Chimpanzees and sound-induced rhythmic movement
Male chimpanzee making a rhythmic display at the enclosure in the Primate Research Institute, Kyoto University, Japan.
Music influences rhythmic movement in humans, suggesting a link between the brain’s auditory and motor areas. Understanding chimpanzees’ predisposition to process music could shed light on the evolutionary origins of humans’ response to music. Yuko Hattori and Masaki Tomonaga (pp. 936–942) examined how music affects rhythmic movement, or repetitive movement of the entire body or body parts, in 7 chimpanzees who listened to 6 2-minute piano sounds with different tempos for 6 days. In response to an auditory stimulus, the chimpanzees often swayed and sometimes made rhythmic hand clapping and foot tapping. Compared with female chimpanzees, male chimpanzees were more likely to respond to sound with vocalization and sway rhythmically for longer durations. A separate experiment focused on the chimpanzee most responsive to the auditory stimuli. The chimpanzee was exposed to 4 2-minute sound sessions for 24 days. Both random and regular beats induced rhythmic swaying in the chimpanzee, and beat tempo affected the chimpanzee in a bipedal but not quadrupedal posture. The chimpanzee also stayed longer in a sound source area when there was an auditory stimulus compared to when the area had no sound, suggesting that the chimpanzee sought auditory stimulation. The findings suggest a foundation for dancing in a common ancestor of chimpanzees and humans, according to the authors. — M.S.
Genetic basis of thumb development in mice
Compared with control (Left, green arrows), a lack of Hoxd13 due to excess Gli3 transcription in digit 1 territory leads to digit 1 agenesis in Hoxa13 mutants (Right, red arrows).
The acquisition of an opposable thumb is a crucial innovation in human evolution. Although this and other morphological differences in tetrapod fingers and toes reflect key functional adaptions, the molecular mechanisms that drive digit morphology are not well understood. Maria Félix Bastida, Rocío Pérez-Gómez, et al. (pp. 1090–1096) investigated the role of homeobox (Hox) gene expression on thumb formation by studying the limbs of the Hoxa13 mouse mutant, a line that lacks both the Hoxa13 gene and the thumb, also known as the number 1 digit. The authors show that in Hoxa13 mutants, the expression of another Hox gene, Hoxd13, does not extend to the putative digit 1 region, thereby explaining why the digit fails to form. Furthermore, this agenesis correlates with an increase in Gli3 repressor (Gli3R) activity due to the loss of the negative transcriptional regulation normally exerted by Hoxa13 and Hoxd13. Initiation of Hoxd gene expression in the handplate depends on the sonic hedgehog (Shh) protein preventing Gli3R formation, and the study reveals the complex interactions between Hox genes and the Shh/Gli3 pathway. According to the authors, Gli3 and Hox13 paralogs mutually antagonize each other to produce anterior–posterior asymmetry in the handplate and trigger thumb formation. — T.J.
Tool sharing in wild chimpanzees
Juvenile chimpanzee fishing for termites. Image courtesy of Christopher Walker (North Carolina State University, Raleigh, NC).
The social underpinnings of tool development in early human evolution are unclear, but understanding related behaviors in chimpanzees may provide insight. Stephanie Musgrave et al. (pp. 969–976) compared how wild chimpanzees in the Goualougo Triangle, Republic of Congo, versus those in Gombe, Tanzania, transferred tools to each other during termite gathering. The tool transfers have been previously shown to function as a form of teaching among Goualougo chimpanzees. Chimpanzees in both populations used fishing-probe style tools, and Goualougo chimpanzees also used different types of tools sequentially, which the apes made from certain plant species. Goualougo chimpanzees also improved the design of fishing probes. Compared with Gombe, where tool requests were usually refused, at Goualougo, there was a higher probability of tool transfer following an individual’s request for a tool. Chimpanzee mothers at Goualougo were 3 times more likely than mothers at Gombe to transfer tools to offspring. Female and juvenile chimpanzees were more successful at acquiring tools than male and infant chimpanzees, respectively. The findings indicate a significant role for social learning in the context of complex tool use. The capacity for such helping behaviors may have a shared evolutionary origin among chimpanzees and humans, according to the authors. — M.S.
Flu vaccines and cancer immunotherapy in mice
Cancer immunotherapy, which uses the body’s immune system to destroy tumor cells, is particularly effective in tumors in an immune-infiltrated hot state. Only a minority of tumors are hot, however, limiting the number of people who can benefit from immunotherapies. Jenna Newman et al. (pp. 1119–1128) injected seasonal flu vaccine without synthetic adjuvants, which are compounds that enhance immune response, directly into tumors in mice. Monitoring indicators of tumor immune sensitivity, the authors found that cold tumors injected with the vaccine experienced systemic immune responses and sensitivity to treatments that block tumors’ antiimmune defenses. The results suggest that the tumors had become hot, and that the injection had the additional benefit of conferring protection against influenza. Similar injection of flu vaccine with a synthetic adjuvant resulted in a different response, in which mice were protected from influenza, but the tumors’ antiimmune defenses remained in place. Removal of the adjuvant or depletion of immune-suppressive tumor B cells restored the vaccine’s proimmune effect on tumors. According to the authors, antipathogen vaccines may find additional benefit as cancer immunotherapies and, by virtue of their safety profiles and Food and Drug Administration approval status, could find potential clinical application. — P.G.