Environmental variation and selection on performance curves

Many aspects of physiological and organismal performance varywith some continuous environmental variable: e.g., photosyntheticrate as a function of light intensity; growth rate or sprintspeed as a function of temperature. For such ‘performancecurves’, the environment plays two roles: it affects boththe levels of performance expressed, and the relationship betweenperformance and fitness. How does environmental variation withina generation determine natural selection on performance curves?We describe an approach to this question that has three components.First, we quantify natural environmental variation and assessits impact on performance in the field. Second, we develop asimple theoretical model that predicts how fine-grained environmentalvariation determines selection on performance curves. Third,we describe how directional selection on performance curvesmay be estimated and compared to theoretical predictions. Weillustrate these steps using data on performance curves of short-termgrowth rate as a function of temperature (thermal performancecurves) in Pieris caterpillars. We use this approach to explorewhether selection acts primarily on growth rate at specifictemperatures, or on more integrated aspects of growth.     

Heritability of three condition surrogates in the yellow dung fly

Condition capture has been proposed as a general mechanism maintainingadditive genetic variation, V_a, in sexually selected traitsunder directional selection. It relies on two main assumptions:condition-dependent trait expression and V_a in condition. Althoughthere is evidence for the former, direct evidence that conditionis heritable is scarce, although this is a requirement of mostmodels of handicap sexual selection. We used a parent–offspring,full-sib, two-container laboratory breeding design in the yellowdung fly Scathophaga stercoraria to demonstrate the broad- andnarrow-sense heritability of three surrogates of condition commonlyused in sexual selection studies: lipid and glycogen reserves(i.e., physiological condition), body size, and fluctuatingasymmetry. All three measures are nutrition dependent and havebeen linked to sexual selection in free-living yellow dung flies.While lipid reserves and body size were heritable, asymmetryand glycogen reserves were not. Moreover, the evolvability ofphysiological condition was higher than that of the other twotraits. Of the three surrogates, physiological condition ismost akin to the original definition, but all have their limitations.We conclude that condition is a useful heuristic concept inevolutionary ecology, but its practical value may be limitedby the fact that it cannot be measured directly.     

Bioenergetic prediction of climate change impacts on northern mammals

Climate change will likely alter the distribution and abundanceof northern mammals through a combination of direct, abioticeffects (e.g., changes in temperature and precipitation) andindirect, biotic effects (e.g., changes in the abundance ofresources, competitors, and predators). Bioenergetic approachesare ideally suited to predicting the impacts of climate changebecause individual energy budgets integrate biotic and abioticinfluences, and translate individual function into populationand community outcomes. In this review, we illustrate how bioenergeticscan be used to predict the regional biodiversity, species rangelimits, and community trophic organization of mammals underfuture climate scenarios. Although reliable prediction of climatechange impacts for particular species requires better data andtheory on the physiological ecology of northern mammals, tworobust hypotheses emerge from the bioenergetic approaches presentedhere. First, the impacts of climate change in northern regionswill be shaped by the appearance of new species at least asmuch as by the disappearance of current species. Second, seasonallyinactive mammal species (e.g., hibernators), which are largelyabsent from the Canadian arctic at present, should undergo substantialincreases in abundance and distribution in response to climatechange, probably at the expense of continuously active mammalsalready present in the arctic.     

The Physiological Ecology of the Zebra Mussel, Dreissena polymorpha, in North America and Europe

