Coexistence of similar genotypes of Daphnia magna in intermittent populations: response to thermal stress

We investigated the diversity and thermal response of a fitness related trait, juvenile growth rate, in seasonal population samples of Daphnia magna from two temperate ponds. Both populations were intermittent, i.e. they disappeared from the water body and recolonized seasonally by hatching from resting eggs in the sediment.
Temporally isolated clones of Daphnia magna showed the typical asymmetric response for growth rate with temperature and a sharp decline after the maximum response at 26°C (TMR). There was no evidence for genetically adapted seasonal groups. Despite significant genetic variation among clones and for phenotypic plasticity (G×E interactions without genetic correlations), seasonal groups of clones showed no shift in TMR and mean temperature reaction norms were similar among groups and both populations. Heritabilities remained similar among temperatures despite a large increase in genetic variance at stressfully high temperatures of 29°C and 32°C, due to simultaneous increase in environmental variance. Further, heritabilities remained high among sample periods and were not eroded during several months of asexual reproduction.
Regular diapause, an intrinsic feature of intermittent Daphnia populations, may replace the need for physiological temperature adaptation and promote maintenance of diversity through phenotypic similarity by reducing the time over which competitive interactions occur. Such populations are unlikely to be directly affected by elevated temperatures. They have a large potential for phenotypic plasticity as their TMR is higher than the temperature normally encountered.     

Changes in response to drought stress of triticale and maize genotypes differing in drought tolerance

Direct effects and after-effects of soil drought for 7 and 14 d were examined on seedling dry matter, leaf water potential (ψ), leaf injury index (LI), and chlorophyll (Chl) content of drought (D) resistant and sensitive triticale and maize genotypes. D caused higher decrease in number of developed leaves and dry matter of shoots and roots in the sensitive genotypes than in the resistant ones. Soil D caused lower decrease of ψ in the triticale than maize leaves. Influence of D on the Chl b content was considerably lower than on the Chl a content. In triticale the most harmful D impact was observed for physiologically younger leaves, in maize for the older ones. A period of 7-d-long recovery was too short for a complete removal of an adverse influence of D.     

Differential response to stocking rates and feeding by two genotypes of Holstein-Friesian cows in a pasture-based automatic milking system

The throughput of automatic milking systems (AMS) is likely affected by differential traffic behavior and subsequent effects on the milking frequency and milk production of cows. This study investigated the effect of increasing stocking rate and partial mixed ration (PMR) on the milk production, dry matter intake (DMI), feed conversion efficiency (FCE) and use of AMS by two genotypes of Holstein-Friesian cows in mid-lactation. The study lasted 8 weeks and consisted in a factorial arrangement of two genotypes of dairy cattle, United States Holstein (USH) or New Zealand Friesian (NZF), and two pasture-based feeding treatments, a low stocking rate system (2 cows/ha) fed temperate pasture and concentrate, or a high stocking rate system (HSR; 3 cows/ha) fed same pasture and concentrate plus PMR. A total of 28 cows, 14 USH and 14 NZF, were used for comparisons, with 12 cows, six USH and six NZF, also used for tracking of animal movements. Data were analyzed by repeated measure mixed models for a completely randomized design. No differences (P>0.05) in pre- or post-grazing herbage mass, DMI and FCE were detected in response to increases in stocking rate and PMR feeding in HSR. However, there was a significant (P<0.05) grazing treatment×genotype×week interaction on milk production, explained by differential responses of genotypes to changes in herbage mass over time (P<0.001). A reduction (P<0.01) in hours spent on pasture was detected in response to PMR supplementation in HSR; this reduction was greater (P=0.01) for USH than NZF cows (6 v. 2 h, respectively). Regardless of the grazing treatment, USH cows had greater (P=0.02) milking frequency (2.51 v. 2.26±0.08 milkings/day) and greater (P<0.01) milk yield (27.3 v. 16.0±1.2 kg/day), energy-corrected milk (24.8 v. 16.5±1.0 kg/day), DMI (22.1 v. 16.6±0.8 kg/day) and FCE (1.25 v. 1.01±0.06 kg/kg) than NZF cows. There was also a different distribution of milkings/h between genotypes (P<0.001), with patterns of milkings/h shifting (P<0.001) as a consequence of PMR feeding in HSR. Results confirmed the improved FCE of grazing dairy cows with greater milk production and suggested the potential use of PMR feeding as a tactical decision to managing HSR and milkings/day in AMS farms.     

