Archaeological Analysis Does Not Support Intentionality in the Production of Brushed Ends on Chimpanzee Termiting Tools

Some chimpanzees use 2 types of tools to extract underground termites for consumption. Chimpanzees insert thin, flexible probes into tunnels or holes in termite mounds (fishing), and sometimes use stouter, rigid sticks to first puncture the holes and also possibly to fish. Many puncturing sticks have distinctive “brushed” ends. Researchers have hypothesized that chimpanzees create the brushed ends intentionally to increase their affixibility to biting termites (Sugiyama, 1985). The results of our archaeological analysis of a large collection of puncturing sticks used by Central African chimpanzees falsifies this hypothesis, and instead agrees with the recent behavioral observations of Sanz et al. (2004; cf. Bermejo and Illera, 1999) that brushing is a coincidental result of procuring sticks from vegetation sources. The results highlight the positive contribution of an archaeological approach to problems in chimpanzee material culture and emphasize to primatologists the value of curating artifacts.     

Replication-Defective Vector Based on a Chimpanzee Adenovirus

An adenovirus previously isolated from a mesenteric lymph node from a chimpanzee was fully sequenced and found to be similar in overall structure to human adenoviruses. The genome of this virus, called C68, is 36,521 bp in length and is most similar to subgroup E of human adenovirus, with 90% identity in most adenovirus type 4 open reading frames that have been sequenced. Substantial differences in the hexon hypervariable regions were noted between C68 and other known adenoviruses, including adenovirus type 4. Neutralizing antibodies to C68 were highly prevalent in sera from a population of chimpanzees, while sera from humans and rhesus monkeys failed to neutralize C68. Furthermore, infection with C68 was not neutralized from sera of mice immunized with human adenovirus serotypes 2, 4, 5, 7, and 12. A replication-defective version of C68 was created by replacing the E1a and E1b genes with a minigene cassette; this vector was efficiently transcomplemented by the E1 region of human adenovirus type 5. C68 vector transduced a number of human and murine cell lines. This nonhuman adenoviral vector is sufficiently similar to human serotypes to allow growth in 293 cells and transduction of cells expressing the coxsackievirus and adenovirus receptor. As it is dissimilar in regions such as the hexon hypervariable domains, C68 vector avoids significant cross-neutralization by sera directed against human serotypes.     

Establishing a Corky Ringspot Disease Plot for Research Purposes

A method to establish two experimental corky ringspot disease (CRS) plots that had no prior CRS history is described. CRS is a serious disease of potato in the Pacific Northwest caused by tobacco rattle virus (TRV) and transmitted primarily by Paratrichodorus allius. ‘Samsun NN’ tobacco seedlings were inoculated with viruliferous P. allius in the greenhouse before they were transplanted into the field soil at the rate of 3,000 plus seedlings/ha. Care was taken to keep soil around plants in the greenhouse and transplants in the field moist to avoid vector mortality. The vector population in the soil of one of the fields was monitored by extraction, examination under microscope and bioassay on tobacco seedlings to ascertain that they were virus carriers. Presence of virus in tobacco bioassay plants was determined by visual symptoms on tobacco leaves and by testing leaves and roots using ELISA. Although TRV transmission was rapid, there was loss of infectivity in the first winter which necessitated a re-inoculation. After two years of planting infected tobacco seedlings, 100% of soil samples collected from this field contained viruliferous P. allius. In the second field, all five commercial potato cultivars, known to be susceptible, expressed symptoms of CRS disease indicating that the procedure was successful.     

Chimpanzee (Pan troglodytes schweinfurthii) Group Sleep and Pathogen-Vector Avoidance: Experimental Support for the Encounter-Dilution Effect

International Journal of Primatology - Sleep is essential for survival, yet it represents a time of extreme vulnerability, including through exposure to parasites and pathogens transmitted by...     

Visual Search for Human Gaze Direction by a Chimpanzee (Pan troglodytes)

Background

Humans detect faces with direct gazes among those with averted gazes more efficiently than they detect faces with averted gazes among those with direct gazes. We examined whether this “stare-in-the-crowd” effect occurs in chimpanzees (Pan troglodytes), whose eye morphology differs from that of humans (i.e., low-contrast eyes, dark sclera).

