Genetic diversity and population structure of Apis cerana complementary sex determiner (csd) genes in China

Abstract

In honeybees, fertilized eggs with homozygous complementary sex determiner (csd) alleles develop into sterile diploid males, which are eliminated by workers during the larval stage. A decrease in csd allele diversity leads to increased inbreeding and a higher occurrence of diploid males, significantly decreasing the population growth rate and effective population size. Therefore, understanding and maintaining csd gene diversity is crucial. This study aims to analyze the genetic diversity and population structure of Apis cerana csd genes in China. We sequenced the exon 6–8 region of the csd gene in 250 workers across 13 geographical populations, identifying 234 nucleotide haplotypes and 141 unique amino acid sequences, 89 of which were newly discovered. The csd gene in these populations shows high genetic diversity comparable to that of Apis mellifera; however, the distribution of alleles did not show clusters based on geographic regions. Analyses of genetic differentiation showed variable genetic distance among populations. Our results demonstrate a high diversity of csd genes of A. cerana populations across China, suggesting a low risk of inbreeding in the populations.