Body mass in comparative primatology

Sex-biased dispersal is an almost ubiquitous feature of mammalian life history, but the evolutionary causes behind these patterns still require much clarification. A quarter of a century since the publication of seminal papers describing general patterns of sex-biased dispersal in both mammals and birds, we review the advances in our theoretical understanding of the evolutionary causes of sex-biased dispersal, and those in statistical genetics that enable us to test hypotheses and measure dispersal in natural populations. We use mammalian examples to illustrate patterns and proximate causes of sex-biased dispersal, because by far the most data are available and because they exhibit an enormous diversity in terms of dispersal strategy, mating and social systems. Recent studies using molecular markers have helped to confirm that sex-biased dispersal is widespread among mammals and varies widely in direction and intensity, but there is a great need to bridge the gap between genetic information, observational data and theory. A review of mammalian data indicates that the relationship between direction of sex-bias and mating system is not a simple one. The role of social systems emerges as a key factor in determining intensity and direction of dispersal bias, but there is still need for a theoretical framework that can account for the complex interactions between inbreeding avoidance, kin competition and cooperation to explain the impressive diversity of patterns.

Advances in our understanding of mammalian sex-biased dispersal.

The last decade's lemur research includes successes in discovering new living and extinct species and learning about the distribution, biogeography, physiology, behavior, and ecology of previously little-studied species. In addition, in both the dry forest and rain forest, long-term studies of lemur demography, life history, and reproduction, have been completed in conjunction with data on tree productivity, phenology, and climate. Lemurs contrast with anthropoids in several behavioral features, including female dominance, targeted female-female aggression, lack of sexual dimorphism regardless of mating system, sperm competition coupled with male-male aggression, high infant mortality, cathemerality, and strict seasonal breeding. Hypotheses to explain these traits include the "energy conservation hypothesis" (ECH) suggesting that harsh and unpredictable climate factors on the island of Madagascar have affected the evolution of female dominance, and the "evolutionary disequilibrium hypotheses" (EVDH) suggesting that the recent megafauna extinctions have influenced lemurs to become diurnal. These hypotheses are compared and contrasted in light of recent empirical data on climate, subfossils, and lemur behavior. New data on life histories of the rain forest lemurs at Ranomafana National Park give further support to the ECH. Birth seasons are synchronized within each species, but there is a 6-month distribution of births among species. Gestation and lactation lengths vary among sympatric lemurs, but all lemur species in the rain forest wean in synchrony at the season most likely to have abundant resources. Across-species weaning synchrony seen in Ranomafana corroborates data from the dry forest that late lactation and weaning is the life history event that is the primary focus of the annual schedule. Lemur adaptations may assure maximum offspring survival in this environment with an unpredictable food supply and heavy predation. In conclusion, a more comprehensive energy frugality hypothesis (EFH) is proposed, which postulates that the majority of lemur traits are either adaptations to conserve energy (e.g., low basal metabolic rate (BMR), torpor, sperm competition, small group size, seasonal breeding) or to maximize use of scarce resources (e.g., cathemerality, territoriality, female dominance, fibrous diet, weaning synchrony). Among primates, the isolated adaptive radiation of lemurs on Madagascar may have been uniquely characterized by selection toward efficiency to cope with the harsh and unpredictable island environment.

Lemur traits and Madagascar ecology: coping with an island environment.

Here we report on the ninth iteration of the biennial listing of a consensus of the 25 primate species considered to be among the most endangered worldwide and the most in need of conservation measures. The 2016–2018 list of the world’s 25 most endangered primates has five species from Africa, six from Madagascar, nine from Asia, and five from the Neotropics.

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Primates in Peril: The World's 25 Most Endangered Primates 2008–2010

The evolution of social monogamy has intrigued biologists for over a century. Here, we show that the ancestral condition for all mammalian groups is of solitary individuals and that social monogamy is derived almost exclusively from this social system. The evolution of social monogamy does not appear to have been associated with a high risk of male infanticide, and paternal care is a consequence rather than a cause of social monogamy. Social monogamy has evolved in nonhuman mammals where breeding females are intolerant of each other and female density is low, suggesting that it represents a mating strategy that has developed where males are unable to defend access to multiple females.

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The Evolution of Social Monogamy in Mammals

The Alaotran gentle lemur Hapalemur griseus alaotrensis is a poorly known primate found in the reed and papyrus beds around Lac Alaotra, Madagascar. Because of its restricted distribution, which does not contain any protected areas, it was classified as of highest conservation priority in the Lemur Action Plan [1]. Little is known about this taxon, it having been studied only briefly in 1969 [2] and 1984 [3]. These studies were based on limited direct observation and most information was derived from interviews with local people. In order to find out more about the lemur, in particular what its conservation and population status really were, two field studies were carried out in the wet (March–April) and dry seasons (October–November) of 1993 [4, 5], followed by a 6month study from February to August 1994 [6]. Information on distribution, population size, conservation status [7, 8] and threats to H. griseus alaotrensis [9] has already been published. In this paper, we present information from the three studies on group size, diet and activity pattern.

