Submitted to: Apidologie
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2020
Publication Date: 12/1/2020
Citation: Bilodeau, A.L., Avalos, A., Danka, R.G. 2020. Genetic diversity of the complementary sex-determiner (csd) gene in two closed breeding stocks of Varroa-resistant honey bees.. Apidologie. 51(6):1125-1132. https://doi.org/10.1007/s13592-020-00790-1.
Interpretive Summary: Low genetic diversity, in particular at the complementary sex determiner (csd) locus, can be catastrophic to honey bee populations. Breeding programs that use closed mating systems are particularly vulnerable because of the increased risk, of inbreeding. In this study we examine genetic diversity within csd in two stocks bred for resistance to Varroa destructor: Pol-line and Hilo, both of which use closed mating systems. We found that diversity levels were comparable to those in other closed breeding populations as well as other open-mated populations of Apis mellifera. We did find the distinct patterns of allele distribution between the stocks suggesting of the beginning of divergence and recommend periodic monitoring of csd diversity going forward.
Technical Abstract: Honey bee breeding programs that use a closed mating system are particularly vulnerable to low genetic diversity, especially at the complementary sex-determiner (csd) locus. In typical commercial populations, queens are open mated and csd diversity is fostered by high rates of introgression. In this study we examine genetic diversity within the highly variable region (HVR) of csd in two stocks bred for resistance to Varroa destructor: Pol-line and Hilo, both of which use closed mating systems. We sampled 47 Pol-line colonies and 41 Hilo colonies, and found 73 protein alleles that were further distilled into 35 functional allele groupings. We found that proportionately, HVR diversity levels were comparable to those in other closed breeding populations as well as open-mated populations of Apis mellifera worldwide. Phylogeny and frequency distributions showed distinct patterns of allele distribution between the stocks suggesting of the beginning of divergence. When compared to an African outgroup, both stocks shared alleles with the outgroup, suggesting ancestral lineages are present and not all diversity is due to new mutations. Periodic monitoring of csd diversity is recommended for closed breeding programs, such as those described here.