This peak negligibly affects protein coding sequence, but is closely linked to a lncRNA putatively homologous to ANTSR, which work in Linepithema implicated in having a role in sex determination.

This selection against homozygosity leads to "balancing selection" at CSD loci, which can support many different alleles at intermediate frequency. We explored this by looking at genome-wide "nucleotide diversity" in clonal raider ants, and found a peak within the mapped candidate CSD locus.

This suggests that the role of this locus in complementary sex determination evolved over 110 million years ago at the base of the formicoid clade of ants!

The candidate clonal raider ant CSD locus is homologous to the locus mapped in Linepithema and Vollenhovia, but not the one known from Honeybees.

Consistently, this pattern was indeed due to large segmental losses of heterozygosity found in diploid males.

To test this hypothesis and map a CSD locus in clonal raider ants, I compared the genomes of diploid males and females, looking for sites that were heterozygous in females but homozygous in diploid males. This identified a single peak on chromosome 4.

At the start of this project, we knew that clonal raider ants occasionally produced diploid males. If they also reproduced using CSD, then we'd expect that these might occur via rare segmental losses of heterozygosity that occur due to their mode of reproduction.

Whiting called this system "complementary sex determination" (I'll call this "CSD") because different alleles at the same sex determination locus can "complement" each other, meaning that heterozygosity triggers female development, while homozygosity or hemizygosity permits male development.

In the second paper (currently a preprint) from my Ph.D. with @danielkronauer.bsky.social we expand the understanding of ant sex determination by mapping a candidate sex determination locus in the clonal raider ant. doi.org/10.1101/2025...

Clonal raider ants leaving twitter to join blue sky

Clonal raider ants