Phenotypic flexibility of digestive system in Atlantic cod (Gadus morhua)

This study examined the restoration of the digestive capacity of Atlantic cod (Gadus morhua Linnaeus) following a long period of food deprivation. Fifty cod (48 cm, 1 kg) were food-deprived for 68 days and then fed in excess with capelin (Mallotus villosus Müller) on alternate days. Ten fish were sampled after 0, 2, 6, 14 and 28 days and the mass of the pyloric caeca, intestine and carcass determined. Two metabolic enzymes (cytochrome c oxidase and citrate synthase) were assayed in white muscle, pyloric caeca and intestine, and trypsin activity was measured in the pyloric caeca. A delay of 14 days was required before body mass started to increase markedly, whereas most of the increase in mass of both the pyloric caeca and intestine relative to fish length occurred earlier in the experiment. By day 14, the activities of trypsin and citrate synthase in the pyloric caeca as well as citrate synthase in the intestine had reached maxima. The growth of the digestive tissues and restoration of their metabolic capacities thus occur early upon refeeding and are likely required for recovery growth to take place. The phenotypic flexibility of the cod digestive system is therefore remarkable: increases in trypsin activity and size of pyloric caeca resulted in a combined 29-fold increase in digestive capacity of the fish during the refeeding period. Our study suggests that Atlantic cod are able to cope with marked fluctuations in food availability in their environment by making a rapid adjustment of their digestive capacity as soon as food availability increases.     

Phenotypic flexibility of body composition associated with seasonal acclimatization in passerine birds

Improved winter cold tolerance is widespread among small birds overwintering in cold climates and is associated with improved shivering endurance and elevated summit metabolic rate (M_sum). Phenotypic flexibility resulting in elevated M_sum could result from either increased skeletal muscle mass (perhaps with support from similar adjustments in “nutritional organs”) and/or cellular metabolic intensity. We investigated seasonal changes in body composition of three species of passerine birds resident in cold winter climates, all of which show large seasonal variations in M_sum (>25%); white-breasted nuthatch (Sitta carolinensis), black-capped chickadee (Poecile atricapillus), and house sparrow (Passer domesticus). All three species displayed significant winter increases in pectoralis and heart masses, and supracoracoideus mass also increased in winter chickadees. Gizzard mass increased in winter for all three species, but masses of other nutritional organs did not vary consistently with season. These data suggest that winter increases in pectoralis and heart masses are important contributors to elevated thermogenic capacity and cold tolerance, but seasonal variation in nutritional organ masses, other than gizzard, which is likely associated with dietary changes, are not universally associated with seasonal phenotypes. The winter increases in pectoralis and heart masses are consistent with data from other small passerines showing marked seasonal changes in cold tolerance and support the Variable Maximum Model of seasonal phenotypic flexibility, where physiological adjustments that promote improved cold tolerance, also result in elevated M_sum.     

Climate warming,ecological mismatch at arrival and population decline in migratory birds

Climate is changing at a fast pace, causing widespread, profound consequences for living organisms. Failure to adjust the timing of life-cycle events to climate may jeopardize populations by causing ecological mismatches to the life cycle of other species and abiotic factors. Population declines of some migratory birds breeding in Europe have been suggested to depend on their inability to adjust migration phenology so as to keep track of advancement of spring events at their breeding grounds. In fact, several migrants have advanced their spring arrival date, but whether such advancement has been sufficient to compensate for temporal shift in spring phenophases or, conversely, birds have become ecologically mismatched, is still an unanswered question, with very few exceptions. We used a novel approach based on accumulated winter and spring temperatures (degree-days) as a proxy for timing of spring biological events to test if the progress of spring at arrival to the breeding areas by 117 European migratory bird species has changed over the past five decades. Migrants, and particularly those wintering in sub-Saharan Africa, now arrive at higher degree-days and may have therefore accumulated a ‘thermal delay’, thus possibly becoming increasingly mismatched to spring phenology. Species with greater ‘thermal delay’ have shown larger population decline, and this evidence was not confounded by concomitant ecological factors or by phylogenetic effects. These findings provide general support to the largely untested hypotheses that migratory birds are becoming ecologically mismatched and that failure to respond to climate change can have severe negative impacts on their populations. The novel approach we adopted can be extended to the analysis of ecological consequences of phenological response to climate change by other taxa.     

