The effects of natural substrate discontinuities on the quadrupedal gait kinematics of free‐ranging Saimiri sciureus

Wild primates encounter complex matrices of substrates that differ in size, orientation, height, and compliance, and often move on multiple, discontinuous substrates within a single bout of locomotion. Our current understanding of primate gait is limited by artificial laboratory settings in which primate quadrupedal gait has primarily been studied. This study analyzes wild Saimiri sciureus (common squirrel monkey) gait on discontinuous substrates to capture the realistic effects of the complex arboreal habitat on walking kinematics. We collected high‐speed video footage at Tiputini Biodiversity Station, Ecuador between August and October 2017. Overall, the squirrel monkeys used more asymmetrical walking gaits than symmetrical gaits, and specifically asymmetrical lateral sequence walking gaits when moving across discontinuous substrates. When individuals used symmetrical gaits, they used diagonal sequence gaits more than lateral sequence gaits. In addition, individuals were more likely to change their footfall sequence during strides on discontinuous substrates. Squirrel monkeys increased the time lag between touchdowns both of ipsilaterally paired limbs (pair lag) and of the paired forelimbs (forelimb lag) when walking across discontinuous substrates compared to continuous substrates. Results indicate that gait flexibility and the ability to alter footfall patterns during quadrupedal walking may be critical for primates to safely move in their complex arboreal habitats. Notably, wild squirrel monkey quadrupedalism is diverse and flexible with high proportions of asymmetrical walking. Studying kinematics in the wild is critical for understanding the complexity of primate quadrupedalism.     

AVPR1b variation and the emergence of adaptive phenotypes in Platyrrhini primates

Platyrrhini (New World monkeys, NWm) are a group of primates characterized by behavioral and reproductive traits that are otherwise uncommon among primates, including social monogamy, direct paternal care, and twin births. As a consequence, the study of Platyrrhine primates is an invaluable tool for the discovery of the genetic repertoire underlying these taxon‐specific traits. Recently, high conservation of vasopressin (AVP) sequence, in contrast with high variability of oxytocin (OXT), has been described in NWm. AVP and OXT functions are possible due to interaction with their receptors: AVPR1a, AVPR1b, AVPR2, and OXTR; and the variability in this system is associated with the traits mentioned above. Understanding the variability in the receptors is thus fundamental to understand the function and evolution of the system as a whole. Here we describe the variability of AVPR1b coding region in 20 NWm species, which is well‐known to influence behavioral traits such as aggression, anxiety, and stress control in placental mammals. Our results indicate that 4% of AVPR1b sites may be under positive selection and a significant number of sites under relaxed selective constraint. Considering the known role of AVPR1b, we suggest that some of the changes described here for the Platyrrhini may be a part of the genetic repertoire connected with the complex network of neuroendocrine mechanisms of AVP–OXT system in the modulation of the HPA axis. Thus, these changes may have promoted the emergence of social behaviors such as direct paternal care in socially monogamous species that are also characterized by small body size and twin births.     

Species differences in adrenocortical activity of new world primates: Response to dexamethasone suppression

The effect of dexamethasone-induced alteration of adrenocortical activity was assessed in two species of New World primates: Saimiri sciureus and Callicebus moloch. Basal and stress levels of corticosteroids were determined following treatment with three doses of dexamethasone (0, 50, or 500 μg/kg). Saimiri showed substantially higher basal levels of corticosteroids than did Callicebus and a greater incremental corticosteroid response to physical restraint. Dexamethasone was found to reduce basal corticosteroids in both species, although this effect was greater for Callicebus than for Saimiri Moreover, the adrenocortical response to physical restraint was reduced by dexamethasone treatment in Callicebus but not in Saimiri. The pattern of results suggests that the species differ in the mechanisms mediating adrenocortical activity.     

Impacts of human activity and climate change on the distribution of snub‐nosed monkeys in China during the past 2000 years

Aim

In this article, we analysed two millennia of historical records and environmental information to reconstruct the past distribution and examine the current distribution of snub‐nosed monkeys (Rhinopithecus) in China.

Location

China.

Methods

We applied trend surface analysis (TSA) to document patterns of range shifting in snub‐nosed monkeys over time. Random forest was used to study the association between explanatory variables and changes in the distribution of snub‐nosed monkeys over the past 2000 years.

