Alexandra E. Müller

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.

A Preliminary Report on the Social Organisation of Cheirogaleus medius (Cheirogaleidae; Primates) in North-West Madagascar

Key WordsLemuriformes · Madagascar · Nocturnal prosimians · Cheirogaleus medius ·Dwarf lemur · Radio-tracking · Social organisation · Solitary speciesIntroductionBoth currently recognised species of the genus Cheirogaleus, C. majorand C.medius, are notable for seasonal storage of fat (especially in the tail) and for extendedtorpor phases during the austral winter, i.e. the dry season [1, 2]. The fat-tailed dwarflemur, C. medius, has been reported to hibernate for 6–8 months and such a longperiod would inevitably have a major influence on social organisation [2]. Firstly, theanimals have only a few months to reproduce and rear offspring. Secondly, the ani-mals have to ensure sufficient fat storage to survive during the following dry season.To date, knowledge of the ecology and behaviour of C. mediushas been based onoccasional field observations [1–3], a few longer-term studies [4], investigations incaptivity [for citations see 2, 5, 6] and zoo reports [7], but social organisation has sofar been poorly documented [2, 8].Inferences concerning the social organisation of nocturnal prosimians can bemade from range overlap between individuals, associations within ranges (at particu-lar sleeping sites) and patterns of dispersal of individuals from their natal areas [9].For C. medius , Hladik et al. [4] determined individual ranges with a maximal diameterof 200 m and a population density of 300–400 animals/km

Duetting in the Titi Monkey Callicebus cupreus: Structure, Pair Specificity and Development of Duets

Duets from a total of 6 female and 6 male titi monkeys (Callicebus cupreus) were analysed in order to provide an in-depth analysis of the duet structure, to investigate whether duets are pair specific and to examine whether duets of newly formed pairs differ from those of established pairs. Callicebus duets are composed of alternately uttered male and female contributions. Duets were pair specific as a result of a summation of individual attributes of the two mates rather than due to unidirectional or reciprocal song adaptation by mates. The two examined newly formed pairs produced species-typical duets from the first day on, but their duets showed greater variability in sequence durations than those of established pairs.

Aspects of social life in the fat-tailed dwarf lemur (Cheirogaleus medius): inferences from body weights and trapping data.

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. Am. J. Primatol. 49:265–280, 1999.

Social Organization of the Fat-Tailed Dwarf Lemur (Cheirogaleus Medius) in Northwestern Madagascar

The strictly nocturnal dwarf lemurs(Cheirogaleus)are extraordinary among primates in showing extensive torpor phases during the austral winter, which is thought to be an adaptation to seasonal variation in food availability. The Fat-tailed Dwarf Lemur(C. medius)is found throughout the west and south of Madagascar and enters torpor for six to eight months. Such a long period of dormancy may influence their social organization. A 20-month field study carried out at the Station Forestiure d’ Ampijoroa revealed a monogamous social pattern forC. medius.

Female Social Dominance in Two Eulemur Species With Different Social Organizations

Female social dominance is rare in mammals, but common in lemurs. We investigated social dominance in two Eulemur species; the polygynous crowned lemur (E. coronatus) and the monogamous red-bellied lemur (E. rubriventer), using four and two social groups, respectively. We collected data on agonistic interactions and two types of affiliative behavior (grooming and maintaining spatial proximity). We used a combination of focal watches of individuals, instantaneous scan-sampling of groups, and all-occurrence of some behaviors in groups. We found that overall rates of agonistic interactions were higher in E. coronatus, and they also had more decided intersexual agonistic interactions than E. rubriventer. However, in both species the females won the vast majority of these agonistic interactions. E. coronatus females were groomed more often by males than vice versa, whereas no sex differences in grooming were observed in E. rubriventer. We found that males were responsible for maintaining spatial proximity in E. coronatus whereas in E. rubriventer, females were responsible. In one group of E. coronatus, the male was overweight and dominant to the female and this is the first observation of male dominance in a lemur species typically described as female dominant. We suggest that body weights in captivity be monitored for maintaining normal dominance relationships. Overall, agonistic behaviors were consistent with clear female social dominance in both E. coronatus and E. rubriventer. The affiliative behaviors also provided clear evidence for female dominance E. coronatus, but not for E. rubriventer. Zoo Biol 0: 1-14, 2007. (c) 2007 Wiley-Liss, Inc.

A Note on the Activity Cycle of Captive White-Fronted Lemurs (Eulemur fulvus albifrons)

We studied the activity cycle of captive-born white-fronted lemurs (Eulemur fulvus albifrons) at Zurich Zoo with the aim to discuss current hypotheses on the evolution of cathemerality in lemurs. In contrast to their relatives in the wild, these lemurs were active exclusively during the day. If cathemerality is a strategy to increase food intake or to avoid predators, then nocturnal activity is not essential for captive animals and may be suppressed simply due to the absence of stimuli. This suggests that cathemerality includes a distinct element of flexibility regarding the distribution of diurnal and nocturnal activity, with the option to omit nightly activities.

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).