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521.
Individuals of species that change sex from male to female may gain a “size advantage” from that sex change; that is, as males become larger, they become female, thus increasing their fecundity with their size. However, males could also gain an early and different reproductive size advantage by choosing large females as mates. While male preference for large females has been observed in many dioecious species, we know little about male size preference in sex-changing species. In choice experiments, we examined whether males of two congeneric species of marine sex-changing snails, Crepidula fornicata and C. convexa, chose large females over small ones as partners. We also used choice tests to see whether males of C. fornicata, a species whose members form long-term, multi-animal stacks, would choose two females in a stack over a single female. Surprisingly, males of neither species showed a preference for large females, in spite of the documented fecundity advantage associated with large female-size. Males of C. fornicata chose slightly, but not significantly, more single females than stacks, suggesting that neither number nor size drives mate choice in these animals. Key factors that may influence this lack of size preference include long association time, the likelihood of sperm competition, and the cost of extended mate search; it may also be that sex-change itself, the very factor that creates female-biased sexual size dimorphism in these species, prevents size preference, as males may gain sufficient reproductive advantage from eventually becoming large females themselves to offset any benefit of choosing large females.  相似文献   
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本文提出怎样理解产学研相结合的问题,并从产学研不同层面进行分析,提出以市场为目标、以制度为保证实现产学研有效结合的思路。  相似文献   
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Fetal cardiac function is increasingly recognized as a marker of disease severity and prognosis in selected fetal conditions. Magnetic resonance imaging (MRI) has been used in experimental (animal) fetal cardiology but the lack of a noninvasive fetal electrocardiogram (ECG) to trigger image acquisition remains a major limiting factor precluding its application in humans. Fetal medicine specialists are therefore limited to ultrasound to evaluate human fetal cardiac function. In this review, we aim to provide a complete overview of the different ultrasound techniques that can be used for fetal cardiac function assessment and we discuss their (theoretical) strengths and shortcomings. Conventional methods include M-mode assessment of ventricular contractility and Doppler assessment of the precordial veins and cardiac output (CO). More recent techniques such as the measurement of the myocardial performance index (MPI), myocardial motion analysis with tissue Doppler, speckle tracking and three-dimensional (3D) ultrasound techniques are also discussed. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
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In the FAIR project “Pheromaize”, CT96-1302, the main objective is to provide European growers with a reliable, cost effective and environmentally friendly technology based on pest mating disruption. The project is mainly focused on Mediterranean Corn Borer (MCB), Sesamia nonagroides, the key pest of maize grown under Mediterranean conditions. TNO has developed a sprayable formulation consisting of a biodegradable matrix in which␣the pheromone is dissolved, together with a UV––stabilizer, an antioxidant, a surfactant and a sticker material. During outdoor exposure experiments release of pheromone was found to be high enough for more than 30 days. This formulation has been tested in large scale field experiments by helicopter spraying on 5 ha maize by field partners in Spain, Greece and France.  相似文献   
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The purpose of this study was to improve risk management and to investigate build-up of the costs of fire in waste-fuel stores, to make the authorities and the population in general aware of the substantial monetary and non-material benefits connected with preventive measures being taken. To summarize, the results from the case studies show that the fires occurred by self-ignition of organic materials, the storage facilities were badly and/or not properly designed, and the waste fuels were not handled properly. On the basis of two case studies the main finding was that there must be one person only in charge during the fire to lead the action, and the fire brigade must not leave the area too early. Nowadays, the real cost for the fire is not calculated properly, or at all, by the waste-management company. It is concluded that waste-management companies, society, and insurance companies could save money by implementation of precautionary measures. Such relevant measures are reviewed. It is recommended: not to store waste fuels too high, in volumes which are too large or too close to town districts; to promote better cooperation between waste companies and the fire brigades and the local EPA; and to make insurance companies demand implementation of more security measures before signing the insurance contracts.  相似文献   
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