Evidence of Social Nesting in the Ceratina of Borneo (Hymenoptera: Apidae)

Abstract

The bee tribe Ceratinini is important for understanding early stages in social evolution. Their extant sister tribe Allodapini contains no strictly solitary species, and while some Ceratinini are commonly regarded as solitary, little behavioural data exist to substantiate this. Studies on Asian congeners have shown recurrent sociality in temperate and subtropical ranges while behavioural data are lacking in tropical regions. Field work along the west coast of Borneo in Sarawak, Malaysia, has provided some insight into these tropical taxa. Here we describe the nesting biology and social behaviour of four taxonomically described yet behaviourally unclassified Ceratina species. These four species are from three subgenera, namely Ceratina (Ceratinidia) accusator Cockerell, C. (Ceratinidia) nigrolateralis Cockerell, C. (Neoceratina) dentipes Friese, C. (Pithitis) smaragdula Fabricius. Nests of all species were typically attended by an adult female while all species except C. accusator had a low frequency of multi-female nesting assemblages. The four tropical ceratinines described here and all other behaviourally classified species exhibit recurrent patterns of maternal care, maternal longevity, and nest protection. Prolonged parental care found across the genus and occasional transitions into sociality make Ceratina of future interest for the study of life history and social evolution. The evolution of eusociality is considered one of the major transitions in evolution (Maynard Smith and Szathamary, 1995). In solitary species, offspring disperse and reproduce independently whereas workers in eusocial societies remain at the natal nest and largely forego reproduction to aid the queen in rearing siblings. Socially polymorphic lineages, those containing both solitary and social species, retain the plasticity to allow intra-specific comparisons of solitary with social life. The key to understanding the transition to sociality requires a group of closely related taxa possessing broad social, taxonomic and geographic diversity. Bees provide numerous contrasts to offer insights into the origin of sociality with their range of solitary to social forms. The small carpenter bees Hymenoptera: Apidae (Xylocopinae: Ceratinini) are commonly regarded as solitary (Michener, 1974). All behaviourally classified species share a relatively simple life history. Females disperse from their natal nests and find appropriate nesting substrate. These twig-nesting bees excavate linear burrows in the cores of dead exposed pithy stems. Subsequent to burrow construction, females forage for pollen and nectar provisions that they form into a pollen mass on which they lay an egg. After provisioning and oviposition, brood cells are cappe dw ith a partition of wood pith, and the process is repeated in a serial manner along the linear nest chamber.