Despite all efforts,long-term changes in the adult sex ratios of breeding duck populations are still unclear;this uncertainty is especially true for male-bias populations,which are often under the scrutiny of research...Despite all efforts,long-term changes in the adult sex ratios of breeding duck populations are still unclear;this uncertainty is especially true for male-bias populations,which are often under the scrutiny of researchers lacking convenient results for the active protection of endangered species.Species with male-bias populations are usually strongly affected by a decline in population size that leads to a higher extinction risk.In this study,we examined our long-term data of the abundance of breeding populations in six duck species(Mallard Anas platyrhynchos,Gadwall Mareca strepera,Red-crested Pochard Netta rufina,Common Pochard Aythya ferina,Tufted Duck Aythya fuligula,and Common Goldeneye Bucephala clangula)from fishponds in South Bohemia,Czechia,between 2004 and 2022.This evidence was used to assess long-term changes in the adult sex ratio in these breeding populations and investigate the possible effects of the NAO index(North Atlantic Oscillation index)on them,indicating climate conditions in winter.We determined a long-term decrease of the proportion of females in the breeding season in two of the six examined species:Common Pochard and Red-crested Pochard,which is driven by the long-term increase in the number of males in contrast to the decreasing or stable number of females likely caused by different migration behaviours between females and males.In the case of Common Pochard,in breeding populations,we estimated 60-65%of males in the early 2000s rising to 75-80%in the early 2020s.However,we establish no significant effects linked to climate conditions of the previous winter in these species as a crucial cause of the changes of the proportion of females in the breeding population.展开更多
Pine wood nematode(PWN), Bursaphelenchus xylophilus, is a serious pathogen of pines throughout the world. Previous work indicated that different concentrations of a-pinene could affect nematode reproduction,however th...Pine wood nematode(PWN), Bursaphelenchus xylophilus, is a serious pathogen of pines throughout the world. Previous work indicated that different concentrations of a-pinene could affect nematode reproduction,however the mechanism of that influence is not clear. In order to examine the reproductive strategies of PWN in response to the stress of the volatile material a-pinene, we investigated different aspects of population changes of B.xylophilus under two concentrations of a-pinene. The results show that a high concentration(214.5 mg ml-1)promoted population growth while a low concentration(56.33 mg ml-1) decreased the population. Population structure was analyzed and it was found that a high concentration of a-pinene decreased the percentage of adults but increased the percentages of larvae and eggs.Furthermore, from the results of an evaluation of sex ratios(female/male), it was determined that a high concentration could elevate sex ratios but a low concentration decreased ratios sharply. These results suggest that the PWN could regulate its population by changing sex ratios under stress of a-pinene. This study has provided a theoretical basis for the prevention and control of pine wilt disease caused by the pine wood nematode.展开更多
Background:The long-term monitoring of demographic changes in waterbird populations remains limited,but such information can be valuable for conservationists and waterbird managers.Biased sex ratios can indicate diffe...Background:The long-term monitoring of demographic changes in waterbird populations remains limited,but such information can be valuable for conservationists and waterbird managers.Biased sex ratios can indicate differences in survival rates between sexes.In particular,differences in the sex ratios of fledged juveniles and adults can provide insight into the development of male bias among populations.Methods:In this study,we used data from individual birds captured over a 57-year period to assess the extent,and temporal variability in male bias in nine populations of ducks wintering in the United Kingdom:Gadwall(Mareca strepera),Northern Mallard(Anas platyrhynchos),Northern Pintail(Anas acuta),Common Pochard(Aythya ferina),Common Shelduck(Tadorna tadorna),Northern Shoveler(Spatula clypeata),Eurasian Teal(Anas crecca),Tufted Duck(Aythya fuligula),and Eurasian Wigeon(Mareca penelope).Results:Overall,eight of these populations were significantly male-biased and adults were more male-biased than first-winter juveniles for all nine populations.The increased male bias among adults is consistent with the hypothesis that factors such as higher mortality of reproductive-age females during the breeding season is a major cause of male bias in duck populations.However,such predation cannot explain the male bias detected in first-winter juveniles in four of the populations.The temporal trends in male bias differed between adults and first-winter juveniles in Northern Mallard,Northern Pintail,Common Pochard,Common Shelduck,Eurasian Teal,Tufted Duck,and Eurasian Wigeon.Over the study period we found increased male bias among adult Northern Mallard,Northern Pintail,Common Pochard,Common Shelduck,and Tufted Duck as well as both adult and first-winter juvenile Northern Shoveler.Conclusions:We provide evidence that among wintering duck populations,sex ratios are typically male-biased,with adults exhibiting stronger male-biased sex ratios than first-winter juveniles.Improved monitoring of sex ratios of wintering waterbirds would help to increase our understanding of changes in waterbird demography,population structure,and observed population trends;our study shows that birds caught during ringing projects can be a valuable source of such data.展开更多
