Female sexual behavior, but not sex skin swelling, reliably indicates the timing of the fertile phase in wild long-tailed macaques ( Macaca fascicularis)

• Published in: Hormones and behavior Vol. 47; no. 2; pp. 195 - 204
• Main Authors: Engelhardt, Antje, Hodges, J. Keith, Niemitz, Carsten, Heistermann, Michael
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.02.2005; Elsevier
• Subjects: Anal Canal; Animal ethology; Animals; Biological and medical sciences; Estrogens - metabolism; Estrous Cycle - physiology; Fecal steroids; Feces; Female; Female behavior; Fertile phase; Fertility - physiology; Fundamental and applied biological sciences. Psychology; Macaca; Macaca fascicularis; Macaca fascicularis - physiology; Male; Mammalia; Primates; Progesterone - metabolism; Psychology. Psychoanalysis. Psychiatry; Sex skin swellings; Sexual Behavior, Animal - physiology; Skin; Social Behavior; Vertebrata; Fecal steroids; Sex skin swellings; Fertile phase; Macaca fascicularis; Female behavior; Animal communication; Swelling; Sexual behavior; Breeding behavior; Vertebrata; Visual stimulus; Mammalia; Reproductive state; Fertility; Primates; Simioidea; Captivity; Female; Estrous cycle
• ISSN: 0018-506X; 1095-6867
• DOI: 10.1016/j.yhbeh.2004.09.007

The extent to which catharrine primate males are able to discern the fertile phase during the female ovarian cycle under natural conditions is still debated. In a recent study, we showed that wild male long-tailed macaques are able to detect the fertile phase, but the cues males used to assess female reproductive status remained unclear. In the present study, we tested female sex skin swelling and specific female behaviors for their reliability in signaling the fertile phase, as determined by measurement of fecal estrogens (E) and progestogens (P) during nine ovulatory cycles in seven free-ranging females. We found that changes in sex skin swellings showed a significant positive correlation to the E/P ratio, but swelling size did not significantly differ between cycle phases. In contrast, the frequency of two of the tested female behaviors, namely initiation of sexual interactions and reaching back for the male during copulation, was not only correlated with female reproductive hormones, but was significantly elevated during the fertile phase compared to nonfertile phases of the cycle. We thus conclude that female sex skin swelling does not reliably indicate the timing of the fertile phase in long-tailed macaques, whereas certain female behaviors do. Since cycles differed considerably in the number of males with which females had sexual interactions as well as in the number of sexual interactions with dominant males, the signaling character of these specific female behaviors appears to be robust against inconsistencies in these social variables. Female behavior might therefore play an important role in the recognition of the fertile phase by male macaques under natural conditions.