Oak gallwasp invasion genetics and phylogeography
European oak gallwasps are at their most diverse in southern and eastern oak forests - particularly in Hungary and the Balkans, and in Southern Italy. The Iberian Peninsular and the oak forests of the Atlas in Morocco have many of the same species found elsewhere, but their faunas are also distinct from the rest of Europe. The gallwasp fauna of northern Europe has been enriched over the last 500 years or so by a series of gallwasp invasions and introductions, all triggered by human transport and planting of the Turkey oak, Quercus cerris, an important gallwasp hostplant. At least 7 oak gallwasp species have followed this hostplant into northern Europe (Stone and Sunnucks 1993, Stone et al 2001, Stone et al 2002), and one species - the marble gallwasp Andricus kollari - was deliberately imported to southern Britain in the 1840's as a source of tannin for the manufacture of dyes (the history of this introduction is described in detail in Walker et al 2002) and the current state of the invaders is described by Schonrogge et al (1998).
We have used population genetic techniques to reconstruct the origin and invasion routes of some of these invaders, and to infer which of a number of possible models of dispersal is most appropriate for them. Much of this work has been in collaboration with Dr. Paul Sunnucks, now based at La Trobe University in Australia. Our key focal species all reached Britain between 1950 and 1970 - Andricus corruptrix, A. kollari, A. lignicola and A. quercuscalicis). These same species have been the subject of community ecology studies on the development of parasitoid communities centred on novel hosts (Stone et al 1995, Schönrogge et al. 1994, 1996a,b). We are now extending the same methods to a more recent group of invaders - Andricus aries, A. grossulariae, A. lucidus and Aphelonyx cerricola.
We are also using DNA sequence data to reconstruct much more ancient invasions. Specifically, we want to know where European gallwasps came from, and whether the community of associated enemies and inquilines travelled with them. Many gallwasps we would regard as European have distributiosn that extend as far east as Iran and the Caucasus, and evidence so far suggests that oak gallwasps invaded Europe from the east several million years ago (Rokas et al 2003). Current work is focussed on the phylogeography of multiple trophic levels within oak gall communities, and, in particular, of the parasitoids (with student Alex Hayward). Our long term aim is to establish the extent to which members of these communities show concordant phylogeographic histories (with student Richard Challis), and so the extent to which the whole community can be said to have a phylogeographic history.
