Unraveling the Sex Determination Mechanism of Bees and Ants! Foundational Science Beneficial for Beekeeping and Conservation: What "Diploid Males" Have Taught Us

"Was the 'Switch to Determine Sex' Shared by Bees and Ants?"

Many organisms on Earth have sexes, but "what determines sex" is surprisingly diverse across species. Among them, many Hymenoptera such as bees, ants, and sawflies have a system called haplodiploidy, where fertilized eggs (2n) usually become females and unfertilized eggs (n) become males. However, the contents of the primary switch that "initiates" the sex cascade have long remained a mystery. The latest findings reported by the news site Phys.org delve into this core issue. It connects the fact that the sex determination locus of the red mason bee overlaps with a long non-coding RNA (lncRNA) called ANTSR, and that this gene was shown in previous studies to determine sex in ants. This strengthens the possibility that bees and ants share a common "switch".Phys.org

Key Points of the Study: CSD Locus Converged to a "Narrow Region" of 2kb

The team from Uppsala University screened numerous nest tubes of the red mason bee (Osmia bicornis), commonly found in garden "bee hotels," and discovered a rare individual known as a diploid male. A diploid male indicates that the CSD locus is homozygous, serving as a "marker" to backtrack its genomic location. Through whole-genome comparison and linkage analysis, the CSD was fine-mapped to a very narrow region of about 2 kilobases, which was found to overlap with ANTSR. Furthermore, this locus exhibits extremely high haplotype diversity, suggesting that polymorphism is maintained by frequency-dependent selection.DOI Resolver

This finding resonates with the mechanism reported in Argentine ants (Linepithema humile). The 2024 study showed that heterozygosity at the CSD locus increases ANTSR expression, guiding the known sex determination cascade (transformer → doublesex splicing control) toward the female route. In other words, although ANTSR is a non-coding RNA, it functions as a primary switch.PubMed

The Hypothesis of a "Common Switch" Continuing for 150 Million Years

The current PLOS Biology paper suggests that ANTSR (or its locus) is widely conserved in at least five genera of bees and ants, potentially dating back to over 150 million years ago (the era of the common ancestor of Apoidea and Formicidae). This implies that "the sex determination of bees and ants has been operating through a common mechanism since ancient times." Interestingly, honeybees (Apis mellifera) are the only "exception" that use a protein-coding gene, csd, as the primary switch. Why only honeybees took a different route remains a **"mystery,"** according to the paper's authors.DOI ResolverPLOS

Insights from "Diploid Males" for Conservation and Beekeeping

In the world of CSD, if the mother and father share the same CSD allele, the fertilized egg becomes homozygous, resulting in a diploid male. Most are infertile, posing a genetic cost to the colony. The high polymorphism of the locus suggests that natural populations are evolving to reduce the risk of **"homozygous fertilization."** Conversely, in small populations or under inbreeding conditions, the occurrence of diploid males may increase.

With ANTSR as a concrete indicator, the future may see the realization of breeding designs that maintain diverse haplotypes and the optimization of breeding management based on inbreeding avoidance. This also relates to the **conservation of native pollinators.**DOI Resolver

The Era When lncRNA Becomes the "Main Player"

For many readers, the fact that "non-coding RNA determines sex" may seem counterintuitive. However, research on Argentine ants showed that knocking down ANTSR leads to masculinization, and the study on the red mason bee pinpointed the corresponding genomic locus. **Non-coding RNA becomes the "switch,"** controlling the alternative splicing of classical genes like transformer (tra) upstream—Hymenoptera sex determination has entered a stage that cannot be fully explained by coding genes alone.PubMed

The Art of Method: Field Observation × Whole Genome Analysis

Behind this achievement lies the meticulous fieldwork of opening each nest tube, weighing cocoons, and identifying individuals. From there, they identified diploid males, narrowed down the locus through whole genome comparison, and verified the distribution of polymorphisms across public data (genomes of multiple genera). The fine mapping to the narrow 2kb region was made possible by the combination of fieldwork × computation.DOI Resolver

Why Are Honeybees Different?—The Next Point of Discussion

As the hypothesis of a "common switch" for bees and ants strengthens, the reason why only honeybees use csd stands out. Was there a switch change somewhere in evolution, or did the interaction between ANTSR and csd change due to environmental or social structures? In any case, comparisons involving conservation and domestication history will be a focus for the future. The paper explicitly states that **"why only honeybees are different remains unexplained."**DOI Resolver

Reactions on Social Media and Early Spread (Observation Notes)

• Increased Exposure in Academic Distribution
  The press release from Uppsala University (EurekAlert!) was published and reprinted in specialized media like Bioengineer.org. Key phrases such as the possibility that ANTSR is a common sex determination gene in bees and ants and its conservation for over 150 million years were disseminated.EurekAlert!

• Attention at the Preprint Stage
  The summer 2025 bioRxiv version was featured in preprint newsletters and highlight articles (such as the Node), and the perspective of **"ANTSR connecting bees and ants"** was shared early on.thenode.biologists.com

• Initial Altmetric Scores
  In the Metrics section of PLOS Biology, the "Discussed" metric immediately after publication is not yet large. It is customary for it to grow within days to weeks after publication, requiring further tracking.PLOS

• Reception by the Research Community (Overview)
  In the insect and evolution clusters, there is surprise at the **"commonality between bees and ants," and attention is drawn to the paradoxical interest of "honeybees being an exception." Meanwhile, in the beekeeping and conservation clusters, there is interest in the potential applications for inbreeding avoidance and breeding design—this is the current qualitative trend** (based on the author's organization from the above distributions, highlights, and comment section trends).

※Direct quotes from individual posts are avoided, and the initial sentiment is outlined based on official releases, media distributions, preprint discussions, and metrics from publication platforms.

• Designing for Inbreeding Avoidance

  The key is maintaining haplotype diversity at the CSD locus (ANTSR).
  In small-scale breeding or artificial environments, breeding designs that reduce the risk of allele overlap are likely effective.DOI Resolver

• New Indicators for Monitoring
  In the future, if a polymorphism panel of the ANTSR locus is established, it could be used for predicting diploid males and assessing community health.DOI Resolver

• Materials for Education and Public Relations
  Messages such as "non-coding RNA as the main player" and "the switch continuing from the common ancestor of bees and ants" are suitable for educational materials in citizen science and school education.PubMed##HTML