SYNOPSIS. The zebra mussel, Dreissena polymorpha (Pallas), wasintroduced into North America in 1986. Initial North American(N.A.) studies suggested that physiological responses variedbetween N.A. and European populations. However, literature reviewindicates agreement on most aspects of physiological adaptationincluding: respiratory responses; hypoxia/anoxia tolerance;salinity limits; emersion tolerance; freezing resistance; environmentalpH limits; calcium limits; starvation responses; and bioenergeticpartitioning. The main differences among N.A. and European musselsappear to be elevated upper thermal limits and temperaturesfor optimum growth among N.A. populations. N.A. zebra musselsprobably originated from the northern shore of the Black Seain the warmest portion of the mussel's European range. However,most European physiological data come from northern Europe wherepopulations may be adapted to colder temperatures. Alternatively,N.A. research suggests that mussels may have a capacity forseasonal temperature acclimatization such that responses recordedin warmer N.A. waters may be different from those recorded innorthern Europe even after short-term laboratory acclimation.Studies of genetic variation and physiological response amongEuropean and N.A. D. polymorpha populations are required toelucidate the basis for physiological differentiation. Recentlyevolved D. polymorpha has poor resistance adaptations comparedto unionacean and sphaeriid bivalves with longer freshwaterfossil histories. Poor resistance adaptations make it less suitedfor stable habitats, instead, its high fecundities, early maturity,and rapid growth are adaptations to unstable habitats whereextensive resistance adaptations are of little value.     

Population Differentiation in Locomotor Performance and the Potential Response of a Terrestrial Organism to Global Environmental Change

SYNOPSIS. Models of global climate change predict an increasein the mean surface temperature between 1.5° and 4.5°Cby the middle of the next century. Even a moderate increaseof 3°C is likely to result in a shift in the distributionof North American habitat types and vegetational associations,either in latitude or elevation or both. The challenge to ConservationBiology is to predict the responses of terrestrial organismsto the expected alteration in habitats and ecosystems. Recentbiophysical models have been expanded to demonstrate the intimateassociations between the thermal environment, organismal physiologyand ecology. Thus, the expected turnover in habitats may havea profound influence on the distribution of organisms. I describeone possible approach that couples temporal and spatial variationin an ecologically relevant physiological trait, locomotoryperformance, in a widespread species of lizard, Urosaurus ornatus,to predict the expected response of species to global change. Estimates of maximum velocity and endurance capacity were obtainedfrom 16 populations throughout the range of U. ornatus. Informationon spatial variation was supplemented with data on temporalvariation spanning an eight year period from a single referencepopulation. I used thesedata to address two questions: 1) isthere an association between locomotory performance and theexpected habitat changes predicted from global climate modelsand 2) is there sufficient variation within a population torespond to habitat modification. Populations of U. ornatus varied significantly in sprint speedand stamina. Several environmental factors expected to correlatewith global climatechange were evaluated using the patternsof variation in locomotor performance. Results from this studysuggest that high elevation populations found in ponderosa pineforests should be most susceptible to changes in climate. Within-populationvariation was found to span the range of variation seen amongpopulations and was sensitive to temporal variation in climaticconditions. Given the expected and rapid change in environments,small, ectothermic, terrestrial species may not have the abilityto modify their geographic distribution. However, the resultspresented here suggest that only certain populations are atrisk; yet the evolutionary response of the population may belong relative to the rate of environment change.     

Thermal performance curves under daily thermal fluctuation: A study in helmeted water toad tadpoles

Most research in physiological ecology has focused on the effects of mean changes in temperature under the classic “hot vs cold” acclimation treatment; however, current evidence suggests that an increment in both the mean and variance of temperature could act synergistically to amplify the negative effects of global temperature increase and how it would affect fitness and performance-related traits in ectothermic organisms. We assessed the effects of acclimation to daily variance of temperature on thermal performance curves of swimming speed in helmeted water toad tadpoles (Calyptocephalella gayi). Acclimation treatments were 20 °C ± 0.1 SD (constant) and 20 °C ± 1.5 SD (fluctuating). We draw two key findings: first, tadpoles exposed to daily temperature fluctuation had reduced maximal performance (Z_max), and flattened thermal performance curves, thus supporting the “vertical shift or faster-slower” hypothesis, and suggesting that overall swimming performance would be lower through an examination of temperatures under more realistic and ecologically-relevant fluctuating regimens; second, there was significant interindividual variation in performance traits by means of significant repeatability estimates.Our present results suggest that the widespread use of constant acclimation temperatures in laboratory experiments to estimate thermal performance curves (TPCs) may lead to an overestimation of actual organismal performance. We encourage the use of temperature fluctuation acclimation treatments to better understand the variability of physiological traits, which predict ecological and evolutionary responses to global change.     

