefore, the concept of a dispersed harem system as the ancestral condition of primate social organisation can no longer be supported. In combination with data on social organisation patterns in ‘primitive’ placentals and marsupials, and in monotremes, it is in fact most probable that promiscuity is the ancestral pattern for mammalian social organisation. Subsequently, a dispersed multi‐male system derived from promiscuity should be regarded as the ancestral condition for primates. We further suggest that the gregarious patterns of social organisation in Aotus and Avahi, and the dispersed form in Tarsius evolved from the gregarious patterns of diurnal primates rather than from the dispersed nocturnal type. It is consequently proposed that, in addition to Aotus and Tarsius, Avahi is also secondarily nocturnal.

Food resource characteristics in two nocturnal lemurs with different social behavior: Avahi occidentalis and Lepilemur edwardsi

I present results from a comparative field study on the feeding behavior of the gregarious Avahi occidentalis and the solitary-but-social Lepilemur edwardsi to evaluate hypotheses relating to social organization and food resources. While Avahi and Lepilemur are both nocturnal, have comparable body weights and positional behaviors, and are both folivorous, they differ in their social organization. Therefore, they present an ideal model for assessing food resource characteristics through comparisons of food selection in both species with regard to forest composition. The monogamous Avahi tend to select under-represented resources. They are repeatedly exploited, which suggests that their location must be known. It is worthwhile and probably imperative to defend those resources. Such defense imposes ranging limitations on male Avahi. Females may prefer familiar mates that will share their knowledge of resource location and defend the resources. A stable monogamous pattern could be the optimal strategy. In contrast, food selection by Lepilemur is based on common resources to a higher degree, but they show a lower degree of exploitation. Lepilemur males would be less restricted and could potentially opt for a different strategy, e.g., a dispersed harem. It is unclear whether this strategy is realized or not. I discuss other possible correlates of monogamy—infanticide protection, predation avoidance—but the gregarious pattern in Avahi may best be seen as a retention, and its nocturnal activity as a secondary adaptation.

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

BackgroundThe 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.ResultsInterspecific 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.ConclusionOur 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.

The indris of Anjanaharibe-Sud, northeastern Madagascar

During a short field trip to the Special Reserve of Anjanaharibe-Sud in northeastern Madagascar, data concerning pelage coloration, behavior (especially vocalization), and ecology of indris were collected. Anjanaharibe-Sud is the northernmost locality of indri distribution. In comparison to the better-known indris from the southern part of their distribution, the indris in this region show different pelage coloration. Several types of loud vocalizations are analyzed, based on a small sample of tape recordings. Their song structure is more complicated than previously reported, containing distinct sequences of duetting. Data on behavior and ecology were collected by interviewing guides and local inhabitants. Some information contrasts with reports on the more southern indri populations. The conservation status of indris in Anjanaharibe-Sud and the future of the reserve are outlined.

Distribution and Geographic Variation in the Western Woolly Lemur (Avahi occidentalis) with Description of a New Species (A. unicolor)

The western woolly lemur is distributed through central western, northwestern and possibly northern Madagascar and is traditionally viewed as a monotypic species (Avahi occidentalis) or as a subspecies of A. laniger. We present new data on body weights of Avahi which, together with previously available body weights, provide additional evidence for recognizing eastern and western woolly lemurs as two distinct species. We then reexamine the distributions of, and chromatic variation within and between, populations of western woolly lemurs. A comparative study of wild subjects and museum skins reveals that several geographically discrete morphs exist in western Avahi, which is clearly polytypic. Marked differences between populations in fur coloration suggest that ≥3 distinct taxa should be recognized. The populations differ considerably in their habitat structure. In addition, field observations suggest clear differences in population density between ≥2 of the populations. We describe and name one new species.

Lemurs in Bemaraha (World Heritage Landscape, Western Madagascar)

A visit to the Tsingy de Bemaraha in Western Madagascar was undertaken in 1991 to survey the lemurs of this little known reserve. Preliminary results of field observations and interviews with local inhabitants are presented together with notes on the forests, the human population and the conservation status of the region.

New Views on the Origin of Primate Social Organization

The origin of primate social organization has attracted considerable interest from primatologists. A so-called solitary pattern, believed to be present in most nocturnal prosimians, has generally been considered to be the most primitive of primate social systems (Crook and Gartlan, 1966; Eisenberg et al., 1972). There have been extensive discussions regarding possible explanations of why some primates forage in groups while others do not. Several factors have been inferred to be responsible for a “solitary” lifestyle. These include nocturnality, small body size, insectivory, and predation pressure (Bearder, 1987; Clutton-Brock and Harvey, 1977; Dunbar, 1988; Kappeler, 1997a; van Schaik, 1983; van Schaik and van Hooff, 1983). However, none of these explanations are satisfactory (Kappeler, 1997a), and it has been suggested that a combination of several factors may be involved in determining social organization in primates (Muller and Thalmann, 2000).

Conservation Assessment of the Recently Described John Cleese's Woolly Lemur, Avahi cleesei (Lemuriformes, Indridae)

Abstract John Cleeses woolly lemur (Avahi cleesei) was discovered in 1990 and officially defined and named in 2005. This nocturnal lemur is known to occur only in the Tsingy de Bemaraha Strict Nature Reserve, a UNESCO World Heritage Site in central western Madagascar. In this article we summarize available relevant information on morphology, distribution, habitat, and behavior including vocalizations to assess the conservation status and facilitate future investigations, surveys in particular. According to the IUCN Red List categories, A. cleesei is clearly in the category Endangered. Further studies might show, however, that the species should be classified as Critically Endangered, because of its very limited distribution and particularly specialized biological requirements.

Behavioral and Ecological Adaptations in Two Small Folivorous Lemurs with Different Social Organization: Avabi and Lepilemur

Woolly lemurs (genus Avahi, family Indridae) and sportive lemurs (genus Lepilemur, family Lepilemuridae or Megaladapidae) provide an excellent field model to investigate hypotheses linking behavior and ecology (e.g., Ganzhorn, 1988; Ganzhorn et al., 1985; Thalmann, 1996, 2001, 2002; Warren, 1994). While they are both nocturnal, have comparable body weights and positional behaviors (Vertical Clingers and Leapers), and are both folivorous, they differ in their social organization. In some forests they live sympatrically in the very same

Teaching Primatology at the Université de Mahajanga (NW Madagascar)

In 1995, the course “Introduction to Anthropology/Primatology” was organized at the Universite de Mahajanga in collaboration with the Anthropological Institute of the University of Zurich as a pilot project. The defined goals were: (1) presentation of primatology as an interesting and important subject, which may be of special relevance for Madagascar; (2) initiation of a test case to see how it would operate in general; ((3) provision of a starting point for future adjustments and potential extensions. Two questionnaires filled out by students before and after the course showed that they came from all over the island (such that knowledge would potentially be widely distributed later), that they were relatively old for the study level achieved, and that knowledge of the natural richness of Madagascar at the beginning of the lectures was lower than expected. Students judged the course to be interesting and worth following, feeling that it should be offered again; many believed that they had understood quite a lot. In fact, however, some of the messages of the lecture course did not transfer very well. As a pilot project, the course was successful in several realms but failed to catalyze longer term teaching and research activities for various reasons. An evaluation of the experiences made and of results of the questionnaires is presented.