In tamarins and marmosets, long-term stable sociosexual relationships are formed between heterosexual adults, but these "monogamous" relationships are often formed in groups that contain multiple adults of both sexes. The patterning of interactions during pair formation may therefore be shaped by this demographic profile. We evaluated the development of sociosexual relationships in six captive pairs of Wied's black tufted-ear marmosets (Callithrix kuhli) during the 80 days from the initial day of pairing. Social behavior, sexual behavior and activity profiles were recorded. Social behaviors, including allogrooming, grooming solicitation, and intragroup monitoring calls, increased across the four 20-day time blocks. Males were more responsible than females for maintaining intrapair proximity during the first 40 days of pairing. Females and males were equally responsible for intrapair proximity maintenance after this time. The highest rates of sexual behavior, including copulation and proceptive open mouth displays, occurred upon pairing and then decreased non-significantly over time. The results indicate that sexual relationships in callitrichid primates are not dependent on the prior existence of a social relationship between males and females. Higher rates of copulation, greater male responsibility for proximity maintenance, and male initiative in sexual interactions early in pairing are consistent with a male reproductive strategy in which male-male competition may be common. 0 1995 Wiley-Liss, Inc.
Urine, feces, and copulation frequency were collected from two captive muriqui females, Brachyteles arachnoides, at the Centro de Primatologia do Rio de Janeiro following the resumption of postpartum ovarian cycles. Fecal steroid profiles from seven wild muriqui females at the Estação Biologica de Caratinga, Minas Gerais, Brazil, were compared to the captive females to determine the approximate patterns of steroid excretion relative to the urinary LH peak. Hormonal profiles from one of the captive female muriquis revealed a discrete urinary LH peak. For this female, fecal progesterone increased on the same day as the urinary LH peak, while fecal estradiol increased 6 days later and urinary steroids increased 5 days later. For both captive females, the onset of fecal progesterone increase was preceded by the onset of copulations, which occurred during at least a 5-day period. The complete fecal hormonal profiles of the one captive female for which continuos data were available were similar to those found in wild muriqui monkeys, with the onset of an increase in sustained progesterone levels occurring several days prior to the onset of sustained estradiol increase. These patterns suggest that fecal progesterone may be excreted rapidly in this species. The onset of sustained increase in fecal progesterone levels, together with the consistent delay in the onset of the sustained increase in estradiol, may provide the best indicators of the periovulatory period for muriqui females.
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