Physiological Variation in Clonal Anemones: Energy Balance and Quantitative Genetics

Our understanding of evolutionary mechanisms leading to populationdifferences in mean performance values relies on understandingperformance variation within single populations. Unfortunately,relatively little information about physiological variabilitywithin natural populations of organisms is available. In particular,to begin to understand how physiological traits evolve we needinformation on the extent of physiological variability relatedto the extent of genetic variability over a range of environmentalconditions experienced by individual populations. Clonal organismsmay be particularly well-suited to such studies because theyprovide an opportunity to use replicated genotypes (i.e., clonemates)in controlled experiments. We are using the cosmopolitan seaanemone Haliplanella lineata to explore physiological variancein natural populations. Growth, absorption and routine ratesof oxygen uptake do not vary among three clones from a singlepopulation when measured at 15°C, the approximate midpointin the seasonal range of water temperatures experienced by thispopulation. Broad-sense heritabilities for routine rates ofoxygen consumption and ammonia excretion (0.14 and 0.09, respectively),indicate a relatively low fraction of variance in these physiologicalrates is attributable to genetic variation among five clonesin this population. Although some literature indicates thatsuch low heritabilities may be expected when physiological traitsare measured at environmental mid-range as opposed to extremes,other evidence indicates that it will be difficult to predictthe trend between environmental stress and genetic variancein physiological performance.     

Evolutionary Analyses of Morphological and Physiological Plasticity in Thermally Variable Environments

SYNOPSIS. Morphological and physiological plasticity is oftenthought to represent an adaptive response to variable environments.However, determining whether a given pattern of plasticity isin fact adaptive is analytically challenging, as is evaluatingthe degree of and limits to adaptive plasticity. Here we describea general methodological framework for studying the evolutionof plastic responses. This framework synthesizes recent analyticaladvances from both evolutionary ecology and functional biology,and it does so by integrating field experiments, functionaland physiological analyses, environmental data, and geneticstudies of plasticity. We argue that studies of plasticity inresponse to the thermal environment may be particularly valuablein understanding the role of environmental variation in theevolution of plasticity: not only can thermally-relevant traitsoften be mechanistically and physiologically linked to the thermalenvironment, but also the variability and predictability ofthe thermal environment itself can be quantified on ecologicallyrelevant time scales. We illustrate this approach by reviewinga case study of seasonal plasticity in the extent of wing melanizationin Western White Butterflies (Pontia occidentalis). This reviewdemonstrates that 1) wing melanin plasticity is heritable, 2)plasticity does increase fitness in nature, but the effect variesbetween seasons and between years, 3) selection on existingvariation in the magnitude of plasticity favors increased plasticityin one melanin trait that affects thermoregulation, but 4) themarked unpredictability of short-term (within-season) weatherpatterns substantially limits the capacity of plasticity tomatch optimal wing phenotypes to the weather conditions actuallyexperienced. We complement the above case study with a casualreview of selected aspects of thermal acclimation responses.The magnitude of thermal acclimation ("flexibility") is demonstrablymodest rather than fully compensatory. The magnitude of geneticvariation (crucial to evolutionary responses to selection) inthermal acclimation responses has been investigated in onlya few species to date. In conclusion, we suggest that an understandingof selection and evolution of thermal acclimation will be enhancedby experimental examinations of mechanistic links between traitsand environments, of the physiological bases and functionalconsequences of acclimation, of patterns of environmental variabilityand predictability, of the fitness consequences of acclimationin nature, and of potential genetic constraints.     

