title: DNA transposons and the role of recombination in mutation accumulation in Daphnia pulex.
abstract: BACKGROUND
  We identify DNA transposons from the completed draft genome sequence of Daphnia pulex, a cyclically parthenogenetic, aquatic microcrustacean of the class Branchiopoda. In addition, we experimentally quantify the abundance of six DNA transposon families in mutation-accumulation lines in which sex is either promoted or prohibited in order to better understand the role of recombination in transposon proliferation.
  
  
  RESULTS
  We identified 55 families belonging to 10 of the known superfamilies of DNA transposons in the genome of D. pulex. DNA transposons constitute approximately 0.7% of the genome. We characterized each family and, in many cases, identified elements capable of activity in the genome. Based on assays of six putatively active element families in mutation-accumulation lines, we compared DNA transposon abundance in lines where sex was either promoted or prohibited. We find the major difference in abundance in sexuals relative to asexuals in lab-reared lines is explained by independent assortment of heterozygotes in lineages where sex has occurred.
  
  
  CONCLUSIONS
  Our examination of the duality of sex as a mechanism for both the spread and elimination of DNA transposons in the genome reveals that independent assortment of chromosomes leads to significant copy loss in lineages undergoing sex. Although this advantage may offset the so-called 'two fold cost of sex' in the short-term, if insertions become homozygous at specific loci due to recombination, the advantage of sex may be decreased over long time periods. Given these results, we discuss the potential effects of sex on the dynamics of DNA transposons in natural populations of D. pulex.
authors.affiliation: Department of Biology, University of Texas-Arlington, 501 S, Nedderman Drive, Arlington, TX 76019, USA. schaackmobile@gmail.com
authors.forename: Sarah
authors.initials: S
authors.lastname: Schaack
authors.forename: Eunjin
authors.initials: E
authors.lastname: Choi
authors.forename: Michael
authors.initials: M
authors.lastname: Lynch
authors.forename: Ellen J
authors.initials: EJ
authors.lastname: Pritham
mesh_terms: D000818:Animals; D056915:DNA Copy Number Variations; D004251:DNA Transposable Elements; D003621:Daphnia / Q000235:genetics*; D016678:Genome; D009154:Mutation; D011995:Recombination, Genetic
chemical_list: D004251:DNA Transposable Elements