Existing theories do not explain sex ratio variation at birth in monomorphic roe deer (Capreolus capreolus)     

Stefan Jacob VREUGDENHIL  Leo VAN BREUKELEN  Sipke Egbert VAN WIEREN 《Integrative zoology》2007,2(1):10-18

The phenomenon of skewed sex ratios at birth has been reported in many ungulate species. So far, no consistent trend has emerged for roe deer (Capreolus capreolus), because male‐biased, female‐biased and equal sex ratios at birth have all been found. Nevertheless, both the Trivers‐Willard hypothesis and the theory of local resource competition have gained support. Despite the great number of studies carried out regarding the ecology of roe deer, too many aspects remain unclear, and contradictory results have been produced with respect to several crucial elements. Without further research, the discussion on which theory applies will therefore remain inconclusive. We put forward the argument that eventually the theories of Trivers‐Willard and local resource competition can be considered as being not essentially different. After all, both theories explain the observed skewed sex ratios as being due to the effect of the progeny's sex on the mother's body condition and hence her reproductive success in subsequent years. Furthermore, neither theory is likely to prove to be suitable for roe deer, as several assumptions are unlikely to be met. In roe deer, skewed ratios probably only have a temporal character. As a matter of fact, several observations of skewed sex ratios in birds and mammals did not withstand the accumulation of further data, as sex ratios that were initially believed to be biased turned out to be equal in the long term. This is likely to be the case in roe deer as well. We hypothesize that roe deer, as r‐strategists, will produce as many offspring as possible, regardless of sex.  相似文献   

The effect of a restriction of the feed intake on the composition of the blood and on the development and composition of different tissues of sheep during growth. 2. The development of different tissues and the concentration of protein, DNA and RNA]     

E Kolb  T van Dich  M Leo  M Ulbrich  R Süss 《Berliner und Münchener tier?rztliche Wochenschrift》1992,105(6):192-197

The concentration of protein in the cerebrum of sheep after a period of feed restriction (group 2) was lower (94.5 +/- 10.2) than in normally fed sheep of group 4 (101.4 +/- 9.4 mg/g wet weight). In the group 2 the concentration of protein in the M. longissimus dorsi and in the M. semimembranosus was also smaller. A high DNA-concentration was determined in the intestinal lymph nodes, in the spleen and in the lung. The DNA-concentration of the testes of group 2 (7.17 +/- 2.92) was higher than that of the group 4 (4.46 +/- 1.70 mg/g w. w.), also that of the renal fat tissue (0.39 +/- 0.18 resp. 0.20 +/- 0.09). The highest protein: DNA-relation in group 4 was found in the fat tissue (203.5: 1) and the lowest in the spleen (15.3: 1). A high RNA-concentration was analysed in the lymph nodes, in the spleen and in the lung. The RNA-concentration in the fat tissue of group 2 (0.34 +/- 0.13) was higher that that in group 4 (0.15 +/- 0.08 mg/g w. w.).  相似文献   

Antibody multispecificity mediated by conformational diversity     

James LC  Roversi P  Tawfik DS 《Science (New York, N.Y.)》2003,299(5611):1362-1367

A single antibody was shown to adopt different binding-site conformations and thereby bind unrelated antigens. Analysis by both x-ray crystallography and pre-steady-state kinetics revealed an equilibrium between different preexisting isomers, one of which possessed a promiscuous, low-affinity binding site for aromatic ligands, including the immunizing hapten. A subsequent induced-fit isomerization led to high-affinity complexes with a deep and narrow binding site. A protein antigen identified by repertoire selection made use of an unrelated antibody isomer with a wide, shallow binding site. Conformational diversity, whereby one sequence adopts multiple structures and multiple functions, can increase the effective size of the antibody repertoire but may also lead to autoimmunity and allergy.  相似文献   

Spectral dependence of photosynthesis and light absorptance in single leaves and canopy in rose     

Roberta Paradiso  Esther Meinen  Jan F.H. Snel  Pieter De Visser  Wim Van Ieperen  Sander W. Hogewoning  Leo F.M. Marcelis 《Scientia Horticulturae》2011

Little is known about the effects of leaf pigmentation (related to leaf ontogeny), on the spectral dependence of photosynthesis and most observations have been limited so far to single leaves. This study aimed to investigate photosynthesis and the related optical properties of two types of rose leaves, young reddish leaves and middle age green leaves, and to quantify the spectral dependence of photosynthesis at the canopy level.  相似文献   

Crop coefficient, yield response to water stress and water productivity of teff (Eragrostis tef (Zucc.)     

