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Abstract

Social organization in Hymenoptera is quite variable, but most group-living species have a reproductive division of labor. Communal species, by definition, do not; all individuals work and all are reproductive. In order to understand the evolution and maintenance of such cooperative societies the essential first step is characterization of the behavioral interactions between individuals. In particular, it is important to investigate the influence of common group membership (familiarity) on these interactions.

Circle-tube arenas were used to observe the interactions between 42 pairs of field-collected Lasioglossum (Chilalictus) hemichalceum females either from the same nest, from different nests but the same nest aggregation, or from different aggregations. Identical procedures were applied to 24 pairs of females from laboratory colonies. There was a striking lack of agonistic behavior with Lunging occurring in only 0.03% of all bouts, and C-Postures (threat behavior) in only 19% of bouts using field bees and 27 % of bouts using females held in the laboratory. Passing was virtually ubiquitous, occurring in 98 % of all bouts. None of these behavior patterns is significantly associated with the level of familiarity between females. The lack of agonistic behavior and the indiscriminate cooperative behavior (Passing) suggest that all conspecifics are accepted and are treated similarly. This is in contrast to previous studies of L. (Dialictus) zephyrum that demonstrated both kin recognition and nepotism.

While Avoidance behavior was rare, significantly more was seen between bees taken from different nest aggregations. Trophallaxis Solicitation occurred in 13 bouts between field bees. While the proportion of bouts in which this occurred is not associated with familiarity, the number of solicitations per bout is greater between females from different nest aggregations. These minor but statistically significant differences suggest that L. hemichalceum females can discriminate between familiar and unfamiliar individuals.

Therefore the proximate mechanism underlying universal acceptance of all conspecifics cannot be a lack of recognition cue expression or recognition cue perception. Rather, it is due to a lack of clearly preferential treatment toward familiar individuals. This suggests that some component of fitness is positively associated with group membership per se, or group size.

The high levels of mutual tolerance suggest, as do other lines of evidence (Kukuk & Schwarz 1987), that communal societies are not intermediate between solitary and eusocial species.