Scientific note updating allelic nomenclature standards of the highly diverse complementary sex-determiner locus in honey bees

Authors: Ihle, Kate; Payne, Alexandria; ELSIK, CHRISTINE - University Of Missouri; Bilodeau, Anita

Submitted to: Apidologie
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2025
Publication Date: 3/3/2025
Citation: Ihle, K.E., Payne, A.N., Elsik, C., Bilodeau, A.L. 2025. Scientific note updating allelic nomenclature standards of the highly diverse complementary sex-determiner locus in honey bees. Apidologie. https://doi.org/10.1007/s13592-025-01161-4.
DOI: https://doi.org/10.1007/s13592-025-01161-4

Interpretive Summary: Genetic diversity is very important for the health and productivity of honey bee colonies. This is especially true for the complementary sex-determiner (csd) gene. In honey bees, individuals with two copies of their genes will develop into females, while those with only one copy will develop into males. The csd gene regulates this process: normal females must have two different copies, or alleles, of this gene and normal males only have a single allele. However, if a bee has two of the same alleles, they will develop into an abnormal diploid drone--a male bee with two copies of its genes. These diploid drones are usually removed by workers when they're very young larvae. This means that if there is very little diversity in the pool of csd alleles, colonies loose strength and productivity because they can't build up their workforce of female worker bees as fast as they need to. Over the last 10 years there have been lots of studies around the world that identify the csd alleles in different local honey bee populations. Often times, these studies find the same alleles, but because there are no standard names for them, it is difficult for scientists to see if they have found copies of csd that others have already found. We are updating a data base of standardized names for the csd alleles to make this easier for scientists to do comparisons with many other studies. This is important for understanding global patterns of genetic diversity and also for honey bee breeders who likely start with fewer different csd alleles as they breed their specialized bee stocks.

Technical Abstract: Honey bees rely on haplodiploidy for sex determination. Here diploid eggs develop into females (i.e., queens and workers) and haploid eggs develop into males (i.e., drones). This system is regulated by the complementary sex-determiner (csd) locus—a single, multi-allelic locus with very high diversity. Honey bees heterozygous at the csd locus will develop into females, while hemizygosity results in normal male development. Homozygosity at csd results in abnormal males, which are usually destroyed by the workers early in development which can negatively impact colony population, growth, and productivity. As such, maintaining genetic diversity at csd is critical for the health and productivity of honey bee populations, especially those that are isolated either geographically or through selective breeding. We present an updated database of all csd sequences deposited into GenBank, since our last publication in 2020. In only the last four years, 370 new csd sequences were deposited, including 154 novel alleles. All alleles received standardized names to enable cross-study comparisons and improve our understanding of local and global genetic diversity of honey bee csd.