A. Araya  Leo StroosnijderG. Girmay  S.D. Keesstra 《Agricultural Water Management》2011,98(5):775-783

In the semi-arid region of Tigray, Northen Ethiopia a two season experiment was conducted to measure evapotranspiration, estimate yield response to water stress and derive the crop coefficient of teff using the single crop coefficient approach with simple, locally made lysimeters and field plots. During the experiment we also estimated the water productivity of teff taking into account long-term rainfall probability scenarios and different levels of farmers’ skills. During the experimental seasons (2008 and 2009), the average potential evapotranspiration of teff ranged from 260 to 317 mm. The total seasonal water requirement of teff was found to lower in contrast to the assumptions of regional agronomists that teff water requirement is comparable to that of wheat and barley (375 mm). The average single crop coefficient values (k_c) for the initial, mid and late season stages of teff were 0.8-1, 0.95-1.1 and 0.4-0.5, respectively. The seasonal yield response to water stress was 1.04, which indicates that teff exhibits a moderately sensitive and linear response to water stress. The results suggest that teff is likely to give significantly higher grain yield when a nearly optimal water supply is provided. The study showed that, in locations where standard equipment is not affordably available, indicative (rough) crop evapotranspiration values can be obtained by using field plots and employing locally made lysimeters. The difference in economic water productivity (EWP) and the crop water productivity (CWP) for teff were assessed under very wet, wet, normal, dry and very dry scenarios. In addition two groups of farmers were evaluated, a moderately (I) and a highly skilled (II) group. The results showed that higher EWP and CWP were obtained under very wet scenario than very dry scenario. There was also a 22% increase in EWP and CWP under group II compared to group I farmers. The increase was due to a 22% reduction in unwanted water losses achieved through use of improved technology and better irrigation skills. Both EWP and CWP can be used to evaluate the pond irrigation water productivity (IWP) for a given climate, crop and soil type, and skill and technology level of the farmer. For special crops like teff extra criteria may be needed in order to properly evaluate the pond irrigation water productivity. During the experimental seasons, a high IWP for teff was attained when about 90% of the optimal water need of the crop was met. IWP can be used as an indicator as how much supplementary irrigation has to be applied in relation to the rainfall and other sources of water supply in order to assure greatest yield from a total area. However, the supplemental irrigation requirement of the crops may vary with season due to seasonal rainfall variability.  相似文献   

Novel antioxidant reactions of cinnamates in wine     

Gislason NE  Currie BL  Waterhouse AL 《Journal of agricultural and food chemistry》2011,59(11):6221-6226

Plant-derived polyphenolic compounds have received much attention for their ability to sequester high-energy free radicals in a great variety of food-related and biological systems, protecting those systems from oxidative change. The ability of these compounds to scavenge free radicals has always been attributed to their phenolic functionality, from which a hydrogen atom can be easily abstracted. In this study, the cinnamates and the ubiquitous hydroxycinnamates were found to equally suppress the formation of oxidation products in wine exposed to the Fenton reaction (catalytic Fe(II) with hydrogen peroxide). Mechanistic investigations led to the unexpected discovery that the α,β-unsaturated side chain of cinnamic acids could efficiently trap 1-hydroxyethyl radicals, representing a newly discovered mode of antioxidant radical scavenging activity for these broadly occurring compounds in a food system. The proposed pathway is supported by prior fundamental studies with radiolytically generated radicals.  相似文献   