Methodology/Principal Findings

An adult female chimpanzee was trained to search for an odd-item target (front view of a human face) among distractors that differed from the target only with respect to the direction of the eye gaze. During visual-search testing, she performed more efficiently when the target was a direct-gaze face than when it was an averted-gaze face. This direct-gaze superiority was maintained when the faces were inverted and when parts of the face were scrambled. Subsequent tests revealed that gaze perception in the chimpanzee was controlled by the contrast between iris and sclera, as in humans, but that the chimpanzee attended only to the position of the iris in the eye, irrespective of head direction.

Conclusion/Significance

These results suggest that the chimpanzee can discriminate among human gaze directions and are more sensitive to direct gazes. However, limitations in the perception of human gaze by the chimpanzee are suggested by her inability to completely transfer her performance to faces showing a three-quarter view.     

Chimpanzee deaths at Mahale caused by a flu-like disease

A flu-like disease spread among chimpanzees (Pan troglodytes schweinfurthii) of the M group at Mahale Mountains National Park, Tanzania, from June to July 2006. This epizootic or epidemic killed up to 12 chimpanzees. The obvious evidence of their deaths came from finding the bodies of three infants who had previously shown some symptoms of the disease. At least one of these infants died of pneumonia. In addition, nine chimpanzees were missing after the outbreak. These individuals were assumed to have been killed by this epizootic because most of them had contact with the infected individuals on the last days they were observed. We also found two dead bodies during this period, which were thought to be those of two missing individuals. We confirmed 23 (35.4%) of 65 individuals of the M group showed some symptoms of the disease, although most of them (20/23) did not die. More than half of them (14/23) had kin showing symptoms. Since this epizootic may have been caused by contact with humans, it will be necessary to establish and follow appropriate protocols for researchers, tourists, and park staff to observe chimpanzees, and to explore the mechanism of disease transmission from humans to chimpanzees and among chimpanzees.     

Chimpanzee Alarm Call Production Meets Key Criteria for Intentionality

Determining the intentionality of primate communication is critical to understanding the evolution of human language. Although intentional signalling has been claimed for some great ape gestural signals, comparable evidence is currently lacking for their vocal signals. We presented wild chimpanzees with a python model and found that two of three alarm call types exhibited characteristics previously used to argue for intentionality in gestural communication. These alarm calls were: (i) socially directed and given to the arrival of friends, (ii) associated with visual monitoring of the audience and gaze alternations, and (iii) goal directed, as calling only stopped when recipients were safe from the predator. Our results demonstrate that certain vocalisations of our closest living relatives qualify as intentional signals, in a directly comparable way to many great ape gestures. We conclude that our results undermine a central argument of gestural theories of language evolution and instead support a multimodal origin of human language.     

Chimpanzee vocal signaling points to a multimodal origin of human language

The evolutionary origin of human language and its neurobiological foundations has long been the object of intense scientific debate. Although a number of theories have been proposed, one particularly contentious model suggests that human language evolved from a manual gestural communication system in a common ape-human ancestor. Consistent with a gestural origins theory are data indicating that chimpanzees intentionally and referentially communicate via manual gestures, and the production of manual gestures, in conjunction with vocalizations, activates the chimpanzee Broca's area homologue--a region in the human brain that is critical for the planning and execution of language. However, it is not known if this activity observed in the chimpanzee Broca's area is the result of the chimpanzees producing manual communicative gestures, communicative sounds, or both. This information is critical for evaluating the theory that human language evolved from a strictly manual gestural system. To this end, we used positron emission tomography (PET) to examine the neural metabolic activity in the chimpanzee brain. We collected PET data in 4 subjects, all of whom produced manual communicative gestures. However, 2 of these subjects also produced so-called attention-getting vocalizations directed towards a human experimenter. Interestingly, only the two subjects that produced these attention-getting sounds showed greater mean metabolic activity in the Broca's area homologue as compared to a baseline scan. The two subjects that did not produce attention-getting sounds did not. These data contradict an exclusive "gestural origins" theory for they suggest that it is vocal signaling that selectively activates the Broca's area homologue in chimpanzees. In other words, the activity observed in the Broca's area homologue reflects the production of vocal signals by the chimpanzees, suggesting that this critical human language region was involved in vocal signaling in the common ancestor of both modern humans and chimpanzees.     

Correction to: Chimpanzee (Pan troglodytes schweinfurthii) Group Sleep and Pathogen-Vector Avoidance: Experimental Support for the Encounter-Dilution Effect

International Journal of Primatology - The original version of this article unfortunately contained a mistake in the authorgroup section.