Preliminary Field Data on Group Size, Diet and Activity in the Alaotran Gentle Lemur Hapalemur griseus alaotrensis

Hapalemur griseus alaotrensisa relatively small-bodied (1240 ± 140 g, n = 58), folivorous lemur, was studied over a period of 15 months at Lac Alaotra. The study showed thatH. g. alaotrensishad an exclusively folivorous diet and mainly fed on leaves and stems of grasses and sedges. However, since folivorous diets are known to be poor sources of readily available energy and small-bodied animals generally have high metabolic requirementsH. g. alaotrensisis expected to have adaptations at several levels (morphological, physiological, behavioral) to resolve this conflict. The present study onH. g. alaotrensisshowed that dietary diversity was extremely low and food choice highly selective, but chemical composition of the food items yielded no evidence thatH. g. alaotrensisselected higher quality foods than larger folivores, nor was there evidence thatH. g. alaotrensisminimized energy expenditure at the behavioral or physiological level. This lack of behavioral or physiological adaptations to folivory imply that the digestive ability ofH. g. alaotrensismay be higher than predicted for an animal of its size.

Folivory in a Small-Bodied Lemur

The Alaotran gentle lemur Hapalemur griseus alaotrensis is found only in the marsh vegetation surrounding Lac Alaotra in Madagascar. This habitat is shrinking and becoming fragmented due to conversion to rice cultivation. In addition, lemurs are hunted for pets and food. There is no protected area within their limited range. This paper presents the results of a 6-month field study assessing the distribution, population size and conservation status of the lemur. The population consists of about 7500 animals, split into at least two subpopulations. If no conservation action is taken in the near future, drainage of the remaining 13,000 ha block of marsh vegetation will probably lead to the extinction in the wild of this primate taxon.

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Conservation status and distribution of the Alaotran gentle lemur Hapalemur griseus alaotrensis

Group composition and mating system were investigated in wild Alaotran gentle lemurs (Hapalemur griseus alaotrensis) using genetic markers. These small‐bodied herbivorous and cathemeral primates are endemic to the reed and papyrus beds around Lac Alaotra in Madagascar. They live in small groups in small, defended territories. Data were collected during the rainy seasons in 1996, 1997, and 1999, and include 99 individuals from 22 neighboring social groups and an additional 30 animals from other areas representing most of the geographic range. Animals were located by researchers canoeing in the marshes bordering the lake. After a group's size was determined by direct observation, all individuals were captured, marked, and released. During handling each individual was weighed and sexed, and hair samples for DNA extraction were collected. A 342 bp mtDNA control region sequence and 10 nuclear microsatellite loci provided multilocus genotypes that were used to assess pedigree relations and population structure. Alaotran gentle lemurs were found in groups of two to nine individuals (mean: 4.3), comprising one or two breeding females, their offspring, and one reproducing male. Solitary individuals of both sexes were encountered rarely. Breeding females were the permanent core of the social groups, whereas intergroup transfer of reproductive males was relatively frequent. Forty percent of all reproducing groups contained two breeding females, which were related to each other as closely as mother–daughter or full sisters. Parentage assessment revealed a variable mating system ranging from serial monogamy to polygyny within social groups. At least 8% of paternities involved extragroup males. Additional data on life history and reproduction are presented, and the social system of the Alaotran gentle lemur is discussed in the light of the new genetic findings. Am. J. Primatol. 57: 157–176, 2002. © 2002 Wiley‐Liss, Inc.

RESEARCH ARTICLES Social System of the Alaotran Gentle Lemur (Hapalemur griseus alaotrensis): Genetic Characterization of Group Composition and Mating System

During a 3 month field study, 18 group encounters between four groups of Alaotran gentle lemurs (Hapalemur griseus alaotrensis) were observed in the Lake Alaotra marshland in Madagascar. Behaviors observed during group encounters are described, and quantitative data on intergroup interactions and ranging patterns are discussed in the context of territoriality. Intergroup interactions varied in their intensity, ranging from visual monitoring, scent marking, and display locomotion to penetrating the neighboring range. A quarter (27%) of the encounters were aggressive, involving chases and confrontation displays, and no affiliative interactions were observed. Both adult males and females were involved in intergroup encounters, with males playing more active roles. All encounters took place in the small overlapping areas of neighboring home ranges. The outcome of an aggressive encounter was determined by its location, with the resident group always driving out the intruding one. The Alaotran gentle lemur actively advertised and consistently defended a large area of its home range against intrusion of neighboring groups and can therefore be considered territorial.

Thomas Mutschler

Papers

Preliminary Field Data on Group Size, Diet and Activity in the Alaotran Gentle Lemur Hapalemur griseus alaotrensis

Folivory in a Small-Bodied Lemur

Conservation status and distribution of the Alaotran gentle lemur Hapalemur griseus alaotrensis

RESEARCH ARTICLES Social System of the Alaotran Gentle Lemur (Hapalemur griseus alaotrensis): Genetic Characterization of Group Composition and Mating System

Group encounters and territoriality in wild Alaotran gentle lemurs (Hapalemur griseus alaotrensis).