Phenotypic plasticity of temperature induced Daphnia gene expression; experiment 1

This study measured the differential expression of genes from a single clonal Daphnia pulex isolate obtained from an eutrophic flooded opencast mine near Gräfenhain (Saxony, Germany) and has been kept in the laboratory since 2002. The daphniids (50 adult animals per batch) were raised in 3-L glass beakers under a 16 h:8 h L:D photoperiod. Three-quarter of the culture medium (M4) was renewed once a week, and the animals were equally fed ad libitum with algae (Desmodesmus subspicatus; SAG 53.80, Göttingen, Germany). Long-term-acclimated animals were kept at three different temperatures (i.e., 10 ± 0.5°C, 20 ± 0.3°C, and 24 ± 0.3°C) under normoxia (Po2 ≥ 20 kPa) for at least twelve weeks. Time-resolved experiments (acute heat stress) were carried out with long-term 20°C acclimated animals, which were exposed for three different time intervals (2, 4, and 8 h) to either 30 ± 0.2°C (test conditions) or 20 ± 0.3°C (control conditions). For this, 50 animals each were rapidly transferred with a sieve (mesh size: 1.2 mm) from 20°C-medium to a set of beakers containing 30°C-medium. As control, 50 animals each were transferred from 20°C-medium to another set of beakers with 20°C-medium. Only adult female animals with a body length of 2−2.5 mm (between the base of the apical spine and the anterior part of the head) and carrying parthenogenetic eggs and embryos were used for experiments. Animals were not fed during short-term exposures. During experiments, all animals were in good physical condition. After thermal acclimation or heat exposure, animals were transferred into 1.5-ml microcentrifuge tubes and shock-frozen in liquid nitrogen after removing adhering water with a tissue paper. Samples were short-term stored at -80°C. For all experimental conditions, four independent replicates (50 animals each) were analyzed. This GEO record is for the contrasts between animals conditioned to 10 degrees Celsius (condition 1) versus 20 degrees Celsius (condition 2), 10 degrees Celsius (condition 1) versus 24 degrees Celsius (condition 3), and 20 degrees Celsius (condition 2) versus 24 degrees Celsius (condition 3) We compared the gene expression patterns for condition 1 versus condition 2, condition 1 versus condition 3, and condition 2 versus condition 3 using four biological replicates for each condition, including balanced dye-swaps. All probes including random probes were quantile-normalized across chips, subarrays, samples and replicates.