Figure 2: Subordinate eviction and alloparental brood care.

(a) Subordinates’ probability of eviction decreased significantly with the difference in female size (dominant female body size—subordinate female body size), but did not depend on female kinship (blue filling: kin, red filling: non-kin). Inset shows number of subordinates accepted (Acc), tolerated (Tol) and evicted (Evi), depending on kinship. The line shows the predicted probability of eviction from the ordinal regression. For clarity, blue and red symbols were slightly off-set to avoid overlap. (b) Day of eviction since release (latency in days) of subordinate females did not depend on kinship (NK, non-kin groups; kin, kin groups). (c) Care provided to dominant female (DF) clutches and (d) subordinate female (SF) clutches per treatment (blue filled symbols: kin, red filled symbols: non-kin) and the group member (dominant females: circles; subordinate females: squares). Unrelated subordinate provided significantly more alloparental brood care to dominant female clutches than related ones. This did however not affect the maternal investment in brood care of dominant females. Subordinate clutches received very low levels of alloparental care from the dominant females, and maternal levels of brood care in subordinate females were higher in the non-kin groups. (e) Dominant and (f) subordinate female residual single-egg mass (corrected for intercept and female body size effects). Subordinate females laid heavier eggs in the kin groups, whereas egg mass in dominant female clutches did not differ between treatments. (g) Sand removal when dominant female clutches were present per kinship treatment (red filled symbols: non-kin, blue filled symbols: kin) and the group member (dominant females: circles; subordinate females: squares). Unrelated subordinate females exhibited higher levels of sand removals than related females. Dominant females did not differ between the treatments in their investment in digging. Depicted are means±s.e.m. See Tables 1, 2, 3, 4 for model details. The upper error bar of the values of non-kin subordinate females in panel d is cutoff in favour of a generally greater resolution of values on the ordinate. Sample sizes are indicated in the graph. Asterisk denotes significance.