Background:One of the most challenging tasks in wildlife conservation and management is clarifying which and how external and intrinsic factors influence wildlife demography and long-term viability.The wild population...Background:One of the most challenging tasks in wildlife conservation and management is clarifying which and how external and intrinsic factors influence wildlife demography and long-term viability.The wild population of the Crested Ibis(Nipponia nippon)has recovered to approximately 4400,and several reintroduction programs have been carried out in China,Japan and Korea.Population viability analysis on this endangered species has been limited to the wild population,showing that the long-term population growth is restricted by the carrying capacity and inbreeding.However,gaps in knowledge of the viability of the reintroduced population and its drivers in the release environment impede the identification of the most effective population-level priorities for aiding in species recovery.Methods:The field monitoring data were collected from a reintroduced Crested Ibis population in Ningshan,China from 2007 to 2018.An individual-based VORTEX model(Version 10.3.5.0)was used to predict the future viability of the reintroduced population by incorporating adaptive patterns of ibis movement in relation to catastrophe frequency,mortality and sex ratio.Results:The reintroduced population in Ningshan County is unlikely to go extinct in the next 50 years.The popula-tion size was estimated to be 367,and the population genetic diversity was estimated to be 0.97.Sensitivity analysis showed that population size and extinction probability were dependent on the carrying capacity and sex ratio.The carrying capacity is the main factor accounting for the population size and genetic diversity,while the sex ratio is the primary factor responsible for the population growth trend.Conclusions:A viable population of the Crested Ibis can be established according to population viability analysis.Based on our results,conservation management should prioritize a balanced sex ratio,high-quality habitat and low mortality.展开更多
Monthly investigatiom were made on the population of Chinese freshwater crab, Sinopotamon yangteskiense Bott, 1967 from April, 1984 to Match, 1985. The data on 4413 specimens show that the growth was affected mainly b...Monthly investigatiom were made on the population of Chinese freshwater crab, Sinopotamon yangteskiense Bott, 1967 from April, 1984 to Match, 1985. The data on 4413 specimens show that the growth was affected mainly by temperature. During the April to November growth period, the crabs’ major development occured from June through October. One year was required for a fine white oocyte to develop into a mature egg. The reproduction period was June-October. Females bearing eggs were taken from June-August, and crabs with young were found from July-October. The females reproduced once a year but could for more than one year. The number of eggs carried by a female varied greatly according to the size of the crab, ranging from 30 to 100 eggs. New-bom crabs become mature after 1-2 yeats. The sex ratio was approximately 1:1 in the overall population. However, the larger crabs are predominantly male. The age distribution of S. yangtsekinese was estimated from size frequency histograms. There were more adult展开更多
Zonal distribution and population biology of llyoplaxfrater were studied in a mangrove mudflat area of Pakistan. The crabs were collected from Korangi creek through transect and quadrat method from low tide level to h...Zonal distribution and population biology of llyoplaxfrater were studied in a mangrove mudflat area of Pakistan. The crabs were collected from Korangi creek through transect and quadrat method from low tide level to high tide level. Two transects were delimited in a mangrove area of Korangi creek （24°79′N/67°20′E）. On each transect, three 0.25 m quadrats were sampled at three tidal levels on a monthly basis during low tide periods from March 2001 to February 2002. A total of 1124 crabs were obtained, of which 482 were males and 642 were females. Density of crabs varied between 0 and 90/m^2. The density and size distribution varied and showed significant differences from low to high tide level, and were positively correlated with the percent moisture, percent organic matter and sediment grain size. The carapace width （CW） ranged from 2.5 to 11.5 mm for male and 2.5 to 11.0 mm for female and was not significantly different. The overall sex ratio did not differ significantly from the expected 1：1 throughout the year in small crabs but was significantly different in adult crabs （Z2 = 49.73） with more male crabs, Size frequency distribution showed recruitment of juvenile crabs （〈 4 mm） nearly throughout the year except during June and July. Presence of ovigerous females in all months with seasonal peaks in September, October, December and May indicates seasonal continuous breeding. Weight of egg mass increases with weight of ovigerous females and show positive linear relationship. The estimated mean diameter of egg was 2.83±0.25μm, and the average number of eggs was 3065±902.展开更多
