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91.
A new type of device can prepare liposomes continuously, in large quantities and with excellent aqueous space capture efficiency. At initial lipid concentration of 300 μmol/ml these liposomes capture approx. 75% of cytosine arabinoside used as an aqueous space marker. Liposome size can be reduced by increasing the number of times the preparations are recycled through the microemulsifier. Liposomes less than 0.1 μm in diameter, as shown by electron microscopy, can be made easily. Liposomes prepared at 300 μmol/ml, composed of phosphatidylglycerol/phosphatidylcholine/cholesterol in a 0.1:0.4:0.5 molar ratio leaked less than 1% of entrapped cytosine arabinoside (Ara-C) at 4°C, and less than 10% Ara-C at 37°C plus serum, over a 48 h period. These liposomes could be useful for a number of applications including diagnostics, therapeutics and model membrane studies. 相似文献
92.
Migratory bird species have smaller brains than non-migratory species. The behavioural flexibility/migratory precursor hypothesis suggests that sedentary birds have larger brains to allow the behavioural flexibility required in a seasonally variable habitat. The energy trade-off hypothesis proposes that brains are heavy, energetically expensive and therefore, incompatible with migration. Here, we compared relative brain, neocortex and hippocampus volume between migratory and sedentary bats at the species-level and using phylogenetically independent contrasts. We found that migratory bats had relatively smaller brains and neocortices than sedentary species. Our results support the energy trade-off hypothesis because bats do not exhibit the same degree of flexibility in diet selection as sedentary birds. Our results also suggest that bat brain size differences are subtler than those found in birds, perhaps owing to bats'' shorter migration distances. Conversely, we found no difference in relative hippocampus volume between migratory and sedentary species, underscoring our limited understanding of the role of the hippocampus in bats. 相似文献
93.
Current patterns of floral design in Pedicularis must have undergone an evolutionary process of interacting among components of floral traits, and then formed internal relationships among these traits. To detect such correlations, which may provide insight to understand flower evolution, 40 Pedicularis species representing all corolla types of the genus were studied. Results show that, interspecifically, pollen size correlates negatively with pollen number, but positively with pistil length. This suggests that plants evolve an optimal pollen size, which balances the advantages of large pollen size for gametophytic competition against the fecundity disadvantages of fewer pollen grains. In contrast to sex allocation theory, this study does not find a trade-off, but an interspecific positive correlation between pollen and ovule number. This is consistent with the hypothesis that genetic variation for resource acquisition may in part be responsible for the lack of negative correlation between male and female function.This work was supported by the State Key Basic Research and Development Plan, China (Grant No. G2000046804) to YHG. The authors would like to thank Peter K. Endress and two anonymous reviewers for providing critical comments and helpful suggestions, Qing-Feng Wang, Jing-Yuan Wang and Jin-Ming Chen for their helpful suggestions. Shi-Guo Sun, Jing Xia, and Qian Yu are thanked for their assistance in both the field work and laboratory phases of the project. 相似文献
94.
95.
Sex ratios under asymmetrical local mate competition in the parasitoid wasp Nasonia vitripennis 总被引:1,自引:0,他引:1
Sex ratio theory has proved remarkably useful in testing theadaptive nature of animal behavior. A particularly productivearea in this respect is Hamilton's theory of local mate competition(LMC), which has been extended in numerous directions to includegreater biological realism, allowing more detailed tests inspecific organisms. We have presented one such extension, termedasymmetrical LMC, which occurs when egg laying by females ona patch is asynchronous, and emerging males do not disperse,resulting in the extent of LMC on a patch varying over time.Our aim here is to test whether the parasitoid wasp Nasoniavitripennis responds to variation in the degree of asymmetricalLMC. Specifically, we show that females adjust their offspringsex ratios in response to (1) variation in the amount of asynchronyin emergence between broods on a patch and (2) the number andproportion of previously parasitized hosts on the patch. Ourresults provide qualitative support for the predictions of theory,suggesting new levels of complexity in the sex ratio behaviorof this much-studied organism. However, our results do not alwaysprovide quantitative support for theory, suggesting furthercomplexities that must be clarified. 相似文献
96.
97.
