Effects of allocare-givers on fitness of infants and parents in callitrichid primates

The effects of callitrichid primate helpers (allocare-givers other than an infant's father) on the survival, reproduction or behavior of infants and p arents are reviewed, using both published studies and data from free-rangin g golden lion tamarins (Leontopithecus rosalia). Three lines of evidence su ggest that helpers may increase their own inclusive fitness: (1)The number of adult males acting as helpers in free-ranging groups is correlated with the number of surviving infants in 3 callitrichid species. However, the lac k of a negative correlation with number of infants dying suggests that acti vities other than direct infant care (e.g. territory defense) may be more i mportant, especially in newly formed groups. (2) In 2 species, captive grou ps with helpers carry infants for longer periods of time than do groups wit hout helpers. Whether such differences would translate into meaningful surv ival differences in free-ranging groups is unclear. (3) Helpers reduce the energetic burden of parents by reducing the amount of time they spend trans porting or provisioning infants in at least 4 species. Reproductive males a re more likely than reproductive females to benefit from the presence of he lpers, reducing their investment in infant care activities as the number of helpers in the group increases. In free-ranging golden lion tamarins, the reproductive tenure of males, but not females, increases with the number of helpers in the group, suggesting that a reduction in energetic investment may translate into increased survival. 'Decisions' made by helpers to parti cipate in infant transport are weighed against competing needs for foraging , vigilance, territory defense and, in some cases, prospecting for breeding opportunities. Given this complexity, a sophisticated model may be require d to answer the question of how helpers 'decide' to participate in infant c are versus other activities. Copyright (C) 2000 S. Karger AG. Basel.