Giving your daughters the edge: bequeathing reproductive dominance in a primitively social bee

The fitness associated with behavioural strategies is usually estimated in terms of offspring number and size. However, in group-living animals the reproductive value of offspring may also depend on their social rank. We show here that in an allodapine bee Exoneura robusta, dominant mothers can behaviourally influence their daughters' reproductive rank by controlling insemination of other potential mothers. In E. robusta, group living is near mandatory and reproductive dominance among female nestmates is determined by order of adult emergence. Nests are single, undivided burrows and the dominant female assumes a guarding position closest to the nest entrance. We show that before the egg-laying period, subordinate females who have been absent from the nest are 'screened' by the reproductive guard upon attempted re-entry. Those who have been in contact with foreign males are less likely to be granted access back into the nest than those who have been in contact with foreign females or with no bees at all. We argue that by controlling insemination patterns of their nestmates, dominant females ensure that their own daughters eclose first and are therefore more likely to assume dominance in the next generation. This presents a situation where dominance is bequeathed to daughters by behavioural means. The ability of mothers to influence social hierarchies in subsequent generations introduces a fitness component additional to the number and size of offspring produced.