Variation in population structure across the ecological range of the Queensland fruit fly, Bactrocera tryoni

Abstract

We sampled a pest fruit fly species, the Queensland fruit fly, Bactrocera tryoni, across its entire ecological range in eastern Australia, from ancestral high-density populations in tropical regions through to isolated outbreak populations in marginal arid areas. Using DNA microsatellite markers, we found that in ancestral areas, population differentiation was low and populations were genetically homogeneous over large distances. In more temperate areas, populations were far more genetically differentiated but there was no pattern of isolation-by-distance (no drift/migration equilibrium). Genetic drift appeared to be the major influence on population differentiation. The transition between these extremes was abrupt and unexpectedly far from the species border. Limited geographic structuring among the non-equilibrium populations was apparent from patterns of genetic differentiation, patterns of allelic richness and an ordination analysis. Our results also suggested that there might be recurring migration of flies into a neighbouring quarantine area.

The genetic structure of populations of an invading pest fruit fly, Bactrocera tryoni, at the species climatic range limit

“…The unanticipated feature of our results was the cline in microsatellite allele frequencies. Earlier studies of central populations of B. tryoni showed minimal genetic differentiation between populations spread over almost 3000 km of tropical Australia (Yu et al, 2001;Gilchrist et al, 2006). Consequently, the microsatellite cline identified here, which covers the southern 500 km of the species range, was unexpected.…”

“…Site 1 appears to be at the edge of an abrupt transition zone where the homogeneous central populations give way to fragmented town-based populations. A preliminary survey of the towns in the present study area showed higher levels of genetic differentiation between towns (0.01oF ST o0.12; Gilchrist et al, 2006). In contrast to the central populations, the inland populations appear to have a metapopulation structure approaching the current southern species border.…”

“…Genetic structuring studies to the north and east of this study region showed minimal detectable genetic differentiation among core populations of B. tryoni (Yu et al, 2001;Gilchrist et al, 2006). Genetic differentiation between Site 1 (Figure 1) and the central populations to the north and east was at the limit of detectability (F ST o0.005).…”

“…Overall, 95% confidence intervals for f were estimated from 10 000 bootstrap replicates. Allelic richness and significance values were calculated as detailed in Gilchrist et al (2006).…”

Roving and stationary release of adult sterile Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera; Tephritidae)

“…Originally, endemic to the tropical rainforests of north-eastern Australia (Gilchrist et al, 2006), its successful spread to cultivated fruit and vegetables (Lewontin and Birch, 1966) saw a subsequent rise to pest status. The polyphagous nature of this pest, climatic suitability and the expansion of its cultivated host range have, among other factors, enabled its spread throughout eastern Australia.…”