Journal of Experimental Biology - Latest Issue

• The metabolic cost of producing joint moments is greater at the hip than at the ankle

  ABSTRACT

  Older adults walk using their hips relatively more and their ankles relatively less than young adults. This ‘distal-to-proximal redistribution’ in leg joint mechanics is thought to drive the age-related increase in metabolic rate during walking. However, many morphological differences between hip and ankle joints make it difficult to predict how, or whether, the distal-to-proximal redistribution affects metabolic rate during walking. To address this uncertainty, we compared the metabolic rate of participants while they repeatedly produced isolated hip and ankle moment cycles on a dynamometer following biofeedback. Overall, participants produced greater joint moments at their ankle versus hip and correspondingly activated their largest ankle extensor muscle more than their largest hip extensor muscle. Cycle average muscle activation across other hip and ankle extensors was nondifferent. Despite producing greater joint moments using slightly more relative muscle activation at the ankle, participants expended more net metabolic power while producing moments at the hip. Therefore, producing joint extension moments at the hip requires more metabolic energy than that at the ankle. Our results support the notion that the distal-to-proximal redistribution of joint mechanics contribute to greater metabolic rate during walking in older versus young adults.

• Nutritional stress in larvae induces adaptive responses that transcend generations in males of a model insect

  ABSTRACT

  The ability of organisms to cope with poor quality nutrition is essential for their persistence. For species with a short generation time, the nutritional environments can transcend generations, making it beneficial for adults to prime their offspring to particular diets. However, our understanding of adaptive generational responses, including those to diet quality, are still very limited. Here, we used the vinegar fly, Drosophila melanogaster, to investigate whether females developing as larvae on a nutritionally poor diet produce offspring that are primed for nutrient deficiencies in the following generations. We found that females developed on low-quality diets produced offspring that, on similarly low-quality diets, had both increased egg-to-adult viability and starvation tolerance compared with offspring of females experiencing a nutrient-rich diet. When testing the persistence of such generational priming, we found that just one generation of high-quality diet is sufficient to erase the signal of priming. A global transcriptomic profile analysis on male offspring suggests that the observed phenotypic priming is not a constitutive transcriptomic adjustment of adults; instead, offspring are probably primed as larvae, enabling them to initiate an adaptive response as adults when exposed to low-quality diets. Our results support that generational priming is an important adaptive mechanism that enables organisms to cope with transient nutritional fluctuations.

• Style shift makes walking harder as we get older

• Ecophysiological responses to heat waves in the marine intertidal zone

  ABSTRACT

  One notable consequence of climate change is an increase in the frequency, scale and severity of heat waves. Heat waves in terrestrial habitats (atmospheric heat waves, AHW) and marine habitats (marine heat waves, MHW) have received considerable attention as environmental forces that impact organisms, populations and whole ecosystems. Only one ecosystem, the intertidal zone, experiences both MHWs and AHWs. In this Review, we outline the range of responses that intertidal zone organisms exhibit in response to heat waves. We begin by examining the drivers of thermal maxima in intertidal zone ecosystems. We develop a simple model of intertidal zone daily maximum temperatures based on publicly available tide and solar radiation models, and compare it with logged, under-rock temperature data at an intertidal site. We then summarize experimental and ecological studies of how intertidal zone ecosystems and organisms respond to heat waves across dimensions of biotic response. Additional attention is paid to the impacts of extreme heat on cellular physiology, including oxidative stress responses to thermally induced mitochondrial overdrive and dysfunction. We examine the energetic consequences of these mechanisms and how they shift organismal traits, including growth, reproduction and immune function. We conclude by considering important future directions for improving studies of the impacts of heat waves on intertidal zone organisms.

• Taurine efflux counters the hydrodynamic impact of anaerobic metabolism to protect cardiorespiratory function under acute thermal stress in brook char ( Salvelinus fontinalis )

  ABSTRACT

  Upper thermal tolerance may be limited by convective oxygen transport in fish, but the mechanisms constraining heart function remain elusive. The activation of anaerobic metabolism imposes an osmotic stress on cardiomyocytes at high temperatures that must be countered to prevent swelling and cardiac dysfunction. We tested the hypothesis that cardiac taurine efflux is required to counter the osmotic impact of anaerobic end product accumulation in brook char, Salvelinus fontinalis. Fish were fed a diet enriched in β-alanine, a competitive inhibitor of the taurine transporter, to induce taurine deficiency and inhibit transporter function. In vivo, stroke volume increased by 60% and cardiac output doubled in control fish during a 2°C h⁻¹ thermal ramp. Stroke volume was temperature insensitive in taurine-deficient (TD) fish, so cardiac output was 30% lower at high temperatures. The thermal sensitivity of aerobic metabolism did not differ, and lactate accumulated to a similar degree in the two diet treatment groups, indicating that taurine deficiency does not impact energy metabolism. Heart taurine efflux was absent and ventricular muscle osmolality was 40 mOsmol kg⁻¹ higher in TD brook char following thermal stress. Swelling and decreased ventricular compliance likely impair diastolic filling to constrain stroke volume in TD fish. The adrenaline sensitivity of cardiac contractility and the regulation of intracellular pH in the brain and liver were also impacted in TD brook char. Taurine efflux appears necessary to counteract the hydrodynamic impact of activating anaerobic metabolism and this process may limit heart function under acute thermal stress.