Comparative Perspectives on Bimaturism, Ontogeny, and Dimorphism in Lemurid Primates

We address questions regarding the general absence of dimorphism in lemurid primates (Hapalemur, Eulemur, and Varecia) through comparative analyses of ontogeny. We described and analyzed body mass growth data for 9 lemurid taxa and compared them to similar data for anthropoid primates. Lemurids tend to grow rapidly over a short period of time when compared to anthropoid primates of similar body sizes. Size variation among lemurid taxa arises primarily as a consequence of differences in rates of growth. Comparative analyses of body mass growth data suggest that natural selection has produced ontogenetic adaptations in lemurids that center on relatively short periods of growth. Reduced growth periods preclude the evolution of sexual dimorphism through bimaturism—a sex difference in the length of the growth period—despite high levels of intermale competition. Selective factors related to seasonal variability of lemurid habitats play important roles in limiting the potential for the evolution of bimaturism. Other selective factors that limit bimaturism are related to female reproductive synchrony. In combination, they favor relatively early male maturation, precluding sexual selection that would otherwise promote the evolution of dimorphism through bimaturism. Natural selection on growth rates may preclude somatic responses to sexual selection that involve elevated male growth rates. In general, existing ontogenetic or life history adaptations appear to restrict responses to sexual selection in male lemurids.     

Estimating the body size of eocene primates: A comparison of results from dental and postcranial variables

Estimating body weights for fossil primates is an important step in reconstructing aspects of their behavior and ecology. To date, the body size of Eocene euprimates—the Adapidae and Omomyidae—has been estimated only from molar area. Studies on other primates and mammals demonstrate that body weights estimated from teeth are not always concordant with those estimated from postcranial variables. We derive estimates for Eocene primates based on tarsal bone variables to compare with previously published values derived from dental measures. Stepsirhine-wide, family-level, and subfamily-level models are developed and compared. We also compare the accuracy and precision of dental- and tarsal-based regression models for predicting weight in extant species. Tarsal bone and dental area measures prove to be equally robust in predicting body weight; however, highly disparate estimates are often obtained from different variables. Equations based on lower-level taxonomic groups perform better than more widely based models. However, all equations considered yield fairly large errors, which can affect interpretations of paleoecology. The choice of the more robust prediction is not straightforward.     

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.     

Toothcomb homology and toothcomb function in extant strepsirhines

Contrary to some recent assertions, there are no persuasive ways for determining the homologies of indriid toothcomb teeth and the resulting dental formulas. Most of the presumably distinctive features of procumbent “canines” are also seen in incisors, and vice versa. Thus, there are at least three plausible dental formulas for indriid deciduous teeth and two for the permanent dentition. All formulas are compatible with the distribution of teeth in fossil strepsirhines. Similar arguments apply to strepsirhine toothcombs as a whole, but the absence of three-incisored ancestors in the fossil record strongly supports the conclusion that the dental formula of nonindriids is 2.1.3.3. for the lower dentition. There are also alternative interpretations of the original function of the toothcomb. Recent arguments which purport to demonstrate that the toothcomb evolved originally as a sap-feeding adaptation fail that purpose. The ontogeny of infant lemur behavior suggests that the original function involved grooming rather than feeding if the data are interpreted in a Haeckelian context.     

Phylogeny and Evolution of Selected Primates as Determined by Sequences of the ε-Globin Locus and 5′ Flanking Regions

We studied phylogenetic relationships of 39 primate species using sequences of the -globin gene. For 13 species, we also included flanking sequences 5 of this locus. Parsimony analyses support the association of tarsiers with the anthropoids. Our analysis of New World monkeys supports the model in which the callitrichines form a clade with Aotus, Cebus, and Saimiri, with Cebus and Saimiri being sister taxa. However, analysis of the 5 flanking sequences did not support grouping the atelines with Callicebus and the pitheciins. Our data support the classification of platyrrhines into three families, Cebidae (consisting of Cebus, Saimiri, Aotus, and the callitrichines; Atelidae—the atelines; and Pitheciidae—Callicebus and the pithiciins. The strepsirhines form well-defined lemuroid and lorisoid clades, with the cheirogaleids (dwarf and mouse lemurs) and Daubentonia (aye-aye) in the lemuroids, and the aye-aye being the most anciently derived. These results support the hypothesis that nonhuman primates of Madagascar descended from a single lineage. Local molecular clock calculations indicate that the divergence of lemuroid and lorisoid lineages, and the earliest diversification of lemuroids, occurred during the Eocene. The divergence of major lorisoid lineages was probably considerably more recent, possibly near the Miocene–Oligocene boundary. Within hominoids some estimated dates differ somewhat from those found with more extensive noncoding sequences in the -globin cluster.     

Test of the Optimal Body Size Model for Strepsirhines

We determined if data on strepsirhine body and home range sizes support an optimal body size (OBS) model of 100 g, as predicted from studies of energetics in terrestrial mammals. We also tested the following predictions of the OBS model: 1) relationships between body and home range sizes will change slope and sign above and below the OBS threshold of 100 g and 2) best-fit lines for OBS regression models (above and below the 100-g threshold) will intersect at ca. 100 g (range of 80–250 g). We collected data on body mass, home range size, and vertical ranging behavior for 37 strepsirhines from the literature. Linear regression analyses and phylogenetic independent contrasts methods revealed that body size is a significant determinant of both 2-dimensional (ha) and 3-dimensional (km³) home range sizes only in taxa weighing >100 g. There were consistent changes in the sign of the slopes above and below the OBS threshold. The intersections of the best-fit lines were within the OBS range for the body size to 3-dimensional home range comparisons. Thus, the data provide some support for the OBS model in strepsirhines. However, no regression model was statistically significant for the taxa below the OBS threshold, which may reflect small sample sizes. Also, no slope differed significantly between taxa above and below the OBS. Significant correlations between body and home range sizes for the complete data sets refute the √-shaped constraint space predicted via the OBS model.