Grandmothering in captive Galago senegalensis braccatus (Senegal galago)

Abstract

This is the first detailed analysis of allonursing in a galago, a relatively nongregarious African strepsirrhine. Existing data on allonursing in galagos are scarce due to the difficulties of observing wild infant behavior in nocturnal species that frequently raise young in nests, and to the rarity of colonies with multiple co-housed lactating females. We determined the kin relations between subjects, quantified the prevalence of allonursing, searched for opportunities for allonursing in which it did not occur, and qualitatively compared growth rates of infants that were and were not allonursed. Focal adult and infant observations of Galago senegalensis braccatus were made in the Arizona State University colony between 1976 and 1990. The colony contained two matrilines caged separately because unrelated adult females are extremely aggressive to each other. The groups ranged from two to seven individuals. The availability of simultaneously lactating females within one group varied over time. Allonursing occurred in both matrilines and in a total of four infants (two males, two females). For one male, this represented a single event with an older sister. More prevalent allonursing occurred in both matrilines with the remaining male and two females, each allonursed by maternal grandmothers in 21% (n=104), 25% (n=52), and 27% (n=92) of their observed nursing bouts, respectively. Qualitative comparisons do not suggest that allonursed and non-allonursed infants grow at different rates. Intriguingly, maternal grandmothers frequently allonursed grandchildren, but adult daughters rarely reciprocated by allonursing younger siblings. Overall, our findings suggest that grandmothering may be a form of kin selection in this species and that it may enable older females, some of which had lost a neonate, to increase their reproductive success.