Aggressive and neutral interventions in conflicts in captive groups of brown lemurs (Eulemur fulvus fulvus)

Third-party interventions in conflicts have revealed complexity in primate social relationships. This type of intervention has seldom been analyzed in prosimians, although many of these species exhibit complex (multimale/multifemale) social organizations. The present study on captive brown lemurs (Eulemur fulvus fulvus) shows that dominant individuals were more likely to intervene in conflicts. Both males and females intervened aggressively in conflicts. Female aggressive interventions occurred mainly on behalf of close kin, whereas males mainly intervened on behalf of juveniles. This study also provides the first record of neutral or peaceful interventions in lemurs. Although females intervened neutrally, almost all neutral interventions were by dominant males. Dominant males intervened in conflicts neutrally more often than aggressively, principally in conflicts between adults and juveniles or between juveniles. Neutral interventions by males always ended the conflicts and were often followed by affiliative contacts between participants (intervenors and opponents). In lemurs, female interventions can be explained by kin selection, while the nature of dominant males' interventions suggests a control role. Interventions by males on behalf of juveniles may increase the formers' fitness.     

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.     

Evidence of early butchery of giant lemurs in Madagascar

We report here definitive evidence of butchery, most probably associated with hunting, of giant extinct lemurs by early human settlers in Madagascar. Specimens of Palaeopropithecus ingens and Pachylemur insignis from two sites in southwestern Madagascar, Taolambiby and Tsirave, show classic signs of butchering. We compared these to the bones (also from Taolambiby) of butchered Propithecus verreauxi, a lemur still living in the region. The characteristics of the tool-induced extinct-lemur bone alterations (sharp cuts and chop marks near joints, oblique cuts along the shafts, spiral fractures, and percussion striae) suggest skinning, disarticulation, and filleting. Conclusive evidence of megafaunal modification by humans in Madagascar was limited previously to a few hippo and elephant bird bones and one extinct aye-aye tooth. New evidence comes not from archaeological sites, but from specimens collected in the early 1900s, without stratigraphic records, at "subfossil" sites (i.e., sites renowned for their late Pleistocene or Holocene fossils, often lacking human artifacts). Whereas these are hardly the most ideal samples for analysis of this kind, careful scrutiny of the characteristics of the cut marks has allowed us to document butchery beyond any reasonable doubt. One bone with definitive cut marks has been dated to the very earliest part of the human period in Madagascar. Continued, careful research on the bones in subfossil collections is warranted.     

Use of total dietary fiber across four lemur species (Propithecus verreauxi coquereli,Hapalemur griseus griseus,Varecia variegata,and Eulemur fulvus): Does fiber type affect digestive efficiency?

In vivo digestibility and transit of two experimental diets were compared across four lemur species for which gastrointestinal morphology and preliminary data on physiology differ:Varecia variegata (VV), Eulemur fulvus (EF), Propithecus verreauxi (PV), and Hapalemur griseus (HG). Since free-ranging groups consume varied amounts of slowly fermentable insoluble fiber (IF) and rapidly fermentable soluble fiber (SF), differences in digestibility may be related to variation in the fiber types consumed. To investigate this, two diets were designed to provide 28% of dry matter (DM) as total dietary fiber (TDF). The ratio of IF/SF (g/g) differed across the diets (12.15:1 for the IF diet, and 3.76:1 for the IF/SF diet). The DM digestibility (DMD) of both diets differed across species: DMD was lower for EF and VV (approximately 56-58%), and higher for PV (72%) and HG (76%). The fiber digestibility results were as follows: TDF digestibility was similar for VV and EF (23% and 28%), higher for PV (56%), and highest for HG (66%). IF digestibility was lower for VV and EF (20% and 28%), and higher for PV and HG (53% and 62%). The transit times (TTs) of the two markers Cr and Co were similar (approximately 3.5 hr for VV and EF, 25 hr for PV, and 30 hr for HG). The mean retention times (MRTs) showed the same trend. The results from these captive groups suggest there are large differences in digestive efficiency that are likely related to the varied fiber composition of the free-ranging diet, and the amount of time the digesta are retained in the gut.     

