Thermoregulatory behaviour in Tropidurus torquatus (Squamata, Tropiduridae) from Brazilian coastal populations: an estimate of passive and active thermoregulation in lizards

Geographical variation in the degree of thermoregulatory behaviour of the lizard Tropidurus torquatus was studied in 10 restinga populations along approximately 1500 km of Brazilian coast. An index of thermoregulation was estimated using the difference between body and environmental (air and substrate) temperatures and the percentage of negative values for these differences (proportion of body temperatures lower than environmental temperatures). In most populations, the lizards primarily used active thermoregulation, through behavioural means, and mainly in relation to substrate temperatures. Along the restingas, the degree of active thermoregulation increased as a function of the increase in the local environmental temperatures along the restingas. Behavioural thermoregulation of T. torquatus helps the lizards to maintain their body temperatures within an optimal range in which to perform their normal daily activities.     

Identification of a genetic network for an ecologically relevant behavioural phenotype in Drosophila melanogaster

Pupation site choice of Drosophila third‐instar larvae is critical for the survival of individuals, as pupae are exposed to various biotic and abiotic dangers while immobilized during the 3–4 days of metamorphosis. This singular behavioural choice is sensitive to both environmental and genetic factors. Here, we developed a high‐throughput phenotyping approach to assay the variation in pupation height in Drosophila melanogaster, while controlling for possibly confounding factors. We find substantial variation of mean pupation height among sampled natural stocks and we show that the Drosophila Genetic Reference Panel (DGRP) reflects this variation. Using the DGRP stocks for genome‐wide association (GWA) mapping, 16 loci involved in determining pupation height could be resolved. The candidate genes in these loci are enriched for high expression in the larval central nervous system. A genetic network could be constructed from the candidate loci, which places scribble (scrib) at the centre, plus other genes known to be involved in nervous system development, such as Epidermal growth factor receptor (Egfr) and p53. Using gene disruption lines, we could functionally validate several of the initially identified loci, as well as additional loci predicted from network analysis. Our study shows that the combination of high‐throughput phenotyping with a genetic analysis of variation captured from the wild can be used to approach the genetic dissection of an environmentally relevant behavioural phenotype.     

Predicting potential responses to future climate in an alpine ungulate: interspecific interactions exceed climate effects

The altitudinal shifts of many montane populations are lagging behind climate change. Understanding habitual, daily behavioural rhythms, and their climatic and environmental influences, could shed light on the constraints on long‐term upslope range‐shifts. In addition, behavioural rhythms can be affected by interspecific interactions, which can ameliorate or exacerbate climate‐driven effects on ecology. Here, we investigate the relative influences of ambient temperature and an interaction with domestic sheep (Ovis aries) on the altitude use and activity budgets of a mountain ungulate, the Alpine chamois (Rupicapra rupicapra). Chamois moved upslope when it was hotter but this effect was modest compared to that of the presence of sheep, to which they reacted by moving 89–103 m upslope, into an entirely novel altitudinal range. Across the European Alps, a range‐shift of this magnitude corresponds to a 46% decrease in the availability of suitable foraging habitat. This highlights the importance of understanding how factors such as competition and disturbance shape a given species’ realised niche when predicting potential future responses to change. Furthermore, it exposes the potential for manipulations of species interactions to ameliorate the impacts of climate change, in this case by the careful management of livestock. Such manipulations could be particularly appropriate for species where competition or disturbance already strongly restricts their available niche. Our results also reveal the potential role of behavioural flexibility in responses to climate change. Chamois reduced their activity when it was warmer, which could explain their modest altitudinal migrations. Considering this behavioural flexibility, our model predicts a small 15–30 m upslope shift by 2100 in response to climate change, less than 4% of the altitudinal shift that would be predicted using a traditional species distribution model‐type approach (SDM), which assumes that species’ behaviour remains unchanged as climate changes. Behavioural modifications could strongly affect how species respond to a changing climate.     

