Diversification, cospeciation, and host plant evolution in Fergusonina galling flies feeding on Myrtaceae

Fergusonina flies (Diptera: Fergusoninidae) and Fergusobia nematodes (Tylenchida: Neotylenchidae) together form galls on plants in the Myrtaceae in a unique insect-nematode mutualism.  Each fly/nematode association is specific and induces formation of a specific type of gall, for example, shoot buds, axial or terminal leaf buds, leaf blades, or flower buds. The Fergusonina/Fergusobia pairs have been reared from seven genera within the Myrtaceae including Angophora, Corymbia, Eucalyptus, Leptospermum, Melaleuca, Metrosideros, and Syzygium (Taylor et al. 2005; Taylor et al. 2007) indicating a broad distribution across the Myrtaceae lineages. Phylogenetic analysis of the Fergusonina flies is compared to that for its plants hosts in the Myrtaceae in order to test hypotheses of coevolution, particularly with regard to cospeciation and host-tracking. Phylogenetic analysis coupled with divergence time analysis of both Myrtaceae hosts and the Fergusonina flies suggest that the crown radiation of Fergusonina occurred well after the crown radiation of Myrtaceae.  We predict that cospeciation and host tracking between flies and their host plants should only occur in relatively recently diverged host clades, and not at deeper, older levels.