The effects of ecology and evolutionary history on robust capuchin morphological diversity.

Recent molecular work has confirmed the long-standing morphological hypothesis that capuchins are comprised of two distinct clades, the gracile (untufted) capuchins (genus Cebus, Erxleben, 1777) and the robust (tufted) capuchins (genus Sapajus Kerr, 1792). In the past, the robust group was treated as a single, undifferentiated and cosmopolitan species, with data from all populations lumped together in morphological and ecological studies, obscuring morphological differences that might exist across this radiation. Genetic evidence suggests that the modern radiation of robust capuchins began diversifying ∼2.5 Ma, with significant subsequent geographic expansion into new habitat types. In this study we use a morphological sample of gracile and robust capuchin craniofacial and postcranial characters to examine how ecology and evolutionary history have contributed to morphological diversity within the robust capuchins. We predicted that if ecology is driving robust capuchin variation, three distinct robust morphotypes would be identified: (1) the Atlantic Forest species (Sapajus xanthosternos, S. robustus, and S. nigritus), (2) the Amazonian rainforest species (S. apella, S. cay and S. macrocephalus), and (3) the Cerrado-Caatinga species (S. libidinosus). Alternatively, if diversification time between species pairs predicts degree of morphological difference, we predicted that the recently diverged S. apella, S. macrocephalus, S. libidinosus, and S. cay would be morphologically comparable, with greater variation among the more ancient lineages of S. nigritus, S. xanthosternos, and S. robustus. Our analyses suggest that S. libidinosus has the most derived craniofacial and postcranial features, indicative of inhabiting a more terrestrial niche that includes a dependence on tool use for the extraction of imbedded foods. We also suggest that the cranial robusticity of S. macrocephalus and S. apella are indicative of recent competition with sympatric gracile capuchin species, resulting in character displacement.

Increased aggressive and affiliative display behavior in intrauterine growth restricted baboons.

BACKGROUND: We hypothesized intrauterine growth restricted offspring (IUGR) demonstrate higher rates of aggression and higher dominance ranks than control (CTR) offspring with normal weight at term; if aggressive behavior is advantageous during resource scarcity, developmental programming may lead to an association between aggression and IUGR. METHODS: We studied 22 group-housed baboons (ages 3-5 years). CTR (male n = 8, female n = 5) mothers ate ad libitum. IUGR (male n = 4, female n = 5) mothers were fed 70% feed eaten by CTR mothers during pregnancy and lactation. RESULTS: IUGR showed higher rates of aggressive displays (P < 0.01) and friendly displays (P < 0.02). Dominance ranks and physical aggression rates did not differ between groups. CONCLUSIONS: High rates of IUGR aggressive display might reflect developmental programming of behavioral phenotypes enhancing fitness. Friendly displays may reflect reconciliation. Potential mechanisms include neurodevelopment and learning. Exploration of IUGR as a risk factor for behavioral patterns is important for developing diagnostic and therapeutic strategies.

Taxonomy of the Bornean slow loris, with new species Nycticebus kayan (Primates, Lorisidae).

More species of nocturnal primates are now recognized than in the past, because many are cryptic species. Subtle morphological disparities, such as pelage pattern and color variation, vocal cues, and genetics have aided in elucidating the number of diagnosable species in a genus. The slow lorises (genus Nycticebus) once included only two species, but recent taxonomic studies resulted in the description of three additional species; further incompletely explored variability characterizes each of the currently described species. The Bornean loris in particular is characterized by pelage and body size variation. In this study, we explored facemask variation in the Bornean loris (N. menagensis). Differing facemask patterns, particularly influenced by the amount of white on the face, significantly clustered together by geographic regions, separated by notable geographic boundaries. Our results support the recognition of four species of Bornean lorises: N. menagensis, N. bancanus, N. borneanus, and N. kayan. Genetic studies are required to support these findings and to refine further our understanding of the marked variability within the Bornean loris populations.

Feeding and resting postures of wild northern muriquis (Brachyteles hypoxanthus).

Increased body size in Brachyteles has been regarded as an important evolutionary adaptation that allowed a greater reliance on leaves compared to other more frugivorous Atelidae, but its association with muriqui positional behavior and substrate use is still unknown. Here, we present original data on the feeding and resting postures of the northern muriqui (Brachyteles hypoxanthus) and evaluate predictions about the relationships between body size, postural behavior, and substrate use derived from previously published data for other atelids (e.g. Alouatta, Ateles, and Lagothrix). The study was undertaken from August 2002 to July 2003 on a large group of well-habituated muriquis inhabiting the Reserva Particular do Patrimônio Natural - Felíciano Miguel Abdala in Minas Gerais, Brazil. Consistent with our predictions, we found that B. hypoxanthus was highly suspensory during postural feeding (60.9%) and commonly used tail-hind limb suspension/horizontal tripod (38.0%) or tail-forelimb/hind limb suspension (21.4%). However, although tail-suspensory postures permitted the muriquis to use the terminal canopy and small-sized substrates, these areas were also accessed via tail-assisted above-branch postural behaviors involving multiple substrates. Unexpectedly, tail-suspensory postures were found to be frequently associated with large substrates, tree trunks, and the understory. We suggest that Brachyteles' ability to access food resources from all areas of a feeding tree and from tree crowns at different canopy levels may account for their ability to efficiently exploit food resources in seasonal disturbed forest fragments of the Brazilian Atlantic Forest today.

