Biology subjects

Norin, T.

Publications and source records attributed to Norin, T..

3 recordsLinked to original sources

bioRxiv2021

Fast ontogenetic growth drives steep evolutionary scaling of metabolic rate

Metabolic rate (MR) changes with body mass (BM) as MR = aBMb, where a is a normalisation constant (log-log intercept) and b the scaling exponent (log-log slope). This scaling relationship is fundamental to biology and widely applied, yet a century of research has provided little consensus on why and how steeply metabolic rate scales with body mass. I here show that ontogenetic (within-individual) b can be strongly and positively related to growth rates of juvenile fish when food availability is naturally restricted, with fast growing individuals having steep and near-isometric metabolic scaling (b {approx} 1). I suggest that the steep evolutionary (among-species) scaling also found for fishes (b also approaching 1) is a by-product of natural selection for these fast growing individuals early in ontogeny, and that a weaker relationship between metabolic scaling and growth later in life causes variation in b at lower taxonomic levels (within orders or species). I support these ideas by showing that b within fish orders is linked to natural mortality rates of fish larvae.

ecology↗

bioRxiv2021

Metazoans, migrations, and the ocean's biological carbon pump

The daily vertical migrations of fish and other metazoans actively transport organic carbon from the ocean surface to depth, contributing to the biological carbon pump. We use an oxygen-constrained, game-theoretic food-web model to simulate diel vertical migrations and estimate global carbon fluxes and sequestration by fish and zooplankton due to respiration, fecal pellets, and deadfalls. Our model provides estimates of the carbon export and sequestration potential for a range of pelagic functional groups, despite uncertain biomass estimates of some functional groups. While the export production of metazoans and fish is modest (~20% of global total), we estimate that their contribution to carbon sequestered by the biological pump (~ 800 PgC) is conservatively more than 50% of the estimated global total (~1300 PgC) and have a significantly longer sequestration time scale (~250 years) than previously reported for other components of the biological pump. Fish and multicellular zooplankton contribute about equally to this sequestered carbon pool. This essential ecosystem service could be at risk from both unregulated fishing on the high seas and ocean deoxygenation due to climate change.

ecology↗

bioRxiv2019

Brain cooling marginally increases maximum thermal tolerance in Atlantic cod

The physiological mechanisms determining thermal limits in fishes are debated but remain elusive. It has been hypothesised that loss of motor function observed as a loss of equilibrium during an acute thermal challenge is due to direct thermal effects on brain neuronal function. To test this hypothesis, we mounted cooling plates on the head of Atlantic cod (Gadus morhua) and quantified whether local cooling of the brain increased whole-organism critical thermal maxima (CTmax). Brain cooling reduced brain temperature by 2-6{degrees}C and increased CTmax by 0.5-0.7{degrees}C relative to instrumented and uninstrumented controls, suggesting that direct thermal effects on brain neurons might contribute to setting upper thermal limits in fish. However, the improvement in CTmax with brain cooling was small relative to the difference in brain temperature, demonstrating that other mechanisms (e.g., failure of spinal and peripheral neurons, or muscle) may also contribute to controlling acute thermal tolerance in fishes.\n\nSummary statementWe tested whether brain temperature sets the upper thermal limit in a fish. Selectively cooling the brain during whole-organism thermal ramping marginally increased thermal tolerance.

physiology↗