Widespread psychoactive pollutant augments daytime restfulness and disrupts diurnal activity rhythms in fish

Pharmaceutical pollution is a major driver of global change, with the capacity to alter key behavioural and physiological traits in exposed animals. Antidepressants are among the most commonly detected pharmaceuti-cals in the environment. Despite well-documented pharmacological effects of antidepressants on sleep in humans and other vertebrates, very little is known about their ecologically relevant impacts as pollutants on non-target wildlife. Accordingly, we investigated the effects of acute 3-day exposure of eastern mosquitofish (Gambusia holbrooki) to field-realistic levels (nominal concentrations: 30 and 300 ng/L) of the widespread psychoactive pollutant, fluoxetine, on diurnal activity patterns and restfulness, as indicators of disruptions to sleep. We show that exposure to fluoxetine disrupted diel activity patterns, which was driven by augmentation of daytime inactivity. Specifically, unexposed control fish were markedly diurnal, swimming farther during the day and exhibiting longer periods and more bouts of inactivity at night. However, in fluoxetine-exposed fish, this natural diel rhythm was eroded, with no differences in activity or restfulness observed between the day and night. As a misalignment in the circadian rhythm has been shown to adversely affect fecundity and lifespan in animals, our findings reveal a potentially serious threat to the survival and reproductive success of pollutant-exposed wildlife

No evidence that the widespread environmental contaminant caffeine alters energy balance or stress responses in fish

Anthropogenic sources of environmental pollution are ever-increasing as urban areas expand and more chemical compounds are used in daily life. The stimulant caffeine is one of the most consumed chemical compounds worldwide, and as a result, has been detected as an environmental contaminant in all types of major water sources on all continents. Exposure of wildlife to environmental pollutants can disrupt the energy balance of these organisms, as restoration of homeostasis is prioritised. In turn, energy allocated to other key biological processes such as growth or reproduction may be affected, consequently reducing the overall fitness of an individual. Therefore, we aimed to investigate if long-term exposure to environmentally relevant concentrations of caffeine had any energetic consequences on wildlife. Specifically, we exposed wild eastern mosquitofish (Gambusia holbrooki) to one of three nominal concentrations of caffeine (0, 100 and 10,000 ng/L) and assayed individuals for metabolic rate, general activity, antipredator and foraging behaviour and body size as measures of energy expenditure or energy intake. We found no differences in any measured traits between any of the given exposure treatments, indicating that exposure to caffeine at current environmental levels may not adversely affect the energy balance and fitness of vulnerable freshwater fish

Frontiers in quantifying wildlife behavioural responses to chemical pollution

Animal behaviour is remarkably sensitive to disruption by chemical pollution, with widespread implications for ecological and evolutionary processes in contaminated wildlife populations. However, conventional approaches applied to study the impacts of chemical pollutants on wildlife behaviour seldom address the complexity of natural environments in which contamination occurs. The aim of this review is to guide the rapidly developing field of behavioural ecotoxicology towards increased environmental realism, ecological complexity, and mechanistic understanding. We identify research areas in ecology that to date have been largely overlooked within behavioural ecotoxicology but which promise to yield valuable insights, including within- and among-individual variation, social networks and collective behaviour, and multi-stressor interactions. Further, we feature methodological and technological innovations that enable the collection of data on pollutant-induced behavioural changes at an unprecedented resolution and scale in the laboratory and the field. In an era of rapid environmental change, there is an urgent need to advance our understanding of the real-world impacts of chemical pollution on wildlife behaviour. This review therefore provides a roadmap of the major outstanding questions in behavioural ecotoxicology and highlights the need for increased cross-talk with other disciplines in order to find the answers

The origin and maintenance of metabolic allometry in animals

Organisms vary widely in size, from microbes weighing 0.1 pg to trees weighing thousands of megagrams - a 10-fold range similar to the difference in mass between an elephant and the Earth. Mass has a pervasive influence on biological processes, but the effect is usually non-proportional; for example, a tenfold increase in mass is typically accompanied by just a four- to sevenfold increase in metabolic rate. Understanding the cause of allometric scaling has been a long-standing problem in biology. Here, we examine the evolution of metabolic allometry in animals by linking microevolutionary processes to macroevolutionary patterns. We show that the genetic correlation between mass and metabolic rate is strong and positive in insects, birds and mammals. We then use these data to simulate the macroevolution of mass and metabolic rate, and show that the interspecific relationship between these traits in animals is consistent with evolution under persistent multivariate selection on mass and metabolic rate over long periods of time

