Where are we with CSD? The candidate regions and population dynamics of hymenopteran complementary sex determination
Year: 2025
Type: review
Abstract: All Hymenoptera (bees, ants, wasps, sawflies) have haplodiploid sex determination. Unfertilized eggs develop into haploid males and fertilized eggs develop into diploid females. Many species further have complementary sex determination (CSD), a mechanism by which hemizygosity results in normal male development, and heterozygosity results in normal female development. However, homozygosity (at one or multiple CSD loci) results in aberrant diploid males that are frequently reproductively challenged and threaten population health. CSD is broadly distributed taxonomically, but only honey bee csd and a few candidate genomic regions in a few other species are known. Honey bee csd has been a flagship model for 20 years. Recent studies expand on mechanisms at multiple levels which maximize CSD diversity and functional heterozygosity, from molecular aspects to population dynamics. This demonstrates that similar depth of knowledge for other CSD species is achievable, but there are technical limitations to discovering CSD loci and interpreting downstream population impacts. These include, lack of diploid males needed for loci identification (particularly for ml-CSD systems), and challenges to functional validation. Here, we suggest practical solutions. This review summarizes recent discoveries of CSD properties in the honey bee and new candidates in several species of bees, parasitoid wasps, and ants. Notably, there is both evidence of independent de-novo evolution (e.g. honey bees) and deep-level conservation (i.e. ants, mason bee, bumble bee) of CSD mechanisms. We then highlight ways to develop an integrative framework for understanding the implications of CSD knowledge for control of invasive populations and conservation of endangered populations. • Complementary sex determination (CSD) is prevalent across hymenopterans. Under CSD, hemizygotes of a CSD locus/loci are normal haploid males and heterozygotes are normal diploid females, but homozygotes are reproductively impaired aberrant diploid males that can cause population declines. • The flagship CSD study species Apis mellifera (the honey bee) indicates multiple mechanisms to maximize functional female heterozygosity. • Recent CSD candidate region discovery in several ants, bees, and parasitoid wasps suggests both independent de-novo evolution events and deep-level phylogenetic conservation. • Impediments in specimen collection, functional validation, and homological analyses have prevented identifying CSD loci and mechanisms in other systems, hindering assessment of allelic diversity and impacts on population health. • Advances in candidate discovery and validation will improve CSD knowledge, which is emerging as critical for proper management of captive and wild populations.
Institutions: Wageningen University & Research, University of Groningen
Language: English
Subfield: Genetics
Domain: Life Sciences
Open Access status: hybrid
Estimated APC paid: $4,610
OpenAlex ID: W7117134391