不同西瓜基因型对干旱胁迫的生理响应及其抗旱性评价

以来源于不同地区的12个西瓜基因型为试材,采用盆栽控水的方式进行持续干旱处理,研究干旱胁迫对西瓜幼苗株高、根长、鲜质量及干物质积累等生长状况的影响,比较不同基因型材料对干旱胁迫的生理响应差异,同时依据旱害指数对其抗旱性进行直接评价,并采用隶属函数法进一步验证和综合评价.结果表明: 干旱处理下,12个西瓜基因型对干旱胁迫的耐受能力存在明显差异,各基因型开始出现旱害症状的时间和发生旱害的程度各不相同.干旱胁迫降低了西瓜幼苗的株高、地上、地下鲜质量和地上干物质积累量,普遍提高了根冠比,而对根长和地下干质量存在正向和负向两种不同的影响.干旱处理后,西瓜叶片的相对含水量和叶绿素含量均不同程度降低,丙二醛、过氧化氢和超氧阴离子含量增加,脯氨酸大量积累,而可溶性蛋白含量以及抗氧化酶活性则因基因型的不同而表现出不同的结果.分析认为,3个野生型材料M20、KY-3和Y-2为抗旱性强的西瓜种质,Y34、金美人和04-1-2为敏感种质,而其余基因型为中抗种质.     

Differential response of tropical maize genotypes to zinc and manganese nutrition

Summary In order to examine the differential response of tropical maize genotypes to Zn and Mn nutrition, a pot experiment was conducted and the results subsequently evaluated in a field trial. Zn was rendered ‘physiologically immobile’ in the root tissue as revealed by a substantial reduction in shoot concentration as compared to root concentration. This effect was most pronounced in the inbred line CM-111. Quite contrasting to Zn, the root concentration of Mn was substantially lower while the shoot concentration was comparable with that of Zn indicating that under identical supply of Zn and Mn to substrate, more of Zn is root absorbed and also ‘root immobilized’, while, of the quantities absorbed by root, relatively more of Mn is translocated to shoot. Maximum root and shoot dry matter yields were obtained at specific Zn/Mn ratio in each of the genotype studied. Available Mn estimated at periodic interval (15 days) during plant growth showed consistent increase corresponding to higher rates applied while available Zn showed an initial (on 15th day of sampling) decrease corresponding to higher rates (possibly initial reversion?) and subsequent (on 45th day of sampling) increase (possibly later release through plant root activity in rhizosphere?). Significant and positive correlation coefficients were obtained between available Zn and root Zn while in the case of available Mn it was so only with shoot Mn. In field experiment Ganga-5 outyielded all the other genotypes and showed a positive response to Mn application. Publication No. 899 under journal series of the G. B. Pant University of Agriculture and Technology, Pantnagar, India. Publication No. 899 under journal series of the G. B. Pant University of Agriculture and Technology, Pantnagar, India.     

Differential response of soybean genotypes to soil pH and manganese application

An experiment was conducted at Tamil Nadu Agricultural University, Coimbatore, India during 1982 wet season (June–July) to study the root activity and rooting pattern of IR-20 rice as influenced by urea insecticide combinations by a³²P absorption technique. The treatments involved a factorial combination of four levels of N (0, 60, 90 and 120 kg N/ha) as urea and three levels of insecticides (no insecticide, carbofuran @ 0.75 kg a.i./ha and phorate @ 1.0 kg a.i./ha). The root activity measured in terms of the amount of³²P absorbed by the plant, increased considerably by the application of urea and insecticides (carbofuran or phorate) as well as due to their interactions. The root activity increased upto 120 kg N ha⁻¹. Carbofuran or phorate application increased root activity and the effect of carbofuran was greater than that of phorate. Nitrogen-insecticide interaction was positive on root activity upto 120 kg N ha⁻¹ and the effect was more marked with carbofuran and N combinations. But the percentage distribution of active roots of rice could not be influenced by levels of N, insecticides or their interactions. About 80 percent of the roots of IR 20 rice forage within 10 cm from the surface. The enhanced root activity due to application of N and insecticides (carbofuran and phorate) increased the uptake of major and micro-nutrients. the phytotonic effects of carbofuran and phorate on rice works by triggering the root activity of the crop.     