Clutch size and the costs of incubation in the house wren 总被引:3,自引:1,他引:2
Trade-offs in the allocation of finite resources among differentstages of a breeding attempt as well as between different reproductiveevents should shape the evolution of life-history traits. Toinvestigate the effects of incubation effort on within-broodand between-brood trade-offs in house wrens (Troglodytes aedon),we manipulated the clutch size that females incubated. We isolatedeffects of incubation by reversing the manipulation at hatchingto allow all parents to provision their natural brood sizes.Females that incubated enlarged clutches had longer incubationperiods than control females, both early and late in the season,suggesting that the experimental treatment increased incubationeffort. Contrary to predictions, however, increased incubationeffort did not adversely affect the allocation of effort tonestling provisioning. Rather, in the early season, but notin the late season, females that incubated enlarged clutchesappeared to allocate more effort to nestling provisioning, producingheavier and larger fledglings than control females. Althoughfemales with enlarged early-season clutches consequently lostmore mass than control females, this was likely an adaptiveresponse to reduce wing loading in anticipation of high provisioningdemands. There were no treatment-related differences in fledglingmass or size, or in female mass loss, in the late season. Thus,elevated incubation demands negatively affected a fitness-relatedtrait (duration of incubation) that may constrain clutch sizebut not the allocation of resources to subsequent stages ofthe same breeding event or to subsequent breeding events. Wesuggest that environmental conditions may mediate clutch-sizeeffects on trade-offs in allocation of resources between incubationand nestling provisioning. 相似文献
98.
Robin Elahi Peter J. Edmunds 《Journal of experimental marine biology and ecology》2007,349(1):183-193
For many marine invertebrates, the maximum size of an individual is influenced heavily by environmental factors and may be limited by energetic constraints. In this study, an energetic model developed originally for anemones was applied to the free-living scleractinian Fungia concinna (Verrill) from Moorea (French Polynesia) to test the hypothesis that energetic constraints limit the size of this solitary coral. The modified model assumed that photosynthesis was the primary source of metabolic energy, and that metabolic costs were represented by aerobic respiration; these sources and sinks of energy were compared using daily energy budgets that were analyzed using double logarithmic regressions of energy against coral size. With this approach, energy limitation is characterized by a scaling exponent for energetic cost (bcost) that is larger than the scaling exponent for energy intake (bintake). For the size range of F. concinna studied, bintake = 0.73 ± 0.09 and bcost = 0.46 ± 0.10, thereby demonstrating that large individuals accumulated an energetic surplus, even when the expenditure associated with host tissue and symbiont growth was included in the model. The surplus of energy that this coral acquires as it grows appears to be driven by the scaling of traits associated functionally with the scaling of respiration and photosynthesis. Specifically, tissue biomass displayed a strong positive allometry with respect to surface area (i.e., b > 1), and this constraint on surface area may be the mechanistic basis of the low scaling exponent for metabolic cost. In contrast, the capacity for autotrophy - defined indirectly as Symbiodinium population density and chlorophyll content - increased isometrically with surface area, and likely contributed to the higher scaling exponent for intake relative to cost. Our results suggest that growth in F. concinna is not limited strictly by energy, but instead maximum size must be determined by alternative physiological or ecological constraints. 相似文献
99.
A study was conducted in the spring of 2009, the winters of 2010 and 2013, and in the summer of 2012 at 13 stations in Boughrara Lagoon, Tunisia (southern Mediterranean). The countrys largest lagoon, it is considered to be an anthropogenically stressed area, though a major tourist centreDjerba Islandis located along its northern shores. The lagoon bottoms were studied via analyses of grain size, surface sediment composition, total organic matter (TOM) and through the trophic and functional organisation of benthic macrofauna. The results indicate that the bottoms are composed of fine, medium or coarse sands and that sediment distribution is controlled by water movement. Estimation of TOM content revealed that the studied samples present both normal and imbalanced sediments. The structure and organisation of the lagoons benthic macrofauna are dominated by select deposit feeders and underwent significant changes during the period 20102013.Subjected for decades to increased pollution due to growing human activities in the surrounding area, Boughrara Lagoon now appears to be impacted by certain environmental/anthropogenic stressors, as indicated by the presence of pollution-tolerant bio-indicator species in the imbalanced area. The response of the lagoon ecosystem to changes in benthic sediment deposition provides a potential assessment tool for similar habitats elsewhere. 相似文献
100.