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1. Relationships between sex, body mass and tooth wear in Cayo Santiago rhesus monkeys (Macaca mulatta)

   Guatelli-Steinberg, Debbie ; Maldonado, Elizabeth ; Kensler, Terry B ; Kohn, Luci AP ; Zhao, Martin Q ; Wang, Q. ( January 2021 , American journal of physical anthropology)

   null (Ed.)

   Understanding factors affecting tooth wear in primates is of interest because as teeth wear, their chewing efficiency can change—in some species positively and in others negatively. It is well known that teeth wear with age, but relationships between sex and tooth wear and between body size and tooth wear are less well understood. Here we analyze molar wear scores from a cross-sectional sample of 212 Cayo Santiago rhesus monkey (Macaca mulatta) adults examined in 1985. Because males are generally larger than females --potentially processing more food over their lifetimes--we hypothesized that with age included in an ordinal logistic regression model, males would exhibit significantly greater wear than females. We further hypothesized that males of larger body mass would exhibit greater wear than males of smaller body mass. Finally, because many of the females were pregnant or lactating at the time of dental examination, we hypothesized that there would be no relationship between body mass and wear in females. We found that with age included in ordinal logistic regression models, males had significantly more worn molars than females, larger males had more worn molars than smaller males, and that for females, molar wear was not significantly related to body mass. These results suggest that over the life course, animals with larger body sizes (males vs. females and larger vs. smaller males) may accumulate more wear than those with smaller body sizes. Future analyses to be conducted on the Cayo Santiago monkeys’ skeletal remains will further evaluate this possibility. Funding Sources: The Cayo Santiago colony is supported by NIH 5P40OD012217. This project is supported by NSF grants to DG-S., LK., MZ, and QW (NSF #1926528, 1926481, 1926402, and 1926601). 

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2. Relationships between sex, body mass and tooth wear in Cayo Santiago rhesus monkeys (Macaca mulatta)

   Guatelli-Steinberg, Debbie ; Maldonado, Elizabeth ; Kensler, Terry B ; Kohn, Luci AP ; Zhao, Martin Q ; Wang, Q. ( January 2021 , American journal of physical anthropology)

   null (Ed.)

   Understanding factors affecting tooth wear in primates is of interest because as teeth wear, their chewing efficiency can change—in some species positively and in others negatively. It is well known that teeth wear with age, but relationships between sex and tooth wear and between body size and tooth wear are less well understood. Here we analyze molar wear scores from a cross-sectional sample of 212 Cayo Santiago rhesus monkey (Macaca mulatta) adults examined in 1985. Because males are generally larger than females --potentially processing more food over their lifetimes--we hypothesized that with age included in an ordinal logistic regression model, males would exhibit significantly greater wear than females. We further hypothesized that males of larger body mass would exhibit greater wear than males of smaller body mass. Finally, because many of the females were pregnant or lactating at the time of dental examination, we hypothesized that there would be no relationship between body mass and wear in females. We found that with age included in ordinal logistic regression models, males had significantly more worn molars than females, larger males had more worn molars than smaller males, and that for females, molar wear was not significantly related to body mass. These results suggest that over the life course, animals with larger body sizes (males vs. females and larger vs. smaller males) may accumulate more wear than those with smaller body sizes. Future analyses to be conducted on the Cayo Santiago monkeys’ skeletal remains will further evaluate this possibility. Funding Sources: The Cayo Santiago colony is supported by NIH 5P40OD012217. This project is supported by NSF grants to DG-S., LK., MZ, and QW (NSF #1926528, 1926481, 1926402, and 1926601). 

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3. Oral Processing Behavior in Bornean Orangutans of Different Age and Sex Classes

   Wyszynski, Sofia I ; Kane, Erin E ; Bakley, Tori D ; Rinaldi, R ; Susanto, Wahyu ; Knott, Cheryl D. ( November 2021 , Northeastern Evolutionary Primatologists)

