Why do lactating females nurse alien offspring? A review of hypotheses and empirical evidence

摘要: Female mammals sometimes nurse offspring that are not their own. The causes and function of allonursing for females remain puzzling given lactation is energetically costly augments the risk pathogen transmission between mothers alien offspring. To date five hypotheses have been put forward to explain why (1) Allonursing results from misguided parental behaviour. (2) Females reciprocate by nursing each other's (3) related juveniles inclusive fitness benefits. (4) evacuate milk own did drink. (5) Inexperienced lactate spontaneously without reproducing themselves or lost litter improve maternal skills. A review empirical evidence showed observations were consistent with predictions misdirected care, kin selection evacuation but reciprocity parenting hypotheses. However, probably because study a trivial exercise, it unclear what extent hypothesis can account inter- intraspecific variation in female propensity Since mutually exclusive, some said support may also be an alternative one. tease apart exact role competitive I propose experimental designs. detailed discussion reveals reason more intricate than was previously believed.