Abstract
Mitochondrial genomes (mitogenomes) are involved in cellular energy metabolism and have been shown to undergo adaptive evolution in organisms with increased energy-consuming activities. The genetically selected high royal jelly-producing bees (RJBs, Apis mellifera ligustica) in China can produce 10 times more royal jelly, a highly nutritional and functional food, relative to unselected Italian bees (ITBs). To test for potential adaptive evolution of RJB mitochondrial genes, we sequenced mitogenomes from 100 RJBs and 30 ITBs. Haplotype network and phylogenetic analysis indicate that RJBs and ITBs are not reciprocally monophyletic but mainly divided into the RJB- and ITB-dominant sublineages. The RJB-dominant sublineage proportion is 6-fold higher in RJBs (84/100) than in ITBs (4/30), which is mainly attributable to genetic drift rather than positive selection. The RJB-dominant sublineage exhibits a low genetic diversity due to purifying selection. Moreover, mitogenome abundance is not significantly different between RJBs and ITBs, thereby rejecting the association between mitogenome copy number and royal jelly-producing performance. Our findings demonstrate low genetic diversity levels of RJB mitogenomes and reveal genetic drift and purifying selection as potential forces driving RJB mitogenome evolution.
Highlights
As the major source of cellular energy, mitochondria produce roughly 90% of the energy in the form of ATP through oxidative phosphorylation (OXPHOS) (Schon et al, 2012; Castellani et al, 2020)
We examined genetic diversity and phylogenetic positions of RJBs from a mitogenome viewpoint, explored selection patterns acting on mitochondrial genes, and quantified Mitochondria contain their own DNA (mtDNA) copy abundance in the brain, hypopharyngeal glands, and mandibular glands
Whole genomic DNA was extracted from each sample using a DNeasy Blood & Tissue kit (Qiagen, Hilden, Germany), and potential RNA was removed using RNase A (Solarbio, Beijing, China)
Summary
As the major source of cellular energy, mitochondria produce roughly 90% of the energy in the form of ATP through oxidative phosphorylation (OXPHOS) (Schon et al, 2012; Castellani et al, 2020). Mitochondria contain their own DNA (mtDNA), a maternally inherited genome (mitogenome), which in metazoans generally contains 37 genes. Of these genes, 13 encode subunits of protein complexes directly involved in OXPHOS and 24 encode genes (two ribosomal RNAs and 22 transfer RNAs) for the mitochondrial translational machinery. Accumulating evidence indicates variations in mtDNA copy number depending on physiological conditions and energy demands (Schon et al, 2012; D’Erchia et al, 2015; Castellani et al, 2020).
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