Epigenetic mechanisms of insect polyphenisms

2018-02-20T14:12:19Z (GMT) by Zoe Natasha Lonsdale
Insects are emerging as a key lineage for the study of epigenetic phenomena. This is due to the variety of polyphenisms found in insects. In this thesis, the caste polymorphism of the buff-tailed bumblebee Bombus terrestris and the phase polymorphism of the desert locust Schistocerca gregaria are studied to elucidate the underlying epigenetic mechanisms. I establish the presence of allele-specific expression and methylation in B. terrestris. I used next-generation RNA-sequencing to establish the DNA methylation, alternative splicing, and gene expression patterns of B. terrestris worker reproduction. The presence of allele-specific methylation and allele-specific expression were then determined in the same context. Correlations with the aforementioned epigenetic mechanisms were drawn. One major finding was that a higher degree of methylation was witnessed in more highly expressed genes. Higher methylation levels were also associated with more differentially expressed genes and isoforms between workers of a different reproductive state. However, the association between allele-specific expression and allele-specific methylation was weak. The relationship between alternative splicing and the circadian clock in S. gregaria was investigated. The first evidence of genes with differential circadian isoform expression patterns is reported. Finally, I analysed whether genome-wide alternative splicing levels are an important component in ascertaining the varying levels of eusociality found in the Hymenoptera. Fewer splicing events per gene with multiple isoforms was found in more highly eusocial species compared with solitary and more primitively eusocial species. Thus this is the first evidence of an association between level of sociality and alternative splicing.

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