The evolution of primate communities and societies in Madagascar

During their 120 to 165 million years of isolation, the flora and fauna of Madagascar evolved, to a large extent, independently of the African mainland.¹ In contrast to other oceanic islands, Madagascar is large enough to house the major components of tropical ecosystems, allowing tests of evolutionary hypotheses on the level of complete communities. Taking lemurs, the primates of Madagascar, as an example, evolutionary hypotheses correctly predict the organization of their community structure with respect to ecological correlates. Lemur social systems and their morphological correlates, on the other hand, deviate in some respects from those of other primates. Apparently, lemur social systems are influenced by several selection pressures that are weak or rare in other primates. These include variable activity patterns and avoidance of infanticide. The interspecific variation in lemur social systems therefore offers a unique opportunity for a comprehensive study of the determinants of primate social systems.     

Kinetic characterization of yeast alcohol dehydrogenases. Amino acid residue 294 and substrate specificity

A three-dimensional model of yeast alcohol dehydrogenase, based on the homologous horse liver enzyme, was used to compare the substrate binding pockets of the three isozymes (I, II, and III) from Saccharomyces cerevisiae and the enzyme from Schizosaccharomyces pombe. Isozyme I and the S. pombe enzyme have methionine at position 294 (numbered as in the liver enzyme, corresponding to 270 in yeast), whereas isozymes II and III have leucine. Otherwise the active sites of the S. cerevisiae enzymes are the same. All four wild-type enzymes were produced from the cloned genes. In addition, oligonucleotide-directed mutagenesis was used to change Met-294 in alcohol dehydrogenase I to leucine. The mechanisms for all five enzymes were predominantly ordered with ethanol (but partially random with butanol) at pH 7.3 and 30 degrees C. The wild-type alcohol dehydrogenases and the leucine mutant had similar kinetic constants, except that isozyme II had 10-20-fold smaller Michaelis and inhibition constants for ethanol. Thus, residue 294 is not responsible for this difference. Apparently, substitutions outside of the substrate binding pocket indirectly affect the interactions of the alcohol dehydrogenases with ethanol. Nevertheless, the substitution of methionine with leucine in the substrate binding site of alcohol dehydrogenase I produced a 7-10-fold increase in reactivity (V/Km) with butanol, pentanol, and hexanol. The higher activity is due to tighter binding of the longer chain alcohols and to more rapid hydrogen transfer.     

Some aspects of the natural history and food selection ofAvahi laniger

Two groups ofAvahi laniger were studied in the Forêt de Analamozoatra near Perinet in the eastern rainforest of Madagascar from August to October 1984. Overlap between the home ranges of neighbouring groups ofA. laniger was minimal. Group size ranged from one to four individuals with a median group size of two. In four out of ten groups a baby was born between August and September.A. laniger were most active after dusk and before dawn. They had an extended resting period around midnight. Their diet consisted mostly of leaves from at least 17 different plant species. They also ate flowers. Fruit eating was recorded twice. Leaves eaten had high contents of protein and sugar but did not contain alkaloids. The concentration of condensed tannins did not differ between food items and non-food items. There was no indication of competition with other prosimians that might explain their nocturnality.     

Test of Fox's assembly rule for functional groups in lemur communities in Madagascar

This paper examines to what extent an assembly rule designed by Fox for small terrestrial mammal communities is also applicable to communities of arboreal lemurs in Madagascar. This approach extends the testing of Fox's assembly rule to a new biogeographic region and a different phylogenetic radiation. The rule operates on a functional rather than on the taxonomic level. It specifies that: "There is a much higher probability that each species entering a community will be drawn from a different functional group, until each group is represented before the cycle repeats" (Fox, 1987: 201). This rule was tested with lemur communities from 14 sites in evergreen rain forests and nine sites in dry deciduous forests of Madagascar. Lemur species were assigned to one of three different functional groups based on dietary preferences: omnivores, frugivores, folivores. The rule applies almost perfectly to extant lemur communities in evergreen rain forest. Present communities in dry deciduous forests are not ordered as perfectly as communities of the rain forest sites, but they also deviate from random assembly as generated by the null model. Including extinct species of the dry forest ecosystem indicates that the at present unfavoured composition of the lemur community has been derived from a favoured state through extinction of the large folivorous and frugivorous lemur species. In the lemur communities of the eastern Malagasy rain forest, the assembly went through at least four, and in the Holocene dry forest ecosystem through even five, cycles without failing. This assigns considerable significance to the underlying mechanisms (most likely interspecific competition) and indicates that they are still effective in the forests of Madagascar. The dry deciduous forests might have been subject to recent natural and anthropogenic changes which interfere with the operation of these deterministic processes.     