Assessing drought risk and irrigation need in northern Ethiopia     

A. Araya  Leo Stroosnijder 《Agricultural and Forest Meteorology》2011,151(4):425-436

Long-term climate data of four stations in the northern Ethiopia were analyzed in combination with information from local farmers and documented materials. From this analysis, a suitable drought-assessing technique was developed and site-specific needs for supplementary irrigation were explored. Results showed that our technique for assessing drought and crop failure corresponded well with farmer observations. The three major causes of crop failure (dry spells, short growing period and “total lack of rain”) which were explicitly listed and ranked by the local farmers were found to match the analyzed data well. The agro-meteorological variables with the most severe consequences were “short growing period” and “total lack of rain”. To prolong the growing period, supplementary irrigation is recommended in the month of September for three of the stations (Maychew, Mekelle and Adigudom) because: (1) rain frequently stops in early September or late August and crops have no other source of water for the rest of the growing period; (2) sufficient surface runoff can be harvested in July and August to be stored in farm ponds and used in September; (3) more cultivable land can be irrigated if supplementary irrigation is scheduled only for the month of September; and (4) giving supplementary irrigation in September can cut yield reduction by over 80% and crop failure by over 50%, except at Alamata. At Alamata, supplementary irrigation must be scheduled for July. The conditions experienced during the famine years of the early 1980s were primarily caused by the continued total rain failure over multiple years. Giving supplementary irrigation in July or September would probably not have mitigated the effects of these droughts, especially at Alamata and Maychew stations.  相似文献   

Molecular structures of citrus flavonoids determine their effects on lipid metabolism in HepG2 cells by primarily suppressing apoB secretion     

Lin Y  Vermeer MA  Bos W  van Buren L  Schuurbiers E  Miret-Catalan S  Trautwein EA 《Journal of agricultural and food chemistry》2011,59(9):4496-4503

This study investigated the underlying mechanisms of action for blood lipid lowering effects of citrus flavonoids and their methoxylated analogues (n = 19; dose range: 0-100 μM) in HepG2 cells. Cholesterol (CH) and triglyceride (TG) syntheses were assessed by measuring the incorporation of (14)C-acetate and (14)C-glycerol, respectively, whereas apoB secretion was determined by ELISA. Results show that two polymethoxylated citrus flavonoids (PMFs), tangeretin and nobiletin, potently inhibited apoB secretion (IC(50) = 13 and 29 μM, respectively) and modestly inhibited CH synthesis (IC(50) = 49 and 68 μM) and TG synthesis (IC(50) = 14 and 73 μM), without effecting LDL-receptor activity. Other PMFs (e.g., sinensetin) and non-PMFs (e.g., hesperetin and naringenin) had only weak effects on CH and TG syntheses and apoB secretion (IC(50) > 100 μM). The structure-activity analysis indicated that a fully methoxylated A-ring of the flavonoid structure was associated with a potent inhibitory activity on hepatic apoB secretion. In conclusion, this study using HepG2 cells indicates that citrus flavonoids with a fully methoxylated A-ring may lower blood CH and TG concentrations primarily by suppressing hepatic apoB secretion as a main underlying mode of action.  相似文献   

The effect of long-term Maresha ploughing on soil physical properties in the Central Rift Valley of Ethiopia     

Birhanu Biazin  Leo Stroosnijder  Melesse Temesgen  Abdu AbdulKedir  Geert Sterk 《Soil & Tillage Research》2011,111(2):115-122

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Global-scale similarities in nitrogen release patterns during long-term decomposition   总被引：2，自引：0，他引：2  

Parton W  Silver WL  Burke IC  Grassens L  Harmon ME  Currie WS  King JY  Adair EC  Brandt LA  Hart SC  Fasth B 《Science (New York, N.Y.)》2007,315(5810):361-364

Litter decomposition provides the primary source of mineral nitrogen (N) for biological activity in most terrestrial ecosystems. A 10-year decomposition experiment in 21 sites from seven biomes found that net N release from leaf litter is dominantly driven by the initial tissue N concentration and mass remaining regardless of climate, edaphic conditions, or biota. Arid grasslands exposed to high ultraviolet radiation were an exception, where net N release was insensitive to initial N. Roots released N linearly with decomposition and exhibited little net N immobilization. We suggest that fundamental constraints on decomposer physiologies lead to predictable global-scale patterns in net N release during decomposition.  相似文献