Bees of the South West Pacific: Evolution of an island pollinator group

Author: Scott Vernon Charles Groom

Groom, Scott Vernon Charles, 2014 Bees of the South West Pacific: Evolution of an island pollinator group, Flinders University, School of Biological Sciences

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Abstract

This thesis investigates the assembly and evolution of the bee fauna in the south western Pacific (SWP) islands using molecular phylogenetics. Previous studies have shown that the majority of bee species in the SWP comprise just two families, Halictidae and Megachilidae, both of which have low species diversity despite an otherwise rich island biota. However, previous assessments were largely focussed on single archipelagos during the early 20th century and were based purely on morphology with no implementation of molecular methods since. With potential for many synonymies or undescribed species of a bee fauna critical to the function of threatened ecosystems, the work presented here looks to understand the composition and role of bees in the Pacific. In this thesis, examination of conspecific and congeneric genetic differences in mitochondrial DNA sequences was the primary method used to explore species diversity in all bee families in the SWP through a variety of phylogenetic methods, whilst Bayesian approaches were used to apply molecular clocks to model diversification and changes in effective population size over time for the endemic halictine bees in the subgenus Homalictus. Results indicated high levels of genetic variation in derived haplotype clades of Fijian halictine bees from low elevations, and indicate that these major diversification changes in these clades arose at a time that coincides with the last glacial maximum (LGM). Basal lineages appear restricted to higher elevations, suggesting that colonising species were adapted to wet forests. Reconstruction of effective population size changes reveals an increase corresponding to a warming climate post-LGM and radiation through lower elevations. The dataset of Fijian haplotypes was then expanded and demonstrated almost identical and simultaneous responses to the last glacial maximum in populations of neighbouring archipelagos of Vanuatu and Samoa. Large-scale population declines in cooler climates of the LGM were followed by considerable increases corresponding to a subsequent period of warming. The presence of at least four species of the family Apidae were also documented in the Pacific, with genetic distances revealing their likely introduction from Australia, Asia, and North America since human colonisation. As long tongued bees, there are large implications for the presence of these genera in the region. Furthermore, bees of the genus Amegilla are able to buzz pollinate, meaning a novel method of pollination has been introduced with their arrival. We explore the implication of these introductions in light of our other research findings. Megachilidae of the Pacific were found to comprise a mixture of species introductions and dispersals from southeast Asia since the last glacial maximum. As species of this family are largely wood boring, it is likely that the arrival of humans in the region and establishment of maritime trade routes has influenced the dispersal of the group. Considered as a whole these results indicate that the bees of the Pacific are not likely to have played a key role in the development of early island ecosystems, and that since the LGM there has been considerable change in the composition of island pollinator suites. This has large implications for the future management of the region's biodiversity and development of agriculture.

Keywords: Fiji,Samoa,Vanuatu,Homalictus,Apidae,Megachilidae,Climate Change
Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2014
School: School of Biological Sciences
Supervisor: Associate Professor Michael P Schwarz