Energetics, reproductive suppression and obligate communal breeding in carnivores

Summary

Social subordinates are reproductively suppressed in some communally breeding species, but not in others. Hypotheses for the evolution of reproductive suppression have focussed on ecological and demographic constraints limiting the benefits of attempting to breed as a subordinate. Factors determining the costs of breeding have received little attention. We use comparative data from communally breeding carnivores (Tables 1 to 5) to show that the energetic costs of reproduction may be a determinant of reproductive suppression. When costs are high, they are more likely to exceed the benefits of attempting reproduction as a subordinate, at which point subordinates should tolerate suppression. Specifically, we show that reproductive suppression is associated with costly gestation (P=0.027; Kruskal-Wallis test) and costly postnatal investment in litter growth (P=0.020; Kruskal-Wallis test).

We then use data from communally breeding dwarf mongooses (Helogale parvula) to show that reproductive energetics may also help to explain why communal breeding is obligate in some species. If energetic costs and degree of reproductive suppression evolve in parallel, they may reinforce each other in a steadily increasing spiral, until costs become so high that they cannot be met without helpers.