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

The interactive effects of ultraviolet-B radiation and other environmental stressors on amphibians

The phenomenon of global amphibian declines is a testament to the profound effects of human-induced global change on natural environments. With amphibians being the most threatened of all vertebrate taxa, and also important bioindicators of environmental health, understanding the causes of their declines is critical for their conservation, and possibly the conservation of other species. While research over the past two decades has identified a range of potential causative agents, it has become widely accepted that amphibian declines are likely to be a result of complex interactions between multiple environmental stressors that lead to compounding negative effects. The overarching aim of this thesis was to examine the interactive effects of ultraviolet-B radiation (UVBR) and other environmental stressors (predation and temperature) on the early life stages of a model amphibian species, the striped marsh frog Limnodynastes peronii. UVBR is highly damaging to living organisms and has increased globally as a consequence of stratospheric ozone depletion. The coincident timing of the beginning of stratospheric ozone depletion and the beginning of rapid amphibian declines in the late 1970s and early 1980s prompted interest in increased environmental UVBR as a potential contributor to amphibian declines with numerous studies showing that exposure to UVBR is detrimental to amphibians. UVBR has also been shown to interact synergistically with other environmental stressors, including a range of contaminants, aquatic acidification, low temperature, and infectious disease, such that the effect of the stressors combined is greater than that caused by the additive effects of the stressors independently. With the rapid disappearance of amphibian populations from seemingly pristine habitats around the world, understanding how UVBR interacts with natural stressors, such as predation and temperature, is particularly important given that anthropogenic stressors, such as contaminants, may have less of an impact in these habitats. The first specific aim of this thesis was to examine the independent and interactive effects of UVBR and predation stress in the form of predatory chemical cues (PCC) on L. peronii tadpole survival and morphology (Chapter 2). Using a controlled laboratory experiment the following questions were addressed: (1) do UVBR and PCC interact synergistically to enhance the mortality of tadpoles above the additive effects of the stressors independently?; and (2), does exposure to UVBR affect the ability of tadpoles to morphologically respond to PCC? UVBR and PCC were found to interact synergistically to enhance the mortality of L. peronii tadpoles by nearly two-fold above the additive mortality caused by the stressors independently. Exposure to UVBR was also found to suppress the development of predator-induced morphological defences. Specifically, tadpoles simultaneously exposed to UVBR and PCC did not develop the deep tail that was expressed by tadpoles exposed to PCC alone. A deep tail is a prominent feature of tadpoles exposed to predators and is strongly associated with increased tadpole survival in the presence of predators, thus the lack of a deep tail in tadpoles exposed to UVBR and PCC has implications for their fitness in a predator environment. The fitness consequences of UVBR-induced sublethal effects is poorly studied, thus the second specific aim of this thesis was to examine the independent and interactive effects of UVBR and PCC on a suite of traits of L. peronii embryos and tadpoles (embryonic hatching success and hatching time, post-hatch tadpole survival, size, morphology, behaviour, and locomotor performance), and assess tadpole survival time in a predator environment to evaluate the potential fitness consequences (Chapter 3). Exposure to a 3−6% increase in UVBR, which is comparable to changes in terrestrial UVBR associated with ozone depletion, was found to have no effect on any of the traits measured, except survival time in a predator environment, which was reduced by 22−28%. Exposure to PCC caused tadpoles to hatch earlier, have reduced hatching success, have improved locomotor performance, and survive for longer in a predator environment, but had no effect on tadpole survival, behaviour or morphology. Unlike the findings in Chapter 2, simultaneous exposure to UVBR and PCC resulted in no interactive effects. These findings demonstrate that increased UVBR has the potential to reduce tadpole fitness by compromising their ability to survive encounters with predators, though critically such an effect might not be detectable via some performance measures, such as locomotor performance, which was not altered by exposure to an increase in UVBR. Exposure to PCC, on the other hand, improves tadpole locomotor performance and fitness, which suggests that an increase in locomotor performance does confer some benefit to survival in a predator environment as one would expect, but with regard to the effects of UVBR, there are clearly additional factors that need to be considered when investigating predator-prey interactions. The third specific aim of this thesis was to evaluate the energetic costs associated with being exposed to UVBR, both alone and in combination with PCC (Chapter 4), in order to understand the physiological basis for the observed negative synergistic effect on tadpole survival in Chapter 2. While several studies have examined the lethal and sublethal effects of UVBR, alone and in combination with other environmental stressors, on amphibians, few have considered how UVBR affects amphibian metabolism, or how amphibian metabolism may change in response to exposure to other stressors in addition to UVBR. Using a controlled laboratory experiment, the independent and interactive effects of UVBR and PCC on the tissue and whole-animal metabolic rate (MR) and activity of L. peronii tadpoles were examined. Exposure to UVBR caused tissue MR to increase by 36%, but whole-animal MR to decrease by 14%, which is most likely due to tadpoles reducing their activity levels by 56%. Exposure to PCC had no significant effect on tissue or whole-animal MR, but caused tadpoles to reduce their activity levels by 36%, indicating that the whole-animal MR of tadpoles exposed to PCC is elevated relative to their activity levels. Compared to tadpoles exposed to neither stressor, tadpoles exposed simultaneously to UVBR and PCC showed no change in whole-animal MR despite reducing their activity levels by 62%. These findings show that, for tadpoles, there is an energetic cost associated with being exposed to UVBR and PCC independently, and that this cost is greater when they are exposed to both stressors simultaneously. The synergistic negative effect of UVBR and PCC on tadpole survival found in Chapter 2 is therefore likely to arise as a consequence of the effect of these combined stressors on metabolic rate. The fifth and final aim of this thesis was to examine the thermal-dependence of UVBR effects in the context of an ecologically-relevant fluctuating UVBR and temperature regime to evaluate whether exposure to peak UVBR levels while the temperature is high (35°C) is more detrimental to pre-metamorphic L. peronii than exposure to peak UVBR levels while the temperature is moderate (25°C) (Chapter 5). This was examined by measuring embryonic hatching success and hatching time, post-hatch tadpole survival, size, morphology, locomotor performance, and survival time in a predator environment. Embryos exposed to peak UVBR levels at 35°C hatched 10 h later than those exposed to peak UVBR levels at 25°C, and as tadpoles, were smaller and consequently swam slower, but in a predator environment exhibited no difference in survival time. There was also no effect of experimental treatment on the hatching success of embryos, nor on the post-hatch survival of tadpoles. These findings, therefore, are not sufficiently strong to support the hypothesis that high temperatures enhance the negative effects of UVBR in pre-metamorphic amphibians. The results from these studies reveal that multiple stressors can interact in ways that are not necessarily predictable from single-factor studies, and that examination of the effects of UVBR in the absence of other ecologically-relevant environment stressors potentially underestimates the impact of UVBR on amphibian populations in natural systems. Researchers in amphibian conservation biology should therefore continue to utilise a multi-factorial experimental approach if we are to gain a comprehensive understanding of the stressors and mechanisms responsible for causing global amphibian declines

