Submitted to: Genes, Genomes, Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/29/2012
Publication Date: 7/19/2012
Publication URL: naldc.nal.usda.gov/download/55219/PDF
Citation: Aw, W.C., Dowell, F.E., Ballard, W.O. 2012. Using near-infrared spectroscopy to resolve the species, gender, age, and the presence of Wolbachia infection in laboratory-reared Drosophila. Genes, Genomes, Genetics. 2:1057-1065. Interpretive Summary: We determined the accuracy of near-infrared spectroscopy (NIRS) for determining species, gender, and age of the small flies, Drosophila, and also the presence of the organism Wolbachia that lives within the flies. Wolbachia may cause sperm and eggs to be unable to form viable offspring. This phenomenon increases the fitness of Wolbachia infected females and may drive the infection to spread rapidly within and between the populations. Wolbachia has also been proposed as a novel-biocontrol agent and the rapid determination of its frequency in populations will impact the success of these endeavors. NIRS was able to correctly classify fly species with about 90% accuracy, while flies were successfully classified by gender with accuracy greater than 90%. In age-grading test, it was possible to predict the age of flies as less than or greater than 9 days of age with about 80% accuracy. NIRS was able to detect Wolbachia-infected flies with about 90% accuracy. These results suggest that NIRS has the potential to quantify the species, gender, age, and presence of Wolbachia in fly populations.
Technical Abstract: The aim of the study was to determine the accuracy of near-infrared spectroscopy (NIRS) in determining species, gender, age and the presence of the common endosymbiont Wolbachia in laboratory reared Drosophila. NIRS measures absorption of light by organic molecules. Initially, a calibration model was developed for each study. An independent set with flies not involved in initial cross validation was then used to validate the accuracy of each calibration model. Flies from the independent sets were correctly classified into Drosophila melanogaster and D. simulans with 94% and 82% accuracy respectively, while flies were successfully classified by gender with accuracy greater than 90%. In the age grading test, correlation plots of the actual and predicted age for males and females of D. melanogaster and D. simulans were shown to be overlapping between the adjacent age groups. It is, however, possible to predict the age of flies as less than 9 days of age with 62-88% accuracy, and flies that are equal to or older than 9 days of age with 91-98% accuracy. Finally, we employed NIRS to detect the presence of Wolbachia in flies. Flies from the independent sets were successfully identified as Wolbachia infected or non-infected with about 90% accuracy. These results suggest that NIRS has the potential to quantify the species, gender and presence of Wolbachia in fly populations. However, additional optimization of the protocol may be necessary before the technique can reliably estimate fly age.