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Repeated increase of transposable elements and satellite DNA in three hybrid (Formica aquilonia × F. polyctena) wood ant populations

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Title: Repeated increase of transposable elements and satellite DNA in three hybrid (Formica aquilonia × F. polyctena) wood ant populations
Author(s): Heidbreder, Patrick
Contributor: University of Helsinki, Faculty of Biological and Environmental Sciences
Degree program: Master's Programme in Ecology and Evolutionary Biology
Specialisation: Ecology and evolutionary biology
Language: English
Acceptance year: 2022
Hybridization between species is widespread across the tree of life and plays a role in adaptation, speciation and evolution. A critical component of hybridization is the compatibility of the combining genomes. Mechanisms that create incompatibilities, such as transposable element (TE) activity, are thus central to understanding and predicting the evolutionary effects of hybridization. The genomic shock hypothesis posits a burst of TE activity in hybrid genomes due to the uncoupling of TEs and their silencers. While many studies on this topic have focused on laboratory hybrids, there is relatively little data for wild hybrid populations, especially in non-model species. Here, I take advantage of a recent (< 50 generations ago), natural, and replicated hybridization events between two wood ant species, Formica aquilonia and F. polyctena, to test for increased TE abundance in hybrids. Analyses of whole genomes (N total = 99) from both parental species and three hybrid populations revealed significantly more total TE copies in all hybrid populations compared to each parental species, and this partly remained after controlling for genome size, suggesting TE reactivation in the hybrids. LINE, DNA, and LTR elements, as well as multiple new and unclassified repeats, contributed most to the observed increase. However, I also found concurrent increases in satellite DNA copies in hybrids, suggesting heterochromatin expansion after hybridization. So while the observed TE-copy number increase I have detected is consistent with the genomic shock hypothesis, additional work is required to demonstrate and fully characterize TE reactivation in hybrids. Overall my work contributes to our understanding of the effects of hybridization on TE reactivation, satellite DNA abundance, and genome size evolution in natural populations.
Keyword(s): Transposons genomic shock genome expansion

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