Unbalanced parental contribution and small effective population size （Ne） are common issues during the artificial breeding of marine bivalves. The impact of hatchery-spawning practices on parental contribution, effe...Unbalanced parental contribution and small effective population size （Ne） are common issues during the artificial breeding of marine bivalves. The impact of hatchery-spawning practices on parental contribution, effective population size, the Ne/Nratio, and genetic diversity are largely unknown. To address this, we conducted a parentage analysis on a complete 3×3 diallel cross of clam Meretrix meretrix using eight microsatellite markers. The genetic diversity of the parents was higher than that of their respective offspring in most crosses （8/9）. Sires or dams from the same family contributed unequally to the pool of offspring from a particular cross, and the same parent clam exhibited large variation in parental contribution among different crosses. The variance in male contribution was higher than that of the female contribution in most crosses, suggesting that male contribution was more skewed than for females. The No/N ratio for nine crosses ranged from 0.58 to 0.86. There was no linear relationship between the sex ratio and the Ne/Nratio （P〉0.05）. Moreover, a sex ratio closer to one-to-one does not necessarily mean a larger effective population size. A solution to small effective population size in commercial breeding programs is increasing broodstoek numbers and attempting to maintain a balanced sex ratio.展开更多
Effective population management relies on assessments of population size and sex ratio.However,these estimates are difficult to obtain for elusive and rare species.Recently,noninvasive genetic census methods have been...Effective population management relies on assessments of population size and sex ratio.However,these estimates are difficult to obtain for elusive and rare species.Recently,noninvasive genetic census methods have been developed as an alternative to tradi-tional capture-mark-recapture methods.In this study,we estimated the size of the Sichuan snub-nosed monkey(Rhinopithecus roxellana) population in the Shennongjia Nature Reserve(SNR) using a noninvasive sampling method based on 16 microsatellite loci.We also used a PCR-based genetic method to sex the sampled individuals and infer the population sex ratio.The population size of R.roxellana in the SNR was estimated to be 1044 individuals(95% CITIRM:613-1409) .The estimated population sex ratio is more female-biased than expected,which we attribute to the sampling biased towards one male units and limited sampling of bachelor male units.Moreover,there is no suggestion that the heavy traffic road through the reserve might block movement of monkeys.The results of this study indicate genetic assessments based on a noninvasive sampling method can provide useful in-formation regarding populations of elusive primates.展开更多
Mutualisms are cooperative interactions between members of different species. We focus on obligate mutualism, where each species cannot survive without the other. From a theoretical aspect, obligate mutualism is simil...Mutualisms are cooperative interactions between members of different species. We focus on obligate mutualism, where each species cannot survive without the other. From a theoretical aspect, obligate mutualism is similar to the relationship between male and female. Empirical data indicate a sex-ratio selection: male and female have a specific ratio in their population sizes. In the present paper, we apply lattice model to obligate mutualism between two species, and present a theory of “ratio selection” which is a generalization of sex-ratio selection. Computer simulations are carried out by two methods: local and global interactions. In the former, interactions occur between neighbouring cells, while in the latter they occur between any pair of cells. Simulations in both interactions show the so-called Allee effect: both species can survive, when both densities are large in some extent. However, we find a large difference between local and global simulations. In the case of local interaction, restriction for survival is found to be extremely severe compared to global interaction. Both species require a proper ratio for their sustainability. This result leads to the theory of ratio selection: when interaction occurs locally, the ratio of both species is uniquely determined. We discuss that the ratio selection explains not only the evolution of endosymbionts from free-living ancestors but also the evolution from endosymbionts to organelles.展开更多
In 2020,China’s sex ratio at birth(SRB)stood at 111.3,still exhibiting a notable bias.Son preference ranks as the most essential and fundamental reason for the skewed SRB.This study,using a mixed-methods approach,see...In 2020,China’s sex ratio at birth(SRB)stood at 111.3,still exhibiting a notable bias.Son preference ranks as the most essential and fundamental reason for the skewed SRB.This study,using a mixed-methods approach,seeks to address what the temporal changes and regional differences in SRB and the gender preferences are in China,whether and why son preference persists,how people practice such preferences and how they relate to the persistently high SRB in the Chinese con-text.Analysis of data from five national sample surveys finds that son preference is waning and daughter preference is gaining momentum,consistent with significant downward trends in SRB.The study also reveals that value shifts and intergenera-tional relations have a strong influence on gender preferences and their translation into reproductive behavior.Additionally,this study highlights the challenges that are hindering the decline in son preference,suggesting that more efforts are needed to empower women and to change social norms.展开更多
基金supported by the project 2021B0038 of the Internal Grant Agency of Faculty of Environmental Sciences,CZU Prague entitled“Effect of incubation behaviour on predation risk in ducks(Common Pochard Aythya ferina and Tufted Duck Aythya fuligula)in two different habitats”the project SS01010280 of the Technology Agency of the Czech Republic entitled“Fishpond management optimization as a tool to biodiversity conservation under climate change”.