   Orangutan diets vary dramatically with food availability. Orangutans preferentially eat fruit when available, but due to dramatic and unpredictable fluctuations in fruit availability, orangutans often consume unripe fruit, bark, seeds, and leaves. Their robust craniodental structure suggests that they are well adapted to consume mechanically challenging foods. Since differences in jaw anatomy and body size pose physiological differences in terms of gape, exerted force, and resistance to wear and breakdown, growth and allometry likely affect an orangutan’s ability to process a mechanically challenging diet. Thus, we predict that orangutans of different ages and sexes process foods differently. Given juveniles' smaller and less powerful craniodental structure, and the time required to develop ecological competence, we hypothesized that juveniles may have more difficulty in processing foods than adults. We recorded the frequency that foods were introduced to the mouth, and chewed with different teeth (incisors, canines, and molars) in 561 feeding videos collected in Gunung Palung National Park in West Kalimantan, Borneo on wild orangutans (Pongo pygmaeus wurmbii). Videos were stratified by age and sex class and foods were categorized by type. Infants and juveniles use their canines significantly more frequently than adult females (p< 0.05) and flanged males (p< 0.05). Molar use also differed by age and sex class (F(3)=2.551, p=0.05), with juveniles chewing with their molars significantly more frequently than adult females (p=0.05). Differences in adult and juvenile oral processing profiles suggest juveniles may process some foods less efficiently than adults. 

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4. The ontogeny of sexual dimorphism in free‐ranging rhesus macaques

   https://doi.org/10.1002/ajpa.24442  

   Turcotte, Cassandra M. ; Mann, Eva H. J. ; Stock, Michala K. ; Villamil, Catalina I. ; Montague, Michael J. ; Dickinson, Edwin ; Cayo Biobank Research Unit ; Surratt, Samuel Bauman ; Martinez, Melween ; Williams, Scott A. ; et al ( January 2022 , American Journal of Biological Anthropology)

   Reconstructing the social lives of extinct primates is possible only through an understanding of the interplay between morphology, sexual selection pressures, and social behavior in extant species. Somatic sexual dimorphism is an important variable in primate evolution, in part because of the clear relationship between the strength and mechanisms of sexual selection and the degree of dimorphism. Here, we examine body size dimorphism across ontogeny in male and female rhesus macaques to assess whether it is primarily achieved via bimaturism as predicted by a polygynandrous mating system, faster male growth indicating polygyny, or both.

   We measured body mass in a cross‐sectional sample of 362 free‐ranging rhesus macaques from Cayo Santiago, Puerto Rico to investigate size dimorphism: (1) across the lifespan; and (2) as an outcome of sex‐specific growth strategies, including: (a) age of maturation; (b) growth rate; and (c) total growth duration, using regression models fit to sex‐specific developmental curves.

   Significant body size dimorphism was observed by prime reproductive age with males 1.51 times the size of females. Larger male size resulted from a later age of maturation (males: 6.8–7.8 years vs. females: 5.5–6.5 years; logistic model) and elevated growth velocity through the pre‐prime period (LOESS model). Though males grew to larger sizes overall, females maintained adult size for longer before senescence (quadratic model).

   The ontogeny of size dimorphism in rhesus macaques is achieved by bimaturism and a faster male growth rate. Our results provide new data for understanding the development and complexities of primate dimorphism.

    

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5. Changes in molar topography and 3D shear crest lengths with tooth wear in two cercopithecid primates from Malaysia

   https://doi.org/10.1002/ajpa.24023  

   Locke, Ellis M ( February 2020 , American Journal of Physical Anthropology)

   As herbivorous, diphyodont mammals with relatively low-crowned molars, primates experience changes in dental function during their lifetimes as teeth become progressively worn. Maintaining tooth function with wear is thought to pose a particular challenge for folivorous primates whose diets emphasize molar shearing actions. Recent studies using dental topographic methods suggest that certain primate folivores have molar morphology that maintains or increases functional shearing surfaces with tooth wear (‘dental sculpting’). Evidence for this phenomenon has been found in folivorous but not frugivorous New World monkeys, supporting the hypothesis that dental sculpting is an adaptive trait linked to diet. This analysis extends these methods to two sympatric Old World monkeys from Sabah, Malaysia, possessing distinct diets and dental morphologies: the folivorous colobine Trachypithecus cristatus (n=25) and the more frugivorous cercopithecine Macaca fascicularis (n=22). For each species, 3D shear crest lengths and four dental topographic variables (relief index, slope, angularity, and Dirichlet Normal Energy [DNE]) were measured from variably worn lower second molars. Preliminary results indicate that for any given degree of wear, Trachypithecus has longer shear crest lengths and higher relief, slope, angularity, and DNE than Macaca. The two species exhibit different patterns and degrees of change in topography and shearing crest lengths across the wear series. However, these changes do not always match expectations based on their respective diets. Correlations between 3D shear crest lengths and other dental topographic measurements suggests that the type of metric used to assess shearing potential may affect whether or not dental sculpting is detected. 

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