Print PageGenetic diversity in introduced species is typically thought to be low as a result of bottlenecks and drift. Actual levels depend on the number of founder individuals, introduction frequency, source population structure, outcrossing, and selection, among other factors. Molecular analyses have shown that co-introduction of closely related species or ecotypes may not be so uncommon. Cryptic diversity can broaden the range of ecological conditions suitable for invaders, while diversity within and among populations may promote local adaptation to regionally variable hosts or climate. Effects on invasion success or the effectiveness of biological control are unknown. Gonipterus scutellatus, a leaf-feeding Eucalyptus weevil, has spread from Australia to all continents where its host is planted as an exotic. The insect has been present in South Africa since 1916, where control by a parasitic wasp, Anaphes nitens, was once considered highly effective. Recently, control by Anaphes appears to have weakened and varies geographically. We hypothesized that accumulated diversity in Gonipterus from subsequent introductions contributes to patterns of variable control by Anaphes in South Africa. We assessed COI (mtDNA) haplotype diversity in both Gonipterus (n=109) and Anaphes (n=94) in 19 sites throughout South Africa. We developed 11 microsatellite markers for Gonipterus to examine gene flow/introgression among putatively distinct ecotypes or species.
Results/Conclusions
Gonipterus scutellatus in South Africa is highly diverse, comprising 22 (COI) haplotypes out of the 109 sequenced individuals. Phylogenetic trees based COI clearly show the existence of two distinct groups, with > 8.2% sequence divergence between them. We suspect that these groups are likely to represent distinct species and are in the process of confirming this using microsatellite markers and inter-group mating experiments. The dominant Gonipterus clade was shown to be common and widely distributed throughout the country, especially at higher elevations. The second group was comparatively uniform genetically (7 haplotypes) and of restricted range along coastal areas near the port of Durban, a pattern that is consistent with a second, more recent introduction. In contrast, A. nitens is genetically uniform throughout the range of its host; our sampling revealed only two closely-related COI haplotypes countrywide. We are currently assessing niche breadth in the Gonipterus complex compared to that of Anaphes and comparing rates of parasitism in the two Gonipterus clades using controlled growth trials and reciprocal field transplants.
