By 2100, greenhouse gases are predicted to reduce ozone and cloud cover over the tropics causing increased exposure of organisms to harmful ultraviolet-B radiation (UVBR). UVBR damages DNA and is an ...important modulator of immune function and disease susceptibility in humans and other vertebrates. The effect of UVBR on invertebrate immune function is largely unknown, but UVBR together with ultraviolet-A radiation impairs an insect immune response that utilizes melanin, a pigment that also protects against UVBR-induced DNA damage. If UVBR weakens insect immunity, then it may make insect disease vectors more susceptible to infection with pathogens of socioeconomic and public health importance. In the tropics, where UVBR is predicted to increase, the mosquito-borne dengue virus (DENV), is prevalent and a growing threat to humans. We therefore examined the effect of UVBR on the mosquito Aedes aegypti, the primary vector for DENV, to better understand the potential implications of increased tropical UVBR for mosquito-borne disease risk. We found that exposure to a UVBR dose that caused significant larval mortality approximately doubled the probability that surviving females would become infected with DENV, despite this UVBR dose having no effect on the expression of an effector gene involved in antiviral immunity. We also found that females exposed to a lower UVBR dose were more likely to have low fecundity even though this UVBR dose had no effect on larval size or activity, pupal cuticular melanin content, or adult mass, metabolic rate, or flight capacity. We conclude that future increases in tropical UVBR associated with anthropogenic global change may have the benefit of reducing mosquito-borne disease risk for humans by reducing mosquito fitness, but this benefit may be eroded if it also makes mosquitoes more likely to be infected with deadly pathogens.
•Contamination of the environment with agricultural pollutants is a major problem.•We tested for impacts of the endocrine disruptor 17β-trenbolone on tadpoles.•Exposure did not impact tadpole ...growth.•Nor did it effect antipredator response, anxiety-like behaviour, or foraging.
Pollutants, such as endocrine disrupting chemicals (EDCs), are increasingly being detected in organisms and ecosystems globally. Agricultural activities, including the use of hormonal growth promotants (HGPs), are a major source of EDC contamination. One potent EDC that enters into the environment through the use of HGPs is 17β-trenbolone. Despite EDCs being repeatedly shown to affect reproduction and development, comparatively little is known regarding their effects on behaviour. Amphibians, one of the most imperilled vertebrate taxa globally, are at particular risk of exposure to such pollutants as they often live and breed near agricultural operations. Yet, no previous research on amphibians has explored the effects of 17β-trenbolone exposure on foraging or antipredator behaviour, both of which are key fitness-related behavioural traits. Accordingly, we investigated the impacts of 28-day exposure to two environmentally realistic concentrations of 17β-trenbolone (average measured concentrations: 10 and 66 ng/L) on the behaviour and growth of spotted marsh frog tadpoles (Limnodynastes tasmaniensis). Contrary to our predictions, there was no significant effect of 17β-trenbolone exposure on tadpole growth, antipredator response, anxiety-like behaviour, or foraging. We hypothesise that the differences in effects found between this study and those conducted on fish may be due to taxonomic differences and/or the life stage of the animals used, and suggest further research is needed to investigate the potential for delayed manifestation of the effects of 17β-trenbolone exposure.
Metabolic cold adaptation, or Krogh's rule, is the controversial hypothesis that predicts a monotonically negative relationship between metabolic rate and environmental temperature for ectotherms ...living along thermal clines measured at a common temperature. Macrophysiological patterns consistent with Krogh's rule are not always evident in nature, and experimentally evolved responses to temperature have failed to replicate such patterns. Hence, temperature may not be the sole driver of observed variation in metabolic rate. We tested the hypothesis that temperature, as a driver of energy demand, interacts with nutrition, a driver of energy supply, to shape the evolution of metabolic rate to produce a pattern resembling Krogh's rule. To do this, we evolved replicate lines of
at 18, 25 or 28°C on control, low-calorie or low-protein diets. Contrary to our prediction, we observed no effect of nutrition, alone or interacting with temperature, on adult female and male metabolic rates. Moreover, support for Krogh's rule was only in females at lower temperatures. We, therefore, hypothesize that observed variation in metabolic rate along environmental clines arises from the metabolic consequences of environment-specific life-history optimization, rather than because of the direct effect of temperature on metabolic rate. This article is part of the theme issue 'The evolutionary significance of variation in metabolic rates'.
