2). Consistent selleck chemical with previous work on this species (Fewell & Page Jr, 1999), the distribution of task sharing in excavation of observed pairs was significantly lower than that predicted from the extent of intrinsic variation in excavation behavior displayed by queens when founding colonies alone (2011: predicted median = 0.55, observed median = 0.19, P < 0.01; 2012: predicted = 0.44, observed = 0.27, P < 0.05; Supporting Information Fig. S1), with the largest

excess in the most extreme level of excavation skew, where one queen performed little or no excavation while the behavior of the excavation specialist was either slightly but significantly lower (2011: t44 = 2.25, P < 0.05) or not significantly different (2012: t62 = 0.61, P = 0.54) from that of solitary queens (Fig. 2). Relative performance of excavation behavior was significantly predicted by patterns of queen–queen aggression during the first 15 min of pair formation

(t50 = 2.02, P < 0.05; Fig. 1c), but not by relative size differences (t50 = −0.24, P = 0.81; Fig. 1b). Both paired queens survived to brood collection in 6 of 28 colonies in 2011 and in 14 of 35 colonies in 2012. In contrast to excavation, Pembrolizumab order total productivity in colonies with two surviving queens was significantly higher than productivity in single nests (main effect of queen number, F1,60 = 23.51, P < 0.001), with the two nest types not differing significantly in average per capita productivity (Student's t-test, t57 = 1.38, P = 0.17; Fig. 3). As with excavation, however, the allocation of offspring in paired nests was significantly more skewed toward a single queen than that predicted by the

distribution of productivity values from single queens (predicted median = 0.60, observed median = 0.40, P < 0.01; Supporting Information Fig. S2). This was caused by both a significant increase in reproduction by HF queens (t38 = 2.05, P < 0.05) and by a reduction in reproduction by the LF queen (t46 = 5.39, P < 0.001) relative to single queens (Fig. 3). Reproductive role was not significantly associated with relative size (t13 = 0.52, P = 0.61; Fig. 4a), relative social dominance (t13 = 0.39, P = 0.71; Fig. 4b) or excavation role (t13 PDK4 = 0.49, P = 0.63; Fig. 4c). Social life involves a complex interplay between individual behavior and patterns expressed at the level of the group as a whole, with the potential for complex group-level patterns and collective behavior from relatively simple individual decision rules (Camazine et al., 2001). Critically, higher level patterns emerge whenever individuals form interactive groups, which may or may not be adaptive but in many cases mimic the properties of socially adapted taxa (Parrish et al., 2002). Our experimental results support the notion that self-organization can produce reproductive division of labor, as predicted by an emergent property model.