Abstract
Bactrocera dorsalis (Diptera: Tephritidae) is mainly distributed in tropical and subtropical Asia and in the Pacific region. Despite its economic importance, very few studies have addressed the question of the wide genetic structure and potential source area of this species. This pilot study attempts to infer the native region of this pest and its colonization pathways in Asia. Combining mitochondrial and microsatellite markers, we evaluated the level of genetic diversity, genetic structure, and the gene flow among fly populations collected across Southeast Asia and China. A complex and significant genetic structure corresponding to the geographic pattern was found with both types of molecular markers. However, the genetic structure found was rather weak in both cases, and no pattern of isolation by distance was identified. Multiple long-distance dispersal events and miscellaneous host selection by this species may explain the results. These complex patterns may have been influenced by human-mediated transportation of the pest from one area to another and the complex topography of the study region. For both mitochondrial and microsatellite data, no signs of bottleneck or founder events could be identified. Nonetheless, maximal genetic diversity was observed in Myanmar, Vietnam and Guangdong (China) and asymmetric migration patterns were found. These results provide indirect evidence that the tropical regions of Southeast Asia and southern coast of China may be considered as the native range of the species and the population expansion is northward. Yunnan (China) is a contact zone that has been colonized from different sources. Regions along the southern coast of Vietnam and China probably served to colonize mainly the southern region of China. Southern coastal regions of China may also have colonized central parts of China and of central Yunnan.
Highlights
Determining the source area and understanding the colonization routes of invasive pests are key issues when developing management strategies [1,2]
We merged these sequences with previously published sequences from five populations in Yunnan province (YN, YJ, YW, YM and YL) and three Southeast Asian populations (MO, VY and LM) [17,18] to obtain a final alignment for 580 B. dorsalis flies from 29 localities
Among all the B. dorsalis populations analyzed from China, all the genetic diversity indices were high in GZ while the four indices were lowest in YW
Summary
Determining the source area and understanding the colonization routes of invasive pests are key issues when developing management strategies [1,2]. Because of its wide host range and K-selected demographic strategy [5,6], it has been suggested that B. dorsalis would be adapted for growth and establishment in near optimal environmental conditions, taking advantage of the most productive niches [7] Concerning genetic studies, most papers focused so far on molecular taxonomy and species delimitations within the species complex [12,13,14] or on intraspecific genetic structure at regional scales [15,16,17,18,19,20] These preliminary data suggested that the fly had high levels of genetic diversity even at a local scale, and showed very little genetic structure. Shi et al [17,18] even hypothesized that Yunnan could be within the source area of this fly, or that the fly colonized Yunnan a long time ago
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