Accelerated Diversification in the Fruit Fly Genus Bactrocera Macquart (Diptera: Tephritidae) Facilitated by Generalist Host Breadth

The tribe Dacini is a highly diverse clade of tephritid fruit flies native to Africa, Asia, Australia, and the western Pacific. High levels of co-distribution and host-use overlap have been recorded for many species within the tribe, particularly within the genus Bactrocera Macquart. Furthermore, Bactrocera demonstrates high levels of host-use generalism, with approximately 40% of taxa utilising multiple plant families as hosts. Our understanding of the mechanisms that have facilitated the diversification of the tribe are limited. Using an existing, dated phylogeny containing 122 species across three genera—Bactrocera, Dacus Fabricius, and Zeugodacus Hendel from the Australo-Papuan and South Pacific regions—we sought to detect species radiations and assess the influence of host breadth on diversification within the clade. Our Bayesian Analyses of Macroevolutionary Mixtures (BAMM) analysis found Bactrocera diversification rates increased between 33 and 25 mya after a significant shift occurring approximately 33 mya. No such diversification rate increases were detected for Dacus and Zeugodacus. The Hidden State Speciation and Extinction (HiSSE) model found that host breadth likely had a significant influence on diversification with generalist taxa demonstrating higher net diversification rates than specialist species. We propose that generalist populations were able to adapt to novel environments as the genus expanded into the Australo-Papuan region throughout the Oligocene and early Miocene. Early island formation throughout the region also likely provided conditions conducive for allopatric speciation. Analytically, our results also highlight the need to explore the effects of assignment of missing trait data in diversification analyses, especially for diverse taxa and traits that require direct observations in the field.