relevant feature here therefore is extensive allomaternal care, rather than cooperative breeding defined according to some more narrow definitions, such as extreme reproductive skew due to suppressed reproduction in the helpers (Burkart, Hrdy, & van Schaik, 2009; Hrdy, 2009). Extensive allomaternal care also has consequences. The load reduction of life history mothers supplied by helpers allows females higher reproductive rates. In nonhuman primates, higher levels of allomaternal care is correlated with shorter gestation and lactation periods, and higher reproductive rates (Isler & van Schaik, 2012a; Mitani & Watts, 1997; Ross & MacLarnon, 2000). This pattern is particularly striking in the cooperatively breeding callitrichid monkeys, who exhibit the highest level of allomaternal care among nonhuman primates, and the highest reproductive rates. After a short gestation time (relative to body size) of less than five months, callitrichid monkeys usually give birth to twins (rather than singleton, which is the case in all other primates). Furthermore, females show no lactational amenorrhea but experience a estrus and can thus get pregnant again almost immediately after giving birth (Digby, Ferrari, & Saltzman, 2007). Mothers can afford these high reproductive rates only because other group members help by carrying the infants and sharing food. Nevertheless, the reproductive burden of mothers is high, because the surplus energy provided by allomothers is directly invested into a higher number of offspring. Despite this fast-paced reproduction, immatures show relatively long periods of dietary dependence, for instance compared to the more independently breeding squirrel monkeys or the owl and titi monkeys where non-parental individuals usually don’t contribute to infant rearing (Garber, 1997; Garber & Leigh, 1997). Cooperative breeding thus enables a peculiar mix of life-history traits. In particular, fast reproductive rates can coexist without a shortening of the developmental periods, because others
relevant feature here therefore is extensive allomaternal care, rather than cooperative breeding defined according to some more narrow definitions, such as extreme reproductive skew due to suppressed reproduction in the helpers (Burkart, Hrdy, & van Schaik, 2009; Hrdy, 2009). Extensive allomaternal care also has life history consequences. The load reduction of mothers supplied by helpers allows females higher reproductive rates. In nonhuman primates, higher levels of allomaternal care is correlated with shorter gestation and lactation periods, and higher reproductive rates (Isler & van Schaik, 2012a; Mitani & Watts, 1997; Ross & MacLarnon, 2000). This pattern is particularly striking in the cooperatively breeding callitrichid monkeys, who exhibit the highest level of allomaternal care among nonhuman primates, and the highest reproductive rates. After a short gestation time (relative to body size) of less than five months, callitrichid monkeys usually give birth to twins (rather than singleton, which is the case in all other primates). Furthermore, females show no lactational amenorrhea but experience a estrus and can thus get pregnant again almost immediately after giving birth (Digby, Ferrari, & Saltzman, 2007). Mothers can afford these high reproductive rates only because other group members help by carrying the infants and sharing food. Nevertheless, the reproductive burden of mothers is high, because the surplus energy provided by allomothers is directly invested into a higher number of offspring. Despite this fast-paced reproduction, immatures show relatively long periods of dietary dependence, for instance compared to the more independently breeding squirrel monkeys or the owl and titi monkeys where non-parental individuals usually don’t contribute to infant rearing (Garber, 1997; Garber & Leigh, 1997). Cooperative breeding thus enables a peculiar mix of life-history traits. In particular, fast reproductive rates can coexist without a shortening of the developmental periods, because others