Characterizing gastrointestinal transit time in four lemur species using barium-impregnated polyethylene spheres (BIPS)

Differences in dietary profiles and gastrointestinal (GI) morphologies observed across lemur species suggest that there may be variation in patterns of digesta flow through the GI tract related to the method of digesta processing. Using radio-opaque barium-impregnated polyethylene spheres (BIPS), we characterized such patterns in four lemur species: Varecia variegata (VV), Eulemur fulvus (EF), Propithecus verreauxi (PV), and Hapalemur griseus (HG) (n = 2 per species). After an initial radiograph was taken under light sedation, the animals were fed the BIPS together with a small meal. A combination of 30 small (1.5 mm) and 10 large (5 mm) BIPS was administered. Radiographs were then taken on a species-dependent basis up to 48 hr post-dosage. For small BIPS, the gastric transit time (GTT; time of first exit of BIPS from stomach) was 0.25-2 hr for VV, EF, and HG, and approximately 10 hr for PV. The oro-rectal transit time (ORTT; time of first appearance in the rectum) was < 2 hr for VV and EF, and 24.0 hr for PV and HG. The intestinal transit time (ITT, measured as ORTT - GTT) was < 1.5 hr for VV and EF, and approximately 14 hr and 22 hr for PV and HG, respectively. These data suggest that the GTT of digesta as measured with BIPS was rapid for VV, EF, and HG. For VV and EF, the ORTT and ITT were also rapid, while for HG they were much slower. PV was characterized by delayed GTT, and a more rapid ITT compared to HG. Thus, patterns of flow for PV and HG, despite similar ORTT, differed in that HG emptied BIPS more rapidly and ITT was slower. The flow of BIPS did not differ for VV and EF. These data reveal new information in addition to the total tract transit time, and complement existing knowledge regarding anatomy and diet.     

Mandibular growth and function in Archaeolemur

Ontogenetic changes in the morphology of the mandibular symphysis are described in Archaeolemur so as to infer the functional significance of symphyseal fusion in this subfossil Malagasy lemur. The first regions of the symphysis to show a more complex morphology were the lower and anterior borders of the joint and, to a lesser extent, the lingual borders of the superior and inferior transverse tori. During growth, these regions became increasingly rugose and encroached upon a centrally located, smooth, “oval” region, which may have been a principal pathway for neurovascular structures communicating with the unfused joint. In subadults, the symphysis was completely fused except for the lingual surface of the inferior transverse torus, where a patent suture and potential space were present between dentaries. Thus, in Archaeolemur there was an age- and size-related pattern of increased symphyseal ossification or fusion that was complete by adulthood. The morphology of the interlocking bony processes and the sequence of ossification in the symphysis suggest that increased dorsoventral shear stress during mastication was the most likely determinant of symphyseal fusion in Archaeolemur: The allometric pattern of greater symphyseal fusion may be linked to the presence of relatively greater dorsoventral shear in adults due to an increased recruitment of balancing-side jaw-muscle force. There is little indication that the symphysis of juvenile Archaeolemur was buttressed to resist forces associated with “wishboning” during mastication or vertical bending during incision. Our observations, as well as those of others, suggest that symphyseal fusion in primates occurs initially as a response to increased dorsoventral shear during mastication. Therefore, wishboning stress might only become a major determinant of symphyseal form and function in those taxa that develop a fused symphysis to counter increased dorsoventral shear. © 1994 Wiley-Liss, Inc.     

Affiliative relationships between adult males and immature group members in naturally occurring ringtailed lemurs (Lemur catta)

Affiliative relations between adult males and immature group members were studied in three naturally occurring groups of ringtailed lemurs (Lemur catta) over a 12-month period at Beza-Mahafaly Reserve, southwestern Madagascar. No statistically significant difference was found in rates of affiliative interactions between adult males and older immatures (juveniles and adolescents) over reproductive seasons. However, some of the adult males in two focal groups increased their rates of affiliative behaviors with older immatures during the lactation and subsequent 1993 postmigration periods. Female involvement with infants during lactation season, the increasing independence of juveniles and adolescents, and length of male tenure may be factors contributing to such a pattern. Neither adult males nor immatures were significantly responsible for the initiation and maintenance of proximity in male-immature dyadic interactions. Neither dominance rank nor age-class of the adult male affected their rates of affiliative behavior with immatures. The majority of focal males exhibited an interest in infants and occasionally participated in alloparental care. It is suggested that adult males can benefit from affiliative relations with immatures in terms of opportunities for greater spatial centrality in the group, which can lead to enhanced predator protection and greater opportunities to develop affiliative relationships with females. Immatures can benefit from affiliation with males in relation to enhanced predator detection and protection, alloparental care, and opportunities to develop social skills. Am J Phys Anthropol 103:163–171, 1997. © 1997 Wiley-Liss, Inc.