Simple Summary
Over 1000 species of true fruit flies from the tribe Dacini occur naturally throughout Africa, Asia, Australia and the western Pacific, with many species overlapping in range and host use. Furthermore, many species within the genus Bactrocera Macquart can utilise host fruit from multiple plant families. Our understanding of the timing and drivers of diversification within these flies is limited. We used an existing, dated phylogenetic tree consisting of 122 species across three genera from the Australo-Papuan and South Pacific regions to run a suite of phylogenetic comparative methods. Our aims were to elucidate species radiation events and to understand the role of host breadth in facilitating species diversification. The Bayesian Analysis of Macroevolutionary Mixtures (BAMM) analysis identified a single significant shift in diversification rates within the Bactrocera clade. The shift occurred approximately 33 mya and was followed by a period of accelerated rates between 33 and 25 mya. The Hidden State Speciation and Extinction (HiSSE) model revealed that generalist taxa demonstrated higher rates of diversification than specialists, suggesting that host breadth had a significant influence on diversification. We suggest that the timing of the shift in diversification rates coincided with a geographic landscape that was conducive to rapid speciation occurring with plasticity associated with generalist host use facilitating adaptation to novel hosts.
Abstract
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.