Fitness and physiology in a variable environment

The relationship between physiological traits and fitness often depends on environmental conditions. In variable environments, different species may be favored through time, which can influence both the nature of trait evolution and the ecological dynamics underlying community composition. To determine how fluctuating environmental conditions favor species with different physiological traits over time, we combined long-term data on survival and fecundity of species in a desert annual plant community with data on weather and physiological traits. For each year, we regressed the standardized annual fitness of each species on its position along a tradeoff between relative growth rate and water-use efficiency. Next, we determined how variations in the slopes and intercepts of these fitness-physiology functions related to year-to-year variations in temperature and precipitation. Years with a relatively high percentage of small rain events and a greater number of days between precipitation pulse events tended to be worse, on average, for all desert annual species. Species with high relative growth rates and low water-use efficiency had greater standardized annual fitness than other species in years with greater numbers of large rain events. Conversely, species with high water-use efficiency had greater standardized annual fitness in years with small rain events and warm temperatures late in the growing season. These results reveal how weather variables interact with physiological traits of co-occurring species to determine interannual variations in survival and fecundity, which has important implications for understanding population and community dynamics.     

Plant phenotypic plasticity in a changing climate

Climate change is altering the availability of resources and the conditions that are crucial to plant performance. One way plants will respond to these changes is through environmentally induced shifts in phenotype (phenotypic plasticity). Understanding plastic responses is crucial for predicting and managing the effects of climate change on native species as well as crop plants. Here, we provide a toolbox with definitions of key theoretical elements and a synthesis of the current understanding of the molecular and genetic mechanisms underlying plasticity relevant to climate change. By bringing ecological, evolutionary, physiological and molecular perspectives together, we hope to provide clear directives for future research and stimulate cross-disciplinary dialogue on the relevance of phenotypic plasticity under climate change.     

The effects of creatine loading on thermoregulation and intermittent sprint exercise performance in a hot humid environment

The purpose of this study was to determine the effects creatine (Cr) loading may have on thermoregulatory responses during intermittent sprint exercise in a hot/humid environment. Ten physically active, heat-acclimatized men performed 2 familiarization sessions of an exercise test consisting of a 30-minute low-intensity warm-up followed by 6 x 10 second maximal sprints on a cycle ergometer in the heat (35 degrees C, 60% relative humidity). Subjects then participated in 2 different weeks of supplementation. The first week, subjects ingested 5 g of a placebo (P, maltodextrin) in 4 flavored drinks (20 g total) per day for 6 days and were retested on day 7. The second week was similar to the first except a similar dose (4 x 5 g/day) of creatine monohydrate (Cr) replaced maltodextrin in the flavored drinks. Six days of Cr supplementation produced a significant increase in body weight (+1.30 +/- 0.63 kg), whereas the P did not (+0.11 +/- 0.52 kg). Compared to preexercise measures, the exercise test in the heat produced a significant increase in core temperature, a loss of body water determined by body weight change during exercise, and a relative change in plasma volume (%PVC); however, these were not significantly different between P and Cr. Sprint performance was enhanced by Cr loading. Peak power and mean power were significantly higher during the intermittent sprint exercise test following 6 days of Cr supplementation. It appears that ingestion of Cr for 6 days does not produce any different thermoregulatory responses to intermittent sprint exercise and may augment sprint exercise performance in the heat.     

Tropical forests in a changing environment

Understanding and mitigating the impact of an ever-increasing population and global economic activity on tropical forests is one of the great challenges currently facing biologists, conservationists and policy makers. Tropical forests currently face obvious regional changes, both negative and positive, and uncertain global changes. Although deforestation rates have increased to unprecedented levels, natural secondary succession has reclaimed approximately 15% of the area deforested during the 1990s. Governments have also protected 18% of the remaining tropical moist forest; however, unsustainable hunting continues to threaten many keystone mammal and bird species. The structure and dynamics of old-growth forests appear to be rapidly changing, suggesting that there is a pantropical response to global anthropogenic forcing, although the evidence comes almost exclusively from censuses of tree plots and is controversial. Here, I address ongoing anthropogenic change in tropical forests and suggest how these forests might respond to increasing anthropogenic pressure.     