Comparative response of maize and rice genotypes to heat stress: status of oxidative stress and antioxidants

In the present study, two genotypes each of maize and rice were compared for their response to varying degrees of temperature stress (35/30, 40/35, 45/40°C) with controls growing at 30/25°C. At elevated temperatures of 40/35 and 45/40°C, the rice genotypes were inhibited to a significantly higher extent, especially for their shoot growth compared to maize genotypes. The stress injury measured as damage to membranes, loss of chlorophyll and reduction in leaf water status was significantly higher in rice plants, especially at 45/40°C. The components of oxidative stress particularly the level of malondialdehyde was significantly greater in rice plants while the differences for hydrogen peroxide concentrations were small at 40/35 and 45/40°C. The expression of enzymatic antioxidants like catalase, ascorbate peroxidase and glutathione reductase was found to be higher in maize plants compared to rice plants while no variations existed for superoxide dismutase at 45/40°C. In addition, the non-enzymatic antioxidants like ascorbic acid, glutathione and proline were maintained at significantly greater levels at 45/40°C in maize than in rice genotypes. These findings suggested that maize genotypes were able to retain their growth under high-temperature conditions partly due to their superior ability to cope up with oxidative damage by heat stress compared to rice genotypes. Since, maize and rice belong to C₄ and C₃ plant groups, respectively, these observations may also reflect the relative sensitivity of these plant groups to heat stress.     

Eco-physiological response to water stress of drought-tolerant and drought-sensitive tomato genotypes

Water stress is an increasing environmental constraint affecting tomato growth and yield in Mediterranean areas. Solanum pennellii is a wild tomato species that exhibits a higher water use efficiency compared with cultivated S. lycopersicum. In particular, a cultivated line carrying a small S. pennellii region on chromosome 9 (IL 9-2-5) was identified as more tolerant to water deficit. In this work, the tolerant (IL 9-2-5) and the susceptible (M82) genotypes were subjected to three different water regimes: irrigation with 100% (V1), 50% (V2) and 25% (V3) field capacity. To evaluate the physiological response of IL 9-2-5 and M82 to water deficit, leaf functional traits, plant biomass production and maximal PSII photochemical efficiency were measured together with photosynthetic pigments and phenolic compounds. The higher tolerance to water deficiency of IL 9-2-5 was associated with the development of a better antioxidant system, especially in treatment V3. In addition, IL 9-2-5 had higher values of sclerophylly and leaf dry matter content thus confirming that the tolerance of IL 9-2-5 can be attributed to traits related to leaf morphology and physiology. In future, identification of polymorphisms in key-genes controlling these traits can guide breeding efforts aimed at improving susceptible genotypes.     

Differential responses of oat genotypes: oxidative stress provoked by aluminum

The phytotoxic effects of aluminum and the mechanisms of genetically-based Al tolerance have been widely investigated, as reported in many papers and reviews. However, investigations on many Al-sensitive and Al-resistant species demonstrate that Al phytotoxicity and Al-resistance mechanisms are extremely complex phenomena. The objective of the present study was to analyze the effects of aluminum on the activity of antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX). Also was evaluated the lipid peroxidation, H₂O₂ content, levels of ascorbic acid (ASA), non-protein thiols (NPSH) and Al content in three genotypes of oat, Avena sativa L. (UFRGS 930598, UFRGS 17, and UFRGS 280). The genotypes were grown in different concentrations of Al ranging from 90 to 555???M for 5?days. The antioxidant system was unable to overcome toxicity resulting in negative effects such as lipid peroxidation and H₂O₂ content in UFRGS 930598. The results showed that UFRGS 930598 was the most sensitive genotype. UFRGS 17 and UFRGS 280 were more resistant to Al toxicity. These results suggest that UFRGS 17 has mechanisms of external detoxification and UFRGS 280 has mechanisms of internal detoxification. The different behavior of enzymatic and non-enzymatic antioxidants of the genotypes showed that aluminum resistance in UFGRS 17 and UFRGS 280 may be related to oxidative stress.     

