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Mutual Genital Touch in the Mahale M-Group Chimpanzees

Hitonaru Nishie1,2
1 JSPS Research Fellow
2 Graduate School of Science, Kyoto University, Japan



INTRODUCTION

Mutual genital touch (MGT) is a type of greeting behavior, which was first documented in the chimpanzees of Bossou, Guinea (Nakamura & Nishida 2006). MGT occurs when two female chimpanzees meet after some time apart, they approach and closely pass by each other, pause with oneís face close to the otherís hip, and then they simultaneously and gently touch each otherís genital area from underneath with the outer hand (ibid.; Figure 1). Nakamura and Nishida (2006) suggested that MGT is a type of greeting behavior between females as its context is similar to some other greeting behaviors, such as peering into the face, kissing, or extending a hand. They also stated that MGT had never been observed at Mahale. In addition, this behavior has not been reported from other study sites.

However, during 2015, I observed two instances of MGT in the M-group chimpanzees at Mahale, Tanzania, as reported here in detail (See Nakamura et al. (2015) for the details of the Mahale M-group chimpanzees).




Figure 1. Mutual genital touch (reproduced with permission from Nakamura and Nishida (2006)).

OBSERVATIONS
Case 1 on December 9, 2015

At approximately 12:50 h, a large party of the M-group chimpanzees ranged northward along a trail. Some individuals wandered into nearby bush, whereas others exited from the bush and entered the trail. I followed the alpha male walking along the trail. After some time, the alpha male overtook some adult females walking in a line and disappeared from view, following which I slowly followed after the females. At 13:24 h, an adolescent female, GN, exited the bush, entered the trail, and approached an adult female, EF, walking at the end of the line, thereby coming directly in front of me. EF stamped on her right foot once, following which GN came close to EF from her right side, brought her face toward EFís hip, and touched EFís genital area with her left hand. EF also simultaneously touched GNís genital area with her left hand. Both EF and GN showed no genital swelling. Subsequently, EF and GN left together along the trail.


Case 2 on December 9, 2015

The party described in Case 1 ranged further north and encountered another party, including some adult females and their offspring, at 14:30 h. I continued following EF. When EF encountered the other party, a lactating female, ZL, showing no genital swelling, approached EF, and they simultaneously touched each otherís genital area with their left hands. The infant of ZL, two years old at that time, was out of my sight at the moment. They soon left together without any subsequent interactions.


DISCUSSION

Although MGT at Mahale has not been previously reported, I observed two instances of MGT in a single day. The adult female, EF, was involved in both instances; however, I did not witness any more MGT while following EF. Although I carefully observed many subsequent encounters between females, no other instances of MGT occurred. In some instances, only one female of a pair touched the otherís genital area, similar to instances of genital inspection customarily performed by adult males on females at Mahale (Nishida 1970, 1997; Nishida et al. 1999). The fact that these two instances of MGT occurred during an encounter between two females is consistent with the presumption by Nakamura and Nishida (2006) that MGT is a type of greeting behavior between females.

The reason why I managed to observe two instances of MGT in a single day remains unclear. I suggest some plausible but not mutually exclusive reasons as follows: 1) the Mahale M-group chimpanzees have recently adopted the MGT behavior, which is getting prevalent; 2) only a few individuals are accustomed to performing MGT in the M-group, and we rarely observe MGT because of its low frequency; 3) we researchers are not sufficiently attentive to notice any quick MGT as we have to assess all the individuals and monitor the surrounding situation when a social encounter occurs. The first proposed reason is plausible, and we have need to ascertain the manner in which MGT will be getting increasingly prevalent in the group. The second proposed reason is also plausible; however, further investigation on the presence/absence of MGT in the behavioral repertoire of the M-group members is required to derive any conclusions. From these two observed instances, I presumed that the chimpanzees performed MGT quite naturally as if it was a habitual behavior rather than an unusual one. This implies that at least some members have included MGT in their behavioral repertoires and that they perform it in a habitual manner. The third presumption is not likely as many expert researchers have conducted long-term, intensive observations on chimpanzee behaviors, and it is unlikely that the rarity of the observation of MGT can be attributed to the insufficient attention of the researchers. When I asked fellow researchers about MGT, some stated that they had observed MGT-like behaviors, one instance in 2011 and two instances in 2014 (Shunkichi Hanamura, Noriko Itoh, personal communication; Shimada 2014). In these previous instances observed by fellow researchers, at least one individual of a pair exhibiting MGT-like behavior was an adolescent female who had immigrated to the M-group a few years ago, as was the case with GN in Case 1 of the present study who had immigrated to the M-group in 2012. This implies that MGT is a relatively new behavioral pattern recently introduced to the M-group chimpanzees from another group. On the other hand, the fact that MGT was performed between two adult females, EF and ZL, who had immigrated to the M-group in 1997 and 1998, respectively, implies that MGT was already prevalent in the group. However, further investigation is required to derive any conclusions on MGT in the Mahale M-group chimpanzees.


ACKNOWLEDGMENTS

I thank COSTECH, TAWIRI, and TANAPA for permission to conduct the field research; MMNP and MGWRC for logistic support; Shunkichi Hanamura, Noriko Itoh, and Masaki Shimada for providing information on the observed instances of MGT-like behaviors; the researchers of the Mahale Mountains Chimpanzee Research Project for their cooperation at the field; Kazuhiko Hosaka and Michio Nakamura for helpful comments on the manuscript. This study was financially supported by Grant-in-Aid for JSPS Fellows (#14J00963).


REFERENCES

Nakamura M, Hosaka K, Itoh N, Zamma K (eds) 2015. Mahale Chimpanzees: 50 Years of Research. Cambridge University Press, New York.

Nakamura M, Nishida T 2006. Subtle behavioral variation in wild chimpanzees, with special reference to Imanishi’s concept of kaluchua. Primates 47: 35–42.

Nishida T 1970. Social behavior and relationship among wild chimpanzees of the Mahali Mountains. Primates 11: 47–87.

Nishida T 1997. Sexual behavior of adult male chimpanzees of the Mahale Mountains National Park, Tanzania. Primates 38: 379–398.

Nishida T, Kano T, Goodall J, McGrew WC, Nakamura M 1999. Ethogram and ethnography of Mahale chimpanzees. Anthropol Sci 107: 141–188.

Shimada M 2014. Homosexual interactions among young female wild chimpanzees: an example of social pretend play? Pan Afr News 21: 6–8.



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