Results of the general linear mixed model (GLMM) for subsets of females with sAA activity as response variable, species, age and time of day as fixed effects, and zoo and subject as random effects (MCMC = Markov Chain Monte Carlo; SE = Standard error).

<p>Results of the general linear mixed model (GLMM) for subsets of females with sAA activity as response variable, species, age and time of day as fixed effects, and zoo and subject as random effects (MCMC = Markov Chain Monte Carlo; SE = Standard error).</p

Measurements of Salivary Alpha Amylase and Salivary Cortisol in Hominoid Primates Reveal Within-Species Consistency and Between-Species Differences

<div><p>Salivary alpha amylase (sAA) is the most abundant enzyme in saliva. Studies in humans found variation in enzymatic activity of sAA across populations that could be linked to the copy number of loci for salivary amylase (AMY1), which was seen as an adaptive response to the intake of dietary starch. In addition to diet dependent variation, differences in sAA activity have been related to social stress. In a previous study, we found evidence for stress-induced variation in sAA activity in the bonobos, a hominoid primate that is closely related to humans. In this study, we explored patterns of variation in sAA activity in bonobos and three other hominoid primates, chimpanzee, gorilla, and orangutan to (a) examine if within-species differences in sAA activity found in bonobos are characteristic for hominoids and (b) assess the extent of variation in sAA activity between different species. The results revealed species-differences in sAA activity with gorillas and orangutans having higher basal sAA activity when compared to <i>Pan</i>. To assess the impact of stress, sAA values were related to cortisol levels measured in the same saliva samples. Gorillas and orangutans had low salivary cortisol concentrations and the highest cortisol concentration was found in samples from male bonobos, the group that also showed the highest sAA activity. Considering published information, the differences in sAA activity correspond with differences in AMY1 copy numbers and match with general features of natural diet. Studies on sAA activity have the potential to complement molecular studies and may contribute to research on feeding ecology and nutrition.</p></div

Results of the general linear mixed models (GLMMs) of the four subsets with salivary cortisol levels as response variable, and with age, time of day (both z-transformed) and sex as fixed effects.

<p>The parameters zoo and subject were scored as random effects (MCMC = Markov Chain Monte Carlo; SE = Standard error).</p

Results of the general linear mixed model (GLMM) obtained by analysing subsets of samples from females, with salivary cortisol concentration as response variable, with species, age and time of day as fixed effects, and zoo and subject as random effects (MCMC = Markov Chain Monte Carlo; SE = Standard error).

<p>Results of the general linear mixed model (GLMM) obtained by analysing subsets of samples from females, with salivary cortisol concentration as response variable, with species, age and time of day as fixed effects, and zoo and subject as random effects (MCMC = Markov Chain Monte Carlo; SE = Standard error).</p

Average salivary alpha amylase (sAA) activity in females and males of the four ape species.

<p>The boxes illustrate the 25th and 75th percentiles, bars indicate medians, and circles indicate outliers. The y-axis is log transformed. Sample sizes: total N = 625: N_{bonobo female} = 92, N_{bonobo male} = 98; N_{chimpanzee female} = 113, N_{chimpanzee male} = 41; N_{gorilla female} = 60, N_{gorilla male} = 39; N_{orangutan female} = 107, N_{orangutan male} = 75.</p

Results of the general linear mixed model (GLMM) obtained by analysing subsets of samples males, with salivary cortisol concentration as response variable, with species, age and time of day as fixed effects, and zoo and subject as random effects (MCMC = Markov Chain Monte Carlo; SE = Standard error).

<p>Results of the general linear mixed model (GLMM) obtained by analysing subsets of samples males, with salivary cortisol concentration as response variable, with species, age and time of day as fixed effects, and zoo and subject as random effects (MCMC = Markov Chain Monte Carlo; SE = Standard error).</p

Results of the general linear mixed models (GLMMs) of the four subsets for each species with sAA activity as response variable, and with age, time of day (both z-transformed) and sex as fixed effects.

<p>The parameters zoo and subject were scored as random effects (MCMC = Markov Chain Monte Carlo; SE = Standard error).</p

Average salivary cortisol concentrations for females and males of each species.

<p>The boxes illustrate the 25th and 75th percentiles, bars indicate median, and circles indicate outliers. Cortisol values on the y-axis are log transformed. Sample sizes: total N = 615, N_{bonobo female} = 90, N_{bonobo male} = 94; N_{chimpanzee female} = 112, N_{chimpanzee male} = 39; N_{gorilla female} = 59, N_{gorilla male} = 39; N_{orangutan female} = 107, N_{orangutan male} = 75.</p

Results of the two General Linear Mixed Models of the two subsets for orangutans and bonobos for medical positive reinforcement training with salivary cortisol as response variable (sex, age, and session number are included as fixed effects.

<p>Animal and session ID were included as random intercept terms (MCMC = Markov Chain Monte Carlo)). Bold values indicate P<0.05.</p>†<p>overall effect of the factor.</p><p>Results of the two General Linear Mixed Models of the two subsets for orangutans and bonobos for medical positive reinforcement training with salivary cortisol as response variable (sex, age, and session number are included as fixed effects.</p

Average salivary cortisol concentration of males and females of a bonobo group during four medical PRT sessions (two training sessions with the whole group and two with half of the group).

<p>The boxes illustrate the 25th and 75th percentiles, bars indicate medians, and circles indicate outliers.</p