The evolution of social behavior and nest architecture in sweat bees of the subgenus Evylaeus (Hymenoptera : Halictidae): a phylogenetic approach

Abstract

Phylogenetic studies are required to establish the direction of evolutionary change in behavioral characters. Here I produce a phylogeny for 8 Old World species of the subgenus Evylaeus based upon cladistic analysis of 26 informative allozyme loci. By mapping behavioral character states upon the resulting cladogram, the following major conclusions could be drawn: (1) Social Evylaeus species share sociality by descent from a eusocial common ancestor which might not have been an Evylaeus species; the solitary behavior of Lasioglossum (E.) fulvicorne may be a derived condition. (2) One reversal to solitary behavior within Evylaeus is proven for a Japanese montane population of L. (E.) calceatum. (3) The perennial societies of L. (E.) marginatum are derived from an annual social cycle and do not represent an independent evolution of sociality. (4) Multiple-foundress associations are a derived condition within Evylaeus, suggesting that if social behavior evolved within the group, then the semisocial route was not the one taken by these bees. (5) The nest architectural trait of excavating a cavity around clustered brood cells is a ground plan characteristic of Evylaeus but with a reversal in L. (E.) marginatum. (6) It is likely that extended opening of brood cells during juvenile development has originated independently twice among the species considered. Another benefit of phylogenetic studies is their use in predicting which taxa are most likely to exhibit particularly interesting behavioral states. In this regard, the phylogeny suggests that close relatives of L. (E.) fulvicorne and also most of the major species groups of Evylaeus which have not received any field study should be investigated both phylogenetically and behaviorally for a full evaluation of behavioral evolution in Evylaeus.