Evolution of a transposon in Daphnia hybrid genomes

Abstract

AbstractBackgroundTransposable elements play a major role in genome evolution. Their capacity to move and/or multiply in the genome of their host may have profound impacts on phenotypes, and may have dramatic consequences on genome structure. Hybrid and polyploid clones have arisen multiple times in theDaphnia pulexcomplex and are thought to reproduce by obligate parthenogenesis. Our study examines the evolution of a DNA transposable element namedPokeyin theD. pulexcomplex.ResultsPortions ofPokeyelements inserted in the 28S rRNA genes from variousDaphniahybrids (diploids and polyploids) were sequenced and compared to sequences from a previous study to understand the evolutionary history of the elements.Pokeysequences show a complex phylogenetic pattern. We found evidence of recombination events in numerousPokeyalleles from diploid and polyploid hybrids and also from non-hybrid diploids. The recombination rate inPokeyelements is comparable to recombination rates previously estimated for 28S rRNA genes in the congener,Daphnia obtusa.Some recombinantPokeyalleles were encountered inDaphniaisolates from multiple locations and habitats.ConclusionsPhylogenetic and recombination analyses showed that recombination is a major force that shapesPokeyevolution. Based onPokeyphylogenies, reticulation has played and still plays an important role in shaping the diversity of theD. pulexcomplex. Horizontal transfer ofPokeyseems to be rare and hybrids often possessPokeyelements derived from recombination among alleles encountered in the putative parental species. The insertion ofPokeyin hotspots of recombination may have important impacts on the diversity and fitness of this transposable element.