TABLE CONTENTS

Host Specificity, Speciation, and Coevolution in Fergusobia (Nematoda:
Neotylenchidae) - Fergusonina (Diptera: Fergusoninidae) Galling
Mutualists on Myrtaceae
Davies, K. (1), R. Giblin-Davis (2), Y.E. Weimin (3), G. Taylor (1), K. Thomas (4)
& S. Scheffer (5)
(1) Australian Centre for Evolutionary Biology & Biodiversity, The University of Adelaide, Adelaide, South
Australia 5005, Australia; (2) Fort Lauderdale Research & Education Center, University of Florida, 3205
College Ave, Davie, FL 33314-7799, USA; USDA Agricultural Research Service, Systematic Entomology Lab,
10300 Baltimore Ave, BARC-West, Beltsville, MD, 20705-0000, USA; (3) Nematode Assay Section,
Agronomic Division, North Carolina Department of Agriculture & Consumer Services, 4300 Reedy Creek
Road, Raleigh, NC 27607, USA; (4) Hubbard Centre for Genome Studies, University of New Hampshire,
Durham, NH 03824, USA; (5) USDA Agricultural Research Service, Systematic Entomology Lab, 10300
Baltimore Ave, BARC-West, Beltsville, MD, 20705-0000, USA
A unique tritrophic association between Fergusobia nematodes and Fergusonina flies forms
galls on various myrtaceous hosts. Fly/nematode associations occur on Eucalyptus in
Australasia, Angophora, Corymbia, Leptospermum, and Melaleuca in Australia, Syzygium in
Australia and India, and Metrosideros in New Zealand. Fergusobia has a complex life cycle,
involving a plant-parasitic generation followed by an insect-parasitic generation. Feeding
activity by the plant-parasitic stages of the nematode apparently leads to formation of a gall
in which the fly larvae feed. The adult female fly provides nutrition for the insect-parasitic
stage of the nematode and ensures its dispersal. Nematodes developing with male flies
apparently die when the fly larvae pupate. Because both organisms appear to benefit, the
association between Fergusonina and Fergusobia can be described as a mutualism.
Transmission of nematodes between flies is vertical (mother to offspring), suggesting
cospeciation between flies and nematodes.
Galls, flies and nematodes were collected from myrtaceous plants from Australia and New
Zealand. Molecular phylogenies for Fergusobia nematodes and Fergusonina flies were
generated using multiple genes and standard techniques. Inferred trees were compared with
each other, myrtaceous host phylogeny, gall form and fly morphology. The associations are
highly host-plant specific, and each species of nematode is associated with a single species of
fly. There is good phylogenetic congruence of the terminal, but not the deeper nodes of the
compared nematode/ fly phylogenies. These results are consistent with a general model of
cospeciation of nematodes and flies. Speciation by nematode/ fly associates appears to be
accompanied by periodic host plant shifts; there is strong evidence of evolutionary
conservation of plant host genus.
5 th International Congress of Nematology, 2008 9