Thermal biology, torpor use and activity patterns of a small diurnal marsupial from a tropical desert: sexual differences

Many small desert dasyurids employ torpor almost daily during winter, because cold nights and low food availability impose high energetic costs. However, in Western Australia the arid zone extends into tropical, coastal regions, where winter temperature conditions are far less severe. We studied the thermal biology and activity patterns of free-ranging kaluta (~27 g), a dasyurid restricted to these tropical spinifex deserts, during the Austral winter (June–July) and in addition quantified activity patterns in captivity. Unlike most dasyurids, wild and captive kalutas were almost exclusively diurnal and retreated into underground burrows during the night. Despite being active during the warmer part of the day, kalutas entered torpor daily. However, torpor patterns differed remarkably between males and females. While females spent most of the night torpid at body temperatures (T _b) as low as 21°C, close to soil temperature, males entered multiple short and shallow bouts (T _b > 25°C) during the night. Males also maintained higher T _bs during the early morning when active, occupied larger home ranges and covered greater distances while foraging than females. Hence, males appear to expend more energy than the similar-sized females both while foraging and during the rest phase. We propose that physiological as well as behavioural preparations for the September mating season that culminate in a complete male die-off might already impose energetic costs on males during winter.     

Activity‐specific metabolic rates for diving,transiting, and resting at sea can be estimated from time–activity budgets in free‐ranging marine mammals

Time and energy are the two most important currencies in animal bioenergetics. How much time animals spend engaged in different activities with specific energetic costs ultimately defines their likelihood of surviving and successfully reproducing. However, it is extremely difficult to determine the energetic costs of independent activities for free‐ranging animals. In this study, we developed a new method to calculate activity‐specific metabolic rates, and applied it to female fur seals. We attached biologgers (that recorded GPS locations, depth profiles, and triaxial acceleration) to 12 northern (Callorhinus ursinus) and 13 Antarctic fur seals (Arctocephalus gazella), and used a hierarchical decision tree algorithm to determine time allocation between diving, transiting, resting, and performing slow movements at the surface (grooming, etc.). We concomitantly measured the total energy expenditure using the doubly‐labelled water method. We used a general least‐square model to establish the relationship between time–activity budgets and the total energy spent by each individual during their foraging trip to predict activity‐specific metabolic rates. Results show that both species allocated similar time to diving (~29%), transiting to and from their foraging grounds (~26–30%), and resting (~8–11%). However, Antarctic fur seals spent significantly more time grooming and moving slowly at the surface than northern fur seals (36% vs. 29%). Diving was the most expensive activity (~30 MJ/day if done non‐stop for 24 hr), followed by transiting at the surface (~21 MJ/day). Interestingly, metabolic rates were similar between species while on land or while slowly moving at the surface (~13 MJ/day). Overall, the average field metabolic rate was ~20 MJ/day (for all activities combined). The method we developed to calculate activity‐specific metabolic rates can be applied to terrestrial and marine species to determine the energetic costs of daily activities, as well as to predict the energetic consequences for animals forced to change their time allocations in response to environmental shifts.     

Effect of water temperature on activity of wintering age‐0 Acipenser transmontanus and A. brevirostrum: An artificial stream study

The effect of water temperature on behaviour and life history of wintering age‐0 = young‐of‐the‐year (YOY) northern sturgeons (populations using winter refuge habitat) is poorly understood. Using artificial stream tanks, we observed the effect of water temperature on 1) day‐time activity of cultured YOY Kootenai River white sturgeon, Acipenser transmontanus, during two winters (2008 and 2009–2010), and 2) observed day‐time activity of cultured YOY Connecticut River shortnose sturgeon, A. brevirostrum, in the winter, 2009–2010. Activity of YOY was measured every 2 to 7 days by visual or video observations on each fish to determine the mean number of 10 cm² square gridlines on the tank bottom crossed by all fish in each replicate tank (two replicate tanks, 10 fish in each tank). Daily water temperature was recorded by a logger in one tank every 20 min, 24 hr per day. In 2008, YOY A. transmontanus activity was positively related to decreasing mean daily temperature (R² = 0.96, p < 0.01) with 0 to 5 gridlines (range) crossed by all fish during observation periods at the coldest temperature (≤3°C). During the winter of 2009–2010, activity of both species was significantly related to decreasing temperature, and again, a mean of 0 to 5 gridlines (range) were crossed by fish at ≤3°C. We accept the hypothesis that YOY of both species are mostly inactive in the day when winter water temperature decreases to ≤3°C. Using the daytime inactivity temperature threshold of 3°C for YOY, and recent temperatures in river reaches where wild wintering YOY likely occur, we predict (a) wild wintering YOY A. transmontanus are moderately active in the day, may be energy challenged due to elevated temperatures from the warm river discharge by Libby Dam, and have poor survival in the regulated Kootenay River, and (b) wintering YOY Connecticut River A. brevirostrum are moderately active most winter months due to elevated natural river temperatures and may be energy challenged. More research is needed on YOY wintering activity and energetics relative to temperature to insure management of river temperature includes conservation of sturgeons.     

