Facultative placentotrophy: half-way house or strategic solution?

While yolk is generally the primary source of embryo nutrients in squamates, numerous species supplement this with facultative placentotrophy. We argue that facultative placentotrophy should have selective importance relevant to offspring fitness. In the skink Niveoscincus metallicus, the size of ovulated eggs is unrelated to maternal size but large females produce offspring that are larger than is necessary for survival, providing evidence for facultative placentotrophy. We discuss the circumstances in which facultative placentotrophy might be used to supplement the nutritional support provided by yolk and obligate placentotrophy in this species, and present summary data from experiments designed to investigate these circumstances. Clutch reduction by oviduct removal had no effect on neonate mass or snout-vent length, indicating that the number of embryos does not influence allocation of maternal resources once gestation has commenced. Manipulation of maternal basking opportunity in combination with food intake during pregnancy suggested that an important role of facultative placentotrophy is the optimization of embryonic fat reserves. This hypothesis was supported by the observation that larger neonates have larger abdominal fat bodies. These reserves presumably facilitate survival in the relatively short pre-hibernatory period available to newborn animals. Our data indicate that they also play a vital role in maintaining pre-natal condition if birth is delayed by adverse weather, a common circumstance in this species. In such circumstances the yolk has been used up and the placental membranes have degenerated. Experimental induction of premature ovulation of eggs with reduced yolk, achieved by injecting females with FSH, was followed by fertilization using stored sperm. Gestation length was greatly reduced and the resulting neonates were all < or =75% normal birth mass, with two of the six births being stillborn. Thus facultative placentotrophy does not appear to be a means of compensating for a poor yolk supply. We suggest that facultative placentotrophy in N. metallicus is not a transitional stage en route to greater reliance on obligate placentotrophy, but a uniquely squamate adaptation that provides flexibility in embryonic nutrition, and optimizes offspring fitness in an unpredictable temperate climate.     

海南岛儋州橡胶林生态系统氮储量研究

生态系统N储量是由乔木层、林下植被层、凋落物层和土壤层N储量组成的。对海南岛儋州6个龄级(5、10、15、20、25、30 a)的橡胶林进行调查采样,并进行室内测试分析得出N含量,计算得出各个层次的N储量和生态系统总N储量。结果表明:(1)儋州一代和二代橡胶林土壤N含量和储量均随着土壤层次的增加而减少,橡胶林土壤N含量和储量均表现为0～20 cm内一代小于二代,20～40 cm内两代相差不大,40 cm以下一代均明显大于二代;(2)儋州橡胶林生态系统总N储量范围为5.30～8.53 t·hm^-2,平均为6.447 t·hm^-2,其中土壤N储量5.727 t·hm^-2,植物(包括乔木和林下植被)N储量为0.694 t·hm^-2,凋落物N储量0.026 t·hm^-2; 土壤N储量所占比例最大(88.83%),是橡胶林生态系统N储量最主要的组成部分。说明海南岛儋州橡胶林土壤总体处于缺氮状态,有必要增施氮肥或复合肥。     

The concept of energy height in animal locomotion: separating mechanics from physiology

The distance flown in gliding is proportional to the starting height, not to the starting potential energy, and it is independent of the body mass. By analogy, in powered flight, the quantity of stored fuel can be converted into a virtual "fuel energy height", defined as the height to which the fuel energy could lift the bird against gravity, if it were converted into work. This is a logarithmic function of the fuel fraction, not of the absolute amount of fuel, or of the body mass. It takes account of the strength of gravity, and of the efficiency with which fuel energy is converted into work. The "performance number" is the gradient on which a migrating bird comes "down" from its initial fuel energy height. It is mechanical (not physiological) in character, and corresponds to the lift:drag ratio in a fixed-wing aircraft. The concept of range as an initial energy height multiplied by a performance number can also be applied to swimming and running animals. Performance number, and also the related variable "cost of transport", are both independent of gravity in flying and running, but not in swimming.Migration by thermal soaring is analogous to powered flight with stopovers, except that the bird replenishes its potential energy by climbing in thermals, rather than replenishing fuel energy during stopovers. Rates of climb in thermals are typically higher than fuel energy rates of climb, but the available height band is two orders of magnitude smaller, and the intervals at which energy replenishment is needed are correspondingly shorter. Albatrosses replenish their kinetic energy by exploiting discontinuities in the wind flow over waves, requiring replenishment at intervals of tens of seconds, a further two orders of magnitude shorter than in thermal soaring.Fat energy height can be used as a measure of "condition", which is independent of the size or type of the animal. The fat energy height at which a migrant must arrive on the breeding grounds, in order to breed successfully, reflects the ecological characteristics of the habitat, not the size or character of the bird. Energy height expresses what an animal or machine can do with its stored energy, not the amount of energy.     

