Submitted to: Public Library of Science Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/20/2012
Publication Date: 11/2/2012
Citation: Tsuruda, J.M., Harris, J.W., Bourgeois, A.L., Danka, R.G., Hunt, G.J. 2012. High-Resolution Linkage Analyses to Identify Genes That Influence Varroa Sensitive Hygiene Behavior in Honey Bees. PLOS One. 7(11), e48276. Interpretive Summary: Varroa sensitive hygiene (VSH) is a behavioral trait in honey bees in which workers remove pupae infested with Varroa mites from capped brood cells. This either kills the mites or disrupts their reproductive cycle, and thus serves as a resistance mechanism for the colony against the parasite. VSH is genetically based, but traditional breeding for the trait involves technically challenging screening of colonies for Varroa resistance in lengthy field trials. Another approach could be selective breeding either for the good variations of genes that regulate the trait or for molecular markers in the DNA that are linked to those genes. This approach, called marker-assisted selection (MAS), could be more efficient because screening DNA from potential breeding sources can be completed relatively quickly in the laboratory. The purpose of this experiment was to use DNA markers to identify regions on the chromosomes that are linked to genes that regulate VSH behavior. Using 1,340 DNA markers, we compared 127 worker bees that were observed performing VSH (that is, removing mite-infested pupae) and 111 sister worker bees that did not exhibit VSH. A region on chromosome 9 that contains about 65 candidate genes was associated with the behavior of removing mite-infested pupae; some of these genes (for example, two involved in olfaction) may be important in regulating the VSH trait. Another region that contains 37 candidate genes on chromosome 1 also may be important, but the statistical likelihood was weaker than that for the region on chromosome 9. Future studies will try to narrow the broader regions from this study down to the actual genes that regulate the VSH trait as we develop MAS protocols.
Technical Abstract: Varroa mites (V. destructor) are a major threat to honey bees (Apis melilfera) and beekeeping worldwide and likely lead to colony decline if colonies are not treated. Most treatments involve chemical control of the mites; however, Varroa has evolved resistance to many of these miticides, leaving beekeepers with a limited number of alternatives. A non-chemical control method is highly desirable for numerous reasons including lack of chemical residues and decreased likelihood of resistance. Varroa sensitive hygiene behavior is one of two behaviors identified that are most important for controlling the growth of Varroa populations in bee hives. To identify genes influencing this trait, a study was conducted to map quantitative trait loci (QTL). Individual workers of a backcross family were observed and evaluated for their VSH behavior in a mite-infested observation hive. Bees that uncapped or removed pupae were identified. The genotypes for 1,340 informative single nucleotide polymorphisms (SNPs) were used to construct a high-resolution genetic map and interval mapping was used to analyze the association of the genotypes with the performance of Varroa sensitive hygiene. We identified one major QTL on chromosome 9 (LOD score=3.21) and a suggestive QTL on chromosome 1 (LOD=1.95). The QTL confidence interval on chromosome 9 contains the gene ‘no receptor potential A’ and a dopamine receptor. ‘No receptor potential A’ is involved in vision and olfaction in Drosophila, and dopamine signaling has been previously shown to be required for aversive olfactory learning in honey bees, which is probably necessary for identifying mites within brood cells. Further studies on these candidate genes may allow for breeding bees with this trait using marker-assisted selection.