Piecing together an integrative taxonomic puzzle: microsatellite, wing shape and aedeagus length analyses of Bactrocera dorsalis s.l. (Diptera: Tephritidae) find no evidence of multiple lineages in a proposed contact zone along the Thai/Malay Peninsula

Abstract

Bactrocera dorsalis (Hendel) and B. papayae Drew & Hancock represent a closely related sibling species pair for which the biological species limits are unclear; i.e. it is uncertain if they are truely two biological species, or one biological species which has been incorrectly split taxonomically. The geographical ranges of the two taxa are thought to abut or overlap on or around the Isthmus of Kra, a recognised biogeographic barrier located on the narrowest portion of the Thai Peninsula. We collected fresh material of B. dorsalis s.l. (i.e. B. dorsalis s.s.+ B. papayae) in a north–south transect down the Thai Peninsula, from areas regarded as being exclusively B. dorsalis s.s., across the Kra Isthmus, and into regions regarded as exclusively B. papayae. We carried out microsatellite analyses and took measurements of male genitalia and wing shape, both used previously to separate the taxa. No significant population structuring was found in the microsatellite analysis, consistent with one, predominantly panmictic population. Both morphological datasets showed consistent, clinal variation along the transect, without disjunction. No evidence supported historical vicariance driven by the Isthmus of Kra, and no dataset supported the current taxonomy of two species. Rather, within and across the area of range overlap or abutment between the two species, only continuous morphological and genetic variation was recorded. Recognition that morphological traits previously used to separate these taxa are continuous, and that there is no genetic evidence for population segregation in the region of suspected species overlap, is consistent with a growing body of literature that reports no evidence of biological differentiation between these taxa.

Mating Compatibility Among Four Pest Members of the <I>Bactrocera dorsalis</I> Fruit Fly Species Complex (Diptera: Tephritidae)

“…We believe that in addition to previously reported differences between these species (e.g., pheromone composition), especially for B. carambolae, that behavioral variation (e.g., differences in mating location) contribute to the mating incompatibility observed here between B. carambolae and the remaining three species. While these data alone cannot be used to redeÞne species limits or to assert full sexual compatibility (because of the absence of full postzygotic testing; not completed in this study yet underway) and the inherent caveats of artiÞcial cage studies (Walter 2003), we consider our results closely parallel previous research suggesting that B. dorsalis, B. papayae, and B. philippinensis represent the same biological species (Medina et al 1998, Wee and Tan 2000b, Tan 2003, Krosch et al 2013, Schutze et al 2012. Such an outcome has signiÞcant implications not only for their taxonomic identities, but has consequences for pest management (especially for the SIT for which knowledge of species limits and mating compatibility are critical) and international trade.…”

Molecular clock analysis on fiveBactroceraspecies flies (Diptera: Tephritidae) based on combination ofCOIandNADHsequences

“…For this reason, several studies have been conducted to clarify the taxonomic puzzles, for example on taxonomy, molecular genetics, behaviour, chemical and cytogenetic reactions (Tan et al 2011;Khamis et al 2012;Schutze, Jessup, et al 2012Boykin et al 2013;Krosch et al 2013;Schutze et al 2013;Tan et al 2013). Despite the difficulties, several discoveries have been made at a basic level on its taxonomic situation via the implementation of the tools that have been discussed above.…”

Evidence of weak genetic structure and recent gene flow between Bactrocera dorsalis s.s. and B. papayae, across Southern Thailand and West Malaysia, supporting a single target pest for SIT applications

“…Independent studies using different samples and sets of microsatellite markers (i.e., microsatellite-derived markers from only B. dorsalis s.s. [14] and a combination of microsatellite-derived markers from B. dorsalis s.s. & B. papayae (this study)) present a comparable genetic variation between two morphological forms. These facts imply that F ST of the given species cannot be resolved.…”