In situ estimation of net CO2 assimilation, photosynthetic electron flow and photorespiration in Turkey oak (Q. cerris L.) leaves: diurnal cycles under different levels of water supply

Diurnal time courses of net CO₂ assimilation rates, stomatal conductance and light-driven electron fluxes were measured in situ on attached leaves of 30-year-old Turkey oak trees (Quercus cerris L.) under natural summer conditions in central Italy. Combined measurements of gas exchange and chlorophyll a fluorescence under low O₂ concentrations allowed the demonstration of a linear relationship between the photochemical efficiency of PSII (fluorescence measurements) and the apparent quantum yield of gross photosynthesis (gas exchange). This relationship was used under normal O₂ to compute total light-driven electron fluxes, and to partition them into fractions used for RuBP carboxylation or RuBP oxygenation. This procedure also yielded an indirect estimate of the rate of photorespiration in vivo. The time courses of light-driven electron flow, net CO₂ assimilation and photorespiration paralleled that of photosynthetic photon flux density, with important afternoon deviations as soon as a severe drought stress occurred, whereas photochemical efficiency and maximal fluorescence underwent large but reversible diurnal decreases. The latter observation indicated the occurrence of a large non-photochemical energy dissipation at PSII. We estimated that less than 60% of the total photosynthetic electron flow was used for carbon assimilation at midday, while about 40% was devoted to photorespiration. The rate of carbon loss by photorespiration (R₁) reached mean levels of 56% of net assimilation rates. The potential application of this technique to analysis of the relative contributions of thermal de-excitation at PSII and photorespiratory carbon recycling in the protection of photosynthesis against stress effects is discussed.     

Geographical and latitudinal variation in growth patterns and adult body size of Swedish moose (Alces alces)

We examined the geographical pattern in growth and adult body size among 14 populations of Swedish moose (Alces alces) using data from 4,294 moose (1.5 years old) killed during the hunting season in 1989–1992. In both sexes, adult body mass was significantly positively correlated with latitude. Moose in northern populations had a 15–20% larger adult body mass than moose in the south. Juvenile body mass was correlated with neither latitude nor adult body mass. Thus, variation in time (years) and rate of body growth after the juvenile stage were responsible for most of the variation in adult body mass among populations. Moose in northern populations grew for approximately 2 more years of life than southern moose. In contrast to adult body mass, skeletal size (measured as jawbone length) was not correlated with latitude, suggesting that variation in adult body mass was primarily due to differences in fat reserves. Discrimination between population characteristics, such as moose density, climate, and the amount of browse available to moose, showed climatic harshness to be the most important variable explaining geographical variation in body mass among populations. The results support the notion that in mammals body size increases with latitude in accordance with Bergmann's rule. We conclude that (1) variation in patterns of growth after the juvenile stage is the main cause of the latitudinal trend in adult body size in moose, and (2) climatic conditions are a more important factor than population density and availability of food in explaining geographical variation in growth patterns and adult body mass between populations of Swedish moose.     

Plastid development in germinating wheat (Triticum aestivum) is enhanced by gibberellic acid and delayed by gabaculine

Etioplast development and protochlorophyllide (Pchlide) accumulation was studied in wheat seedlings ( Triticum aestivum L. cv. Walde, Weibull) grown in darkness on gibberellic acid (GA₃), gabaculine (3-amino-2,3-dihydrobenzoic acid), or on a combination of the two. The results were compared with the features of seedlings grown on water only. GA₃ enhanced shoot growth and promoted etioplast development. A correlation was observed between the appearance of prolamellar bodies (PLBs) and of phototransformable Pchlide. Gabaculine, a known tetrapyrrole biosynthesis inhibitor, delayed growth, slowed down the rate of PLB formation and caused structural alterations of the etioplasts up to 48 h of germination. Gabaculine also delayed the formation of phototransformable Pchlide as well as overall Pchlide biosynthesis, as determined by low-temperature fluorescence emission in vivo. The spectral blue-shift of newly formed chlorophyllide (Chlide) was delayed in irradiated dark-grown gabaculine-grown seedlings, indicating an inhibited dissociation of Chlide and NADPH-Pchlide oxidoreductase (Pchlide reductase: EC 1.3.1.33). Thus there is a close correlation between accumulation of Pchlide and etioplast development, also under conditions when development is enhanced or delayed.     

Physiological energetics of the zebra musselDreissena polymorpha in lakes I. Growth and reproductive effort

Shell growth of tagged zebra mussels (Dreissena polymorpha) was monitored in lakes at 3 sites over 1 1/2 years. It varied greatly with the season and was almost absent during winter months. Shell growth was significantly correlated with seston concentration, but not with water temperature. The theoretical maximum size (L∞) of the v. Bertalanffy growth equation did not vary seasonally. Tissue weight underwent a pronounced seasonal cycle. In animals of 20 mm shell length, minimum weights recorded in September only corresponded to one quarter to one third of the maxima in late spring. Tissue weight of animals from the 3 sites was distinctly different. Carbohydrate content of the tissue stayed below 10 per cent and tended to be highest in spring. Spring maxima of lipids were very pronounced. These lipids were primarily located in the digestive gland. These data were combined with data of gonad size by Borcherding (1991). Results imply that production of reproductive tissue even continues at a retarded rate during winter months, if food conditions were favourable. With poor food conditions, no production of reproductive tissue was estimated during winter; this, however, was followed by an elevated rate of reproductive tissue production in spring. Weight specific production decreased with a weight exponent of −0.24. Shell and byssus production contributed only in the range of 10 per cent to total production. Reproductive effort showed maxima of 30 to 45%. It increased with shell length at 2 sites and decreased at the other site with the largest animals.     

