Taste detection threshold of human (Homo sapiens) subjects and taste preference threshold of black-handed spider monkeys (Ateles geoffroyi) for the sugar substitute isomalt.

The artificial sweetener isomalt is widely used due to its low caloric, non-diabetogenic and non-cariogenic properties. Although the sweetening potency of isomalt has been reported to be lower than that of sucrose, no data on the sensitivity of humans for this polyol are available. Using an up-down, two-alternative forced choice staircase procedure we therefore determined taste detection thresholds for isomalt in human subjects (n = 10; five females and five males) and compared them to taste preference thresholds, determined using a two-bottle preference test of short duration, in a highly frugivorous nonhuman primate, the spider monkey (n = 4; one female, three males). We found that both species detected concentrations of isomalt as low as 20 mM. Both humans and spider monkeys are less sensitive to isomalt than to sucrose, which is consistent with the notion of the former being a low-potency sweetener. The spider monkeys clearly preferred all suprathreshold concentrations tested over water, suggesting that, similar to humans, they perceive isomalt as having a purely sweet taste that is indistinguishable from that of sucrose. As isomalt, like most sweet-tasting polyols, may elicit gastric distress when consumed in large quantities, the present findings may contribute to the choice of appropriate amounts and concentrations of this sweetener when it is employed as a sugar substitute or food additive for human consumption. Similarly, the taste preference threshold values of spider monkeys for isomalt reported here may be useful for determining how much of it should be used when it is employed as a low-caloric sweetener for frugivorous primates kept on a vegetable-based diet, or when medication needs to be administered orally.

Principal component analysis of electroencephalographic activity during sleep and wakefulness in the spider monkey (Ateles geoffroyi).

The study of electroencephalographic (EEG) activity during sleep in the spider monkey has provided new insights into primitive arboreal sleep physiology and behavior in anthropoids. Nevertheless, studies conducted to date have maintained the frequency ranges of the EEG bands commonly used with humans. The aim of the present work was to determine the EEG broad bands that characterize sleep and wakefulness in the spider monkey using principal component analysis (PCA). The EEG activity was recorded from the occipital, central, and frontal EEG derivations of six young-adult male spider monkeys housed in a laboratory setting. To determine which frequencies covaried and which were orthogonally independent during sleep and wakefulness, the power EEG spectra and interhemispheric and intrahemispheric EEG correlations from 1 to 30 Hz were subjected to PCA. Findings show that the EEG bands detection differed from those reported previously in both spider monkeys and humans, and that the 1-3 and 2-13 Hz frequency ranges concur with the oscillatory activity elucidated by cellular recordings of subcortical regions. Results show that applying PCA to the EEG spectrum during sleep and wakefulness in the spider monkey led to the identification of frequencies that covaried with, and were orthogonally independent of, other frequencies in each behavioral vigilance state. The new EEG bands differ from those used previously with both spider monkeys and humans. The 1-3 and 2-13 Hz frequency ranges are in accordance with the oscillatory activity elucidated by cellular recordings of subcortical regions in other mammals.

Ecological and social determinants of association and proximity patterns in the fission-fusion society of spider monkeys (Ateles geoffroyi).

Some social species exhibit high levels of fission-fusion dynamics (FFD) that improve foraging efficiency. In this study, we shed light on the way that FFD allows animal groups to cope with fluctuations in fruit availability. We explore the relative contribution of fruit availability and social factors like sex in determining association and proximity patterns in spider monkeys. We tested the influence of fruit availability and social factors on the association and proximity patterns using three-year data from a group of spider monkeys in the Yucatan Peninsula of Mexico. We identified subgroup members and estimated their Interindividual distances through instantaneous scan sampling. We evaluated fruit availability by monitoring the phenology of the 10 most important food tree species for spider monkeys in the study site. Social network analyses allowed us to evaluate association and proximity patterns in subgroups. We showed that association patterns vary between seasons, respond to changes in fruit availability, and are influenced by the sex of individuals, likely reflecting biological and behavioral differences between sexes and the interplay between ecological and social factors. In contrast, proximity patterns were minimally affected by changes in fruit availability, suggesting that social factors are more important than food availability in determining cohesion within subgroups.

Acoustic variation of spider monkey (Ateles geoffroyi) contact calls is related to caller isolation and affects listeners' responses.

Group living animals produce vocalizations denominated "contact calls" to maintain contact with out-of-sight group members. These calls have been shown to vary with caller identity and distance to potential listeners. However, it is not clear whether the acoustic variation of contact calls is related to caller social isolation (e.g., inside or outside a subgroup) and listeners' responses that can be helpful to maintain contact. Here, we addressed these questions in spider monkeys (Ateles geoffroyi), a Neotropical primate that exchanges contact calls denominated "whinnies", which show graded variation related to caller immediate behavior and distance between callers. Using 566 whinnies produced by 35 free-ranging adult spider monkeys recorded at ≤ 20 m from microphones, we first analyzed whether the acoustic variation of spontaneous whinnies (i.e., whinnies that are not responses to previous whinnies) is related to caller social isolation or whether acoustic variation is related to the likelihood of eliciting a response whinny from another individual. Secondly, we assessed whether listeners' responses (i.e., time to respond vocally, acoustic characteristics of response whinnies, orienting behaviors) were related to the acoustic variation of previous whinnies. Our study revealed that callers that were outside a subgroup produced whinnies with a lower fundamental frequency (F0), which travels longer distances, and increases the likelihood of producing a response whinny. Moreover, listeners (i.e., responders) responded faster to lower F0 whinnies. However, the acoustic variation (i.e., F0 variation) in response whinnies was better explained by the separation distance between callers, than by the acoustic variation of the previous whinny. Overall, our results suggest that whinny variation facilitates vocal contact to callers that are outside a subgroup, and that context and whinny variation affect listeners' responses.