Population structure in Zeugodacus cucurbitae (Diptera: Tephritidae) across Thailand and the Thai/Malay\ud peninsula: Natural barriers to a great disperser

The Thai-Malay peninsula represents a well-known transition zone between distinct floral and faunal assemblages of the Sundaland and mainland Asian regions and regional biogeographical patterns are known to be complex. The region represents the mid-point of the native range of the tephritid fruit fly Zeugodacus cucurbitae (Coquillett), which has existed in the region for a substantial proportion of its evolutionary history. Here, we integrate data from multiple markers (morphological: wing shape, male aedeagus length; molecular: cox1, microsatellites) to investigate the relative impacts of historical biogeographical features on Z. cucurbitae across Thailand and the Thai-Malay peninsula. Overall, morphological datasets revealed subtle population structure across the Thai-Malay peninsula that approximates a latitudinal cline rather than abrupt disjunctions associated with biogeographical barriers. Molecular markers provided finer resolution of biogeographical patterns: microsatellites suggested significant structure associated with the Khorat Plateau, both molecular markers indicated populations are structured across the Kangar-Pattani Line, but there was no effect of the Isthmus of Kra. Together, this study suggests that mountainous biogeographical barriers (Khorat Plateau), island isolation, and transitions in climate and vegetation (Kangar-Pattani Line) have significantly influenced population structure in this species. These data contribute vital evidence toward understanding non-traditional biological transition zones along the Thai-Malay peninsula