Over the past few decades, extreme changes have occurred in the characters of exploited fish populations. The majority of these changes have affected the growth traits of fish life history, which include a smaller siz...Over the past few decades, extreme changes have occurred in the characters of exploited fish populations. The majority of these changes have affected the growth traits of fish life history, which include a smaller size-at-age, an earlier age-at-maturation and among others. Currently, the causes of these life history traits changes still require systematic analyses and empirical studies. The explanations that have been cited are merely expressed in terms of fish phenotypic adaptation. It has been claimed that the original traits of fish can be recovered once the intensity of exploitation of the fish is controlled. Sustained environmental and fishing pressure will change the life history traits of most fish species, so the fish individual's traits are still in small size-at-age and at earlier age-at-maturation in exploited fish populations. In this paper, we expressed our view of points that fishing gear has imposed selectivity on fish populations and individuals as various other environmental factors have done and such changes are unrecoverable. According to the existing tend of exploited fish individual's life history traits, we suggested further researches in this field and provided better methods of fishery management and thereby fishery resources protection than those available early.展开更多
Trawl is a main fishing gear in Chinese fishery,capturing large fish and letting small ones at large.However,long-term use of trawl would result in changes of phenotypic traits of the fish stocks,such as smaller size-...Trawl is a main fishing gear in Chinese fishery,capturing large fish and letting small ones at large.However,long-term use of trawl would result in changes of phenotypic traits of the fish stocks,such as smaller size-at-age and earlier age-at-maturation.In this study,we simulated a fish population with size characteristics of trawl fishing and the population produces one generation of offspring and lives for one year,used trawl to exploit the simulated fish population,and captured individuals by body size.We evaluated the impact of the changes on selectivity parameters,such as selective range and the length at 50% retention.Under fishing pressure,we specified the selectivity parameters,and determined that smaller selection rates and greater length at 50% retention were associated with an increased tendency towards miniaturization.展开更多
Genetic analysis of yield and yield components were carried out on three parental clones of Coffea canephora Pierre and their controlled hybrid progenies. There is a possibility to estimate coffee yield capabilities i...Genetic analysis of yield and yield components were carried out on three parental clones of Coffea canephora Pierre and their controlled hybrid progenies. There is a possibility to estimate coffee yield capabilities in simply via the easier measuring traits of yield components since significant correlation between them were detected. We found that among parental show very few significantly differences of all observed characters and even not found between the overall mean of the descendants and their donor parents, whereas some particular descendants show higher values rather than their donor parent in one or more characters. Increased value between the best parent to the best descendent were detected varies from zero to 102%. This situation suggests the difficulty to find out the optimum yield in a single plant by accumulating all of yield components that actually can increase 143% to 278% from actual to potential yields. In addition, observed characters among population were also actually found highly varies from 159% in out-turn in population B to 28,333% in number of productive branch among population A. Low heritability （h2） that generally found in quantitative traits due to polygenic control was present in our studies in almost all characters observed. Therefore, selection for actual high yielding through conventional breeding will not efficient, and more convincing the power of selection using molecular markers to assist for cumulate additive effects in a single genotypes that resulted of high yielding in the future.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
基金the financial support from Special Fund for Agro-scientific Research in the Public Interest (No. 201203018)
文摘Over the past few decades, extreme changes have occurred in the characters of exploited fish populations. The majority of these changes have affected the growth traits of fish life history, which include a smaller size-at-age, an earlier age-at-maturation and among others. Currently, the causes of these life history traits changes still require systematic analyses and empirical studies. The explanations that have been cited are merely expressed in terms of fish phenotypic adaptation. It has been claimed that the original traits of fish can be recovered once the intensity of exploitation of the fish is controlled. Sustained environmental and fishing pressure will change the life history traits of most fish species, so the fish individual's traits are still in small size-at-age and at earlier age-at-maturation in exploited fish populations. In this paper, we expressed our view of points that fishing gear has imposed selectivity on fish populations and individuals as various other environmental factors have done and such changes are unrecoverable. According to the existing tend of exploited fish individual's life history traits, we suggested further researches in this field and provided better methods of fishery management and thereby fishery resources protection than those available early.
基金Supported by the Special Fund for Agro-scientific Research in the Public Interest of China(No.201203018)the National Key Technology Research and Development Program of China(No.2006BAD09A05)
文摘Trawl is a main fishing gear in Chinese fishery,capturing large fish and letting small ones at large.However,long-term use of trawl would result in changes of phenotypic traits of the fish stocks,such as smaller size-at-age and earlier age-at-maturation.In this study,we simulated a fish population with size characteristics of trawl fishing and the population produces one generation of offspring and lives for one year,used trawl to exploit the simulated fish population,and captured individuals by body size.We evaluated the impact of the changes on selectivity parameters,such as selective range and the length at 50% retention.Under fishing pressure,we specified the selectivity parameters,and determined that smaller selection rates and greater length at 50% retention were associated with an increased tendency towards miniaturization.
文摘Genetic analysis of yield and yield components were carried out on three parental clones of Coffea canephora Pierre and their controlled hybrid progenies. There is a possibility to estimate coffee yield capabilities in simply via the easier measuring traits of yield components since significant correlation between them were detected. We found that among parental show very few significantly differences of all observed characters and even not found between the overall mean of the descendants and their donor parents, whereas some particular descendants show higher values rather than their donor parent in one or more characters. Increased value between the best parent to the best descendent were detected varies from zero to 102%. This situation suggests the difficulty to find out the optimum yield in a single plant by accumulating all of yield components that actually can increase 143% to 278% from actual to potential yields. In addition, observed characters among population were also actually found highly varies from 159% in out-turn in population B to 28,333% in number of productive branch among population A. Low heritability （h2） that generally found in quantitative traits due to polygenic control was present in our studies in almost all characters observed. Therefore, selection for actual high yielding through conventional breeding will not efficient, and more convincing the power of selection using molecular markers to assist for cumulate additive effects in a single genotypes that resulted of high yielding in the future.
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.
