霊長類研究
Online ISSN : 1880-2117
Print ISSN : 0912-4047
ISSN-L : 0912-4047
短報
タイ王国に生息する野生ベニガオザルで観察された射精を伴うオス間交渉の事例報告
豊田 有石垣 竜嶌村 泰人河合 よーたり長屋 良典丸橋 珠樹MALAIVIJITNOND Suchinda
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ジャーナル フリー

2019 年 35 巻 2 号 p. 81-85

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The stump-tailed macaque, Macaca arctoides, is the most distinctive in its genus with respect to reproductive anatomy and sexual behavior. Male-male mounting behaviors have been mentioned in many reports; however, ejaculation has not yet been recorded.
Herein, we report a very rare case of ejaculation in the context of male-male mounting in wild stump-tailed macaques in Khao Krapuk Khao Taomor Non-hunting Area, Thailand. The behavior was observed during documentary filming of the animals. Daily observations were conducted for 28 days from July 4th to 31st, 2018, from 8 am to 6 pm. This rare behavior was documented on July 12th, while following and filming the Wngklm group. A young male of this group, WKM-M33, and a young male of another group (Fourth group), FTH-M33, started mounting. Initially, this mounting seemed to be social interaction in the context of a group encounter. However, after a thrust of a few seconds, the mounter, WKM-M33, exhibited ejaculated-like behavior. The mountee, FTH-M33, exhibited teeth-chattering behavior and touched the mounter's genital area. After completion of the mounting, whitish semen dropped to the ground and was eaten by WKM-M33. Then, WKM-M33 squeezed out sperm from the erect penis and ate it. We were therefore convinced that the mounter, WKM-M33, had ejaculated at the time of mounting.
Although it is dificult to draw a definitive conclusion because it is a single case report, we propose two possible interpretations: 1) accidental case owing to extreme tension from group encounters during social interaction or 2) homosexual behavior between males with little access to females.

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© 2019 日本霊長類学会
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