Plasticity of size and growth in fluctuating thermal environments: comparing reaction norms and performance curves

Ectothermic animals exhibit two distinct kinds of plasticityin response to temperature: Thermal performance curves (TPCs),in which an individual's performance (e.g., growth rate) variesin response to current temperature; and developmental reactionnorms (DRNs), in which the trait value (e.g., adult body sizeor development time) of a genotype varies in response to developmentaltemperatures experienced over some time period during development.Here we explore patterns of genetic variation and selectionon TPCs and DRNs for insects in fluctuating thermal environments.First, we describe two statistical methods for partitioningtotal genetic variation into variation for overall size or performanceand variation in plasticity, and apply these methods to availabledatasets on DRNs and TPCs for insect growth and size. Our resultsindicate that for the datasets we considered, genetic variationin plasticity represents a larger proportion of the total geneticvariation in TPCs compared to DRNs, for the available datasets.Simulations suggest that estimates of the genetic variationin plasticity are strongly affected by the number and rangeof temperatures considered, and by the degree of nonlinearityin the TPC or DRN. Second, we review a recent analysis of fieldselection studies which indicates that directional selectionfavoring increased overall size is common in many systems—thatbigger is frequently fitter. Third, we use a recent theoreticalmodel to examine how selection on thermal performance curvesrelates to environmental temperatures during selection. Themodel predicts that if selection acts primarily on adult sizeor development time, then selection on thermal performance curvesfor larval growth or development rates is directly related tothe frequency distribution of temperatures experienced duringlarval development. Using data on caterpillar temperatures inthe field, we show that the strength of directional selectionon growth rate is predicted to be greater at the modal (mostfrequent) temperatures, not at the mean temperature or at temperaturesat which growth rate is maximized. Our results illustrate someof the differences in genetic architecture and patterns of selectionbetween thermal performance curves and developmental reactionnorms.     

Ecology and morphological variability of Aulacoseira granulata (Bacillariophyceae) in Spanish reservoirs

The ecology of Aulacoseira (formerly Melosira) granulata andits different forms in     

Water temperature, predation, and the neglected role of physiological rate effects in rocky intertidal communities

Ecologists and physiologists working on rocky shores have emphasizedthe effects of environmental stress on the distribution of intertidalorganisms. Although consumer stress models suggest that physicalextremes may often reduce predation and herbivory through negativeimpacts on the physiological performance of consumers, few fieldstudies have rigorously tested how environmental variation affectsfeeding rates. I review and analyze field experiments that quantifiedper capita feeding rates of a keystone predator, the sea starPisaster ochraceus, in relation to aerial heat stress, waveforces, and water temperature at three rocky intertidal siteson the Oregon coast. Predation rates during 14-day periods wereunrelated to aerial temperature, but decreased significantlywith decreasing water temperature. There was suggestive butinconclusive evidence that predation rates also declined withincreasing wave forces. Data-logger records suggested that thermalstress was rare in the wave-exposed habitats that I studied;sea star body temperatures likely reached warm levels (>24°C)on only 9 dates in 3 yr. In contrast, wind-driven upwellingregularly generated 3 to 5°C fluctuations in water temperature,and field and laboratory results suggest that such changes significantlyalter feeding rates of Pisaster. These physiological rate effects,near the center of an organism's thermal range, may not reducegrowth or fitness, and thus are distinct from the effects ofenvironmental stress. This study underscores the need to considerorganismal responses both under "normal" conditions, as wellas under extreme conditions. Examining both kinds of responsesis necessary to understand how different components of environmentalvariation regulate physiological performance and the strengthof species interactions in intertidal communities.     