The current policy has the world on track to experience around 3°C of warming by 2100. The responses of organisms to our warming world will be mediated by changes in physiological processes, ...including metabolic rate. Metabolic rate represents the energetic cost of living, and is fundamental to understanding the energy required to sustain populations. Current evidence indicates that animals have a limited capacity to adapt to warmer environments by reducing their metabolic rate. Consequently, animals may be more reliant on metabolic plasticity to ameliorate the thermodynamic effect of rising temperatures on physiological rates. However, metabolic plasticity is influenced by other environmental factors, including the nutritional quality of food. Elevated levels of atmospheric CO2 are expected to reduce the protein and increase the carbohydrate concentration in plants, but we do not know how this will affect the response of metabolic rate to climate warming.
Here we test the interactive effects of developmental dietary protein and carbohydrate concentrations on the metabolic plasticity of adult Drosophila melanogaster in response to a 3°C increase in temperature while accounting for variation associated with body mass and activity (resting metabolic rate).
We show that the thermal sensitivity of resting metabolic rate is modulated by developmental nutrition with animals reared on nutritionally poor, low‐protein diets showing the greatest increase in resting metabolic rate in response to simulated climate warming. We also show that if the nutritional quality of resources is unaffected by climate change, then temperature‐induced increases in resting metabolic rate will be offset by decreases in mass, but the absolute energy requirements of animals will be elevated relative to current conditions despite this. If, on the other hand, temperatures rise and resources become more calorie‐dense and carbohydrate‐rich, then the resting metabolic rate of animals will remain relatively unchanged, but decreases in mass and activity may drive down the absolute energy requirements of animals.
In the absence of evolutionary adaptation, these findings suggest that the combined plastic response of physiological, morphological and behavioural traits to temperature and nutrition may be an important determinant of the ultimate outcome of climate change for populations.
A free Plain Language Summary can be found within the Supporting Information of this article.
A free Plain Language Summary can be found within the Supporting Information of this article.
Globally, amphibian species are experiencing dramatic population declines, and many face the risk of imminent extinction. Endocrine-disrupting chemicals (EDCs) have been recognised as an ...underappreciated factor contributing to global amphibian declines. In this regard, the use of hormonal growth promotants in the livestock industry provides a direct pathway for EDCs to enter the environment—including the potent anabolic steroid 17β-trenbolone. Emerging evidence suggests that 17β-trenbolone can impact traits related to metabolism, somatic growth, and behaviour in non-target species. However, far less is known about possible effects of 17β-trenbolone on anuran species, particularly during early life stages. Accordingly, in the present study we investigated the effects of 28-day exposure to 17β-trenbolone (mean measured concentrations: 10 and 66 ng/L) on body size, body condition, metabolic rate, and anxiety-related behaviour of tadpoles (Limnodynastes tasmaniensis). Specifically, we measured rates of O2 consumption of individual tadpoles as a proxy for metabolic rate and quantified their swimming activity and their time spent in the upper half of the water column as indicators of anxiety-related behaviour. Counter to our predictions based on effects observed in other taxa, we detected no effect of 17β-trenbolone on body size, metabolic rate, or behaviour of tadpoles; although, we did detect a subtle, but statistically significant decrease in body condition at the highest 17β-trenbolone concentration. We hypothesise that 17β-trenbolone may induce taxa-specific effects on metabolic function, growth, and anxiety-related behaviour, with anurans being less sensitive to disruption than fish, and encourage further cross-taxa investigation to test this hypothesis.
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•Hormonal growth promotants (HGPs) used on livestock can result in EDC contamination.•17β-trenbolone (TREN), a HPG metabolite, is widely detected in the environment.•Little is known regarding the effects of TREN on early-life stages of amphibians.•We test the impacts on body size/condition, metabolic rate, and behaviour of tadpoles.•Intriguingly, counter to effects in fish, TREN did not affect these traits in tadpoles.
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°C) is more detrimental to embryonic and larval Limnodynastes peronii than exposure to peak UVBR levels while the temperature is moderate (25°C). 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 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.
Abstract
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.
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