Morphometrics and pattern of growth in wild sifakas (Propithecus edwardsi) at ranomafana national park, madagascar

Diademed sifakas (Propithecus diadema) in intact and degraded forest habitat at Tsinjoarivo, Madagascar, show high reproductive success and no evidence that dental senescence or rainfall affects reproductive output

Sifakas (genus Propithecus) diverge from other lemurs in their strategy to contend with Madagascar’s highly seasonal climate and maximize reproductive success: they have long lifetimes (presumably to wait out unfavorable times) and extreme dental precocity (to allow weanlings to effectively process tough foods and thereby relieve energetic stress on mothers). However, as sifakas age, dental senescence can contribute to reproductive failure, especially when coupled with unfavorable weather conditions (as shown by King et al., 2005 for P. edwardsi at Ranomafana). To extend the effective life of the teeth, compensatory blades maintain functionality for the female sifaka, but wear may eventually have consequences on infant survival in certain climatic scenarios. We investigate the impacts of climate, age, and dental senescence on the reproduction of another sifaka, Propithecus diadema, in fragmented and intact habitats of Tsinjoarivo, Madagascar. We documented birth and infant survival between 2002 and 2017 across twelve groups, including 73 births, and we used 77 dental casts representing 54 adults to estimate age when exact age was not known. We report that sifakas in Tsinjoarivo do not conform to the expectations that link advanced age with dental and reproductive senescence. Propithecus diadema at Tsinjoarivo show slower tooth wear, higher reproductive output and higher infant survival compared to congeners. Likelihood of birth and infant mortality do not correlate with intrinsic (mother’s age, tooth wear) or extrinsic (rainfall or habitat type) stressors. However, the small number of years without births or with infant deaths limits statistical power. At the local level, this study suggests that the long-term viability of Propithecus diadema at Tsinjoarivo is promising and reproductive output is high, even in disturbed fragments where nutrient intakes are reduced. Further research is needed to contextualize and understand these differences among sites and regions within Madagascar and avoid over-generalizing from single study sites.

Morphometric signals of population decline in diademed sifakas occupying degraded rainforest habitat in Madagascar

Anthropogenic habitat change can have varied impacts on primates, including both negative and positive outcomes. Even when behavioural shifts are seen, they may reflect decreased health, or simply behavioural flexibility; understanding this distinction is important for conservation efforts. This study examines habitat-related variation in adult and immature morphometrics among diademed sifakas (Propithecus diadema). We collected morphometric data from sifakas at Tsinjoarivo, Madagascar (19 years, 188 captures, 113 individuals). Captures spanned 12 groups, five within continuous forest ("CONT"), and seven in degraded fragments ("FRAG") where sifakas have lower nutritional intakes. Few consistent differences were found between CONT and FRAG groups. However, using home range quality as a covariate rather than a CONT/FRAG dichotomy revealed a threshold: the two FRAG groups in the lowest-quality habitat showed low adult mass and condition (wasting), and low immature mass and length (stunting). Though less-disturbed fragments apparently provide viable habitat, we suggest the sifakas in the most challenging habitats cannot evolve fast enough to keep up with such rapid habitat change. We suggest other long-lived organisms will show similar morphometric "warning signs" (wasting in adults, stunting in immatures); selected morphometric variables can thus be useful at gauging vulnerability of populations in the face of anthropogenic change.

Ectoparasitism in Black-and-White Ruffed Lemurs ( Varecia variegata) in Southeastern Madagascar

We documented ectoparasites found on wild black-and-white ruffed lemurs ( Varecia variegata) in the southeastern rain forests of Madagascar and describe trends in parasitism. In this study, 235 mesostigmatid mites (1 male, 87 females, 147 nymphs) identified as Liponyssella sp., in the acarine family Macronyssidae, were collected during 87% (34/39) of lemur examinations (mean number/host=7.9). The only other ectoparasite collected was the louse fly ( Allobosca crassipes; 3 males, 8 females) in the dipteran family Hippoboscidae, which was collected during 26% (10/39) of lemur examinations (mean number/host=1.1). The lemur most heavily parasitized by mites was an adult female with 29 adult females and 17 nymphs, all collected from the face.

