The combined selection index used in the breeding of new Yorkshire dam line with high prolificacy according to breeding objects was formulated as /：2.272E- BVNB-0.056EBVDAYS. After 5 generations breeding, the two mai...The combined selection index used in the breeding of new Yorkshire dam line with high prolificacy according to breeding objects was formulated as /：2.272E- BVNB-0.056EBVDAYS. After 5 generations breeding, the two main selected traits such as total number of born and age at 100 kg weight was 12.17 piglets/litter and 165.18 d, respectively. The genetic improvements per generates was 0.156 and -2.198, respec- tively. The breeding objects of the new Yorkshire dam line with high prolificacy were basically reached. It indicated that the methods and index could be used in pig breeding.展开更多
In the present study, the effect of one-generation divergent selection on the growth and survival of the bay scallop （Argopecten irradians concentricus） was examined to evaluate the efficacy of a selection program c...In the present study, the effect of one-generation divergent selection on the growth and survival of the bay scallop （Argopecten irradians concentricus） was examined to evaluate the efficacy of a selection program currently being carried out in Beibu Bay in the South China Sea. A total of 146 adult scallops were randomly selected from the same cultured population ofA. i. concentricus, and divided into two groups in shell length （anterior-posterior measurement）： large （4.91-6.02 cm, n=74） and small （3.31-4.18 cm, n=72）. At the same time, a control group was also randomly sampled （4.21-4.88 cm, n=80）. Mass-spawned F1 progenies from the three size groups were obtained and reared under identical conditions at all growth phases. The effects of two-way （or upward-downward） selection on fertilization rate, hatching rate, survival rate, daily growth in shell length and body weight were assessed in the three size groups. Results show that significant differences （P〈0.01） were found in hatching rate, survival rate and daily growth of F~ progenies, but not in fertilization rate （P〉0.05）, among the three groups. The hatching rate, survival rate and daily growth of the progeny of large-sized parents were greater than those of the control group （P〈0.05）, which in turn were larger than those of small-sized group （P〈0.05）. Responses to selection by shell length and body weight were 0.32±0.04 cm and 2.18±0.05 g, respectively, for the upward selection, and -0.14±0.03 cm and -2.77±0.06 g, respectively, for the downward selection. The realized heritability estimates of shell length and body weight were 0.38±0.06 cm and 0.22±0.07 g for the upward selection, and 0.24±0.06 cm and 0.37±0.09 g for the downward selection, respectively. The change in growth by bidirectional selection suggests that high genetic variation may be present in the cultured bay scallop population in China.展开更多
When hybridization results in reduced fitness, natural selection is expected to favor the evolution of traits that minimize the likelihood of hybridizing in the first place. This process, termed reinforcement （or, mo...When hybridization results in reduced fitness, natural selection is expected to favor the evolution of traits that minimize the likelihood of hybridizing in the first place. This process, termed reinforcement （or, more generally, reproductive character displacement）, thereby contributes to the evolution of enhanced reproductive isolation between hybridizing groups. By enhancing reproductive isolation in this way, reinforcement plays an important role in the final stages of speciation. However, reinforcement can also contribute to the early stages of speciation. Specifically, because selection to avoid hybridization occurs only in sympatric populations, the unfolding of reinforcement can lead to the evolution of traits in sympatric populations that reduce reproduction between conspecifics in sympatry versus those in allopatry. Thus, reinforcement between species can lead to reproductive isolation--and possibly speciation-between populations in sympatry versus those in allopatry or among different sympatric populations. Here, I describe how this process can occur, the conditions under which it is most likely to occur, and the empirical data needed to evaluate the hypothesis that reinforcement can initiate speciation.展开更多
Sexual selection is widespread if not ubiquitous in hermaphroditic organisms. Although many phenomena that have been described as sexual selection in gonochores, （e.g. harem polygamy, multiple mating, elaborate court...Sexual selection is widespread if not ubiquitous in hermaphroditic organisms. Although many phenomena that have been described as sexual selection in gonochores, （e.g. harem polygamy, multiple mating, elaborate courtship, even secondary sexual characters） can be found in some hermaphrodites, what is more interesting is the ways in which sexual selection in her- maphrodites may differ from dioecious taxa. In hermaphrodites, an individual＇s mating success includes its success from both sexual roles. Secondly, in many simultaneously hermaphroditic taxa there is strong evidence of sexual selection and yet the ope- rational sex ratio is 1：1, by definition. Many simultaneous hermaphrodites have elaborate courtship and genital anatomy, suggest- ing sexual selection plays an important role in reproductive success. Sperm competition and cryptic female choice mean that the number of mates acquired is not necessarily a predictor of reproductive success. Even in simultaneous hermaphrodites with re- ciprocal mating, variance in reproductive success through the male role and through the female role may differ in a population. Moreover hermaphrodites may choose to emphasize one sexual role over the other. Data suggest that the preferred role varies in hermaphrodites, which creates an opportunity to test fundamental predictions and assumptions of sexual selection theory. Hermaphrodites may vary their emphasis on one sexual role over the other either developmentally or behaviorally in response to environmental or social parameters. How they use this capability in acquiring more or higher quality mates still requires study展开更多
