De Novo Transcriptome Assembly and Sex-Biased Gene Expression in the Cyclical Parthenogenetic Daphnia galeata.
Daphnia species have become models for ecological genomics and exhibit interesting features, such as high phenotypic plasticity and a densely packed genome with many lineage-specific genes. They are also cyclic parthenogenetic, with alternating asexual and sexual cycles and environmental sex determination. Here, we present a de novo transcriptome assembly of over 32,000 D. galeata genes and use it to investigate gene expression in females and spontaneously produced males of two clonal lines derived from lakes in Germany and the Czech Republic. We find that only a low percentage (18%) of genes shows sex-biased expression and that there are many more female-biased gene (FBG) than male-biased gene (MBG). Furthermore, FBGs tend to be more conserved between species than MBGs in both sequence and expression. These patterns may be a consequence of cyclic parthenogenesis leading to a relaxation of purifying selection on MBGs. The two clonal lines show considerable differences in both number and identity of sex-biased genes, suggesting that they may have reproductive strategies differing in their investment in sexual reproduction. Orthologs of key genes in the sex determination and juvenile hormone pathways, which are thought to be important for the transition from asexual to sexual reproduction, are present in D. galeata and highly conserved among Daphnia species.
Faculty of Biology, Ludwig-Maximilians-Universität München, Planegg, Germany.|Instititute of Science and Technology Austria, Klosterneuburg, Austria.
Ann Kathrin
AK
Huylmans
Institute for Evolution and Biodiversity, Westfälische-Wilhelms Universität Münster, Münster, Germany.
Alberto
A
López Ezquerra
Faculty of Biology, Ludwig-Maximilians-Universität München, Planegg, Germany.
John
J
Parsch
Faculty of Biology, Ludwig-Maximilians-Universität München, Planegg, Germany mathilde.cordellier@uni-hamburg.de.|Zoologisches Institut, Universität Hamburg, Hamburg, Germany.
Mathilde
M
Cordellier
D000818:Animals; D003621:Daphnia / Q000235:genetics* / Q000254:growth & development / Q000502:physiology; D005260:Female; D018507:Gene Expression Regulation, Developmental; D008297:Male; D010312:Parthenogenesis / Q000235:genetics*; D012641:Selection, Genetic; D019849:Sex Determination Processes / Q000235:genetics; D059467:Transcriptome
crustaceans; environmental sex determination; genetic variation; juvenile hormone pathway; males; sexual dimorphism