Energetic solutions of Rock Sandpipers to harsh winter conditions rely on prey quality

Rock Sandpipers Calidris ptilocnemis have the most northerly non‐breeding distribution of any shorebird in the Pacific Basin (upper Cook Inlet, Alaska; 61°N, 151°W). In terms of freezing temperatures, persistent winds and pervasive ice, this site is the harshest used by shorebirds during winter. We integrated physiological, metabolic, behavioural and environmental aspects of the non‐breeding ecology of Rock Sandpipers at the northern extent of their range to determine the relative importance of these factors in facilitating their unique non‐breeding ecology. Not surprisingly, estimated daily energetic demands were greatest during January, the coldest period of winter. These estimates were greatest for foraging birds, and exceeded basal metabolic rates by a factor of 6.5, a scope of increase that approaches the maximum sustained rate of energetic output by shorebirds during periods of migration, but far exceeds these periods in duration. We assessed the quality of their primary prey, the bivalve Macoma balthica, to determine the daily foraging duration required by Rock Sandpipers to satisfy such energetic demands. Based on size‐specific estimates of M. balthica quality, Rock Sandpipers require over 13 h/day of foraging time in upper Cook Inlet in January, even when feeding on the highest quality prey. This range approaches the average daily duration of mudflat availability in this region (c. 18 h), a maximum value that annually decreases due to the accumulation of shore‐fast ice. Rock Sandpipers are likely to maximize access to foraging sites by following the exposure of ice‐free mudflats across the upper Cook Inlet region and by selecting smaller, higher quality M. balthica to minimize foraging times. Ultimately, this unusual non‐breeding ecology relies on the high quality of their prey resources. Compared with other sites across their range, M. balthica from upper Cook Inlet have relatively light shells, potentially the result of the region's depauperate invertebrate predator community. Given the delicate balance between environmental and prey conditions that currently make Cook Inlet a viable wintering area for Rock Sandpipers, small variations in these variables may affect the suitability of the site in the future.     

Morphology,metabolism and behaviour: responses of three fishes with different lifestyles to acute hypoxia

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Together or alone? Foraging strategies in Caenorhabditis elegans

A central goal in Life Sciences is to understand how genes encode behaviour and how environmental factors influence the expression of the genes concerned. To reach this goal a combined ecological, molecular biological and physiological approach is required in combination with a suitable model organism. Such an approach allows the elucidation of all parts of the complicated chain of events that lead from induction of gene expression to behaviour, i.e. from environmental stimulus, sensory organs and extracellular and intracellular neuronal signal processing to activation of effector organs. A particularly good model species with which to take this approach is the nematode Caenorhabditis elegans, as it has been described in great detail at the genomic, cellular and behavioural levels. Different strains of C. elegans display prominent behavioural variation in foraging behaviour. Some strains will form social feeding groups when subjected to certain environmental stimuli, while others do not. This variation is due to the existence of just two isoforms of the gene npr‐1, namely 215F and 215V. Here, we describe these behavioural variations at the molecular and cellular levels to attempt to determine the environmental inputs that cause aggregation of these small nematodes. As many different stimuli affect aggregation either positively or negatively, aggregation behaviour seems to be displayed when it improves survival chances. However, not much is known about the ecological context in which C. elegans lives. Investigation of the habitats of different strains of C. elegans would help us to understand why and how a specific foraging strategy enhances survival. The relatively well‐understood molecular pathways that direct its social feeding behaviour make C. elegans a highly suitable model organism to test ecological and behavioural hypotheses about the mechanisms that differentiate between aggregation and solitary behaviours.     