Growth trajectories in wild geladas (Theropithecus gelada)

Life history and socioecological factors have been linked to species-specific patterns of growth across female vertebrates. For example, greater maternal investment in offspring has been associated with more discrete periods of growth and reproduction. However, in primates it has been difficult to test such hypotheses because very few studies have obtained growth measurements from wild populations. Here we utilize a promising noninvasive photogrammetric method-parallel lasers-to examine shoulder-rump (SR) growth in a wild primate, the gelada (Theropithecus gelada, Simien Mountains National Park, Ethiopia). In this species, a graminivorous diet coupled with high extrinsic infant mortality risk suggests that maternal investment in neonates is low. Therefore, in contrast with other closely related papionins, we expected female geladas to exhibit less discrete periods of growth and reproduction. For both sexes, we compared size-for-age patterns (N = 154 females; N = 110 males) and changes in growth velocity relative to major life history milestones. Female geladas finished 88.5% of SR growth by first sexual swelling, and 97.2% by first reproduction, reaching adult body size by 7.72 years of age. Compared to closely related papionins, gelada females finished more growth by first reproduction, despite producing relatively small, and presumably "cheap," neonates. Male geladas finished 85.4% of growth at dispersal, and 96.0% at estimated first birth. Contrary to other polygynous primates, males are larger than females because they grow for a longer period of time (not because they grow faster), surpassing females around 6 years of age when female growth slows. Our results demonstrate that parallel lasers are an easy and promising new method that can be used to construct comprehensive life history perspectives that were once out of reach for wild populations. Am. J. Primatol. 78:707-719, 2016. © 2016 Wiley Periodicals, Inc.

Age-related changes in molar topography and shearing crest length in a wild population of mountain Gorillas from Volcanoes National Park, Rwanda

OBJECTIVES

Great ape teeth must remain functional over long lifespans. The molars of the most folivorous apes, the mountain gorillas, must maintain shearing function for 40+ years while the animals consume large quantities of mechanically challenging foods. While other folivorous primates experience dental senescence, which compromises their occlusal surfaces and affects their reproductive success as they age, it is unknown whether dental senescence also occurs in mountain gorillas. In this article, we quantified and evaluated how mountain gorilla molars change throughout their long lifespans.

MATERIALS AND METHODS

We collected high-resolution replicas of M(1)s (n = 15), M(2)s (n = 13), and M(3)s (n = 11) from a cross-sectional sample of wild mountain gorilla skeletons from the Virunga Volcanoes, ranging in age from 4 to 43 years. We employed dental topographic analyses to track how aspects of occlusal slope, angularity, relief index, and orientation patch count rotated change with age. In addition, we measured the relative length of shearing crests in two- and three-dimensions.

RESULTS

Occlusal topography was found to decrease, while 2D relative shearing crest length increased, and 3D relative crest lengths were maintained with age.

DISCUSSION

Our findings indicate that shearing function is maintained throughout the long lifetimes of mountain gorillas. Unlike the dental senescence experienced by other folivorous primates, mountain gorillas do not appear to possess senesced molars despite their long lifetimes, mechanically challenging diets, and decreases in occlusal topography with age.

Variation in body mass and morphological characters in Macaca mulatta brevicaudus from Hainan, China

The rhesus macaque (Macaca mulatta) is the most widely distributed nonhuman primate species in the world, with six subspecies distributed through China. From 2012 to 2014, we conducted studies on the body mass and morphological variation of the southernmost subspecies M. m. brevicaudus in Nanwan Nature Reserve for Rhesus Macaque, Hainan, China. We compared measurements with other populations of this species. We also investigated the inter-group body mass variation from seven provisioned free-ranging groups in our study site. Our results show that M. m. brevicaudus has the smallest body size, the smallest body mass, and the shortest tail among rhesus macaque subspecies. Its sexual dimorphism score is also among the lowest, which is similar to other southern distributed subspecies in China, but smaller than northern distributed subspecies. We found that the average body mass of female macaques is not correlated with their dominance ranks. There are significant differences in body mass among the seven adjacent study groups at the same site, suggesting the existence of inter-group competition. Average body mass of a group is better described by a quadratic function of group size than a linear one as predicted by the socio-ecological model. Am. J. Primatol. 78:679-698, 2016. © 2016 Wiley Periodicals, Inc.