Aquatic hyphomycetes in a changing environment

In 1942, Ingold documented an ecologically defined group of fungi, aquatic hyphomycetes, on autumn-shed leaves decaying in streams. They were shown to be vital intermediaries between the nutritionally poor leaf substratum and leaf-eating invertebrates. Research has subsequently emphasized functional aspects such as leaf decomposition and nutritional conditioning by fungi. Structural aspects (community composition) have attracted less attention, partly because of the difficulties of identifying fungal mycelia in situ. Extraction, amplification (PCR, qPCR) and characterization of DNA and RNA, and, more recently, of proteins, allow much greater insights into the presence of fungal taxa, their metabolic status (dead, dormant or active), and their potential and actual participation in decomposition processes. This approach can yield huge amounts of data, and major challenges today are the development and application of suitable bioinformatics techniques. The complexity of data collection and evaluation favour interdisciplinary teams of researchers. Fungi are major players in most ecosystems and are increasingly affected by human impacts. Changing land use, eutrophication/pollution and climate change are among the major factors that affect diversity and ecological functions of aquatic hyphomycetes.     

Sex and adaptation in a changing environment.

In this study we consider a mathematical model of a sexual population that lives in a changing environment. We find that a low rate of environmental change can produce a very large increase in genetic variability. This may help to explain the high levels of heritability observed in many natural populations. We also study asexuality and find that a modest rate of environmental change can be very damaging to an asexual population, while leaving a sexual population virtually unscathed. Furthermore, in a changing environment, the advantages of sexuality over asexuality can be much greater than suggested by most previous studies. Our analysis applies in the case of very large populations, where stochastic forces may be neglected.     

Tracking a changing environment: optimal sampling, adaptive memory and overnight effects

Foraging in a variable environment presents a classic problem of decision making with incomplete information. Animals must track the changing environment, remember the best options and make choices accordingly. While several experimental studies have explored the idea that sampling behavior reflects the amount of environmental change, we take the next logical step in asking how change influences memory. We explore the hypothesis that memory length should be tied to the ecological relevance and the value of the information learned, and that environmental change is a key determinant of the value of memory. We use a dynamic programming model to confirm our predictions and then test memory length in a factorial experiment. In our experimental situation we manipulate rates of change in a simple foraging task for blue jays over a 36 h period. After jays experienced an experimentally determined change regime, we tested them at a range of retention intervals, from 1 to 72 h. Manipulated rates of change influenced learning and sampling rates: subjects sampled more and learned more quickly in the high change condition. Tests of retention revealed significant interactions between retention interval and the experienced rate of change. We observed a striking and surprising difference between the high and low change treatments at the 24 h retention interval. In agreement with earlier work we find that a circadian retention interval is special, but we find that the extent of this ‘specialness’ depends on the subject's prior experience of environmental change. Specifically, experienced rates of change seem to influence how subjects balance recent information against past experience in a way that interacts with the passage of time.     

Perceptual classification in a rapidly changing environment

Humans and monkeys can learn to classify perceptual information in a statistically optimal fashion if the functional groupings remain stable over many hundreds of trials, but little is known about categorization when the environment changes rapidly. Here, we used a combination of computational modeling and functional neuroimaging to understand how humans classify visual stimuli drawn from categories whose mean and variance jumped unpredictably. Models based on optimal learning (Bayesian model) and a cognitive strategy (working memory model) both explained unique variance in choice, reaction time, and brain activity. However, the working memory model was the best predictor of performance in volatile environments, whereas statistically optimal performance emerged in periods of relative stability. Bayesian and working memory models predicted decision-related activity in distinct regions of the prefrontal cortex and midbrain. These findings suggest that perceptual category judgments, like value-guided choices, may be guided by multiple controllers.     

Assessing rapid evolution in a changing environment

Climate change poses a serious threat to species persistence. Effective modelling of evolutionary responses to rapid climate change is therefore essential. In this review we examine recent advances in phylogenetic comparative methods, techniques normally used to study adaptation over long periods, which allow them to be applied to the study of adaptation over shorter time scales. This increased applicability is largely due to the emergence of more flexible models of character evolution and the parallel development of molecular technologies that can be used to assess adaptive variation at loci scattered across the genome. The merging of phylogenetic and population genetic approaches to the study of adaptation has significant potential to advance our understanding of rapid responses to environmental change.     

Adaptive plasticity of floral display size in animal-pollinated plants

Plants need not participate passively in their own mating, despite their immobility and reliance on pollen vectors. Instead, plants may respond to their recent pollination experience by adjusting the number of flowers that they display simultaneously. Such responsiveness could arise from the dependence of floral display size on the longevity of individual flowers, which varies with pollination rate in many plant species. By hand-pollinating some inflorescences, but not others, we demonstrate plasticity in display size of the orchid Satyrium longicauda. Pollination induced flower wilting, but did not affect the opening of new flowers, so that within a few days pollinated inflorescences displayed fewer flowers than unpollinated inflorescences. During subsequent exposure to intensive natural pollination, pollen removal and receipt increased proportionally with increasing display size, whereas pollen-removal failure and self-pollination accelerated. Such benefit-cost relations allow plants that adjust display size in response to the prevailing pollination rate to increase their attractiveness when pollinators are rare (large displays), or to limit mating costs when pollinators are abundant (small displays). Seen from this perspective, pollination-induced flower wilting serves the entire plant by allowing it to display the number of flowers that is appropriate for the current pollination environment.     