Do high temperatures enhance the negative effects of ultraviolet-B radiation in embryonic and larval amphibians?

For the embryos and tadpoles of amphibian species, exposure to ultraviolet-B radiation (UVBR) can be lethal, or cause a variety of sublethal effects. Low temperatures enhance the detrimental effects of UVBR and this is most likely because the enzyme-mediated processes involved in the repair of UVBR-induced damage function less effectively at low temperatures. Whether these repair processes are also impaired, and thus the negative effects of UVBR similarly enhanced, at high temperatures is not known, but is an ecologically relevant question to ask given that organisms that inhabit environments where the temperature fluctuates widely on a daily timescale are likely to experience high doses of UVBR when temperatures are high. Here we examined the thermal-dependence of UVBR effects in the context of an ecologically-relevant fluctuating UVBR and temperature regime to test the hypothesis that exposure to peak UVBR levels while the temperature is high (35 degrees C) is more detrimental to embryonic and larval Limnodynastes peronii than exposure to peak UVBR levels while the temperature is moderate (25 degrees C). Embryos exposed to peak UVBR levels at 35 degrees C hatched 10 h later than those exposed to peak UVBR levels at 25 degrees C and, as tadpoles, were smaller and consequently swam more slowly but, in an environment with predators, exhibited no difference in survival time. There was also no effect of experimental treatment on the hatching success of embryos, nor on the post-hatch survival of tadpoles. These findings, therefore, are not sufficiently strong to support our hypothesis that high temperatures enhance the negative effects of UVBR in embryonic and larval amphibians. (C) 2012. Published by The Company of Biologists Ltd