Speciation research during the last several decades has confirmed that natural selection frequently drives the genera- tion of new species. But how does this process generally unfold in nature？ We argue that answerin...Speciation research during the last several decades has confirmed that natural selection frequently drives the genera- tion of new species. But how does this process generally unfold in nature？ We argue that answering this question requires a clearer conceptual framework for understanding selection＇s role in speciation. We present a unified framework of speciation, pro- viding mechanistic descriptions of fundamentally distinct routes to speciation, and how these may interact during lineage splitting Two major categories are recognized： reproductive isolation resulting from （1） responses to selection, ＂speciation by selection,＂ or （2） non-selective processes, ＂speciation without selection.＂ Speciation by selection can occur via three mechanisms： （1） similar selection, （2） divergent selection, and （3） reinforcement selection. Understanding ecology＇s role in speciation requires uncovering how these three mechanisms contribute to reproductive isolation, and their relative importance compared to non-selective proce- sses, because all three mechanisms can occur side-by-side during speciation. To accomplish this, we highlight examination of groups of organisms inhabiting replicated environmental gradients. This scenario is common in nature, and a large literature illus- trates that both parallel and non-parallel responses to similar environments are widespread, and each can result in speciation. This recognition reveals four general pathways of speciation by similar or divergent selection--parallel and nonparallel responses to similar and divergent selection. Altogether, we present a more precise framework for speciation research, draw attention to some under-recognized features of speciation, emphasize the multidimensionality of speciation, reveal limitations of some previous tests and descriptions of speciation mechanisms, and point to a number of directions for future investigation [Current Zoology 59 （1）： 31-52, 2013].展开更多
基金Supported by National Science and Technology Support Plan during the Eleventh Five-year Plan(2006BAD01A08-02)Hubei Agricultural Innovation Program(2007-620-004-003)Special Fund for Modern Pig Production Technology Construction(NYCYTX-009)~~
文摘The combined selection index used in the breeding of new Yorkshire dam line with high prolificacy according to breeding objects was formulated as /：2.272E- BVNB-0.056EBVDAYS. After 5 generations breeding, the two main selected traits such as total number of born and age at 100 kg weight was 12.17 piglets/litter and 165.18 d, respectively. The genetic improvements per generates was 0.156 and -2.198, respec- tively. The breeding objects of the new Yorkshire dam line with high prolificacy were basically reached. It indicated that the methods and index could be used in pig breeding.
基金Supported by the National Science and Technology Ministry(No.2007GB2E000183)the Agricultural Ministry of China(No.nyhyzx07-047)
文摘In the present study, the effect of one-generation divergent selection on the growth and survival of the bay scallop （Argopecten irradians concentricus） was examined to evaluate the efficacy of a selection program currently being carried out in Beibu Bay in the South China Sea. A total of 146 adult scallops were randomly selected from the same cultured population ofA. i. concentricus, and divided into two groups in shell length （anterior-posterior measurement）： large （4.91-6.02 cm, n=74） and small （3.31-4.18 cm, n=72）. At the same time, a control group was also randomly sampled （4.21-4.88 cm, n=80）. Mass-spawned F1 progenies from the three size groups were obtained and reared under identical conditions at all growth phases. The effects of two-way （or upward-downward） selection on fertilization rate, hatching rate, survival rate, daily growth in shell length and body weight were assessed in the three size groups. Results show that significant differences （P〈0.01） were found in hatching rate, survival rate and daily growth of F~ progenies, but not in fertilization rate （P〉0.05）, among the three groups. The hatching rate, survival rate and daily growth of the progeny of large-sized parents were greater than those of the control group （P〈0.05）, which in turn were larger than those of small-sized group （P〈0.05）. Responses to selection by shell length and body weight were 0.32±0.04 cm and 2.18±0.05 g, respectively, for the upward selection, and -0.14±0.03 cm and -2.77±0.06 g, respectively, for the downward selection. The realized heritability estimates of shell length and body weight were 0.38±0.06 cm and 0.22±0.07 g for the upward selection, and 0.24±0.06 cm and 0.37±0.09 g for the downward selection, respectively. The change in growth by bidirectional selection suggests that high genetic variation may be present in the cultured bay scallop population in China.