Evolution of migration in a periodically changing environment

The ability to migrate can evolve in response to various forces. In particular, when selection is heterogeneous in space but constant in time, local adaptation induces a fitness cost on immigrants and selects against migration. The evolutionary outcome, however, is less clear when selection also varies temporally. Here, we present a two-locus model analyzing the effects of spatial and temporal variability in selection on the evolution of migration. The first locus is under temporally varying selection (various periodic functions are considered, but a general nonparametric framework is used), and the second locus is a modifier controlling migration ability. First, we study the dynamics of local adaptation and derive the migration rate that maximizes local adaptation as a function of the speed and geometry of the fluctuations in the environment. Second, we derive an analytical expression for the evolutionarily stable migration rate. When there is no cost of migration, we show that higher migration rates are favored when selection changes fast. When migration is costly, however, the evolutionarily stable migration rate is maximal for an intermediate speed of the variation of selection. This model may help in understanding the evolution of migration in a broad range of scenarios and, in particular, in host-parasite systems, where selection is thought to vary quickly in both space and time.     

Fitness consequences of avian personalities in a fluctuating environment

Individual animals differ in the way they cope with challenges in their environment, comparable with variation in human personalities. The proximate basis of variation in personality traits has received considerable attention, and one general finding is that personality traits have a substantial genetic basis. This poses the question of how variation in personality is maintained in natural populations. We show that selection on a personality trait with high heritability fluctuates across years within a natural bird population. Annual adult survival was related to this personality trait (behaviour in novel environments) but the effects were always opposite for males and females, and reversed between years. The number of offspring surviving to breeding was also related to their parents' personalities, and again selection changed between years. The observed annual changes in selection pressures coincided with changes in environmental conditions (masting of beeches) that affect the competitive regimes of the birds. We expect that the observed fluctuations in environmental factors lead to fluctuations in competition for space and food, and these, in association with variations in population density, lead to a variation in selection pressure, which maintains genetic variation in personalities.     

Human choice behaviour in a frequently changing environment

The present experiment provided a replication in humans of an experimental procedure that has been used frequently with nonhumans to investigate choice behaviour in a changing environment. Six volunteers played a computer game, which required tracking of a moving balloon on two simultaneously available response panels for monetary reinforcers. Each of the 15 sessions randomly arranged the following concurrent variable-interval reinforcement schedules, which were in effect until six reinforcers had been obtained: 27:1, 9:1, 3:1, 1:1, 1:3, 1:9, and 1:27. Although many aspects of human performance appeared to be qualitatively similar to that of nonhumans on this procedure, such as the rapid preference shifts towards the within-session reinforcer ratios and the presence of local effects of reinforcers, values of sensitivity to reinforcement were very variable in the present study, as commonly reported in human choice studies. Future variations and refinements of the experimental methods are needed to explore how this variability may be reduced.     

Lactic acid bacteria in a changing legislative environment

The benefits of using lactic acid bacteria in the food chain, both through direct consumption and production of ingredients, are increasingly recognised by the food industry and consumers alike. The regulatory environment surrounding these products is diverse, covering foods and food ingredients, processing aids, feed additives and dietary supplements. On a global basis, there are different approaches taken by the various regulatory authorities. While in Europe, the national legislation is gradually being harmonised, predominantly through the Novel Foods Regulation, there is still a wide disparity between the stringency of regulation of microbial products fed to animals and the comparatively relaxed approach to non-novel microbial products intended for human consumption. In the United States, the onus is on self-regulation of the manufacturer, with the Generally Recognised As Safe (GRAS) and Dietary Supplement Health Education Act (DSHEA) notification schemes encouraging industry to be more open about the ingredients they market. In Japan, the Foods for Special Health Use system continues to gain recognition as more products are approved, and is a potential model for other countries in regulating functional foods. Despite the different approaches to regulating these products, safety of microorganisms such as lactic acid bacteria in the food chain is paramount in all countries. This paper discusses the regulatory requirements of microbial products, predominantly lactic acid bacteria within the global markets, focusing mainly on the developments in Europe.