Increased physical activity does not improve obesity-induced decreases in muscle quality in zebrafish (Danio rerio)

Obesity has a negative effect on muscle contractile function, and the effects of obesity are not reversed by weight loss. It is therefore important to determine how muscle function can be restored, and exercise is the most promising approach. We tested the hypothesis (in zebrafish, Danio rerio) that moderate aerobic exercise (forced swimming for 30 min per day, raising metabolic rates to at least twice resting levels) will alleviate the negative effects of obesity of muscle function. We allocated zebrafish randomly to experimental treatments in a fully factorial design with diet treatment (three levels: lean control, diet-induced obese, obese followed by weigh loss [obese-lean]), and exercise (exercise and sedentary control) as independent factors. Treatments were conducted for 10 weeks, and we measured locomotor performance, isolated muscle mechanics, and myosin heavy chain composition. Obesity led to decreased muscle force production per unit area (p = 0.01), and slowed muscle contraction (p = 0.004) and relaxation rates (p = 0.02). These effects were not reversible by weight loss or exercise. However, at the level implemented in our experimental animals, neither diet nor exercise affected swimming performance or myosin heavy chain concentrations. The moderate levels of exercise we implemented therefore are not sufficient to reverse the effects of obesity on muscle function, and higher intensity or a combination of modes of exercise may be necessary to improve muscle quality during obesity and following weight loss.Funding provided by: Australian Research CouncilCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100000923Award Number: DP18010303

Physiology can predict animal activity, exploration, and dispersal

Physiology can underlie movement, including short-term activity, exploration of unfamiliar environments, and larger scale dispersal, and thereby influence species distributions in an environmentally sensitive manner. We conducted meta-analyses of the literature to establish, firstly, whether physiological traits underlie activity, exploration, and dispersal by individuals (88 studies), and secondly whether physiological characteristics differed between range core and edges of distributions (43 studies). We show that locomotor performance and metabolism influenced individual movement with varying levels of confidence. Range edges differed from cores in traits that may be associated with dispersal success, including metabolism, locomotor performance, corticosterone levels, and immunity, and differences increased with increasing time since separation. Physiological effects were particularly pronounced in birds and amphibians, but taxon-specific differences may reflect biased sampling in the literature, which also focussed primarily on North America, Europe, and Australia. Hence, physiology can influence movement, but undersampling and bias currently limits general conclusions

Low Levels of Physical Activity Increase Metabolic Responsiveness to Cold in a Rat (Rattus fuscipes)

Physical activity modulates expression of metabolic genes and may therefore be a prerequisite for metabolic responses to environmental stimuli. However, the extent to which exercise interacts with environmental conditions to modulate metabolism is unresolved. Hence, we tested the hypothesis that even low levels of physical activity are beneficial by improving metabolic responsiveness to temperatures below the thermal neutral zone, thereby increasing the capacity for substrate oxidation and energy expenditure.We used wild rats (Rattus fuscipes) to avoid potential effects of breeding on physiological phenotypes. Exercise acclimation (for 30 min/day on 5 days/week for 30 days at 60% of maximal performance) at 22°C increased mRNA concentrations of PGC1α, PPARδ, and NRF-1 in skeletal muscle and brown adipose tissue compared to sedentary animals. Lowering ambient temperature to 12°C caused further increases in relative expression of NRF-1 in skeletal muscle, and of PPARδ of brown adipose tissue. Surprisingly, relative expression of UCP1 increased only when both exercise and cold stimuli were present. Importantly, in sedentary animals cold acclimation (12°C) alone did not change any of the above variables. Similarly, cold alone did not increase maximum capacity for substrate oxidation in mitochondria (cytochrome c oxidase and citrate synthase activities) of either muscle or brown adipose tissue. Animals that exercised regularly had higher exercise induced metabolic rates in colder environments than sedentary rats, and temperature induced metabolic scope was greater in exercised rats.Physical activity is a necessary prerequisite for the expression of transcriptional regulators that influence a broad range of physiological functions from energy metabolism to cardiovascular function and nutrient uptake. A sedentary lifestyle leads to decreased daily energy expenditure because of a lack of direct use of energy and a muted metabolic response to ambient temperature, which can be reversed even by low levels of physical activity

Social Interactions Compromise Thermoregulation in Crocodiles Crocodylus johnstoni and Crocodylus porosus

Observations of aggressive encounters between crocodiles in the field showed that intraspecific aggression compromised thermoregulation by subordinate animals. Intraspecific aggression may thus trigger a physiological mechanism for dispersal in crocodiles. We measured body temperature (T_b) and environmental variables concurrently with behavioural observations in wild Crocodylus johnsioni, and Crocodylus porosus free-ranging in captivity. Average daily T_b of crocodiles of both species subordinate in aggressive encounters was significantly lower than when animals were undisturbed. Chased C. johnstoni entered the water at significantly lower Tb after basking than when they retreated voluntarily. However, T_b was most severely affected by longer term changes in patterns of behaviour: when chased from their basking site, C. johnstoni remained mostly submerged for at least 2 h. In contrast, undisturbed crocodiles re-emerged to bask within 2 h of entering the water after a previous basking episode. This long-term difference in behaviour resulted in chased crocodiles experiencing significantly lower operative temperature compared to undisturbed animals. Mathematical simulations show that average daily Tb of chased crocodiles may be up to 6 degrees C below that of undisturbed animals. Intraspecific aggression may compromise individual crocodiles' physiological performance and even their fitness unless they disperse to less contested areas

