Abstract
BackgroundThe insect olfactory system is a highly specific and sensitive chemical detector, which plays important roles in feeding, mating and finding an appropriate oviposition site. The ecological niche of Bombyx mori has changed greatly since domestication from B. mandarina, and its olfactory response to environmental odorants clearly decreased. However, the mechanisms that result in the olfactory impairment are largely unknown.ResultsThe antennal transcriptomes were compared between the domestic and wild silkworms. Comparison of the same sex between the domestic and wild silkworms revealed 1410 and 1173 differentially expressed genes (DEGs) in males and females, respectively. To understand the olfactory impairment, we mainly focused on the olfactory-related genes. In total, 30 olfactory genes and 19 odorant-degrading enzymes (ODEs) showed differential expression in the two comparisons, in which 19 and 14 were down-regulated in the domestic silkworm, respectively. Based on population genomic data, the down-regulated odorant receptors (ORs) showed a higher ratio of unique non-synonymous polymorphisms to synonymous polymorphisms (N/S ratio) in the domestic populations than that in the wild silkworms. Furthermore, one deleterious mutation was found in OR30 of the domestic population, which was located in transmembrane helix 6 (TM6).ConclusionsOur results suggested that down-regulation of the olfactory-related genes and relaxed selection might be the major reasons for olfactory impairment of the domestic silkworm reared completely indoor environment. Reversely, wild silkworm may increase expression and remove deleterious polymorphisms of olfactory-related genes to retain sensitive olfaction.
Highlights
The insect olfactory system is a highly specific and sensitive chemical detector, which plays important roles in feeding, mating and finding an appropriate oviposition site
Overview of the antennal transcriptomes in the silkworms To explore the mechanisms of olfactory adaptation, we collected the intact antennae from the domestic silkworm strain Dazao and wild silkworm
We found that 61–74 genes were highly expressed (FPKM > 1000), in which 46 genes were overlapped among the four samples (Additional file 5: Table S5)
Summary
The insect olfactory system is a highly specific and sensitive chemical detector, which plays important roles in feeding, mating and finding an appropriate oviposition site. Insects rely on a wide range of olfactory senses to locate mates, find an appropriate oviposition site as well as to avoid predators and other dangers. Insect antenna is served as an important periphery olfactory system, which contained several sensillum types, such as sensilla trichodea (medium-length and long), sensilla basiconica and sensilla coeloconica [1]. Odor perception is a selective and sensitive process, which is heavily dependent on the various receptors expressed on olfactory sensory neurons (OSNs) in antennae [2, 3]. Odor molecules are first captured and transported to the receptors by water-soluble extracellular proteins that are located in the fluid surrounding the sensory dendrite of
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