Transcriptomic analysis dissects the mechanistic insight into the Daphnia clonal variation in tolerance to toxic Microcystis

Abstract

Cyanobacteria have become more prevalent than other phytoplankton in freshwater assemblages during summer. In such conditions, cyanobacterial traits may reduce zooplankton fitness and the energy flow efficiency from primary producers to aquatic herbivores. Cladocerans, as the dominant zooplankton grazers in freshwater ecosystems, exhibit clonal variation in their tolerance to cyanobacteria with an increasing gradient in eutrophication history. Hitherto, research on the full modes of action (MoAs) of Daphnia clonal differences in tolerance to toxic Microcystis still remains in its infancy. We conducted fitness and transcriptome analyses on two Daphnia clones, clone TH09 and TH14. A significant decline in body growth rate was detected in the sensitive clone TH09 compared with the tolerant clone TH14 at the presence of toxic Microcystis. Furthermore, transcriptional analysis indicated that major MoAs such as glutathione metabolism, protein processing in endoplasmic reticulum, amino sugar/nucleotide sugar metabolism, and arachidonic acid metabolism were linked to the tolerance fitness in Daphnia similoides. These results provided mechanistic insights into the pathways of genetic and biological processes involved in cyanobacteria tolerance in the Daphnia clonal variation, and propose that the genetic architecture of this fitness‐related trait would be helpful to clarify how zooplankton clones adapt to harmful algal blooms.

The genetic and ecophysiological diversity of Microcystis

“…Exposure of Daphnia to Microcystis can result in varying outcomes, which are dependent both on Daphnia and Microcystis genotypes (Lemaire et al, 2012;Chislock et al, 2013). Many clones of Daphnia found in eutrophic systems can detoxify microcystin (Lyu et al, 2019) and readily feed on Microcystis along with other phytoplankton without harm (Chislock et al, 2013). In contrast, calanoid copepods, not tolerant of microcystin, selectively reject Microcystis with high microcystin content (Ger et al, 2016(Ger et al, , 2019, thereby potentially promoting Microcystis dominance.…”

Environmentally-induced DNA methylation is inherited across generations in an aquatic keystone species (Daphnia magna)

“…Three of these studies used microcystin as stressor [35][36][37], two used zinc [38,39], and one used temperature [40]. Between 6% and 15% of the key genes differentially expressed in response to microcystin, zinc, or temperature as stressor are highly functionally similar to genes identified as differentially methylated in our data, though gene identity was not identical (Tables S13 and S14).…”

Transcriptomic response of Daphnia magna to nitrogen‐ or phosphorus‐limited diet

“…Differentially expressed genes (DEGs) were estimated using “edgeR” in the “Bioconductor” package in R (v 3.4.1; Robinson et al., 2010 ). Gene showing |log 2 (fold change)| > 1 and p ‐value < .05 (quasilikelihood F test) at any of the two comparison groups with triplicated gene expression data (N‐limitation vs. normal and P‐limitation vs. normal) was defined as DEG (Lyu et al., 2019 ). DEGs were further annotated by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) using DIAMOND (v0.9.21.122) with the following parameters: blastp; k parameter = 1; e ‐value = 10 –7 (Buchfink et al., 2015 ).…”

“…The qPCR followed an initial hold at 50℃ for 2 min and 95℃ for 10 min followed by 45 cycles of 95℃ for 15 s and 60℃ for 1 min. The relative abundances of genes were calculated by a 2 −ΔΔCt method, with β‐actin as an internal control (Lyu et al., 2019 ).…”

“…normal) was defined as DEG (Lyu et al, 2019). DEGs were further annotated by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) using DIAMOND (v0.9.21.122) with the following parameters: blastp; k parameter = 1; e-value = 10 -7 (Buchfink et al, 2015).…”