Spare capacity and phenotypic flexibility in the digestive system of a migratory bird: defining the limits of animal design

Flexible phenotypes enable animals to live in environments that change over space and time, and knowing the limits to and the required time scale for this flexibility provides insights into constraints on energy and nutrient intake, diet diversity and niche width. We quantified the level of immediate and ultimate spare capacity, and thus the extent of phenotypic flexibility, in the digestive system of a migratory bird in response to increased energy demand, and identified the digestive constraints responsible for the limits on sustained energy intake. Immediate spare capacity decreased from approximately 50% for birds acclimated to relatively benign temperatures to less than 20% as birds approached their maximum sustainable energy intake. Ultimate spare capacity enabled an increase in feeding rate of approximately 126% as measured in birds acclimated for weeks at −29°C compared with +21°C. Increased gut size and not tissue-specific differences in nutrient uptake or changes in digestive efficiency or retention time were primarily responsible for this increase in capacity with energy demand, and this change required more than 1–2 days. Thus, the pace of change in digestive organ size may often constrain energy intake and, for birds, retard the pace of their migration.     

Phenotypic flexibility in passerine birds: Seasonal variation of aerobic enzyme activities in skeletal muscle

Improved winter cold tolerance is widespread among small passerines resident in cold climates and is generally associated with elevated summit metabolic rate (M_sum=maximum thermoregulatory metabolic rate) and improved shivering endurance with increased reliance on lipids as fuel. Elevated M_sum and improved cold tolerance may result from greater metabolic intensity, due to mass-specific increase in oxidative enzyme capacity, or increase in the masses of thermogenic tissues. To examine the mechanisms underlying winter increases in M_sum, we investigated seasonal changes in mass-specific and total activities of the key aerobic enzymes citrate synthase (CS) and β-hydroxyacyl CoA-dehydrogenase (HOAD) in pectoralis, supracoracoideus and mixed leg muscles of three resident passerine species, black-capped chickadee (Poecile atricapillus), house sparrow (Passer domesticus), and white-breasted nuthatch (Sitta carolinensis). Activities of CS were generally higher in winter than in summer muscles for chickadees and house sparrows, but not nuthatches. Mass-specific HOAD activity was significantly elevated in winter relative to summer in all muscles for chickadees, but did not vary significantly with season for sparrows or nuthatches, except for sparrow leg muscle. These results suggest that modulation of substrate flux and cellular aerobic capacity in muscle contribute to seasonal metabolic flexibility in some species and tissues, but such changes play varying roles among small passerines resident in cold climates.     

细嘴滨鹬春季迁徙中转停歇期间机体结构的表型弹性

通过描述细嘴滨鹬（Calidris tenuirostris）春季在上海中转停歇期间个体与器官表型变化,分析了中转停歇期间机体结构表型弹性的变化。结果表明：细嘴滨鹬中转停歇期间,体质量显著增加,最大增量约相当于平均体质量的52.2％。体质量增加的最大因素是脂肪质量的增加;其次是胸肌质量的增加,胸肌质量随体质量平行变化;腿肌与心质量随体质量的增加也有增加趋势;消化器官的变化分为2方面,一是消化腺（肝、胰）质量增加,二是消化道质量（砂囊、肠）没有大的变化,推测消化道没有大变化的原因可能是保留有一定的备用容量,细嘴滨鹬通过消化腺的增大来快速提高停歇期的觅食效率,同时避免重建消化器官的能量与时间的消耗,提高整体迁徙速度;脑、肺、肾、脾、眼及盐腺等器官质量保持稳定。     

Optimal moult strategies in migratory birds

Avian migration, which involves billions of birds flying vast distances, is known to influence all aspects of avian life. Here we investigate how birds fit moult into an annual cycle determined by the need to migrate. Large variation exists in moulting patterns in relation to migration: for instance, moult can occur after breeding in the summer or after arrival in the wintering quarters. Here we use an optimal annual routine model to investigate why this variation exists. The modelled bird's decisions depend on the time of year, its energy reserves, breeding status, experience, flight feather quality and location. Our results suggest that the temporal and spatial variations in food are an important influence on a migratory bird's annual cycle. Summer moult occurs when food has a high peak on the breeding site in the summer, but it is less seasonal elsewhere. Winter moult occurs if there is a short period of high food availability in summer and a strong winter peak at different locations (i.e. the food is very seasonal but in opposite phase on these areas). This finding might explain why only long-distance migrants have a winter moult.     