Hypoxia tolerance associated with activity reduction is a key adaptation for Laternula elliptica seasonal energetics

Seasonal dormancy is a widespread mechanism for reducing energy expenditure during periods of low energy availability. Seasonal variation in activity and the cost of pumping water through the siphons were investigated to estimate the importance of activity regulation to the seasonal energy budget of the Antarctic clam, Laternula elliptica. In the laboratory, a metabolic rate of 26.35 μmol O₂ h⁻¹ was estimated for a 50-mm shell length L. elliptica pumping water at −0.4 °C. In the field, the proportion of time siphons were visible at the sediment surface varied seasonally (32% visible in June/July compared to 86% in December/January). L. elliptica were actively pumping for a minimum of 19% of each 24-h period during winter (August) compared to a summer maximum when animals were actively pumping for 73% of the time (February). This resulted in a 3.7-fold seasonal difference in the calculated energy consumption of a 50-mm L. elliptica (19.2 μmol O₂ h⁻¹ in February versus 5.0 μmol O₂ h⁻¹ in August), which closely matches the 3.0-fold seasonal variation in metabolic rate found previously. Seasonal variation in activity could therefore be responsible for much of the seasonal difference in energy consumption of L. elliptica. Inter-annual variation in timing of the seasonal activity maxima (January 2004 and March 1999) was correlated with variation in the timing of the summer plankton bloom in Ryder Bay. In the laboratory, periods of extended siphon closure (133 ± 114 min, mean ± SD) were accompanied by long periods of heart arrhythmia (167 ± 135 min), during which time blood oxygen levels dropped to values close to zero. Heart arrhythmia is most likely part of a hypo-metabolic adaptation to reduce energy costs during extended periods of siphon closure. Physiological and behavioural dormancy, with associated hypoxia tolerance, appear to be key mechanisms controlling the seasonal energy budget of L. elliptica.     

Colony‐level behavioural variation correlates with differences in expression of the foraging gene in red imported fire ants

Among social insects, colony‐level variation is likely to be widespread and has significant ecological consequences. Very few studies, however, have documented how genetic factors relate to behaviour at the colony level. Differences in expression of the foraging gene have been associated with differences in foraging and activity of a wide variety of organisms. We quantified expression of the red imported fire ant foraging gene (sifor) in workers from 21 colonies collected across the natural range of Texas fire ant populations, but maintained under standardized, environmentally controlled conditions. Colonies varied significantly in their behaviour. The most active colonies had up to 10 times more active foragers than the least active colony and more than 16 times as many workers outside the nest. Expression differences among colonies correlated with this colony‐level behavioural variation. Colonies with higher sifor expression in foragers had, on average, significantly higher foraging activity, exploratory activity and recruitment to nectar than colonies with lower expression. Expression of sifor was also strongly correlated with worker task (foraging vs. working in the interior of the nest). These results provide insight into the genetic and physiological processes underlying collective differences in social behaviour. Quantifying variation in expression of the foraging gene may provide an important tool for understanding and predicting the ecological consequences of colony‐level behavioural variation.     