The influence of growth patterns on sexual size monomorphism in lemurs

The lack of sexual size dimorphism among lemurs is puzzling given the high degree of polygyny in this clade. It has been proposed that the unique ecological conditions of Madagascar favour rapid completion of growth, limiting the opportunities for bimaturism and sexual size dimorphism in lemurs. Using recently compiled large data sets on many species across the lemur clade, I examined the prevalence of sexual size monomorphism of body mass among lemurs and tested the hypothesis that limited growth durations constrain sexual size dimorphism. I used segmented regression analyses to accurately model growth in each species. The majority of species analysed exhibited a period of rapid growth followed by a distinct period of slow growth prior to attainment of adult body mass. Whereas the first period of growth was constrained by the need to attain the majority of adult body mass prior to the onset of the infant's first dry season, the subsequent period of slow growth was unconstrained and sufficiently long to promote sexual bimaturism. Sex differences in the duration and rate of growth during this second growth phase appeared to account for the sexual size dimorphism exhibited by three lemur species. Therefore, constraints on growth processes do not limit sexual size dimorphism in lemurs, and other explanations for the prevalence of sexual size monomorphism in this clade should be examined. The importance of considering ontogeny in future investigations of sexual size monomorphism in lemurs is highlighted.

The Nutritional Geometry of Resource Scarcity: Effects of Lean Seasons and Habitat Disturbance on Nutrient Intakes and Balancing in Wild Sifakas

Animals experience spatial and temporal variation in food and nutrient supply, which may cause deviations from optimal nutrient intakes in both absolute amounts (meeting nutrient requirements) and proportions (nutrient balancing). Recent research has used the geometric framework for nutrition to obtain an improved understanding of how animals respond to these nutritional constraints, among them free-ranging primates including spider monkeys and gorillas. We used this framework to examine macronutrient intakes and nutrient balancing in sifakas (Propithecus diadema) at Tsinjoarivo, Madagascar, in order to quantify how these vary across seasons and across habitats with varying degrees of anthropogenic disturbance. Groups in intact habitat experience lean season decreases in frugivory, amounts of food ingested, and nutrient intakes, yet preserve remarkably constant proportions of dietary macronutrients, with the proportional contribution of protein to the diet being highly consistent. Sifakas in disturbed habitat resemble intact forest groups in the relative contribution of dietary macronutrients, but experience less seasonality: all groups' diets converge in the lean season, but disturbed forest groups largely fail to experience abundant season improvements in food intake or nutritional outcomes. These results suggest that: (1) lemurs experience seasonality by maintaining nutrient balance at the expense of calories ingested, which contrasts with earlier studies of spider monkeys and gorillas, (2) abundant season foods should be the target of habitat management, even though mortality might be concentrated in the lean season, and (3) primates' within-group competitive landscapes, which contribute to variation in social organization, may vary in complex ways across habitats and seasons.

Seasonal mortality patterns in non-human primates: implications for variation in selection pressures across environments

Examining seasonal mortality patterns can yield insights into the drivers of mortality and thus potential selection pressures acting on individuals in different environments. We compiled adult and juvenile mortality data from nine wild non-human primate taxa to investigate the role of seasonality in patterns of mortality and address the following questions: Is mortality highly seasonal across species? Does greater environmental seasonality lead to more seasonal mortality patterns? If mortality is seasonal, is it higher during wet seasons or during periods of food scarcity? and Do folivores show less seasonal mortality than frugivores? We found seasonal mortality patterns in five of nine taxa, and mortality was more often tied to wet seasons than food-scarce periods, a relationship that may be driven by disease. Controlling for phylogeny, we found a positive relationship between the degree of environmental seasonality and mortality, with folivores exhibiting more seasonal mortality than frugivores. These results suggest that mortality patterns are influenced both by diet and degree of environmental seasonality. Applied to a wider array of taxa, analyses of seasonal mortality patterns may aid understanding of life-history evolution and selection pressures acting across a broad spectrum of environments and spatial and temporal scales.