INCREASED NEST COFOUNDING AND HIGH INTRA-COLONY RELATEDNESS IN THE BEE EXONEURA BICOLOR (HYMENOPTERA, APIDAE) - RESULTS FROM AN EXPERIMENTAL SITUATION

Identifying differences in a key social trait between two populations of the same species is important for understanding the evolution of so ciality. Previous studies of new colonies in Exoneura bicolor, an Aust ralian allodapine bee, have shown that there are high levels of kin co founding in a montane population. The only study to examine intra-colo ny relatedness in a heathland population has found that new multifemal e colonies are not formed by kin. In this study we used an experiment to investigate both cofounding behaviour and intra-colony relatedness in E. bicolor from a heathland population. Nest substrate was placed e ither 0.05 or 1 m distant from source nests in a novel environment. Al though there were no differences in cofounding rate or intra-colony re latedness between the two treatments there was, overall, a high rate o f cofounding: 53% of new nests were multifemale, approximately twice a s high as found in previous field-based studies. Relatedness among cof oundresses was not only different from zero, r +/- SE = 0.597 +/- 0.09 7, but almost identical to that found in montane populations. A constr aint, such as nest substrate distribution, is suggested as a proximate factor affecting the expression of cofounding behaviour in E. bicolor . The implication of such proximate constraints for inferring the phyl ogenetic origins of social behaviour is discussed.