Abstract:
1. Cooperative behaviours by definition are those that provide some benefit to another
individual. Allonursing, the nursing of non-descendent young, is often considered a
cooperative behavior and is assumed to provide benefits to recipient offspring in
terms of growth and survival, and to their mothers, by enabling them to share the
lactation load. However, these proposed benefits are not well understood, in part
because maternal and litter traits and other ecological and social variables are not
independent of one another, making patterns hard to discern using standard univariate
analyses.2. Here, we investigate the potential benefits of allonursing in the cooperatively
breeding Kalahari meerkat, where socially subordinate females allonurse the young of
a dominant pair without having young of their own.
3. We use structural equation modelling to allow us to account for the interdependence
of maternal traits, litter traits and environmental factors.4. We find no evidence that allonursing provides benefits to pups or mothers. Pups that
received allonursing were not heavier at emergence and did not have a higher survival
rate than pups that did not receive allonursing. Mothers whose litters were allonursed
were not in better physical condition, did not reconceive faster, and did not reduce
their own nursing investment compared to mothers who nursed their litters alone.
These patterns were not significantly influenced by whether mothers were in
relatively good, or poor, condition.
5. We suggest that allonursing may persist in this species because the costs to allonurses
may be low. Alternatively allonursing may confer other, more cryptic, benefits to
pups or allonurses, such as immunological or social benefits.
