213W Poster - Population Genetics
Wednesday June 08, 9:15 PM - 10:00 PM

Assessing signatures of selection on transposable elements by accounting for non-uniform transposition rate


Authors:
Mitra Menon 1; Robert Horvath 2; Michelle Stitzer 3; Jeff Ross-Ibarra 1

Affiliations:
1) Department of Evolution and Ecology, University of California; 2) Institute for Plant and Microbial Biology, University of Zurich, Zurich, Switzerland ; 3) Institute for Genomic Diversity and Department of Molecular Biology and Genetics, Cornell University

Keywords:
Molecular Evolution

Transposable elements (TEs) make up a majority of flowering plant genomes and contribute towards phenotypic and genotypic diversity. Most earlier studies have assumed TEs experience strong purifying selection due to their ability to move around in the genome and insert into gene coding regions. However, more recent studies have shown that, like any genomic variants, TEs can be neutrally evolving or experience different selection pressures which may include positive and balancing selection. Approaches developed so far to evaluate selection on TEs have relied on the site frequency spectrum (SFS) of TEs and their deviation from a genome wide SFS. But inferring selection based on the SFS alone is problematic due to the non-constant mutational input of TEs. We present an approach to account for variation in TE activity by estimating the age of TE insertions and using an age-adjusted SFS to compare TEs to putatively neutral variants. We evaluated its effectiveness given different demographic histories via simulation and then explore the dynamics of TE variation across 3 different plant species. Additionally, we evaluated selection at the level of individual TE family and TE element by implementing two approaches that look at signatures of selective sweeps and at signatures of balancing selection. In Brachypodium we show that the age-adjusted SFS approach can effectively pick up signals of purifying selection across TEs. However, in Arabis and maize the pattern is complicated by differences in selective pressures amongst TE families. In maize, we show that a number of TE families appear to be under balancing selection, while in Arabis many appear to be neutrally evolving. Overall, we show that the age-adjusted SFS is robust to varying mutation and demographic history and provides a general idea of selection acting across TEs.