Transcriptomic evidences of local thermal adaptation for the native fish Colossoma macropomum (Cuvier, 1818).

Brazil has five climatically distinct regions, with an annual average temperature difference up to 14 ºC between the northern and southern extremes. Environmental variation of this magnitude can lead to new genetic patterns among farmed fish populations. Genetically differentiated populations of tambaqui (Colossoma macropomum Cuvier, 1818), an important freshwater fish for Brazilian continental aquaculture, may be associated with regional adaptation. In this study, we selected tambaquis raised in two thermally distinct regions, belonging to different latitudes, to test this hypothesis. De novo transcriptome analysis was performed to compare the significant differences of genes expressed in the liver of juvenile tambaqui from a northern population (Balbina) and a southeastern population (Brumado). In total, 2,410 genes were differentially expressed (1,196 in Balbina and 1,214 in Brumado). Many of the genes are involved in a multitude of biological functions such as biosynthetic processes, homeostasis, biorhythm, immunity, cell signaling, ribosome biogenesis, modification of proteins, intracellular transport, structure/cytoskeleton, and catalytic activity. Enrichment analysis based on biological networks showed a different protein interaction profile for each population, whose encoding genes may play potential functions in local thermal adaptation of fish to their respective farming environments.

How will farmed populations of freshwater fish deal with the extreme climate scenario in 2100? Transcriptional responses of Colossoma macropomum from two Brazilian climate regions.

Tambaqui (Colossoma macropomum Cuvier, 1818) is an endemic fish of the Amazon and Orinoco basins, and it is the most economically important native species in Brazil being raised in five climatically distinct regions. In the face of current global warming, environmental variations in farm ponds represent additional challenges that may drive new adaptive regional genetic variations among broodstocks of tambaqui. In an experimental context based on the high-emission scenario of the 5th Intergovernmental Panel on Climate Change (IPCC) report, we used two farmed tambaqui populations to test this hypothesis. RNA-seq transcriptome analysis was performed in the liver of juvenile tambaqui from northern (Balbina Experimental Station, Balbina, AM) and southeastern (Brumado Fish Farming, Mogi Mirim, SP) Brazilian regions kept for 30 days in artificial environmental rooms mimicking the current and extreme climate scenarios. Three Illumina MiSeq runs produced close to 120 million 500 bp paired-end reads; 191,139 contigs were assembled with N50 = 1595. 355 genes were differentially expressed for both populations in response to the extreme scenario. After enrichment analysis, each population presented a core set of genes to cope with climate change. Northern fish induced genes related to the cellular response to stress, activation of MAPK activity, response to unfolded protein, protein metabolism and cellular response to DNA damage stimuli. Genes biologically involved in regulating cell proliferation, protein stabilisation and protein ubiquitination for degradation through the ubiquitin-proteasome system were downregulated. Genes associated with biological processes, including the cellular response to stress, MAPK cascade activation, homeostatic processes and positive regulation of immune responses were upregulated in southeastern fish. The downregulated genes were related to cytoskeleton organisation, energy metabolism, and the regulation of transcription and biological rhythms. Our findings reveal the signatures of promising candidate genes involved in the regional plasticity of each population of tambaqui in dealing with upcoming climate changes.