Date of Award

Fall 2018

Project Type


Program or Major

Biological Sciences

Degree Name

Master of Science

First Advisor

Sandra M Rehan

Second Advisor

Daniel Howard

Third Advisor

Donald S Chandler


Small carpenter bees (Xylocopinae: Ceratinini) in the genus Ceratina are a cosmopolitan group of stem nesting bees. All Ceratina show a degree of mutual tolerance for nestmates as they nest together in pre-dispersal assemblages and display extended maternal care. Many Ceratina also nest facultatively with multiple females per nest. Males usually disperse before the beginning of the reproductive season. Ceratina have emerged as model organisms to study the evolution of social behavior within the Hymenoptera (ants, bees and wasps). As hymenopteran sex is determined by the haplodiploid sex determination system wherein males are haploid and females are diploid, the result is a relatedness asymmetry between brothers and sisters, whereby sisters share a greater proportion of similar genes compared to brothers. Kin selection theory predicts that daughters are more likely to help rear sisters compared to brothers and is used to explain the prevalence of social behavior within the Hymenoptera.

Here the relatedness between populations and within nests of the Australian small carpenter bee Ceratina (neoceratina) australensis is examined with the use 8 polymorphic microsatellite loci. In chapter 1, the eight microsatellite loci are described and applied to three known populations of Ceratina australensis within Australia. Chapter 1 provides evidence for migration from north to south following the river systems of the Murray-Darling River Basin (MRDB). The MRDB has undergone substantial anthropogenic alterations to the natural vegetation communities since European settlement. Chapter 1 provides evidence for the hypothesis that C. australensis expansion into Australia has been aided by the introduction of pithy stemmed plants and establishes how patterns of dispersal can affect the social biology of this species. Chapter 2 deals directly with understanding the presence of male bees within nests of C. australensis that were found predominately, but not exclusively, within the most genetically homogenous population from chapter 1. The existence of inbreeding was not confirmed by visual inspection of genotypes or relatedness estimates between male adults and female offspring. Nests with males had lower brood survivorship compared to solitary nests but reproductive females in nests with males did not have significantly lower fitness compared to reproductive females in other nest types. The inclusive fitness of non-reproductive females was significantly lower than the fitness of reproductive females and the inclusive fitness of males was zero. I speculate that males were potentially delaying reproduction though it is odd that males were not forcefully removed by females. These findings underscore the importance of factors related to the timing of dispersal within the study of social insects.