文摘Despite all efforts,long-term changes in the adult sex ratios of breeding duck populations are still unclear;this uncertainty is especially true for male-bias populations,which are often under the scrutiny of researchers lacking convenient results for the active protection of endangered species.Species with male-bias populations are usually strongly affected by a decline in population size that leads to a higher extinction risk.In this study,we examined our long-term data of the abundance of breeding populations in six duck species(Mallard Anas platyrhynchos,Gadwall Mareca strepera,Red-crested Pochard Netta rufina,Common Pochard Aythya ferina,Tufted Duck Aythya fuligula,and Common Goldeneye Bucephala clangula)from fishponds in South Bohemia,Czechia,between 2004 and 2022.This evidence was used to assess long-term changes in the adult sex ratio in these breeding populations and investigate the possible effects of the NAO index(North Atlantic Oscillation index)on them,indicating climate conditions in winter.We determined a long-term decrease of the proportion of females in the breeding season in two of the six examined species:Common Pochard and Red-crested Pochard,which is driven by the long-term increase in the number of males in contrast to the decreasing or stable number of females likely caused by different migration behaviours between females and males.In the case of Common Pochard,in breeding populations,we estimated 60-65%of males in the early 2000s rising to 75-80%in the early 2020s.However,we establish no significant effects linked to climate conditions of the previous winter in these species as a crucial cause of the changes of the proportion of females in the breeding population.
基金financially supported by Fundamental Research Funds of Research Institute of Forest New Technology,CAF(CAFYBB2018SY037)National Key Research and Development Program(2016YFC1200604)。
文摘Pine wood nematode(PWN), Bursaphelenchus xylophilus, is a serious pathogen of pines throughout the world. Previous work indicated that different concentrations of a-pinene could affect nematode reproduction,however the mechanism of that influence is not clear. In order to examine the reproductive strategies of PWN in response to the stress of the volatile material a-pinene, we investigated different aspects of population changes of B.xylophilus under two concentrations of a-pinene. The results show that a high concentration(214.5 mg ml-1)promoted population growth while a low concentration(56.33 mg ml-1) decreased the population. Population structure was analyzed and it was found that a high concentration of a-pinene decreased the percentage of adults but increased the percentages of larvae and eggs.Furthermore, from the results of an evaluation of sex ratios(female/male), it was determined that a high concentration could elevate sex ratios but a low concentration decreased ratios sharply. These results suggest that the PWN could regulate its population by changing sex ratios under stress of a-pinene. This study has provided a theoretical basis for the prevention and control of pine wilt disease caused by the pine wood nematode.
文摘Background:The long-term monitoring of demographic changes in waterbird populations remains limited,but such information can be valuable for conservationists and waterbird managers.Biased sex ratios can indicate differences in survival rates between sexes.In particular,differences in the sex ratios of fledged juveniles and adults can provide insight into the development of male bias among populations.Methods:In this study,we used data from individual birds captured over a 57-year period to assess the extent,and temporal variability in male bias in nine populations of ducks wintering in the United Kingdom:Gadwall(Mareca strepera),Northern Mallard(Anas platyrhynchos),Northern Pintail(Anas acuta),Common Pochard(Aythya ferina),Common Shelduck(Tadorna tadorna),Northern Shoveler(Spatula clypeata),Eurasian Teal(Anas crecca),Tufted Duck(Aythya fuligula),and Eurasian Wigeon(Mareca penelope).Results:Overall,eight of these populations were significantly male-biased and adults were more male-biased than first-winter juveniles for all nine populations.The increased male bias among adults is consistent with the hypothesis that factors such as higher mortality of reproductive-age females during the breeding season is a major cause of male bias in duck populations.However,such predation cannot explain the male bias detected in first-winter juveniles in four of the populations.The temporal trends in male bias differed between adults and first-winter juveniles in Northern Mallard,Northern Pintail,Common Pochard,Common Shelduck,Eurasian Teal,Tufted Duck,and Eurasian Wigeon.Over the study period we found increased male bias among adult Northern Mallard,Northern Pintail,Common Pochard,Common Shelduck,and Tufted Duck as well as both adult and first-winter juvenile Northern Shoveler.Conclusions:We provide evidence that among wintering duck populations,sex ratios are typically male-biased,with adults exhibiting stronger male-biased sex ratios than first-winter juveniles.Improved monitoring of sex ratios of wintering waterbirds would help to increase our understanding of changes in waterbird demography,population structure,and observed population trends;our study shows that birds caught during ringing projects can be a valuable source of such data.
