Male Homosexual Behaviour Accompanied by Ejaculation in a Free-Ranging Troop of Japanese Macaques (Macaca fuscata)Yuji Takenoshita Folia Primatol 1998; 69: 364-367 Key Words Introduction IntroductionHomosexual behaviour among males in free-ranging Japanese macaques (Macacafuscata) has not been reported, whereas that among females has frequently been reported under both free-ranging and captive conditions [1],[ 2]. Mountings between males, commonly seen in Japanese macaques, have not been regarded as 'sexual behaviour'. In most cases, such interactions consist of a single mount and are not accompanied by ejaculation [3]. In this paper, I analyse observed cases of male-male mountings with ejaculation among a free-ranging troop of Japanese macaques and examine whether this behaviour can be classified as 'sexual behaviour'. The causal factors and effects of such behaviour are discussed. Study Troop and MethodThe study was conducted in the Arashiyama Monkey Park, Kyoto prefecture, Japan, and involved members of the Arashiyama E and F troops. All the monkeys have been individually identified since 1954, and birth dates and matrilineal kin relations are known except for those individuals which came from outside Arashiyama [4]. Soybeans and wheat grains were given to the monkeys by the park staff 4 times a day. Observation periods encompassed two mating seasons, from September 1993 to February 1994 (period 1) and September 1994 to February 1995 (period 2). Total observation days were 162. The number of individuals in each period was 172 and 181 for the E troop, and 134 and 129 for the F troop, respectively. The adult sex ratio (number of males over 7 years old/number of females over 5 years old) was 0.36 in period I and 0.32 in period 2 for the E troop. and 0.35 and 0.33 for the F troop, respectively. Table 1. List of males who engaged in mounting events with ejaculation
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(1) it is a training for mature heterosexual behaviour [9], and | |
First, were the homosexual behaviours training for heterosexual intercourse? The interactions observed in this study included several behavioural elements which are rarely seen in heterosexual intercourse, i.e. mutual mounting, thrusting without intromission and emission of female-like calls by males. If these behavioural elements were seen in heterosexual intercourse, the interaction would become less harmonious and would disturb fertilization. Thus, it is not valid to regard these behaviours as training for heterosexual intercourse. | |
Second, did the homosexual behaviours reduce social tension between the
males? In this study, mounting events did not occur after a fight or at
feeding time. Thus, this hypothesis is not applicable to these cases. |
Although the sex ratio of adults of the Arashiyama troops during the study period was not biased towards males compared to other troops [12], it is difficult for peripheral males to gain access to ovulating females, since the central adult males would attack the peripheral males if they tried to do so. Females did not tend to prefer prepubescent males. In group-living rhesus macaques, the males engaged in homosexual behaviour when their access to females was physically limited [13]. Thus in these cases, it is possible that the males engaged in homosexual behaviour as an alternative to heterosexual intercourse, because their access to ovulating females was socially limited.
I wish to thank Prof. T. Nishida for his guidance and encouragement. Drs. J. Yamagiwa, Y. Takahata. H. Ihobe and D.S. Sprague for stimulating discussion and valuable advice, Dr. S. Suzuki. Ms. L.A. Turner and other members of the Laboratory of Human Evolution Studies of Kyoto University for discussion and helpful criticism and Mr. N. Asaba and other staff of the Iwatayama Monkey Park for their support during the field study.
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