文摘When hybridization results in reduced fitness, natural selection is expected to favor the evolution of traits that minimize the likelihood of hybridizing in the first place. This process, termed reinforcement （or, more generally, reproductive character displacement）, thereby contributes to the evolution of enhanced reproductive isolation between hybridizing groups. By enhancing reproductive isolation in this way, reinforcement plays an important role in the final stages of speciation. However, reinforcement can also contribute to the early stages of speciation. Specifically, because selection to avoid hybridization occurs only in sympatric populations, the unfolding of reinforcement can lead to the evolution of traits in sympatric populations that reduce reproduction between conspecifics in sympatry versus those in allopatry. Thus, reinforcement between species can lead to reproductive isolation--and possibly speciation-between populations in sympatry versus those in allopatry or among different sympatric populations. Here, I describe how this process can occur, the conditions under which it is most likely to occur, and the empirical data needed to evaluate the hypothesis that reinforcement can initiate speciation.
文摘Sexual selection is widespread if not ubiquitous in hermaphroditic organisms. Although many phenomena that have been described as sexual selection in gonochores, （e.g. harem polygamy, multiple mating, elaborate courtship, even secondary sexual characters） can be found in some hermaphrodites, what is more interesting is the ways in which sexual selection in her- maphrodites may differ from dioecious taxa. In hermaphrodites, an individual＇s mating success includes its success from both sexual roles. Secondly, in many simultaneously hermaphroditic taxa there is strong evidence of sexual selection and yet the ope- rational sex ratio is 1：1, by definition. Many simultaneous hermaphrodites have elaborate courtship and genital anatomy, suggest- ing sexual selection plays an important role in reproductive success. Sperm competition and cryptic female choice mean that the number of mates acquired is not necessarily a predictor of reproductive success. Even in simultaneous hermaphrodites with re- ciprocal mating, variance in reproductive success through the male role and through the female role may differ in a population. Moreover hermaphrodites may choose to emphasize one sexual role over the other. Data suggest that the preferred role varies in hermaphrodites, which creates an opportunity to test fundamental predictions and assumptions of sexual selection theory. Hermaphrodites may vary their emphasis on one sexual role over the other either developmentally or behaviorally in response to environmental or social parameters. How they use this capability in acquiring more or higher quality mates still requires study
文摘Speciation research during the last several decades has confirmed that natural selection frequently drives the genera- tion of new species. But how does this process generally unfold in nature？ We argue that answering this question requires a clearer conceptual framework for understanding selection＇s role in speciation. We present a unified framework of speciation, pro- viding mechanistic descriptions of fundamentally distinct routes to speciation, and how these may interact during lineage splitting Two major categories are recognized： reproductive isolation resulting from （1） responses to selection, ＂speciation by selection,＂ or （2） non-selective processes, ＂speciation without selection.＂ Speciation by selection can occur via three mechanisms： （1） similar selection, （2） divergent selection, and （3） reinforcement selection. Understanding ecology＇s role in speciation requires uncovering how these three mechanisms contribute to reproductive isolation, and their relative importance compared to non-selective proce- sses, because all three mechanisms can occur side-by-side during speciation. To accomplish this, we highlight examination of groups of organisms inhabiting replicated environmental gradients. This scenario is common in nature, and a large literature illus- trates that both parallel and non-parallel responses to similar environments are widespread, and each can result in speciation. This recognition reveals four general pathways of speciation by similar or divergent selection--parallel and nonparallel responses to similar and divergent selection. Altogether, we present a more precise framework for speciation research, draw attention to some under-recognized features of speciation, emphasize the multidimensionality of speciation, reveal limitations of some previous tests and descriptions of speciation mechanisms, and point to a number of directions for future investigation [Current Zoology 59 （1）： 31-52, 2013].
