Adaptive radiation of Gondwanan pergid sawflies (Hymenoptera, Pergidae)

The Pergidae are Gondwanan, with Australia and South America being the centres of diversity, and with no species in southern Africa. The majority of Australian pergid species is associated with host plants of the family Myrtaceae, which is typically Gondwanan in distribution.

Eucalyptus leaves are notoriously rich in essential oils, some of which are strong toxins for insects that have no specific defence against them (e.g. cineole). Nevertheless, some herbivores are eucalyptus specialists, and most of these have specialized enzymes to detoxify particular components within their usual diet. Only a few insect groups have managed to adapt to such circumstances and to diversify widely on eucalypts. Of these, the pergine sawflies are unique, even among all herbivorous insects with mandibles: the larvae have a large, soft, sponge-like extension (the scopa mandibularis) on what is usually the grinding surface of the insect mandible (pictures below).

Left: grinding surface of the mandible of larvae of the pergid subfamily Perginae. The pale area with the numerous protrusions is the soft sponge-like extension (the scopa mandibularis). Right: SEM of both mandibles. L, labrum; LM, left mandible; RM, right mandible; SM, scopa mandibularis (from Schmidt et al., 2000).

Our project has two major aims: i) to resolve the phylogenetic relationships of the largely neglected Gondwanan sawfly family Pergidae, of the southern hemisphere, ii) to use phylogenetic information to tackle several central questions in the diversification of phytophagous hymenoptera. The Pergidae are critical to such evaluation because of their unique geographical distribution (picture right) and phylogenetic position among sawflies. In reconstructing the phylogeny of the Pergidae we will contribute to knowledge of the effects of geological events, in particular the break-up of Gondwana, and the subsequent radiation of host plants of the family Myrtaceae on the diversity of pergid sawflies.

The primary focus of the project is to test how a key adaptive innovation, the mandibular oil press and the associated pharyngeal diverticulum, has influenced the radiation of Australian pergid sawflies by affecting their ability to deal with the defences of the modern (post Gondwana breakup) Australian Myrtaceae, particularly host plants in the genus Eucalyptus.

The project is supported by the Deutsche Forschungsgemeinschaft (DFG SCHM1281/3-1).

Project collaborator

G.H. Walter, School of Biological & Chemical Sciences, The University of Queensland, Brisbane, Australia.

References

Schmidt, S. & Walter, G.H. (2011) Adapting to cope with eucalypt oils: Mandibular extensions in pergid sawfly larvae and potential preadaptations in its sister family Argidae (Insecta, Hymenoptera, Symphyta). Journal of Morphology. doi: 10.1002/jmor.10985. Early view.

Schmidt, S., McKinnon, A.E., Moore, C.J. & Walter, G.H. (2010) Chemical detoxification vs mechanical removal of host plant toxins in Eucalyptus feeding sawfly larvae (Hymenoptera: Pergidae). Journal of Insect Physiology 56: 1770-1776. doi:10.1016/j.jinsphys.2010.07.006

Schmidt, S., Walter, G.H., Grigg, J. & Moore, C.J. (2006). Sexual Communication and Host Plant Associations of Australian Pergid Sawflies (Hymenoptera, Symphyta, Pergidae). Pages 173-193 in: Blank, S., Schmidt, S. & Taeger, A. (eds), Recent Sawfly Research: Synthesis and Prospects. Goecke & Evers, Keltern, 720 pp. (PDF, 1,1MB)

Schmidt, S., G.H. Walter & C.J. Moore (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. DOI: 10.1006/bijl.1999.0364