Meeting Abstract
The evolutionary mechanisms underlying the immense variation in genome architecture remain unclear. Repetitive DNA, including transposable elements (TEs), mobile DNA sequences that replicate and insert themselves in a host genome, are a major source of this genomic variation. Understanding the conditions that influence the accumulation of repetitive DNA is thus of central importance to understanding genome evolution. Sexual reproduction is a hallmark eukaryotic trait and transitions to asexuality are expected to have significant consequences for genome evolution. How asexuality impacts TE evolution is complicated because (1) the reduced efficacy of selection should result in greater TE accumulation in asexuals relative sexuals, but (2), TEs should be lost to genetic drift in asexual populations because TEs cannot spread to new lineages in the absence of sex. Here we evaluate genomic consequences of asexuality in Potamopyrgus antipodarum, a freshwater New Zealand snail characterized by frequent coexistence of closely related phenotypically and ecologically similar sexual and asexual individuals. We used whole-genome sequence data from natural populations to compare genomic loads of TEs and other repetitive elements in sexual vs. asexual lineages. While we did not observe an effect of reproductive mode on TE variation, we found a striking pattern of increases in copy number for tandemly repeated rRNA genes (rDNA) and histones – which we discovered are joined in an organization apparently unique to Potamopyrgus – in asexuals relative to sexuals. The rapid and a repeated accumulation of rDNA-histone sequences asexual P. antipodarum indicates that asexuality may have important consequences on genome evolution.