Control of Germination and Seedling Morphology by Ethene: Differential Responses, Related to Habitat of Epilobium hirsutum L. and Chamerion angustifolium (L.) J. Holub

Germination rate and total germination of Epilobium hirsutumseed were increased by treatment with ethene in air (4 volumesper million) but seeds of Chamerion angustifolium were unaffected.Seventeen days from sowing the elongation of primary roots hadbeen reduced by ethene in both species but more markedly inE. hirsutum. Adventitious root formation at the base of hypocotylswas initiated by ethene in E. hirsutum but not in C. angustifolium.Root hair length was reduced by ethene rather more in E. hirsutumthan in C. angustifolium. The results are discussed in relationto the ecology and known differential waterlogging sensitivityof the two species. Epilobium hirsutum, Chamerion angustifolium, Willowherbs, ethene, germination, waterlogging, growth, roots, adventitious, ecology     

PHYLOGENETIC STUDIES OF COADAPTATION: PREFERRED TEMPERATURES VERSUS OPTIMAL PERFORMANCE TEMPERATURES OF LIZARDS

The view that behavior and physiological performance are tightly coadapted is a central principle of physiological ecology. Here, we test this principle using a comparative study of evolutionary patterns in thermal preferences and the thermal dependence of sprinting in some Australian skinks (Lygosominae). Thermal preferences (T_p) differ strikingly among genera (range 24° to 35°C), but critical thermal maxima (CTMax) (range 38° to 45°C) and optimal temperatures for sprinting (T_o, 32° to 35°C) vary less. Diurnal genera have relatively high T_p, T_o, and CTMax. In contrast, nocturnal genera have low T_p but have moderate to high T_o and CTMax. Both nonphylogenetic and phylogenetic (minimum-evolution) approaches suggest that coadaptation is tight only for genera with high T_p. Phylogenetic analyses suggest that low T_p and, thus, partial coadaptation are evolutionarily derived, indicating that low thermal preferences can evolve, even if this results in reduced performance. In one instance, thermal preferences and the thermal dependence of sprinting may have evolved in opposite directions, a phenomenon we call “antagonistic coadaptation.” We speculate on factors driving partial coadaptation and antagonistic coadaptation in these skinks.     

Short-term dynamics of a Melosira population in the plankton of an impoundment in central Chile

Relationships among the chlorophyll-specific photosyntheticbehaviour of a Melosira-dominated phytoplankton, net variationsin the quantity of Melosira in suspension, the rates of sinkingloss of Melosira cells and did fluctuations in water-columnstability were investigated in Embalse Rapel. central Chile.The short study was carried out during the autumnal equinoxialperiod (March. 1984) of maximal Melosira abundance to determinethe extent to which these various components might contributeto the distinctly bimodal seasonal distribution of phytoplanktonabundance in this reservoir. Diurnal photosynthetic productionwithin the illuminated layer and supposed column respirationwere found to be of a similar order, suggesting that net increasethrough cellular growth was already substantially limited byself-shading. Thus observed net changes in the standing populationmay have depended more on the relative magnitude of sinkingloss rates and recruitment through resuspension, which processesare profoundly influenced by alternations in wind-induced mixingand intense, near-surface, thermal stratification. As the relativefrequency and duration of these episodes vary during the year,so does the capacity of the Melosira to maintain or increaseits standing biomass. High cellular photosynthetic efficiencycoupled with rapid sinking rate appear to be of selective advantagewhen the cycle of alternation is approximately diel. The applicationof these findings to the seasonal distribution of M. granulatain the Rapel reservoir and to the ecology of planktonic Melosirapopulations elsewhere is briefly discussed.     

Courtship and Mate Choice in Fishes: Integrating Behavioral and Sensory Ecology

SYNOPSIS. Sexual selection theory predicts a coevolution betweenmale sexual ornamentation and female preference. The implicationof this prediction for sensory ecology is that there shouldbe a tight coupling between the physiology of male signal productionand the physiology of female signal reception. Indicator modelsof sexual selection predict that male ornamentation is correlatedwith male condition, and that female preference is correlatedwith male ornamentation. Indicator models of sexual selectionhave a conceptual overlap with resource acquisition and investmentmodels of behavioral ecology. Empirical studies with fishes,particularlywith guppies (Poecilia reticulata) and threespinesticklebacks (Gasterosteus aculeatus), suggest a strong connectionbetween acquired resources, male condition, male ornamentation,male courtship, and female preference.     