Evolution of sexual dimorphism in body weight in platyrrhines.

Neotropical primates show a remarkable range in body size, spanning two orders of magnitude from the tiny pygmy marmosets (100 g) to the woolly spider monkeys (11,000+ g). Even among the "smaller" platyrrhines, the range is large. In addition, these primates demonstrate a wide diversity in degrees and directions of sexual dimorphism, in both body size and canine size, from marked positive dimorphism (males larger than females), through monomorphic species, to negative dimorphism. Potential correlates or causes of the patterns of dimorphism in body size are investigated, including overall body size, natural selection for life history strategies, sexual selection, diet, habitat, and phylogenetic inertia. Focus is especially on those genera that show species-specific variation in dimorphism (e.g., Saguinus, Pithecia). Results are contrary to those for cross-primate or catarrhine studies, but complementary to recent studies on strepsirhines. They suggest that sexual selection is the primary determinant of degree and pattern of sexual dimorphism in platyrrhines, but that there is also a dietary effect. Natural selection may have some effect, although not the parameters analyzed here. Body size, habitat (primary vs. secondary forest preference), and phylogenetic inertia or constraints do not have any effect on the presence of sexual dimorphism in body weights in New World monkeys. © 1994 Wiley-Liss, Inc.

Craniofacial adaptations to tree-gouging among marmosets.

Many primates rely on exudates as dietary items, but comparatively few elicit exudates via tree-gouging. Marmosets are the only haplorhines to extensively utilize this behavior during feeding. Several studies have explored craniofacial adaptations to this behavior, but its morphological correlates are a matter of debate. Various studies suggest that gougers exhibit bite-force maximizing adaptations, load resistance adaptations, and/or jaw-gape maximizing characteristics. All of these seemingly incompatible biomechanical adaptations have previously been argued for marmosets. This study utilizes multivariate and univariate analyses to compare gouging and non-gouging callitrichids for 25 biomechanically relevant craniofacial variables to address this form-function debate. We show that marmosets differ from non-gouging callitrichids in few craniofacial characteristics. Specifically, three craniofacial features differentiate them from non-gougers: relatively longer basicrania, narrower palates, and shorter coronoid processes. We suggest that these characteristics are consistent with a mosaic model for gouging adaptations. In particular, we argue that: (a) shortening the coronoid processes facilitates relatively larger maximum jaw-gapes, (b) basicranial elongation facilitates the extended neck/head posture utilized by marmosets during gouging to maximize gapes, and (c) narrowing the palate serves to more effectively dissipate forces through the maxillary canines during substrate anchoring. Previous studies have documented some of these characters as typical of marmosets, but this combination has not been interpreted as core elements of the marmoset adaptive complex. Marmosets exhibit a unique anatomical repertoire that biomechanically adapts them to both increased jaw-gape and the force dissipation regime associated with tree-gouging. Comparisons among marmoset taxa may enlighten the evolutionary history of the features reported here.

Dentition of moustached tamarins (Saguinus mystax mystax) from Padre Isla, Peru, part 1: quantitative variation.

Analyses of dental variation in geographically restricted, wild populations of primates are extremely rare; however, such data form the best source for models of likely degrees of variation within and between fossil species. Data from dental casts of a geographically restricted population of moustached tamarins (Saguinus mystax mystax) from Padre Isla, Peru, document high levels of dental variability, as measured by coefficients of variation, in a nonsexually dimorphic species, despite its isolation and small population size. Like other primates, moustached tamarins show lower variability in the dimensions of the first molars and increased variability in the dimensions of the final molars in the toothrow. Moustached tamarins from Padre Isla have a distinctive pattern of variability in the remaining teeth, including more stable tooth lengths in the anterior and posterior portions of the toothrow, and more stable tooth widths in the midregion of the toothrow. High variability in incisor width may be due to age effects of a distinctive diet and pattern of dental wear.

The locomotor behavior of Callicebus brunneus and Callicebus torquatus.

This study presents data on the positional behavior of Callicebus torquatus and Callicebus brunneus collected from two different localities in Peru. C. brunneus primarily utilizes short-distance, bounding leaps, while C. torquatus relies predominantly on quadrupedal walking. Both species utilize small, horizontal and terminal branches more than any other substrate class. We relate the differences in locomotor behaviors between the two species to their utilization of different forest levels. C. brunneus tends to reside in the understory and brush layer forest levels. These more discontinuous strata necessitate higher frequencies of short-distance leaping. C. torquatus occupies the more continuous, interconnected canopy level, and much of its food is found in this level. Comparisons with other species show that Callicebus spp. locomote along smaller-sized, horizontal branches using quadrupedal progression and leaping.