The blubber adipocyte index: A nondestructive biomarker of adiposity in humpback whales (Megaptera novaeangliae)

The ability to accurately evaluate the energetic health of wildlife is of critical importance, particularly under conditions of environmental change. Despite the relevance of this issue, currently there are no reliable, standardized, nonlethal measures to assess the energetic reserves of large, free‐roaming marine mammals such as baleen whales. This study investigated the potential of adipocyte area analysis and further, a standardized adipocyte index (AI ), to yield reliable information regarding humpback whale (Megaptera novaeangliae ) adiposity. Adipocyte area and AI , as ascertained by image analysis, showed a direct correlation with each other but only a weak correlation with the commonly used, but error prone, blubber lipid‐percent measure. The relative power of the three respective measures was further evaluated by comparing humpback whale cohorts at different stages of migration and fasting. Adipocyte area, AI , and blubber lipid‐percent were assessed by binary logistic regression revealing that adipocyte area had the greatest probability to predict the migration cohort with a high level of redundancy attributed to the AI given their strong linear relationship (r = −.784). When only AI and lipid‐percent were assessed, the performance of both predictor variables was significant but the power of AI far exceeded lipid‐percent. The sensitivity of adipocyte metrics and the rapid, nonlethal, and inexpensive nature of the methodology and AI calculation validate the inclusion of the AI in long‐term monitoring of humpback whale population health, and further raises its potential for broader wildlife applications.     

基因工程在能源植物改良中的应用

利用基因工程技术改良能源植物,对降低能源植物向生物燃料(生物乙醇、生物柴油)的转化成本、提高能源转化效率有着非常重要的意义。目前,基因工程技术已被广泛应用于提高植物总的生物产量、降低或改变植物木质素的含量与成分、在植物体中大量表达纤维素降解酶、提高油料植物的产油量以及改变植物油酯的组成成分等方面的研究。概述了利用基因工程技术在以上方面对能源植物进行改良已取得的进展,讨论了现存问题及未来的发展前景。     

深圳福田无瓣海桑-海桑林能量的研究

在研究生物量、生产力的基础上,对深圳福田无瓣海桑-海桑林中2种红树植物海桑和无瓣海桑各组分的干重热值、林分能量现存量、年能量净固定量进行了研究．结果表明,各组分样品干重热值有一定的差异,树叶干重热值最高,纫根干重热值最低;海桑各组分样品干重热值比无瓣海桑相应组分稍高．林分能量现存量(1999年10月)为84774．72kJ·m^2,其中无瓣海桑种群能量现存量为54693．26kJ·m^-2,占林分总的64．54％,海桑种群能量现存量为30051．46kJ·m^-2,占林分总量的35．46％．林分凋落物的能量归还量(1999年)为24549．54kJ·m^-2·年^-1,其中无瓣海桑种群的能量归还量为17223．99kJ·m^-2·年^-1,占总林分的70．16％,海桑种群的能量归还量为7325．55kJ·m^-2·年^-1,占总林分的29．84％．林分能量净固定量为50391．4kJ·m^-2·年^-1,其中无瓣海桑种群和海桑种群的能量净固定量为分别为31778kJ·m^-2·年^-1和18613．4kJ·m^-2·年^-1．     

Drought and shade deplete nonstructural carbohydrate reserves in seedlings of five temperate tree species