Behavioural flexibility and invasion success in birds

Behavioural flexibility has long been thought to provide advantages for animals when they invade novel environments. This hypothesis has recently received empirical support in a study of avian species introduced to New Zealand, but it remains to be determined whether behavioural flexibility is a general mechanism influencing invasion success. In this study, we examined introduction success of 69 bird species in different regions of the world as a function of their degree of behavioural flexibility. Specifically, we predicted that species with relatively large brains and a high frequency of foraging innovations in their area of origin should show a higher probability of establishing themselves where they were introduced than species with small brains and low innovation frequencies. An analysis with general linear modelling (GLM) supported the prediction for relative brain size, even when controlling for phylogenetic biases and potential confounding variables. The only covariates that remained with relative brain size were plumage dimorphism, human commensalism and nest site. A pairwise comparison of closely related species also revealed that successful invaders showed a higher frequency of foraging innovations in their region of origin. This result held even when differences in research effort between species were considered. Overall, the results confirm and generalize the hypothesis that behavioural flexibility is a major determinant of invasion success in birds.     

Protandry and sexual dimorphism in trans-Saharan migratory birds

Earlier arrival to reproductive sites of males relative to females(protandry) is widespread among migratory organisms. Diversemechanisms have been proposed that may select for protandry,including competition for limiting resources (e.g., territories)or mates. In species with large variation in male reproductivesuccess, such as polygamous species and those with intense spermcompetition, early arriving males may accrue a fitness advantagebecause they acquire more mates or have larger chances of paternity.Comparative studies of birds have shown that sexual size dimorphism(SSD) is positively associated with the level of polygyny, whereasintense sperm competition is associated with sexual dichromatism(SD). Positive correlations between protandry and SSD or SDcan therefore be expected to exist across avian species. Becauselarge males are predicted to be better able to cope with adverseecological conditions early in the breeding season, selectionfor protandry, in turn, may have a correlated response on SSDamong migratory species breeding in boreal latitudes. Althoughprevious studies of birds have analyzed the association betweenSSD and protandry, none has analyzed SD in relation to protandry.Here we analyze the association between protandry during springmigration, SSD, and SD in 21 trans-Saharan monogamous migratorybird species. The difference in median migration dates betweenfemales and males, reflecting protandry, was positively associatedwith SD but not with SSD. Because dichromatism is positivelyrelated to sperm competition across species, present resultsare consistent with predictions derived from sexual selectionhypotheses for the evolution of protandry mediated by spermcompetition.     

腐殖质呼吸作用及其生态学意义

腐殖质呼吸是厌氧环境中普遍存在的一种微生物呼吸代谢模式.自1996年发现以来,日益成为生态学与环境科学领域的研究热点.在厌氧条件下,一些微生物能以腐殖质作为唯一电子受体,氧化环境中的有机质或者甲苯等环境有毒物质,产生CO2,参与碳循环;同时,腐殖质呼吸作用产生的还原态腐殖质可以还原环境中的一些氧化态物质,如Fe(III)、Mn(IV)、Cr(VI)、U(VI) 、硝基芳香化合物和多卤代污染物.因此,腐殖质呼吸能够影响环境中C、N、Fe、Mn以及一些痕量金属元素的生物地球化学循环,并且能够促进重金属以及有机污染物的脱毒,在水体自净、污染土壤原位修复、污水处理等方面具有积极作用.     

植物源异戊二烯及其生态意义

异戊二烯为植物挥的众多有机碳氢化合物中的主要成分,它的合成和释放对全球尺度上的C素平衡、温室效应的大气污染都有极其重要的作用。本文系统论述了影响异戊二烯释放的主要因子,异戊二烯的释放量及其计量方法,以及它可能的生态意义,指出了研究多重环境胁迫与异戊二烯合成和释放的关系的必要性。     

Pine root structure and its potential significance for root function

Actively growing roots of pouch-grown Pinus banksiana Lamb. are known to have three anatomically distinct zones, i.e., white, condensed tannin, and cork (in order of increasing distance from the root tip). Roots of pouch and pot-grown Pinus taeda L., and field-grown P. banksiana also develop these three zones. The terminal region of a dormant root resembles the condensed tannin zone, with the addition of a suberized metacutis partially surrounding the apical meristem. White roots are anatomically suited for efficient ion uptake due to the presence of a living cortex. The condensed tannin zones of both growing and dormant roots have a dead cortex but retain passage cells in their endodermal layers, through which some ion uptake could occur. The effect of the maturation from white to condensed tannin zone on water uptake is difficult to predict, but some uptake would occur through the endodermal passage cells. In the young cork zone, no ion and little water absorption should occur. The discrepancies between results of separate anatomical and physiological investigations of tree roots need to be resolved by correlative studies incorporating both approaches in individual experiments. This revised version was published online in June 2006 with corrections to the Cover Date.     