基金The study was supported by Shaanxi Forestry Bureau and National Natural Science Foundation of China(Grant Nos.31872245 and 31572282).
文摘Background:One of the most challenging tasks in wildlife conservation and management is clarifying which and how external and intrinsic factors influence wildlife demography and long-term viability.The wild population of the Crested Ibis(Nipponia nippon)has recovered to approximately 4400,and several reintroduction programs have been carried out in China,Japan and Korea.Population viability analysis on this endangered species has been limited to the wild population,showing that the long-term population growth is restricted by the carrying capacity and inbreeding.However,gaps in knowledge of the viability of the reintroduced population and its drivers in the release environment impede the identification of the most effective population-level priorities for aiding in species recovery.Methods:The field monitoring data were collected from a reintroduced Crested Ibis population in Ningshan,China from 2007 to 2018.An individual-based VORTEX model(Version 10.3.5.0)was used to predict the future viability of the reintroduced population by incorporating adaptive patterns of ibis movement in relation to catastrophe frequency,mortality and sex ratio.Results:The reintroduced population in Ningshan County is unlikely to go extinct in the next 50 years.The popula-tion size was estimated to be 367,and the population genetic diversity was estimated to be 0.97.Sensitivity analysis showed that population size and extinction probability were dependent on the carrying capacity and sex ratio.The carrying capacity is the main factor accounting for the population size and genetic diversity,while the sex ratio is the primary factor responsible for the population growth trend.Conclusions:A viable population of the Crested Ibis can be established according to population viability analysis.Based on our results,conservation management should prioritize a balanced sex ratio,high-quality habitat and low mortality.
文摘Monthly investigatiom were made on the population of Chinese freshwater crab, Sinopotamon yangteskiense Bott, 1967 from April, 1984 to Match, 1985. The data on 4413 specimens show that the growth was affected mainly by temperature. During the April to November growth period, the crabs’ major development occured from June through October. One year was required for a fine white oocyte to develop into a mature egg. The reproduction period was June-October. Females bearing eggs were taken from June-August, and crabs with young were found from July-October. The females reproduced once a year but could for more than one year. The number of eggs carried by a female varied greatly according to the size of the crab, ranging from 30 to 100 eggs. New-bom crabs become mature after 1-2 yeats. The sex ratio was approximately 1:1 in the overall population. However, the larger crabs are predominantly male. The age distribution of S. yangtsekinese was estimated from size frequency histograms. There were more adult
基金funded by the Pakistan Science Foundation project PSF/Res/S-KU/Envr(51) grant to NAQ
文摘Zonal distribution and population biology of llyoplaxfrater were studied in a mangrove mudflat area of Pakistan. The crabs were collected from Korangi creek through transect and quadrat method from low tide level to high tide level. Two transects were delimited in a mangrove area of Korangi creek （24°79′N/67°20′E）. On each transect, three 0.25 m quadrats were sampled at three tidal levels on a monthly basis during low tide periods from March 2001 to February 2002. A total of 1124 crabs were obtained, of which 482 were males and 642 were females. Density of crabs varied between 0 and 90/m^2. The density and size distribution varied and showed significant differences from low to high tide level, and were positively correlated with the percent moisture, percent organic matter and sediment grain size. The carapace width （CW） ranged from 2.5 to 11.5 mm for male and 2.5 to 11.0 mm for female and was not significantly different. The overall sex ratio did not differ significantly from the expected 1：1 throughout the year in small crabs but was significantly different in adult crabs （Z2 = 49.73） with more male crabs, Size frequency distribution showed recruitment of juvenile crabs （〈 4 mm） nearly throughout the year except during June and July. Presence of ovigerous females in all months with seasonal peaks in September, October, December and May indicates seasonal continuous breeding. Weight of egg mass increases with weight of ovigerous females and show positive linear relationship. The estimated mean diameter of egg was 2.83±0.25μm, and the average number of eggs was 3065±902.