Plants that store nonstructural carbohydrates (NSC) may rely on carbon reserves to survive carbon‐limiting stress, assuming that reserves can be mobilized. We asked whether carbon reserves decrease in resource stressed seedlings, and if NSC allocation is related to species' relative stress tolerances. We tested the effects of stress (shade, drought, and defoliation) on NSC in seedlings of five temperate tree species (Acer rubrum Marsh., Betula papyrifera Marsh., Fraxinus americana L., Quercus rubra L., and Quercus velutina Lam.). In a greenhouse experiment, seedlings were subjected to combinations of shade, drought, and defoliation. We harvested seedlings over 32–97 days and measured biomass and NSC concentrations in stems and roots to estimate depletion rates. For all species and treatments, except for defoliation, seedling growth and NSC accumulation ceased. Shade and drought combined caused total NSC decreases in all species. For shade or drought alone, only some species experienced decreases. Starch followed similar patterns as total NSC, but soluble sugars increased under drought for drought‐tolerant species. These results provide evidence that species deplete stored carbon in response to carbon limiting stress and that species differences in NSC response may be important for understanding carbon depletion as a buffer against shade‐ and drought‐induced mortality.     

Detrimental effects of recent ocean surface warming on growth condition of Atlantic salmon

Ocean climate impacts on survivorship and growth of Atlantic salmon are complex, but still poorly understood. Stock abundances have declined over the past three decades and 1992–2006 has seen widespread sea surface temperature (SST) warming of the NE Atlantic, including the foraging areas exploited by salmon of southern European origin. Salmon cease feeding on return migration, and here we express the final growth condition of year‐classes of one‐sea winter adults at, or just before, freshwater re‐entry as the predicted weight at standard length. Two independent 14‐year time series for a single river stock and for mixed, multiple stocks revealed almost identical temporal patterns in growth condition variation, and an overall trend decrease of 11–14% over the past decade. Growth condition has fallen as SST anomaly has risen, and for each year‐class the midwinter (January) SST anomalies they experienced at sea correlated negatively with their final condition on migratory return during the subsequent summer months. Stored lipids are crucial for survival and for the prespawning provisioning of eggs in freshwater, and we show that under‐weight individuals have disproportionately low reserves. The poorest condition fish (～30% under‐weight) returned with lipid stores reduced by ～80%. This study concurs with previous analyses of other North Atlantic top consumers (e.g. somatic condition of tuna, reproductive failure of seabirds) showing evidence of major, recent climate‐driven changes in the eastern North Atlantic pelagic ecosystem, and the likely importance of bottom‐up control processes. Because salmon abundances presently remain at historical lows, fecundity of recent year‐classes will have been increasingly compromised. Measures of year‐class growth condition should therefore be incorporated in the analysis and setting of numerical spawning escapements for threatened stocks, and conservation limits should be revised upwards conservatively during periods of excessive ocean climate warming.     

Primary and secondary vegetation patches as contributors to floristic diversity in a tropical deciduous forest landscape

The floristic diversity of Mexican tropical deciduous forests (TDF) is of critical importance given the high species richness (alpha diversity), species turnover (beta diversity), and the intense deforestation rates. Currently, most TDF landscapes are mosaics of agricultural land, secondary vegetation, and patches of relatively undisturbed primary vegetation. Here we illustrate how both primary forest remnants and secondary vegetation patches contribute to the floristic diversity of TDF in a landscape of volcanic origin in central Veracruz, Mexico. Our objectives were to assess sampling efficiency and inventory completeness, to compare mean and cumulative species richness between primary forest and secondary vegetation sites, and to analyze beta diversity between vegetation types. In an area of 12,300 m2 we recorded 105 families, 390 genera, and 682 species. Species inventories for both vegetation types were about 80% complete. Secondary vegetation is more alpha diverse than primary forest, both in terms of cumulative and mean species richness. We found a remarkably high beta diversity between vegetation types (75% of complementarity, 91.60% of mean dissimilarity). We also identified the species that contribute the most to similarity within vegetation types and to dissimilarity between vegetation types. Our results support the idea that assessing biodiversity on the landscape scale is an appropriate way to ascertain the impact of human activities. For this land mosaic, conservation of the flora would not be possible by focusing solely on primary forest remnants. We propose the implementation of a network of small conservation areas with a flexible structure, following the “archipelago reserve” model.