The systematics, evolution, and extinction risks of tropical bees

Author: James Dorey

Dorey, James, 2022 The systematics, evolution, and extinction risks of tropical bees, Flinders University, College of Science and Engineering

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Bees are a diverse group of insects that are ecologically and agriculturally crucial. Despite this, the taxonomy and biology of most bee species are poorly understood. Such knowledge is foundational for higher level questions and its paucity limits research and conservation of bee species. In this thesis, my first three chapters focus on a relatively simple ecological system — the endemic Fijian bee species in the genus Homalictus (Hymenoptera: Halictidae). My fourth chapter examines another tropical bee species, Pharohylaeus lactiferus (Cockerell, 1910) (Hymenoptera: Colletidae).

The endemic Fijian bee fauna was previously considered to be depauperate, with only four described species of Homalictus. However, recent sampling has uncovered surprising cryptic species diversity. In my first chapter, I used mitochondrial DNA (mtDNA) gene sequences and morphology to described nine new species. This chapter also highlights that the majority of the Fijian Homalictus diversity is found in highland regions (>800 m above sea level) and that there are more species requiring description. The total diversity is at least 22 species, all of which have arisen relatively recently from a single Fijian colonisation event. How this diversity has arisen in Fiji so quickly and predominantly in the highlands is of great interest. In my second chapter, I used phylogenetic analyses of mtDNA and single nucleotide polymorphism (SNP) data to contrast two ecological models of speciation: (i) the taxon cycle model and (ii) phylogenetic niche conservatism. Across most speciation events elevational state was conserved, providing support for phylogenetic niche conservatism over the taxon cycle model. This diversity likely arose through repeated contractions to, and expansions from, the highlands over past climate cycles, encouraging repeated isolation (vicariance) and admixture. With a strong phylogenetic signal across the phylogeny, it is likely that past climate cycles impacted the demography of even lowland Fijian Homalictus species. In my third chapter, I use COI, SNPs, and improved analytical methods to examine the past demography of H. fijiensis on two Fijian islands, Viti Levu and Kadavu. I found that the H. fijiensis population on Viti Levu has undergone a recent population increase that broadly coincided with the arrival and modification of the environment by humans (~3,000 years ago), but not with changing climates. In contrast to this, the Kadavu population has remained stable for the past 11,500 years and acts as a control for human impacts due to its limited history of anthropogenic disturbance. I show that the Fijian Homalictus are (i) species rich, (ii) most diversity in the highlands, (iii) have been impacted by past climate cycles, (iv) likely vulnerable to future climate change, and (v) have been impacted by human modification of the environment.

My final chapter describes the rediscovery, after 100 years, of the Australian tropical bee, Pharohylaeus lactiferus. It reviews the current knowledge of the genus. Then provides novel information about potential host and habitat specialisation and associated anthropogenic threats to P. lactiferus.

This thesis highlights the importance of taxonomy and the utility of tropical bees in studying the impacts of climate and humans on insect evolution, ecology, and conservation.

Keywords: Evolution, climate change, allopatric, tropical ectotherms, thermal specialist, adaptive radiation, Coalescent analyses, population size, Quaternary climate, South West Pacific, mismatch analyses, habitat alteration, Hylaeinae, Queensland, conservation, wildfire, extinction risk, invertebrate conservation, fragmentation, rainforest, Halictida, Homalictus, Lasioglossum, Halictini, Halictinae, GIS, QGIS, R, R-studio, BEAST2, PartitionFinder2, niche conservatism, taxon cycle, island biogeography, taxonomy, systematics, phylogenetics, BayesTraits, Holocene, DIYABC-RF, new species, island bees, biodiversity, speciation, human colonisation, Lapita, Lapita people, Fiji, Australia, climate change, Pharohylaeus lactiferus, Hylaeinae

Subject: Biodiversity and Conservation thesis

Thesis type: Doctor of Philosophy
Completed: 2022
School: College of Science and Engineering
Supervisor: Michael P. schwarz