不同地理种群银杏大蚕蛾COI基因序列变异与遗传分化

银杏大蚕蛾Caligula japonica是亚洲东部的特有种, 既是一种重要的林业害虫, 也是一种珍贵的野生蚕类资源。为了揭示银杏大蚕蛾地理种群间的内在联系, 测定了我国分布的12个地理种群的线粒体细胞色素氧化酶C亚基I（COI）基因部分序列（GenBank登录号: FJ358506-FJ358517）, 对地理种群间的序列变异和遗传分化进行了分析。结果表明: 银杏大蚕蛾地理种群间的COI序列同源性高达99%~100%, 显示出比较小的遗传差异。序列对准后从供试COI序列中仅鉴定出9个变异位点和6个单元型, 其中3种是共享单元型。系统发育分析结果表明种群间已经按地理位置形成了一定的地理格局, AMOVA分析显示北方组和南方组之间已经具有明显的遗传分化（FST=0.478, P<0.001）。综合分析, 我们认为北方组和南方组之间的遗传分化可能与差异巨大的生态条件有关。研究结果为银杏大蚕蛾的种群遗传学和生态学研究提供了一个基本的分子生物学线索。     

Effects of Incubation Temperature on Crocodiles and the Evolution of Reptilian Oviparity

Crocodylus porosus is a mound-nesting crocodilian in which incubationtemperature influences the rate of embryonic development, theprobability that embryos will survive to hatching, post-hatchinggrowth rates and the probability of hatchlings surviving to2 yr of age. Similar responses have been described in Alligatormississippiensis (Joanen et al., 1987) and C. niloticus (Hutton,1987), and they reflect a suite of "non-sexual" effects of incubationtemperature. Temperature-dependent sex determination allocatessex on the basis of these "non-sexual" effects. In C. porosus,it results in maleness being assigned to embryos with high probabilitiesof surviving and good potential for post-hatching growth. Withinthe limits of survival, effects of the moisture environmenton embryological development rate and hatchling fitness seemminor relative to those of the temperature environment. Reptilian orders have either obligate oviparity (chelonians,crocodilians and rhynchocephalians) or facultative oviparity(squamates), depending on the extent of embryonic developmentwithin the oviducts. The distinction is equally one betweenembryos which are buffered from thermal effects within a female'sbody (facultative oviparity) and those that are not (obligateoviparity). Facultative oviparity and internal thermal bufferingmay be the primitive condition within the Class Reptilia, andthe "shell-less" eggs of extant squamates may reflect the originalamniote egg. Obligate oviparity, which also exists in birds,appears to have been a specialized development, and is a blindend in the evolution of viviparity among vertebrates. The significanceof thermal buffering being lost in obligate oviparous reptilesremains unclear.     

Differential Patterns of Gene Expression and Gene Complement in Laboratory-Evolved Lines of E. coli

Laboratory selection experiments play a prominent role in understandingorganismal adaptation. Although bacteria are not yet commonlyused for such experiments, they are well suited for analysesof both the organismic and the genetic basis of adaptation.Bacteria can be maintained in large populations while occupyinglimited laboratory space, have short generation times, are wellcharacterized physiologically, biochemically, and genetically,and are readily frozen and revived from the freezer. In addition,the genomes of many species are completely sequenced and knowledgeof gene function is unparalleled. Here we review general aspectsof selection experiments, the history of using selection experimentsin combination with thermal biology and genomics, and highlightfindings from six lines of Escherichia coli adapted to hightemperature (41.5°C), including changes in organismal fitness,physiological performance, gene complement and gene expression.Our results are an example of the powerful insights that canbe discovered by combining the tools and analyses of many biologicaldisciplines including genomics, evolutionary biology, genetics,and evolutionary physiology.