Abstract
In honeybees, the mechanism of sex determination depends on genetic variation at the complementary sex determiner (CSD) locus, which has a large allelic diversity. In this study, we examined the population genetic structure and genetic diversity within the highly variable region (HVR) of CSD in five Apis mellifera subspecies, in addition to Buckfast and unknown mixed ancestry bees. We sequenced CSD in 329 drones, 146 from Algeria (A. m. intermissa and A. m. sahariensis subspecies) and 183 from Europe (A. m. ligustica, A. m. carnica, A. m. mellifera subspecies, Buckfast samples, and individuals of unknown mixed ancestry). A total of 119 nucleotide haplotypes were detected. These corresponded to 119 protein haplotypes, of which 81 were new. The analysis of these haplotypes showed that HVR diversity levels were comparable with those in other populations of honeybee worldwide. Paradoxically, this high level of diversity at the locus did not allow for a separation of the samples according to their subspecies origin, which suggested either an evolutionary convergence or a conservation of alleles across subspecies, and an absence of genetic drift. Our results can be used to provide more information about the CSD diversity to include in breeding programs of honeybee populations.
Highlights
IntroductionHymenoptera is one of 11 orders of holometabolous insects,Vwohl.:i(c0h12i3n4c5l6u7d8e9s) 200,000 species of sawflies, wasps, ants, and honeybees (Wilson and Holldobler 2005)
The complementary sex determiner (CSD) gene has evolved by a gene duplication event from an ancestral copy of its paralog gene feminizer (FEM) within the honeybee Apis genus
Previous studies have shown that the CSD gene in A. mellifera, A. cerana, and A. dorsata has a very high level of polymorphism in these three honeybee species (Hasselmann and Beye 2004; Cho et al 2006; Hasselmann and Beye 2006; Hasselmann et al 2008; Wang et al 2012)
Summary
Hymenoptera is one of 11 orders of holometabolous insects,Vwohl.:i(c0h12i3n4c5l6u7d8e9s) 200,000 species of sawflies, wasps, ants, and honeybees (Wilson and Holldobler 2005). Hymenoptera lack sex chromosomes, and sex is usually determined by a single locus. Heterozygosity at CSD is required to induce the female pathway by interacting with transformer 2 (a protein that contains the RNAbinding domain) leading to a female-spliced FEM transcript. This creates the protein product that is responsible for the female-specific splicing of the Am-DSX transcript (Gempe et al 2009). The translation is terminated prematurely, and Am-DSX is spliced in a male-specific manner, producing a protein with a male-specific carboxy-terminal end (Nissen et al 2012; Biewer et al 2015; Hasselmann et al 2010)
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