Ocean warming combined with lower omega-3 nutritional availability impairs the cardio-respiratory function of a marine fish

Abstract

Highly unsaturated fatty acids of the omega-3 series (HUFA) are major constituents of cell membranes, yet are poorly synthesised de novo by consumers. Their production, mainly supported by aquatic microalgae, has been decreasing with global change. The consequences of such reductions may be profound for ectotherm consumers, as temperature tightly regulates the HUFA content in cell membranes, maintaining their functionality. Integrating individual, tissue and molecular approaches, we examined the consequences of the combined effects of temperature and HUFA depletion on the key cardio-respiratory functions of the golden grey mullet, an ectotherm grazer of high ecological importance. For 4 months, fish were exposed to two contrasting HUFA diets [4.8% eicosapentaenoic acid (EPA)+docosahexaenoic acid (DHA) on dry matter (DM) versus 0.2% EPA+DHA on DM] at 12 and 20°C. Ventricular force development coupled with gene expression profiles measured on cardiac muscle suggest that combining HUFA depletion with warmer temperatures leads to: (1) a proliferation of sarcolemmal and sarcoplasmic reticulum Ca 2+ channels and (2) a higher force-generating ability by increasing extracellular Ca 2+ influx via sarcolemmal channels when the heart has to sustain excessive effort due to stress and/or exercise. At the individual scale, these responses were associated with a greater aerobic scope, maximum metabolic rate and net cost of locomotion, suggesting the higher energy cost of this strategy. This impaired cardiac performance could have wider consequences for other physiological performance such as growth, reproduction or migration, all of which greatly depend on heart function.

Unorthodox features in two venerid bivalves with doubly uniparental inheritance of mitochondria

“…We used these two cleaned contigs as reference genomes to map Illumina 2 × 150 bp HiSeq sequences (data quality control and pre-processing step as in 78 ) produced from a second individual using Pilon 1.21 79 . HiSeq sequencing of cDNA was performed based on mRNAs purified from sperm and foot tissue (for mapping onto the male and female mitogenomes, respectively) using the Macherey-Nagel Nucleospin RNA kit for NucleoZOL (RNA quality control, cDNA synthesis, library preparation, sequencing, data quality control and pre-processing as in 80 ). By mapping high-quality Illumina reads on our draft nanopore contigs, we were able to further correct sequencing errors.…”

Diet mediates thermal performance traits: implications for marine ectotherms

“…While it was not within the scope of this study, other important performance traits may have differed between the diet treatments. These include, but are not limited to, differences in Journal of Experimental Biology • Accepted manuscript microbiome diversity and function, visual acuity, cognitive ability, digestion efficiency and digestive costs relative to aerobic scope, immune function, aerobic swimming performance, and cardiac stroke volume (Glencross and Rutherford, 2010;Koven et al, 2018;Vagner et al, 2014Vagner et al, , 2019b. It remains unclear whether opaleye and other omnivorous ectotherms consume different proportions of plant: animal to regulate their thermal responses.…”

Cardiac mitochondrial function, nitric oxide sensitivity and lipid composition following hypoxia acclimation in sablefish

“…Chung et al (2018) recently reported that changes in phospholipid FA composition are the primary signature of thermal acclimation in killifish (Fundulus heteroclitus) and that these changes are linked to hepatic mitochondrial performance. Furthermore, Vagner et al (2019) showed that the highly unsaturated fatty acid (HUFA) content of cell membranes, which is known to be tightly regulated by temperature (Pethybridge et al, 2015), influences the cardiorespiratory function of marine fishes. Yet, the effect of hypoxia acclimation on mitochondrial membrane FA composition and fluidity in fishes, and thus on mitochondrial function and performance, have also not been examined.…”