基金Supported by the National High Technology Research and Development Program of China(863 Program)(No.2012AA10A410)the Key Technology R&D Program of Jiangsu Province,China(No.BE2011372)
文摘Unbalanced parental contribution and small effective population size （Ne） are common issues during the artificial breeding of marine bivalves. The impact of hatchery-spawning practices on parental contribution, effective population size, the Ne/Nratio, and genetic diversity are largely unknown. To address this, we conducted a parentage analysis on a complete 3×3 diallel cross of clam Meretrix meretrix using eight microsatellite markers. The genetic diversity of the parents was higher than that of their respective offspring in most crosses （8/9）. Sires or dams from the same family contributed unequally to the pool of offspring from a particular cross, and the same parent clam exhibited large variation in parental contribution among different crosses. The variance in male contribution was higher than that of the female contribution in most crosses, suggesting that male contribution was more skewed than for females. The No/N ratio for nine crosses ranged from 0.58 to 0.86. There was no linear relationship between the sex ratio and the Ne/Nratio （P〉0.05）. Moreover, a sex ratio closer to one-to-one does not necessarily mean a larger effective population size. A solution to small effective population size in commercial breeding programs is increasing broodstoek numbers and attempting to maintain a balanced sex ratio.
基金the Key Project of National Natural Science Foundation of China (31130061)the Project of Public Benefit (201104073)the Max Planck Society
文摘Effective population management relies on assessments of population size and sex ratio.However,these estimates are difficult to obtain for elusive and rare species.Recently,noninvasive genetic census methods have been developed as an alternative to tradi-tional capture-mark-recapture methods.In this study,we estimated the size of the Sichuan snub-nosed monkey(Rhinopithecus roxellana) population in the Shennongjia Nature Reserve(SNR) using a noninvasive sampling method based on 16 microsatellite loci.We also used a PCR-based genetic method to sex the sampled individuals and infer the population sex ratio.The population size of R.roxellana in the SNR was estimated to be 1044 individuals(95% CITIRM:613-1409) .The estimated population sex ratio is more female-biased than expected,which we attribute to the sampling biased towards one male units and limited sampling of bachelor male units.Moreover,there is no suggestion that the heavy traffic road through the reserve might block movement of monkeys.The results of this study indicate genetic assessments based on a noninvasive sampling method can provide useful in-formation regarding populations of elusive primates.
文摘Mutualisms are cooperative interactions between members of different species. We focus on obligate mutualism, where each species cannot survive without the other. From a theoretical aspect, obligate mutualism is similar to the relationship between male and female. Empirical data indicate a sex-ratio selection: male and female have a specific ratio in their population sizes. In the present paper, we apply lattice model to obligate mutualism between two species, and present a theory of “ratio selection” which is a generalization of sex-ratio selection. Computer simulations are carried out by two methods: local and global interactions. In the former, interactions occur between neighbouring cells, while in the latter they occur between any pair of cells. Simulations in both interactions show the so-called Allee effect: both species can survive, when both densities are large in some extent. However, we find a large difference between local and global simulations. In the case of local interaction, restriction for survival is found to be extremely severe compared to global interaction. Both species require a proper ratio for their sustainability. This result leads to the theory of ratio selection: when interaction occurs locally, the ratio of both species is uniquely determined. We discuss that the ratio selection explains not only the evolution of endosymbionts from free-living ancestors but also the evolution from endosymbionts to organelles.
文摘In 2020,China’s sex ratio at birth(SRB)stood at 111.3,still exhibiting a notable bias.Son preference ranks as the most essential and fundamental reason for the skewed SRB.This study,using a mixed-methods approach,seeks to address what the temporal changes and regional differences in SRB and the gender preferences are in China,whether and why son preference persists,how people practice such preferences and how they relate to the persistently high SRB in the Chinese con-text.Analysis of data from five national sample surveys finds that son preference is waning and daughter preference is gaining momentum,consistent with significant downward trends in SRB.The study also reveals that value shifts and intergenera-tional relations have a strong influence on gender preferences and their translation into reproductive behavior.Additionally,this study highlights the challenges that are hindering the decline in son preference,suggesting that more efforts are needed to empower women and to change social norms.
