DNA methylation, genomic imprinting and polyphenism in the bumblebee, Bombus terrestris
thesisposted on 29.06.2015, 11:41 authored by Harindra Eranthi Amarasinghe Kankanamge
Genomic imprinting, the parent-of-origin specific expression of alleles is an important area of research in evolutionary biology and human health (cancers and developmental syndromes). Haig’s kinship theory suggests that the maternally and paternally derived alleles of offspring resource allocation genes have evolved under different selectional pressures. Thus within different kin related individuals they are expressed unequally, each allele favouring their own inclusive fitness. Social insects provide the best independent model system to study the evolution of imprinting. However, imprinting has not been discovered in any social insect. My PhD lays the groundwork for a social insect model of genomic imprinting. Methylation is a common epigenetic tag of genomic imprinting in mammals and flowering plants. I found that a functional methylation system which is involved in the reproductive caste formation, development and social behaviour is present in the bumblebee, Bombus terrestris. Under queenless conditions, reproducing and non-reproducing worker castes show different brain methylome patterns. Alteration of methylation can cause a sterile worker to turn into a reproductive worker with increased aggressive behaviour and ovary development. Next I found monoallelic methylation associated with monoallelic expression in genes predicted to be imprinted by Haig’s theory. Also, differential allele specific expression that are apparently due to parent-of-origin effects is present in reproduction loci of B. terrestris. Reciprocal crosses at these loci is recommended as further work, to check whether these expression patterns are due to genomic imprinting. I assess the effects of maternally and paternally contributed sociobiological factors on worker male production and found that the paternity or the queen mating frequency has a significant influence on worker male production in eusocial Hymenoptera. Finally, I also studied the polyphenism involved in phase dependent behavioural plasticity of locusts. I found that the transition of solitarious to fully gregarious behaviour in the desert locust, Schistocerca gregaria begins without significant changes in the DNA methylation landscape of the CNS but subjected to the pronounced differences at a later stage.