Genetic diversity and differentiation among populations of Tribolium castaneum

The availability of the genome sequence of Tribolium castaneum enables more appropriate selection of molecular markers for analysis of population structure and identification of infestation sources throughout grain processing and distribution channels. In this study we investigated the genetic diversity and differentiation among five populations of T. castaneum using eight polymorphic loci, including microsatellites and insertion-deletion polymorphisms (=”indels”). Samples were collected in food processing/storage facilities located in Kansas (1), Nebraska (2), California (1), and Louisiana (1). Standard population genetic analysis was applied, and an assignment test was used to assign individuals to their genetic population. All loci were polymorphic across populations, with allele richness varying from 2 to 21.2. Among 50 marker-by-population combinations, 28 deviated significantly from Hardy-Weinberg equilibrium, which was associated with a deficiency in heterozygosity. T. castaneum populations show some level of genetic structuring. Genetic differentiation between populations, using either Fst or Rst estimates, was significant for all comparisons with Rst estimates giving slightly higher values in most pair-wise comparisons. Fst varied from 0.01 to 0.09 while Rst varied from 0.004 to 0.12. Analysis of molecular variance indicated that 6.46% of the variation in allele frequency resulted from comparisons among populations. Genetic distance was not significantly correlated with geographic distance. Correct assignment to the genetic population was possible in only 56% of all individuals. Together, these results revealed that geographically distinct populations of T. castaneum were genetically different, but the genotypic profile of the individuals did not provide enough information for fingerprinting them to their particular genetic population.