Parasite burden and constitution of major histocompatibility complex in the Malagasy mouse lemur, Microcebus murinus

We investigated the importance of the major histocompatibility complex (MHC) constitution on the parasite burden of free-ranging mouse lemurs (Microcebus murinus) in four littoral forest fragments in southeastern Madagascar. Fourteen different MHC class II DRB-exon 2 alleles were found in 228 individuals with high levels of sequence divergence between alleles. More nonsynonymous than synonymous substitutions in the functional important antigen recognition and binding sites indicated selection processes maintaining MHC polymorphism. Animals from the four forest fragments differed in their infection status (being infected or not), in the number of different nematode morphotypes per individual (NNI) as well as in the fecal egg counts (FEC) values. Heterozygosity in general was uncorrelated with any of these measures of infection. However, a positive relationship was found between specific alleles and parasite load. Whereas the common allele Mimu-DRB*1 was more frequently found in infected individuals and in individuals with high NNI and FEC values (high parasite load), the rare alleles Mimu-DRB*6 and 10 were more prevalent in uninfected individuals and in individuals with low NNI and FEC values (low parasite load). These three alleles associated with parasite load had unique amino acid motifs in the antigen binding sites. This distinguished them from the remaining 11 Mimu-DRB alleles. Our results support the hypothesis that MHC polymorphism in M. murinus is maintained through pathogen-driven selection acting by frequency-dependent selection. This is the first study of the association of MHC variation and parasite burden in a free-ranging primate.     

Food for folivores: nutritional explanations linking diets to population density

Ecologists want to explain why populations of animals are not evenly distributed across landscapes and often turn to nutritional explanations. In seeking to link population attributes with food quality, they often contrast nutritionally positive traits, such as the concentration of nitrogen, against negative ones, such as fibre concentration, by using a ratio of these traits. This specific ratio has attracted attention because it sometimes correlates with the biomass of colobine primates across sites in Asia and Africa. Although empirically successful, we have identified problems with the ratio that may explain why it fails under some conditions to predict colobine biomass. First, available nitrogen, rather than total nitrogen, is nutritionally important, while the presence of tannins is the major factor reducing the availability of nitrogen in browse plant species. Second, tannin complexes inflate measures of fibre. Finally, simple ratios may be unsound statistically because they implicitly assume isometric relationships between variables. We used data on the chemical composition of plants from three continents to examine the relationships between the concentrations of nitrogen, available nitrogen, fibre and tannins in foliage and to evaluate the nitrogen to fibre ratio. Our results suggest that the ratio of the concentration of nitrogen to fibre in leaves does sometimes closely correlate with the concentration of available nitrogen. However, the ratio may give misleading results when leaves contain high concentrations of tannins. The concentration of available nitrogen, which incorporates measures of total nitrogen, dry matter digestibility and tannins, should give a better indication of the nutritional value of leaves for herbivorous mammals that can readily be extrapolated to habitats.     

Habitat Characteristics and Lemur Species Richness in Madagascar1

In the extant lemur communities of Madagascar the number of lemur species increases with increasing number of tree species. In forests with few tree species lemurs use patches with higher number of tree species than average. However, in forest plots with high number of tree species, lemurs stay in places with lower number of tree species than average. At low tree species diversity a minimum number of different tree species seems to be required within the animals' home range to assure year-round food availability. At high tree species diversity tree species essential for survival might be diluted by resources which are of no use for lemurs, thus increasing energetic expenses for traveling between suitable patches. According to the present analyses, structural diversity is of subordinate importance to the number of tree species as a correlate of lemur species richness. Within limits of disturbance intensity and on a small geographic scale, disturbances increase forest productivity. Lemurs reach higher species numbers and population densities in slightly disturbed areas compared with undisturbed sites. This peaked curve of the number of lemur species over disturbance, however, may not only be a consequence of “resource dilution” in undisturbed sites and higher food abundance in slightly disturbed areas, but also a consequence of selective extinction of lemur species which were unable to cope with the disturbance regime exaggerated by human interference over the last few hundred or thousand years.     

Resting metabolic rates of Lepilemur ruficaudatus

Seventeen sportive lemurs (Lepilemur ruficaudatus) were captured in a dry, deciduous forest in western Madagascar, and the resting metabolic rates were measured. According to the data, resting metabolic rates of Lepilemur ruficaudatus are among the lowest of mammalian folivores recorded so far. © 1996 Wiley-Liss, Inc.     

Vegetation Thresholds for the Occurrence and Dispersal of <Emphasis Type="Italic">Microcebus griseorufus</Emphasis> in Southwestern Madagascar

Primate populations are declining the world over due to anthropogenic threats, including habitat loss and degradation. This raises the important question of how much habitat degradation a species can cope with. Habitat degradation is pronounced in Madagascar, where most of the human population depends on the direct exploitation of natural resources. We aimed to identify the response of Microcebus griseorufus (the gray-brown mouse lemur) to forest degradation and to define the structural traits of the vegetation that might be crucial for the species’ occurrence in anthropogenic landscapes. We documented the occurrence of Microcebus griseorufus in relation to vegetation structures along a gradient of forest degradation, at the edge of and west of Tsimanampetsotsa National Park in April and May 2007 and from October to December 2015. We confirmed the occurrence of Microcebus griseorufus using trapping and visual surveys, and measured vegetation structure. Logistic regression models showed that Microcebus griseorufus has a threshold response to tree density and the diameter of thick trees. The thresholds of occurrence were at 10–15% of the tree density recorded in intact forest and a mean diameter of trees with a diameter at breast height of >10 cm of 14.3 cm. The definition of such thresholds might help to maintain suitable habitat for this species and other primates living in anthropogenic landscapes, providing connectivity between isolated protected areas and allowing dispersal between populations.