Annual Reproductive Strategy of the Squirrel Monkey (Saimiri sciureus)

Abstract

The physiological and behavioral factors underlying the annual reproductive cycle of the squirrel monkey were evaluated under controlled laboratory conditions. Mating activity following the formation of two social groups served to synchronize the reproductive phases during the subsequent year of observation. Changes in male and female reproductive status were assessed during four designated phases: breeding, pregnancy, lactation and fatting. Behavioral and somatic changes in gonadectomized subjects, living in the social groups, were also evaluated. The variations in behavior and physiology across the year were considered in terms of factors constraining the timing of the natural reproductive pattern.

Seasonality in squirrel monkeys (Saimiri sciureus): Social facilitation by females

“…The transition into and out of the breeding season is more or less synchronized among group members [10]. Although ecological factors are undoubtedly important in timing seasonal transitions, there is considerable evidence in squirrel monkeys and other seasonally breeding animals that the coordination of reproductive changes between individuals is mediated by social stimulation [38,39].…”

“…Although ecological factors are undoubtedly important in timing seasonal transitions, there is considerable evidence in squirrel monkeys and other seasonally breeding animals that the coordination of reproductive changes between individuals is mediated by social stimulation [38,39]. In squirrel monkeys, formation of new social groups at most times of the year can increase gonadal activity to levels indicative of breeding readiness in both males and females [21,26,27] and group formation can alter the timing of subsequent breeding seasons [10,29].…”

“…Shortly after peak fatting, gonadal hormone levels increase in males, ovarian cyclicity commences in females, and mating begins [23,24]. Cortisol levels are also higher during the breeding season [7], although the precise timing of increased glucocorticoid activity relative to other seasonal events is not known, ~To whom requests for reprints should be addressed.The transition into and out of the breeding season is more or less synchronized among group members [10]. Although ecological factors are undoubtedly important in timing seasonal transitions, there is considerable evidence in squirrel monkeys and other seasonally breeding animals that the coordination of reproductive changes between individuals is mediated by social stimulation [38,39].…”

“…characteristically engage in mating behavior during a discrete annual period. The onset of the breeding season in squirrel monkeys is signaled by substantial increases in body weight (fatting), particularly in males [10,15]. This change coincides with an increase in androstenedione, possibly of adrenal origin [40].…”

Nursing does affect the duration of the post-partum to ovulation interval in cotton-top tamarins (Saguinus oedipus)

“…For seasonal breeders, such as rhesus macaques, the combination ofthe lactational and seasonal effects can delay ovulations for 1-2 years. New World monkeys, such as the spider monkey (Wolf er ai, 1975), the howler monkey (Carpenter, 1934;Glander, 1980) and the squirrel monkey (Travis & Holmes, 1974;Coe & Rosenblum, 1978) Dixson & Lunn, 1987;Kholkute, 1987) and for the cotton-top tamarin (13-29 days : Ziegler et ai, 1987a). When contrasting nursing and non-nursing females, interbirth intervals have not been statistically different for the common marmoset, the cotton-top tamarin or the saddle-back tamarin (Hampton & Hampton, 1965;Wolfe et ai, 1975;Phillips, 1976;Gengozian et ai, 1978;Lunn & McNeilly, 1982;French, 1983;Tardif et ai, 1984).…”