Are the shoot bud galls of Fergusonina Malloch, 1924 (Diptera: Fergusoninidae) founded by multiple mothers?

Abstract

In a mutual association, FergusoninaMalloch, 1924 flies and FergusobiaCurrie, 1937 nematodes form galls in the bud tissue of trees of the family Myrtaceae. Their unique association is the only known mutualism between insects and nematodes. Because each Fergusonina species supports one particular Fergusobia species, and is generally specific to their host tree species, this tritrophic system provides an excellent model for studies of co-evolution. The galls formed in this system vary from small, inconspicuous growths containing a single fly larva to large terminal bud galls containing hundreds of fly larvae, each in a separate locule. The incidence of multiple female fly foundresses of multilocular galls would have important evolutionary implications, especially for vertically transmitted generations of nematodes, but this has never been tested. In this study, a 663 base pair region of mitochondrial COI was sequenced from 233 flies from 27 galls collected from four Eucalyptus host plant species. Multiple haplotypes were found in all species and 37% of galls, indicating multiple foundresses. However, given the low sensitivity of the marker, the true incidence of multiple founding is likely to be much higher.