Seasonal variation in growth, mortality and fat stores of roach and perch in Lough Neagh, Northern Ireland

The annual cycle for roach ( Rutilus rutilus ) and perch ( Perca fluviatilis ) in Lough Neagh, Northern Ireland can be divided into warm 'growing' and cold 'non-growing' seasons. Summer water temperatures declined between 1991–1993, as did the sizes of 0+ fish of both species. Small overwinter increases in length occurred after poor summers due, in roach, to size-selective mortality. Fat content was size-dependent and increased over the summer in both species. All sizes of roach but only small perch lost fat overwinter. Dead roach collected towards the end of the 1992/3 winter had significantly less fat than live individuals. The allocation of energy to growth (and ultimately reproduction) and to fat (and overwinter survival) was modelled as a tradeoff, assuming that fat has twice the energy density of protein and using observed summer and winter changes in body composition. The predicted allocation optima were close to observed values but, for roach, this entailed a substantial survivorship cost.     

Body water content over a range of ambient salinities in the sheepshead minnow

Body water content was determined on groups of Cyprinodon variegatus after sequential acclimation to ambient salinities in the range from fresh water to 100%. A multiple linear regression model applied to the data included body mass ( M ) of individuals and acclimation salinity ( S ) as independent variables, and body water content ( W ) as the dependent variable. The model that described the relationship was W (g) = 0·059 + 0·723 M (g)–0001 S (%). Converting values of body water content to percent of wet body mass produced a range of values from 74·5% in fresh water to 72·0% at 100%, only a 2·5% difference in body water content over this wide range of ambient salinities.     

A hierarchical response to differences in ration size in the reproductive performance of female three-spined sticklebacks

The response of female three-spined sticklebacks ( Gasterosteus aculeatus ) to differences in food ration during the breeding season was quantified for several variables related to reproductive performance. The measured protein and lipid contents (mg g⁻¹) of eggs were unaffected by ration. Egg size increased with an increase in both ration and female size, but the proportional increase in egg size was much smaller than the proportional increase in ration. The best predictor of mean batch (clutch) fecundity and weight was female size. There was a small but significant increase in batch fecundity with ration, but the increase was not directly proportional to the increase in ration. The rate of spawning, total breeding season fecundity and total weight of eggs spawned over the breeding season were sensitive to ration with breeding season fecundity and weight increasing in direct proportion to ration. Thus, in female sticklebacks, there is a hierarchy of sensitivity to ration in the response of variables related to reproduction.     

Seasonal body weight, lipid content, and impact of starvation and water stress on adult survivorship and longevity ofNezara viridula andEuschistus heros

Fresh and dry body weights (FW, DW) were greater for adult southern green stink bug,Nezara viridula (L.) than for the brown stink bug,Euschistus heros F. throughout the year in southern Brazil. FemalesN. viridula significantly increased FW and DW in late summer-early autumn, and during mid-spring; femaleE. heros did not show the same rates of increase in FW and DW. FemaleN. viridula were heavier than males, particularly during summer; however, female and maleE. heros were generally similar in weight.E. heros contained significantly greater amounts of lipid thanN. viridula, during mid-autumn to early-spring (April–September). Survivorship (%) and total longevity ofE. heros adults provided water only was greater (34.6–24.6 days, for females and males) than that forN. viridula (14.8–13.0 days); without water and food, longevity was drastically reduced (<7 days) for both species.     

Use of inexpensive pressure transducers for measuring water levels in wells

Frequent measurement of below ground water levels at multiple locations is an important component of many wetland ecosystem studies. These measurements, however, are usually time consuming, labor intensive, and expensive. This paper describes a water-level sensor that is inexpensive and easy to construct. The sensor is placed below the expected low water level in a shallow well and, when connected to a datalogger, uses a pressure transducer to detect groundwater or surface water elevations. Details of pressure transducer theory, sensor construction, calibration, and examples of field installations are presented. Although the transducers must be individually calibrated, the sensors have a linear response to changing water levels (r ² .999). Measurement errors resulting from temperature fluctuations are shown to be about 4 cm over a 35°C temperature range, but are minimal when the sensors are installed in groundwater wells where temperatures are less variable. Greater accuracy may be obtained by incorporating water temperature data into the initial calibration (0.14 cm error over a 35C temperature range). Examples of the utility of these sensors in studies of groundwater/surface water interactions and the effects of water level fluctuations on tree growth are provided.     

Transgenic and knockout rodents: Novel insights into mechanisms of body weight regulation

Transgenic animals that over- or underexpress a protein of interest have been used to study obesity development, prevention, and susceptibility to diet-induced obesity such as a high-fat diet. Several transgenic models are resistant to diet-induced obesity including those that overexpress the insulin-sensitive glucose transporter, GLUT4, in adipose tissue only. In this animal there is increased adipose tissue mass but the animal maintains its insulin sensitivity. The overexpression of lipoprotein lipase (LPL) in skeletal muscle and the elimination of a protein kinase A subunit both resulted in lean and obesity resistant animals. By directing the production of the diphtheria toxin A chain to adipose tissue only the resulting animals not only had less adipose tissue mass but were resistant to MSG-induced obesity. Conversely, transgenic models with decreased brown adipose tissue or its function have all resulted in obese animals, highlighting the importance of thermoregulation in body weight maintenance. The use of transgenic technology in the field of obesity has emphasized the regional differences among fat pads as well as the dissimilarity between genders in fuel metabolism. Several transgenic models have separated obesity from insulin resistance allowing the importance of each state to be studied individually. Results using transgenic animals have re-emphasized that obesity is a polygenic disease.