粘液繁殖体及其生态功能

对粘液繁殖体的概念、粘液性质、粘液繁殖体的研究现状及粘液繁殖体研究中存在的问题进行了论述。分布在干旱区的十字花科、爵床科、菊科等植物具有粘液繁殖体。有关粘液繁殖体的研究集中在具有粘液繁殖体植物的识别、粘液形态结构及成分、粘液溶出机制及过程、粘液繁殖体的生态功能等几个方面。尽管已有研究表明,粘液繁殖体具有促进种子远距离传播、促进繁殖体的萌发及苗的发育、使种子免受摩擦损害和动物捕食等生态功能,但目前人们对粘液繁殖体的生态意义尚不十分清楚,从多物种比较研究中阐明粘液繁殖体生态意义的研究尚很少见。继续识别具有粘液繁殖体的植物,改善现有的研究手段,加强粘液繁殖体对植被恢复价值的研究是目前粘液繁殖体研究面临的挑战。     

Conformational flexibility and its functional significance in some protein molecules

Crystallography has contributed much to our knowledge of protein flexibility and here are described some examples of large-scale segmental flexibilities discovered by X=ray diffraction. These examples indicate that flexibility may be required for enzymatic catalysis and other functions of proteins, and also for their regulation.     

Physiological flexibility and climate change: The case of digestive function regulation in lizards

Our planet is undergoing fast environmental changes, which are referred as global change. In this new scenario, it is of paramount relevance to understand the mechanistic basis of animal responses to environmental change. Here we analyze to what extent seasonal changes in the digestive function of the lizard Liolaemus moradoensis is under endogenous (i.e., hard wired) or exogenous (i.e., environmentally determined) control. For this purpose we compared animals collected in the field during autumn, winter and summer, against (experimental) specimens collected in the field at the beginning of autumn and reared in the laboratory under simulated summer conditions until winter. We found that different aspects of the digestive function are under different types of control: small intestine length appears to be under endogenous control (i.e., experimental animals were similar to winter animals), small intestine mass appears to be under exogenous control (i.e., experimental animals were similar to summer animals), and specific enzyme activities did not change throughout the year. Thus, we suspect that processes related with gut length, such as cell division, may be under endogenous control, while others related with gut mass, such as enterocyte size and content, may be determined by exogenous factors, such as the presence of food in the intestinal lumen. Faced with accelerated changing conditions, the ability of vertebrates to cope will be closely related with their plasticity in fitness-associated traits. More studies aimed at determining the levels and limits of physiological flexibility will be necessary to understand this phenomenon.     

The scheduling of molt in migratory birds

Summary We model the yearly cycle of small migratory birds to explain the variation in scheduling of complete molt, in particular why some birds molt immediately after breeding on the breeding grounds (summer molt) whereas others migrate to their wintering grounds before molt is initiated (winter molt). We employ the method of dynamic programming, because of its suitability for modelling life history traits. Feather quality and latitude entered the model as state variables and were assumed to affect survival rate and reproductive success. Migration and molt were assumed to be associated with increased mortality risks. By changing the parameters in the model we were able to generate most existing molt patterns, including summer and winter molt, biannual (summer and winter) molt, and molt migration. Our model suggests that the scheduling of molt is basically a result of a trade-off between having a high feather quality during breeding versus during the non-breeding period. A high impact of feather quality on survival rate in combination with low costs of molt resulted in biannual molt. Winter molt became more likely as the survival rateper se increased. A low seasonal amplitude in survival rate is a prerequisite for the occurrence of molt migration. Molt duration, migration costs and reproductive successper se were found to have no impact on the timing of molt. We also investigated the effect of benefits from prior occupancy at breeding and winter grounds.     

Patterns of phenological changes in migratory birds

The phenology of avian migration appears to be changing in response to climate change. Seemingly contradictory differences in the timing of these annual cycles have been reported in published studies. We show that differences between studies in the choice of songbird species, as well as in the measurements of migration phenology, can explain most of the reported differences. Furthermore, while earlier spring arrival is evident across these studies, trends in timing of departure show large variation between species and according to individual timing of migration (early-arriving vs. late-departing individuals). Much of the variation in departure between species could be explained by each species’ migratory status. We present a detailed analysis of migrants recorded at a Danish migration site, and reveal that although shifts in migration timing can be demonstrated for almost all species, these shifts are either most pronounced in the early arriving/late departing individuals or the changes are similar. Thus most individuals do not seem to change their breeding-area residence time (BART). As BART is likely to reflect ecologically important factors, e.g. number of clutches, we expect that only small effects have been exerted on the breeding ecology of the studied species in the time period investigated. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.