ADAPTATIONS TO HOST PLANTS IN SELECTED AUSTRALIAN PERGID SAWFLIES

Anne-Marie Elizabeth Mckinnon (2010). ADAPTATIONS TO HOST PLANTS IN SELECTED AUSTRALIAN PERGID SAWFLIES MPhil Thesis, School of Biological Sciences, The University of Queensland.

       
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Author Anne-Marie Elizabeth Mckinnon
Thesis Title ADAPTATIONS TO HOST PLANTS IN SELECTED AUSTRALIAN PERGID SAWFLIES
School, Centre or Institute School of Biological Sciences
Institution The University of Queensland
Publication date 2010-10
Thesis type MPhil Thesis
Supervisor Assoc. Prof. Gimme Walter
Dr Stefan Schmidt
Dr Lyn Cook
Total pages 128
Total colour pages 7
Total black and white pages 121
Subjects 06 Biological Sciences
Abstract/Summary Abstract This thesis examines some key aspects of the host associations of Australian pergid sawflies and their adaptations to their hosts. The Australian pergid sawflies form a diverse and interesting group, although somewhat under studied. They have a typically Gondwanan distribution (Australia, Papua New Guinea and the Neotropics, with the exception of four species of Acordulcera in North America and Canada), and the host associations of pergids in Australia show strong links with the evolution of the Australian flora. Sawflies have specialised adaptations to their hosts. One of these is the presence of a scopa mandibularis (SM) and oesophageal diverticula in Perginae sawfly larvae (Schmidt et al., 2000). The apparent function of the SM is to filter out toxic oils from the leaves of their myrtaceous (Eucalyptus) hosts and to direct them into the diverticula for storage and defence. To investigate how the SM functions in relation to the diverticula, the amount of oil stored by feeding larvae that had the SM removed was compared with the amount stored by intact larvae. Removal of the SM led to a greater quantity of oil reaching the gut of the larvae, although this was then quickly digested through enzymatic activity (Chapter 2). The other Myrtaceae feeding sawflies in the subfamilies Pterygophorinae, Phylacteophaginae and Euryinae (Schmidt and Smith, 2006) do not have any such structures for host toxin removal and storage, and it is thought that they break toxins down using biochemical pathways, although this needs further investigation. The next chapter focuses on the phylogenetic relationships and host associations of Australian pergid sawflies. Lophyrotoma analis is the only species in the subfamily Pterygophorinae to be associated with a Polygonaceae host. The other species all feed on plants in the family Myrtaceae. To help establish whether this species has undergone a host switch from Myrtaceae,, its phylogenetic placement relative to the other species within the Pterygophorinae needs to be confirmed. For this purpose, DNA sequence data were obtained from representatives of five of the seven pergid subfamilies, with particular emphasis on the Pterygophorinae (Chapter 3). Results strongly support the placement of L. analis within the subfamily Pterygophorinae. A trait reconstruction of ancestral hosts shows a prevalence of Myrtaceae as the ancestral host for Australian Pergidae, including the Pterygophorinae. The evidence therefore suggests that L. analis underwent a host switch from Myrtaceae to a Polygonaceae host, but more research is needed to establish the timing of this divergence. Aspects of the host switch in L. analis are examined experimentally in Chapter 4. Choice and no choice experiments were performed to test whether L. analis could still associate with a myrtaceous host species. A range of Myrtaceae and Polygonaceae species were used in these experiments, with all of the former being host plants used by other sawfly species within the Pterygophorinae. The Myrtaceae used included species with leaf oils, such as Eucalyptus and Melaleuca, and also species that do not have such oils (e.g. Syzygium). Plants in the family Polygonaceae included representatives from the genera Rumex, Polygonum and Persicaria. Female oviposition and larval feeding responses to each plant were recorded (Chapter 4). Females oviposited, at least to some extent, on all Polygonaceae species tested, but most consistently on Rumex, and also on Persicaria when given no choice. By contrast, no oviposition was recorded on any of the Myrtaceae species that were tested. Larvae fed successfully on all Rumex species tested, but they showed no signs of feeding, produced no frass and perished in a short time when they were placed on any other plants, whether Polygonaceae or Myrtaceae. The results demonstrate that L. analis can no longer associate with Myrtaceae, and successful interactions with Polygonaceae are limited to Rumex species. Through techniques varying from laboratory work (molecular analysis) to field studies (host testing and host records), the co-radiation of Australian sawflies and their hosts have been investigated, with specific emphasis on the host switch of L. analis. The final chapter of this thesis discusses the host associations of Australian pergid sawflies, with particular emphasis on explanations of how L. analis may have switched to Polygonaceae. Further research into host associations and adaptations of Pergidae is also recommended. References Schmidt S & Smith DR. 2006. An annotated systematic world catalogue of the Pergidae (Hymenoptera). Contributions of the American Entomological Institute 34, 1-207. Schmidt S, Walter GH & Moore CJ. 2000. Host plant adaptations in myrtaceous-feeding Pergid sawflies: essential oils and the morphology and behaviour of Pergagrapta larvae (Hymenoptera, Symphyta, Pergidae). Biological Journal of the Linnean Society 70, 15-26.
Keyword host adaptations
co-radiation
host switch
host detoxification
myrtaceae
polygonaceae
symphyta
Additional Notes Colour Pages(7 pages): 4, 25, 28, 75-78 Landscape page (1 page): 99

 
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Created: Mon, 21 Feb 2011, 08:34:32 EST by Miss Anne-marie Mckinnon on behalf of Library - Information Access Service