Solar‐induced chlorophyll fluorescence is strongly correlated with terrestrial photosynthesis for a wide variety of biomes: First global analysis based on OCO‐2 and flux tower observations

Solar‐induced chlorophyll fluorescence (SIF) has been increasingly used as a proxy for terrestrial gross primary productivity (GPP). Previous work mainly evaluated the relationship between satellite‐observed SIF and gridded GPP products both based on coarse spatial resolutions. Finer resolution SIF (1.3 km × 2.25 km) measured from the Orbiting Carbon Observatory‐2 (OCO‐2) provides the first opportunity to examine the SIF–GPP relationship at the ecosystem scale using flux tower GPP data. However, it remains unclear how strong the relationship is for each biome and whether a robust, universal relationship exists across a variety of biomes. Here we conducted the first global analysis of the relationship between OCO‐2 SIF and tower GPP for a total of 64 flux sites across the globe encompassing eight major biomes. OCO‐2 SIF showed strong correlations with tower GPP at both midday and daily timescales, with the strongest relationship observed for daily SIF at the 757 nm (R² = 0.72, p < 0.0001). Strong linear relationships between SIF and GPP were consistently found for all biomes (R² = 0.57–0.79, p < 0.0001) except evergreen broadleaf forests (R² = 0.16, p < 0.05) at the daily timescale. A higher slope was found for C₄ grasslands and croplands than for C₃ ecosystems. The generally consistent slope of the relationship among biomes suggests a nearly universal rather than biome‐specific SIF–GPP relationship, and this finding is an important distinction and simplification compared to previous results. SIF was mainly driven by absorbed photosynthetically active radiation and was also influenced by environmental stresses (temperature and water stresses) that determine photosynthetic light use efficiency. OCO‐2 SIF generally had a better performance for predicting GPP than satellite‐derived vegetation indices and a light use efficiency model. The universal SIF–GPP relationship can potentially lead to more accurate GPP estimates regionally or globally. Our findings revealed the remarkable ability of finer resolution SIF observations from OCO‐2 and other new or future missions (e.g., TROPOMI, FLEX) for estimating terrestrial photosynthesis across a wide variety of biomes and identified their potential and limitations for ecosystem functioning and carbon cycle studies.     

Brain size predicts behavioural plasticity in guppies (Poecilia reticulata): An experiment

Understanding how animal personality (consistent between‐individual behavioural differences) arises has become a central topic in behavioural sciences. This endeavour is complicated by the fact that not only the mean behaviour of individuals (behavioural type) but also the strength of their reaction to environmental change (behavioural plasticity) varies consistently. Personality and cognitive abilities are linked, and we suggest that behavioural plasticity could also be explained by differences in brain size (a proxy for cognitive abilities), since accurate decisions are likely essential to make behavioural plasticity beneficial. We test this idea in guppies (Poecilia reticulata), artificially selected for large and small brain size, which show clear cognitive differences between selection lines. To test whether those lines differed in behavioural plasticity, we reared them in groups in structurally enriched environments and then placed adults individually into empty tanks, where we presented them daily with visual predator cues and monitored their behaviour for 20 days with video‐aided motion tracking. We found that individuals differed consistently in activity and risk‐taking, as well as in behavioural plasticity. In activity, only the large‐brained lines demonstrated habituation (increased activity) to the new environment, whereas in risk‐taking, we found sensitization (decreased risk‐taking) in both brain size lines. We conclude that brain size, potentially via increasing cognitive abilities, may increase behavioural plasticity, which in turn can improve habituation to novel environments. However, the effects seem to be behaviour‐specific. Our results suggest that brain size likely explains some of the variation in behavioural plasticity found at the intraspecific level.     

Partitioning controls on Amazon forest photosynthesis between environmental and biotic factors at hourly to interannual timescales

