Allonursing in reindeer, Rangifer tarandus: a test of the kin-selection hypothesis

• Published in: Journal of Mammalogy
• Main Authors: Sacha C. Engelhardt, Robert B. Weladji, Øystein Holand, Knut H. Røed, Mauri Nieminen
• Format: Text
• Language: English
• Published: American Society of Mammalogists 2016
• Subjects: Rangifer tarandus
• Online Access: https://doi.org/10.1093/jmammal/gyw027

Allonursing, the nursing of nonoffspring, is a form of cooperative breeding. To test the kin-selection allonursing hypothesis, we selected 2 experimental groups, based on genetic relatedness, to assess whether evidence of individual and daily patterns of kin-related allonursing would emerge. Each group consisted of 8 mother– offspring pairs, and observers monitored each group over 5 weeks, starting when the offspring were between 8 and 23 days old. One group of 8 mothers was selected to be closely related, and the other group of 8 mothers was selected to be distantly related, based on genetic relatedness. We recorded 1,652 solicitations, of which 869 were nursing bouts and 161 were allonursing bouts. All mothers nursed their own offspring, and 15 of the 16 mothers allonursed. In both groups, 7 of the 8 offspring were allonursed. The offspring of closely related mothers were allonursed more often than the offspring of distantly related mothers, and we found evidence for this pattern at the individual level and daily over 5 weeks. Our results supported the kin-selection hypothesis but not the compensation hypothesis. We suggest that allonursing may have provided adaptive and nutritional benefits related to kin selection, and offspring from the closely related group may have gained more nutritional benefits and more mass than offspring from the distantly related group. We presented evidence that allonursing contributions detected can depend upon the research design. Furthermore, we suggest that the indirect fitness benefits of alloparental care may have been overestimated, and that kin selection alone is not sufficient to explain alloparental care in cooperative breeding social systems.