Temperature acclimatization in the filtering rates and oxygen consumption of Daphnia ambigua scourfield

• 1.1. Filtering rates and oxygen consumption were measured in the field on a wild population of the fresh-water limnetic cladoceran Daphnia ambigua.
• 2.2. Filtering rates increased with increasing body size and were significantly affected by environmental temperature.
• 3.3. Oxygen consumption increased with increasing body size; there was no significant difference among b values determined at different environmental temperatures but bs were highest at low temperatures. decreased progressively at higher temperatures and increased at the highest temperatures.
• 4.4. Temperature significantly affected the rate of oxygen consumption.
• 5.5. Both filtering rates and oxygen consumption evidenced classical translation to the left in cold-acclimatized animals. An environmental temperature near 12°C apparently separates warm- and cold-acclimatization processes.

     

Differential response of stress fibers and myofibrils to gelsolin

The actin-severing activity of human platelet gelsolin was analyzed on embryonic skeletal and cardiac myofibrils, and on stress fibers in non-muscle cells. These subcellular structures, although in all three cell types composed of contractile proteins arranged in sarcomeric units, were found to respond differently to gelsolin. The myofibrils in permeabilized myotubes or cardiac cells, as well as in living, microinjected muscle cells proved resistant to a wide concentration range of gelsolin. The same was found for the "mini-sarcomeres" which are seen in developing muscle cells. In contrast, stress fibers in microinjected fibroblasts or epithelial cells, as well as in permeabilized cells, were broken down rapidly by the platelet gelsolin. We conclude from these results that the mini-sarcomeres in embryonic myotubes and cardiac myocytes are not identical with stress fibers.     

Resistance and tolerance to mixed nematode infections in chicken genotypes with extremely different growth rates

Fast growing broilers are less able to cope with fitness related challenges. As the allocation of metabolic resources may be traded off between performance and defence functions in parasitized hosts, we hypothesized that fast growing broilers are more sensitive to mixed nematode infections compared with slower growing genotypes under the same environmental conditions. Therefore, we compared male birds of genotypes selected for either meat production (Ross-308, R) or egg production (Lohmann Brown Plus, LB) or for both purposes (Lohmann Dual, LD), to assess their resistance and tolerance to mixed nematode infections with Ascaridia galli and Heterakis gallinarum. While infections reduced feed intake in all three genotypes, feed conversion efficiency was not affected. Infections impaired growth performance only in R birds, indicating lower tolerance in the fast growing genotype compared with slower growing LB and LD genotypes. Impaired tolerance in R birds was associated with a relative nutrient scarcity due to an infection-induced lower feed intake. Resistance to experimentally induced infections depended on host genotype as well as on the worm species involved. Overall, the A. galli burden was higher in R than LB, whereas the burden of LD was not different from that of R and LB. In contrast, the H. gallinarum burden of first generation worms was similar in the three genotypes. Susceptibility to re-infection with H. gallinarum was higher in LB than in LD, whereas very low levels of re-infection were observed in R birds. Our data collectively suggest that resistance and tolerance to mixed nematode infections are sensitive to growth rate in chickens. These differences amongst genotypes may partly be associated with a mismatch between the actual nutrient supply and genotype-specific nutrient requirements.     

