Abstract
BackgroundBactrocera dorsalis s.s. is a pestiferous tephritid fruit fly distributed from Pakistan to the Pacific, with the Thai/Malay peninsula its southern limit. Sister pest taxa, B. papayae and B. philippinensis, occur in the southeast Asian archipelago and the Philippines, respectively. The relationship among these species is unclear due to their high molecular and morphological similarity. This study analysed population structure of these three species within a southeast Asian biogeographical context to assess potential dispersal patterns and the validity of their current taxonomic status.ResultsGeometric morphometric results generated from 15 landmarks for wings of 169 flies revealed significant differences in wing shape between almost all sites following canonical variate analysis. For the combined data set there was a greater isolation-by-distance (IBD) effect under a ‘non-Euclidean’ scenario which used geographical distances within a biogeographical ‘Sundaland context’ (r2 = 0.772, P < 0.0001) as compared to a ‘Euclidean’ scenario for which direct geographic distances between sample sites was used (r2 = 0.217, P < 0.01). COI sequence data were obtained for 156 individuals and yielded 83 unique haplotypes with no correlation to current taxonomic designations via a minimum spanning network. beast analysis provided a root age and location of 540kya in northern Thailand, with migration of B. dorsalis s.l. into Malaysia 470kya and Sumatra 270kya. Two migration events into the Philippines are inferred. Sequence data revealed a weak but significant IBD effect under the ‘non-Euclidean’ scenario (r2 = 0.110, P < 0.05), with no historical migration evident between Taiwan and the Philippines. Results are consistent with those expected at the intra-specific level.ConclusionsBactrocera dorsalis s.s., B. papayae and B. philippinensis likely represent one species structured around the South China Sea, having migrated from northern Thailand into the southeast Asian archipelago and across into the Philippines. No migration is apparent between the Philippines and Taiwan. This information has implications for quarantine, trade and pest management.
Highlights
Bactrocera dorsalis s.s. is a pestiferous tephritid fruit fly distributed from Pakistan to the Pacific, with the Thai/Malay peninsula its southern limit
They were separated based on subtle morphological characters: B. papayae was distinguishable from B. dorsalis s.s. in having a longer aculeus and was deemed separate from B. philippinensis based on morphological variation in the scales on the distal end of the middle segment of the aculeus; and while B. philippinensis was recognised as ‘difficult to separate’ from B. dorsalis s.s. it was considered a new species based on differences in the mean ratio of wing vein lengths (CuA1 along dm cell) to the length of the aculeus (1.19 in B. philippinensis and 1.47 in B. dorsalis s.s.) [4]
We have identified the need to study the genetic and morphological variation of B. dorsalis s.l. in an area which had not previously been investigated, i.e., extending southwards of mainland China and including the region surrounding the South China Sea
Summary
Bactrocera dorsalis s.s. is a pestiferous tephritid fruit fly distributed from Pakistan to the Pacific, with the Thai/Malay peninsula its southern limit. Bactrocera papayae and B. philippinensis were erected as new species separate from B. dorsalis s.s. in 1994 following a revision of the complex [4] They were separated based on subtle morphological characters: B. papayae was distinguishable from B. dorsalis s.s. in having a longer aculeus and was deemed separate from B. philippinensis based on morphological variation in the scales on the distal end of the middle segment of the aculeus; and while B. philippinensis was recognised as ‘difficult to separate’ from B. dorsalis s.s. it was considered a new species based on differences in the mean ratio of wing vein lengths (CuA1 along dm cell) to the length of the aculeus (1.19 in B. philippinensis and 1.47 in B. dorsalis s.s.) [4]. In contrast to the three taxa representing unique biological species structured around the South China Sea, an parsimonious hypothesis is that they are a single widely distributed species for which subtle differences represent variation at the intra- rather than interspecific level
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