Gross ecosystem productivity (GEP) in tropical forests varies both with the environment and with biotic changes in photosynthetic infrastructure, but our understanding of the relative effects of these factors across timescales is limited. Here, we used a statistical model to partition the variability of seven years of eddy covariance‐derived GEP in a central Amazon evergreen forest into two main causes: variation in environmental drivers (solar radiation, diffuse light fraction, and vapor pressure deficit) that interact with model parameters that govern photosynthesis and biotic variation in canopy photosynthetic light‐use efficiency associated with changes in the parameters themselves. Our fitted model was able to explain most of the variability in GEP at hourly (R² = 0.77) to interannual (R² = 0.80) timescales. At hourly timescales, we found that 75% of observed GEP variability could be attributed to environmental variability. When aggregating GEP to the longer timescales (daily, monthly, and yearly), however, environmental variation explained progressively less GEP variability: At monthly timescales, it explained only 3%, much less than biotic variation in canopy photosynthetic light‐use efficiency, which accounted for 63%. These results challenge modeling approaches that assume GEP is primarily controlled by the environment at both short and long timescales. Our approach distinguishing biotic from environmental variability can help to resolve debates about environmental limitations to tropical forest photosynthesis. For example, we found that biotically regulated canopy photosynthetic light‐use efficiency (associated with leaf phenology) increased with sunlight during dry seasons (consistent with light but not water limitation of canopy development) but that realized GEP was nonetheless lower relative to its potential efficiency during dry than wet seasons (consistent with water limitation of photosynthesis in given assemblages of leaves). This work highlights the importance of accounting for differential regulation of GEP at different timescales and of identifying the underlying feedbacks and adaptive mechanisms.     

Entanglement is a costly life‐history stage in large whales

Individuals store energy to balance deficits in natural cycles; however, unnatural events can also lead to unbalanced energy budgets. Entanglement in fishing gear is one example of an unnatural but relatively common circumstance that imposes energetic demands of a similar order of magnitude and duration of life‐history events such as migration and pregnancy in large whales. We present two complementary bioenergetic approaches to estimate the energy associated with entanglement in North Atlantic right whales, and compare these estimates to the natural energetic life history of individual whales. Differences in measured blubber thicknesses and estimated blubber volumes between normal and entangled, emaciated whales indicate between 7.4 × 10¹⁰ J and 1.2 × 10¹¹ J of energy are consumed during the course to death of a lethal entanglement. Increased thrust power requirements to overcome drag forces suggest that when entangled, whales require 3.95 × 10⁹ to 4.08 × 10¹⁰ J more energy to swim. Individuals who died from their entanglements performed significantly more work (energy expenditure × time) than those that survived; entanglement duration is therefore critical in determining whales’ survival. Significant sublethal energetic impacts also occur, especially in reproductive females. Drag from fishing gear contributes up to 8% of the 4‐year female reproductive energy budget, delaying time of energetic equilibrium (to restore energy lost by a particular entanglement) for reproduction by months to years. In certain populations, chronic entanglement in fishing gear can be viewed as a costly unnatural life‐history stage, rather than a rare or short‐term incident.     

Heritability of interpack aggression in a wild pedigreed population of North American grey wolves

Aggression is a quantitative trait deeply entwined with individual fitness. Mapping the genomic architecture underlying such traits is complicated by complex inheritance patterns, social structure, pedigree information and gene pleiotropy. Here, we leveraged the pedigree of a reintroduced population of grey wolves (Canis lupus) in Yellowstone National Park, Wyoming, USA, to examine the heritability of and the genetic variation associated with aggression. Since their reintroduction, many ecological and behavioural aspects have been documented, providing unmatched records of aggressive behaviour across multiple generations of a wild population of wolves. Using a linear mixed model, a robust genetic relationship matrix, 12,288 single nucleotide polymorphisms (SNPs) and 111 wolves, we estimated the SNP‐based heritability of aggression to be 37% and an additional 14% of the phenotypic variation explained by shared environmental exposures. We identified 598 SNP genotypes from 425 grey wolves to resolve a consensus pedigree that was included in a heritability analysis of 141 individuals with SNP genotype, metadata and aggression data. The pedigree‐based heritability estimate for aggression is 14%, and an additional 16% of the phenotypic variation was explained by shared environmental exposures. We find strong effects of breeding status and relative pack size on aggression. Through an integrative approach, these results provide a framework for understanding the genetic architecture of a complex trait that influences individual fitness, with linkages to reproduction, in a social carnivore. Along with a few other studies, we show here the incredible utility of a pedigreed natural population for dissecting a complex, fitness‐related behavioural trait.     