Results

Our results showed that both the longitude and latitude of snub‐nosed monkeys contracted from 0 to 2000 AD. We found that the integrated effects of human population size and changes in temperature in the Northern Hemisphere resulted in a westward and northward contraction of the snub‐nosed monkey distributional range. However, the impact of fluctuating temperature was greatest during periods of low human population density (0–1200 AD), whereas from 1200 to 2000 AD, marked increases in human population size in China leading to extensive deforestation, agricultural expansion, hunting, logging and land terracing have had the greatest negative effects. Further analyses highlighted the fact that the rapid expansion of human population density in regions occupied by snub‐nosed monkeys between 1700 and 2000 has resulted in the recent extirpation of this primate radiation in eastern, south‐eastern and central China.

Main conclusions

We examined the interactive effects of human population growth, deforestation, agricultural expansion and climate variation on the past and current distribution of snub‐nosed monkeys. Our data provide clear evidence that climate change, human population increase and human activities have differentially affected the viability and distribution of snub‐nosed monkey populations over time. In particular, the marked expansion of the human population in China over the past 300 years has resulted in the extinction of Rhinopithecus populations across much of its range.     

Predation on mammals by chimpanzees in the montane forest of Kahuzi, Zaire

The rate of predation on mammals by chimpanzees was determined from carcasses and from fecal specimens found on fresh trails during a 16-month period in the montane forest of Kahuzi-Biega National Park, Zaire. A unit-group of semi-habituated chimpanzees, composed of 22 – 23 individuals including 8 adult or adolescent males, appeared to kill about 18 – 30 mammalian prey (16 – 28Cercopithecus monkeys) per year, if the multiple kills by chimpanzees were not considered. A juvenile l'Hoest's monkey was recorded for the first time as the prey of chimpanzees in this study. Predation occurred in the late dry and the early rainy seasons, when the diversity of ripe fruits was the highest during the year. The Kahuzi chimpanzees tended to kill mammals less frequently but to killCercopithecus monkeys more frequently than chimpanzees in other habitats. The absence of red colobus monkeys, which are the most frequent prey in Gombe, Mahale, and Tai, might be responsible for the low predation rate. However, the estimated rate of predation onCercopithecus monkeys is the highest record among various chimpanzee habitats. At least 11 – 18% of theCercopithecus population seemed to be lost annually as a result of being killed by chimpanzees. Chimpanzees may be the most important predators on these monkeys in the absence of leopards at Kahuzi. The examination of fecal samples and carcasses suggested that adult (probably male) or adolescent chimpanzees tended to eat juvenile or subadult monkeys most frequently, as is also seen for chimpanzees in Gombe, Mahale, and Tai.     

Primary Seed Dispersal by Red Howler Monkeys and the Effect of Defecation Patterns on the Fate of Dispersed Seeds1

The effectiveness of a seed disperser depends on the quantity and quality of dispersal. The quality of dispersal depends in large part on factors that affect the post–dispersal fate of seeds, and yet this aspect of dispersal quality is rarely assessed. In the particular case of seed dispersal through endozoochory, the defecation pattern produced has the potential of affecting the fate of dispersed seeds and consequently, dispersal quality and effectiveness. In this study, I assessed the effects of dung presence and dung/seed densities on seed predation by rodents and secondary dispersal by dung beetles. In particular, I compared seed fates in clumped defecation patterns, as those produced by howler monkeys, with seed fates in scattered defecation patterns, as those produced by other frugivores. I also determined the prevalence of red howler monkeys (Alouatta seniculus) as seed dispersers at the plant community level in Central Amazonia by determining the number of species they dispersed in a 25–month period. I found that dung presence and amount affected rodent and dung beetle behavior. Seed predation rates were higher when dung was present, and when it was in higher densities. The same number of seeds was buried by dung beedes, in dumped versus scattered defecation patterns, but more seeds were buried when they were inside large dung–piles versus small piles. Seed density had no effect on rodent or dung beetle behavior. Results indicate that caution should be taken when categorizing an animal as a high or low quality seed disperser before carefully examining the factors that affect the fate of dispersed seeds. Red howler monkeys dispersed the seeds of 137 species during the study period, which is the highest yet reported number for an Alouatta species, and should thus be considered highly prevalent seed dispersers at the plant community level in Central Amazonian terra firme rain forests.     

Intestinal Parasites of the Free-Ranging Cayo Santiago Rhesus Monkeys (Macaca mulatto)

Free-ranging rhesus macaques on the island of Cayo Santiago, Puerto Rico, were surveyed for intestinal parasites for the first time in over 40 years. Results were compared with the only previous study [10], and the relationships between the prevalence of Strongyloides and dominance rank, body weight, age, and matriline examined in the sampled population.