Biomass-specific respiration rates of benthic meiofauna: Demonstrating a novel oxygen micro-respiration system

Meiofauna (small-sized Metazoa and Foraminifera) may constitute a significant part of seafloor biomass and potentially play an important role in benthic metabolism. However, respiration measurements are limited and the methods used are diverse together complicating comparison or upscaling. Here we describe a novel glass micro-respiration chamber used to perform non-invasive measurements (built-in oxygen-sensitive fluorogenic membrane and stirrer) and together with direct organic carbon measurements report initial biomass-specific respiration rates of common intertidal meiofauna. Results indicate large differences between respiration rates of different taxa (biomass 0.7-5.2 µg C per individual) but very similar organic carbon biomass-specific respiration rates (1.6-2.5 µl O₂ h^− 1 mgC^− 1 or on average 2.0 ± 0.3 µl O₂ h^− 1 mgC^− 1). This new, rapid and accurate method allows the study of metabolic allometry of the different small-sized taxa and determining their functional role in benthic metabolism.     

Growth response to subsurface soil acidity of wheat genotypes differing in aluminium tolerance

Subsurface soil acidity coupled with high levels of toxic Al is a major limiting factor in wheat production in many areas of the world. This study examined the effect of subsurface soil acidity on the growth and yield of two near-isogenic wheat genotypes differing in Al tolerance at a single genetic locus in reconstructed soil columns. In one experiment, plants were grown in columns with limed topsoil and limed or acidic subsurface soils, and received water only to the subsurface soil at a late part of the growth period. While shoot dry weight, ear number and grain yield of Al-tolerant genotype (ET8) were not affected by subsurface soil acidity, liming subsurface soil increased shoot weight and grain yield of Al-sensitive genotype (ES8) by 60% and ear number by 32%. Similarly, root length density of ET8 was the same in the limed and acidic subsurface soils, while the root length density of ES8 in the acidic subsurface soil was only half of that in the limed subsurface soil. In another experiment, plants were grown with limed topsoil and acidic subsurface soil under two watering regimes. Both genotypes supplied with water throughout the soil column produced almost twice the dry weight of those receiving water only in the subsurface soil. The tolerant genotype ET8 had shoot biomass and grain yield one-third higher than ES8 when supplied with water throughout the whole column, and had yield 11% higher when receiving water in the subsurface soil only. The tolerant genotype ET8 produced more than five times the root length in the acidic subsurface soil compared to ES8. Irrespective of watering regime, the amount of water added to maintain field capacity of the soil was up to 2-fold higher under ET8 than under ES8. The results suggest that the genotypic variation in growth and yield of wheat grown with subsurface soil acidity results from the difference in root proliferation in the subsurface soil and hence in utilizing nutrient and water reserves in the subsurface soil layer.     

Differential responses of sorghum genotypes to drought stress revealed by physio-chemical and transcriptional analysis

Molecular Biology Reports - Sorghum is an essential food crop for millions of people in the semi-arid regions of the world, where its production is severely limited by drought stress. Drought in...     

Differential response to frequency-dependent interactions: an experimental test using genotypes of an invasive grass

Positive feedbacks have been suggested as a means for non-indigenous species to successfully invade novel environments. Frequency-dependent feedbacks refer to a species performance being dependent on its local abundance in the population; however, frequency dependence is often described as a monolithic trait of a species rather than examining the variation in response for individual genotypes and fitness traits. Here, we investigate frequency-dependent outcomes for individual genotypes and fitness-related traits for the invasive grass Phalaris arundinacea. We tested for competition-mediated frequency dependence by establishing hexagonal arrays with the center target plant surrounded by either same, different or no genotype neighbors to determine how changing the small-scale frequency neighborhood-influenced invasion success. We used a Bayesian ANOVA approach which allowed us to easily accommodate our non-normal dataset and found that same neighbor plots had greater biomass production than different neighbor plots. Target plants also had greater stem height and aboveground biomass when surrounded by same genotype neighbors. A greenhouse experiment did not support the hypothesis that increased mycorrhizal associations were the cause of positive frequency dependence. We devised a frequency-dependent metric to quantify the extent of fitness-related differences for individual genotypes and found that individual genotypes showed a range of both positive and negative responses to different frequency treatments; however, only positive responses were statistically significant. The small-scale genotypic neighborhood had no effect for the fitness-related traits of leaf number, belowground biomass and total biomass. We demonstrate that individual invasive genotypes respond differently to changing frequency neighborhoods and that growth responses do not respond with the same direction and magnitude. A range of frequency-dependent responses may allow genotypes to invade a wide range of environments.