Genetic basis and fitness correlates of dynamic carotenoid‐based ornamental coloration in male and female common kestrels Falco tinnunculus

Knowledge of the genetic basis of sexual ornaments is essential to understand their evolution through sexual selection. Although carotenoid‐based ornaments have been instrumental in the study of sexual selection, given the inability of animals to synthesize carotenoids de novo, they are generally assumed to be influenced solely by environmental variation. However, very few studies have directly estimated the role of genes and the environment in shaping variation in carotenoid‐based traits. Using long‐term individual‐based data, we here explore the evolutionary potential of a dynamic, carotenoid‐based ornament (namely skin coloration), in male and female common kestrels. We first estimate the amount of genetic variation underlying variation in hue, chroma and brightness. After correcting for sex differences, the chroma of the orange‐yellow eye ring coloration was significantly heritable (h² ± SE = 0.40 ± 0.17), whereas neither hue (h² = 0) nor brightness (h² = 0.02) was heritable. Second, we estimate the strength and shape of selection acting upon chromatic (hue and chroma) and achromatic (brightness) variation and show positive and negative directional selection on female but not male chroma and hue, respectively, whereas brightness was unrelated to fitness in both sexes. This suggests that different components of carotenoid‐based signals traits may show different evolutionary dynamics. Overall, we show that carotenoid‐based coloration is a complex and multifaceted trait. If we are to gain a better understanding of the processes responsible for the generation and maintenance of variation in carotenoid‐based coloration, these complexities need to be taken into account.     

Energetics of Acidianus ambivalens growth in response to oxygen availability

All life requires energy to drive metabolic reactions such as growth and cell maintenance; therefore, fluctuations in energy availability can alter microbial activity. There is a gap in our knowledge concerning how energy availability affects the growth of extreme chemolithoautotrophs. Toward this end, we investigated the growth of thermoacidophile Acidianus ambivalens during sulfur oxidation under aerobic to microaerophilic conditions. Calorimetry was used to measure enthalpy (ΔH_inc) of microbial activity, and chemical changes in growth media were measured to calculate Gibbs energy change (ΔG_inc) during incubation. In all experiments, Gibbs energy was primarily dissipated through the release of heat, which suggests enthalpy‐driven growth. In microaerophilic conditions, growth was significantly more efficient in terms of biomass yield (defined as C‐mol biomass per mole sulfur consumed) and resulted in lower ΔG_inc and ΔH_inc. ΔG_inc in oxygen‐limited (OL) and oxygen‐ and CO₂‐limited (OCL) microaerophilic growth conditions resulted in averages of ?1.44 × 10³ kJ/C‐mol and ?7.56 × 10² kJ/C‐mol, respectively, and average ΔH_inc values of ?1.11 × 10⁵ kJ/C‐mol and ?4.43 × 10⁴ kJ/C‐mol, respectively. High‐oxygen experiments resulted in lower biomass yield values, an increase in ΔG_inc to ?1.71 × 10⁴ kJ/C‐mol, and more exothermic ΔH_inc values of ?4.71 × 10⁵ kJ/C‐mol. The observed inefficiency in high‐oxygen conditions may suggest larger maintenance energy demands due to oxidative stresses and a preference for growth in microaerophilic environments.     

Linking anti‐predator behaviour to prey demography reveals limited risk effects of an actively hunting large carnivore

Ecological theory predicts that the diffuse risk cues generated by wide‐ranging, active predators should induce prey behavioural responses but not major, population‐ or community‐level consequences. We evaluated the non‐consumptive effects (NCEs) of an active predator, the grey wolf (Canis lupus), by simultaneously tracking wolves and the behaviour, body fat, and pregnancy of elk (Cervus elaphus), their primary prey in the Greater Yellowstone Ecosystem. When wolves approached within 1 km, elk increased their rates of movement, displacement and vigilance. Even in high‐risk areas, however, these encounters occurred only once every 9 days. Ultimately, despite 20‐fold variation in the frequency of encounters between wolves and individual elk, the risk of predation was not associated with elk body fat or pregnancy. Our findings suggest that the ecological consequences of actively hunting large carnivores, such as the wolf, are more likely transmitted by consumptive effects on prey survival than NCEs on prey behaviour.