Crocodilian Thermal Relations

Sinusoidal daily and seasonal patterns of change in body temperature (Tb) measured at 15 degrees S latitude in 30-1,000 kg Crocodylus porosus are explicable by comparatively simple mathematical equations into which are fed only behaviour pattern, environmental data and body mass. This confirms that C. porosus and, by implication, other crocodilians in this size range, are simple ectotherms in which endogenous heat production, changes in regional blood flow and mouth gaping are insignificant influences on core temperature. Daily patterns of T_b in Crocodylus johnstoni at 17 degrees S latitude, up to about 20 kg, are more similar to patterns typical of heliothermic reptiles, having a daily preferred T_b range which is achieved by shuttling between basking sites and the water. The preferred T_b range cycled with season in this species, suggesting thermal metabolic acclimatization. Competition for basking sites may prevent lesser status animals from achieving preferred Tb, and this must have significant implications for individual success in the population. Hysteresis of heating and cooling rates is known to occur in C. johnstoni and all other crocodilians in this size range examined so far, and is likely to augment behavioural thermoregulation under field conditions. Amphibious habits and the pronounced daily and seasonal cycles in operative temperatures give crocodilians many options for behaviourally modifying T_b. The options and, hence, the behaviours seen, are vastly different in small and large animals. Small individuals, despite being able to thermoregulate within a preferred range during sunny days, will inevitably face large daily cycles in T_b, even though they live in tropical habitats. This means that most crocodilians conduct most of their lives at temperatures away from their preferred ranges and are well able to hunt prey and be active over a wider range of Tb. Only large individuals, more than perhaps 500 kg, are able to be essentially thermostable (plus or minus 1-2 degrees C) throughout the day and night, but even individuals of 1,000 kg show significant seasonal cycles in T_b. The extent to which these generalizations apply across most crocodilians is unknown, but what data there are from other species suggest that similar patterns probably prevail. Alligatoridae have a wider latitudinal and climatic range than Crocodylidae and this, along with their capacity to tolerate cooler conditions, needs further exploration

The effect of heat transfer mode on heart rate responses and hysteresis during heating and cooling in the estuarine crocodile Crocodylus porosus

The effect of heating and cooling on heart rate in the estuarine crocodile Crocodylus porosus was studied in response to different heat transfer mechanisms and heat loads. Three heating treatments were investigated. C. porosus were: (1) exposed to a radiant heat source under dry conditions; (2) heated via radiant energy while half-submerged in flowing water at 23degreesC and (3) heated via convective transfer by increasing water temperature from 23degreesC to 35degreesC. Cooling was achieved in all treatments by removing the heat source and with C. porosus half-submerged in flowing water at 23degreesC. In all treatments, the heart rate of C. porosus increased markedly in response to heating and decreased rapidly with the removal of the heat source. Heart rate during heating was significantly faster than during cooling at any given body temperature, i.e. there was a significant heart rate hysteresis. There were two identifiable responses to heating and cooling. During the initial stages of applying or removing the heat source, there was a dramatic increase or decrease in heart rate ('rapid response'), respectively, indicating a possible cardiac reflex. This rapid change in heart rate with only a small change or no change in body temperature

Morphological differences between habitats are associated with physiological and behavioural trade-offs in stickleback (Gasterosteus aculeatus)

F.S. and A.J.W.W. were supported by the Australian Research Council, M.M.W. was supported by The University of St Andrews and R.S.J. and J.T. were supported by Coventry UniversityLocal specialization can be advantageous for individuals and may increase the resilience of the species to environmental change. However, there may be trade-offs between morphological responses and physiological performance and behaviour. Our aim was to test whether habitat-specific morphology of stickleback (Gasterosteus aculeatus) interacts with physiological performance and behaviour at different salinities. We rejected the hypothesis that deeper body shape of fish from habitats with high predation pressure led to decreases in locomotor performance. However, there was a trade-off between deeper body shape and muscle quality. Muscle of deeper-bodied fish produced less force than that of shallow-bodied saltmarsh fish. Nonetheless, saltmarsh fish had lower swimming performance, presumably because of lower muscle mass overall coupled with smaller caudal peduncles and larger heads. Saltmarsh fish performed better in saline water (20 ppt) relative to freshwater and relative to fish from freshwater habitats. However, exposure to salinity affected shoaling behaviour of fish from all habitats and shoals moved faster and closer together compared with freshwater. We show that habitat modification can alter phenotypes of native species, but local morphological specialization is associated with trade-offs that may reduce its benefits.Publisher PDFPeer reviewe

Living in flowing water increases resistance to ultraviolet B radiation

Ultraviolet B radiation (UV-B) is an important environmental driver that can affect locomotor performance negatively by inducing production of reactive oxygen species (ROS). Prolonged regular exercise increases antioxidant activities, which may alleviate the negative effects of UV-B-induced ROS. Animals naturally performing exercise, such as humans performing regular exercise or fish living in flowing water, may therefore be more resilient to the negative effects of UV-B. We tested this hypothesis in a fully factorial experiment, where we exposed mosquitofish (Gambusia holbrooki) to UV-B and control (no UV-B) conditions in flowing and still water. We show that fish exposed to UV-B and kept in flowing water had increased sustained swimming performance (U-crit), increased antioxidant defences (catalase activity and glutathione concentrations) and reduced cellular damage (lipid peroxidation and protein carbonyl concentrations) compared with fish in still water. There was no effect of UV-B or water flow on resting or maximal rates of oxygen consumption. Our results show that environmental water flow can alleviate the negative effects of UV-Binduced ROS by increasing defence mechanisms. The resultant reduction in ROS-induced damage may contribute to maintain locomotor performance. Hence, the benefits of regular exercise are `transferred' to improve resilience to the negative impacts of UV-B. Ecologically, the mechanistic link between responses to different habitat characteristics can determine the success of animals. These dynamics have important ecological connotations when river or stream flow changes as a result of weather patterns, climate or human modifications