Recent genomic studies have highlighted the importance of hybridization and gene exchange in evolution. We ask what factors cause variation in the impact of hybridization, through adaptation in hybrids and the likelih...Recent genomic studies have highlighted the importance of hybridization and gene exchange in evolution. We ask what factors cause variation in the impact of hybridization, through adaptation in hybrids and the likelihood of hybrid speciation. During speciation, traits that diverge due to both divergent and stabilizing selection can contribute to the buildup of reproductive isolation. Divergent directional selection in parent taxa should lead to intermediate phenotypes in hybrids, whereas stabilizing se- lection can also produce extreme, transgressive phenotypes when hybridization occurs. By examining existing theory and em- pirical data, we discuss how these effects, combined with differences between modes of divergence in the chromosomal distribu- tion of incompatibilities, affect adaptation and speciation in hybrid populations. The result is a clear and testable set of predic- tions that can be used to examine hybrid adaptation and speciation. Stabilizing selection in parents increases transgression in hy- brids, increasing the possibility for novel adaptation. Divergent directional selection causes intermediate hybrid phenotypes and increases their ability to evolve along the direction of parental differentiation. Stabilizing selection biases incompatibilities to- wards autosomes, leading to reduced sexual correlations in trait values and reduced pleiotropy in hybrids, and hence increased freedom in the direction of evolution. Directional selection causes a bias towards sex-linked incompatibilities, with the opposite consequences. Divergence by directional selection leads to greater dominance effects than stabilizing selection, with major but variable impacts on hybrid evolution [Current Zoology 59 （5）： 675-685, 2013].展开更多
A back propagation （BP） neural network mathematical model was established to investigate the maneuvering control of an air cushion vehicle （ACV）. The calculation was based on four-freedom-degree model experiments ...A back propagation （BP） neural network mathematical model was established to investigate the maneuvering control of an air cushion vehicle （ACV）. The calculation was based on four-freedom-degree model experiments of hydrodynamics and aerodynamics. It is necessary for the ACV to control the velocity and the yaw rate as well as the velocity angle at the same time. The yaw rate and the velocity angle must be controlled correspondingly because of the whipping, which is a special characteristic for the ACV. The calculation results show that it is an efficient way for the ACV＇s maneuvering control by using a BP neural network to adjust PID parameters online.展开更多
文摘Recent genomic studies have highlighted the importance of hybridization and gene exchange in evolution. We ask what factors cause variation in the impact of hybridization, through adaptation in hybrids and the likelihood of hybrid speciation. During speciation, traits that diverge due to both divergent and stabilizing selection can contribute to the buildup of reproductive isolation. Divergent directional selection in parent taxa should lead to intermediate phenotypes in hybrids, whereas stabilizing se- lection can also produce extreme, transgressive phenotypes when hybridization occurs. By examining existing theory and em- pirical data, we discuss how these effects, combined with differences between modes of divergence in the chromosomal distribu- tion of incompatibilities, affect adaptation and speciation in hybrid populations. The result is a clear and testable set of predic- tions that can be used to examine hybrid adaptation and speciation. Stabilizing selection in parents increases transgression in hy- brids, increasing the possibility for novel adaptation. Divergent directional selection causes intermediate hybrid phenotypes and increases their ability to evolve along the direction of parental differentiation. Stabilizing selection biases incompatibilities to- wards autosomes, leading to reduced sexual correlations in trait values and reduced pleiotropy in hybrids, and hence increased freedom in the direction of evolution. Directional selection causes a bias towards sex-linked incompatibilities, with the opposite consequences. Divergence by directional selection leads to greater dominance effects than stabilizing selection, with major but variable impacts on hybrid evolution [Current Zoology 59 （5）： 675-685, 2013].
文摘A back propagation （BP） neural network mathematical model was established to investigate the maneuvering control of an air cushion vehicle （ACV）. The calculation was based on four-freedom-degree model experiments of hydrodynamics and aerodynamics. It is necessary for the ACV to control the velocity and the yaw rate as well as the velocity angle at the same time. The yaw rate and the velocity angle must be controlled correspondingly because of the whipping, which is a special characteristic for the ACV. The calculation results show that it is an efficient way for the ACV＇s maneuvering control by using a BP neural network to adjust PID parameters online.
