A transposon-based genetic marker for species-specific identity in the Bactrocera dorsalis complex

Authors: ZIMOWSKA, GRAZYNA - University Of Florida; XAVIER, NIRMALA - Former ARS Employee; QADRI, MASROOR - University Of Florida; Handler, Alfred - Al

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2023
Publication Date: 1/22/2024
Citation: Zimowska, G.J., Xavier, N., Qadri, M., Handler, A.M. 2024. A transposon-based genetic marker for species-specific identity in the Bactrocera dorsalis complex. Scientific Reports. 14:1924. https://doi.org/10.1038/s41598-023-51068-2.
DOI: https://doi.org/10.1038/s41598-023-51068-2

Interpretive Summary: Many insect pest species have close relatives that cannot be easily distinguished, yet their economic and agricultural importance may vary, or they may be equally destructive, but must be controlled by different methodologies. Thus when these insects inhabit the same geographic area this can be problematic in terms of effective population control, and potentially, whether and how trade barriers or other types of restriction should be instituted. Therefore, methods to define species identity and their relationships to other closely related insects precisely and efficaciously are a high priority for effective control. To improve the identification of specific insect pests, scientists at the USDA-ARS in Gainesville, Florida and collaborators at the University of Florida have identified a new type of genetic marker that can clarify whether insects are members of a common species. This method relies on mobile genetic elements that exist in all organisms by interspecies invasion and which, typically, become immobile due to mutations that accumulate with time. Once a mutated element is identified, it is expected that only insects that actively interbreed within a common species will harbor the same element (having the same mutated sequence) within an identical chromosomal insertion site.

Technical Abstract: Here we describe a molecular approach to species identification that relies on the comparison of a mutated transposable element sequence, and its genomic insertion site, in closely related species. This was explored with a piggyBac transposon, originally discovered in Trichoplusia ni as a 2,472 bp IFP2 functional element, that was subsequently found as mutated elements in seven species within the Bactrocera dorsalis species complex. In a B. dorsalis [Hendel] strain collected in Kahuku, Hawaii, a degenerate 2,420 bp piggyBac sequence (pBacBd-Kah) having ~94.5% identity to IFP2 was isolated, and it was reasoned that common species should share the same evolved element and its precise genomic insertion site. To test this assumption, PCR using primers to pBacBd-Kah and adjacent genomic sequences was used to isolate and compare homologous sequences in strains of four sibling species within the complex. Three of these taxa, B. papayae, B. philippiensis, and B. invadens, previously synonomized with B. dorsalis, were found to share nearly identical pBacBd-Kah homologous elements within the identical insertion site, having ~99.5% nucleotide sequence identity, consistent with conspecific species. The fourth species tested, B. carambolae, considered to be a closely related yet independent species sympatric with B. dorsalis, also shared the pBacBd-Kah sequence and insertion site in a strain from Suriname, but two divergent pBacBd-Kah derivatives were also found in strains from French Guiana and Malaysia. This data, along with the absence of pBacBd-Kah in distantly related Bactrocera, indicates that piggyBac, as well as other invasive mobile mutated elements, could be reliable genomic markers for species identity.