Brood sex ratio in the Yellow-bellied Prinia(Prinia flaviventris)

Background:The adjustment of sex ratios in birds can occur at the egg and nestling stages. Previous studies showed that the sex ratio was affected by environmental factors and parental condition; it may result in seasonal and ecosystem differences.Methods:In this study, the brood sex ratio of the Yellow-bellied Prinia(Prinia flaviventris) in the Nonggang area, Guangxi, southwestern China, was investigated during the breeding season from May to June in 2013 using PCR amplification from whole-genome DNA extracted from blood samples. A total of 31 nests of Yellow-bellied Prinia, including 132 brood fledglings and 31 pairs, were sampled.Results:The results showed that the brood sex ratio of the Yellow-bellied Prinia was 1:1, and sex ratios of different nests were evenly distributed within the study area. No significant relationship was found between parental quality and nest characteristics with the brood sex ratio.Conclusions:The present study indicated that no brood sex ratio bias in the Yellow-bellied Prinia highlighted the complexity of sex ratio adjustment in birds. In spite of our negative results, the lack of an association between brood sex ratio and parental quality and environmental factors in the Yellow-bellied Prinia provides valuable information on the adjustment of sex ratios in birds.

No Male Preference for Large Females in the Asian Common Toad(Duttaphrynus melanostictus):Effect of the Sex Ratio and Breeding System

Mating preferences are common in natural populations of animals.Numerous studies have shown that male mate choice can occur in a wide range of taxa.However,male mating preferences are still poorly understood in anurans.Sexual selection theory predicts that male mate choice is not expected to arise if 1) adult population exhibited a highly male-biased sex ratio which will diminish male mating success;2) males provide less parental care;3) mating success of males is associated with chorus tenure in which males would maximize their fitness by mating with multiple mates.We tested these predictions in the Asian common toad Duttaphrynus melanostictus from southeastern Tibet,China.Our field experimental results indicated that,the breeding population exhibited a highly male-biased sex ratio,called males did not defend sites which contain significant resources required by females and offspring,both sexes provided no parental care after egg-laying,and the toad species was characterized with prolonged breeding season chorus attendance.In male mate choice experiment,males did not show preferences for a larger gravid female over a smaller gravid female.We suggest that male mating success in the Asian common toad is likely determined by the number but not the quality of mates.Future research should focus on how sexual selection on male acoustic signaling and how female preference exert different types of selection pressure on male call traits in this Tibet toad.

Habitat destruction may lead to highly female-biased sex ratios

Local mate competition(LMC) was firstly used to explain extra-ordinary female-biased sex ratios. However, some observations have found that the sex ratios of some species are more female-biased than the predictions of LMC and its extensions; there is not yet a theory that accounts for the mechanisms of more female-biased sex ratio. Here, we assume that LMC occurs at a destructed habitat that reduces the resource for production, and present a new extension for the LMC model. Consequently, our model shows that the evolutionarily stable strategy(ESS) for sex ratio depends on two parameters: the number of foundresses and the degree of habitat destruction. Moreover, the sex ratio decreases as the degree of habitat destruction increases, i.e., the proportion of female increases. These results generally agree with experimental data, and may provide a new basis for the evolution of female-biased sex ratios in local mate competition and a new theory support for conservation of some species.

Adults have more male-biased sex ratios than first-winter juveniles in wintering duck populations

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.

Sperm counts and sperm sex ratio in male infertility patients

在最近的年里，调查者在许多工业化国家向男出生的一个衰退比例注意了一个趋势。当人们忍受决定性的染色体时，它与授精或流产相关的女搭挡的角色可以也改变性比率。我们试图由直接检验他的精子的性染色体决定一个人的第二等的性比率(F1 产生) 。我们为在 situ 杂交(鱼) 经历了精液荧光的所有人检验了我们的男不孕诊所数据库。人口统计的病人和精液参数被记录。摆平 Chi 的分析被用来比较性比率(Y 染色体 / 总数染色体) 。Multivariable 逻辑回归被用来预言在财务以后拥有一个忍受 Y 精子为的机会人口统计并且精液参数。185 个人的一个总数经历了精子鱼。为全部队， Y 忍受染色体的精子的比例是 51.5 &#x00025；。有不到 500 万个能动精子的人有 Y 忍受染色体的精子的一个显著地更低的比例(50.8 &#x00025；) 与有更高的精子计数的人相比(51.6 &#x00025；P=0.02 ) 。在 multivariable 调整以后，更高的精子集中，全部的能动精子计数和精液体积显著地增加了有 Y 的机会忍受染色体的精子(P&#x0003c； 0.01 ) 。作为一个人的精子生产衰落，那么做 Y 忍受染色体的精子的比例。因此，一个人的繁殖潜力可以预言他的能力到陛下男性后代。

Analysis of the Offspring Sex Ratio of Chicken by Using Molecular Sexing

The overall sex ratio of offspring (dead embryos and hatch chicks) from all the fertilized eggs of 140 hens collected for30 days was studied using duplex PCR of certain fragments of sex chromosomes. Additional 894 dead embryos over aperiod of 21 days of incubation were also investigated to verify the sex ratio of the dead embryos. The sex of the earlydead embryos was identified using this molecular sexing technique. The sex ratio of the hatch chicks and the totaloffspring of the hens investigated in this experiment did not differ from the expected sex ratio (i.e., 1:1). However, thenumber of female dead embryos was significantly more than that of males. The data indicated that the differentphysiologic function of males and females contributed to female-biased mortality during incubation. It was also foundby further analysis that the sex ratios of the offspring of some hens were significantly biased to female or male over theperiod investigated, which suggested that the sex ratio of offspring might be influenced by the maternal condition tosome degrees.

Effects of salinity on egg and fecal pellet production, development and survival, adult sex ratio and total life span in the calanoid copepod, A cartia tonsa:a laboratory study

The ef fects of salinity on the copepod, A cartia tonsa in terms of daily egg production rate(EPR), hatching success, fecal pellet production rate(FPR), naupliar development time and survival, sex ratio, and total life span were determined in laboratory conditions through three experiments. In experiment 1, EPR, hatching success, and FPR of individual females were monitored at salinities of 13, 20, 35 and 45 during short-periods(seven consecutive days). Results show EPR was aff ected by salinity with the highest outputs recorded at 20 and 35, respectively, which were considerably higher than those at 13 and 45. Mean FPR was also higher in 35 and 20. In experiment 2, the same parameters were evaluated over total life span of females(long-term study). The best EPR and FPR were observed in 35, which was statistically higher than at 13 and 20. In experiment 3, survival rates of early nauplii until adult stage were lowest at a salinity of 13. The development time increased with increasing of salinity. Female percentage clearly decreased with increasing salinity. Higher female percentages(56.7% and 52.2%, respectively) were signifi cantly observed at two salinities of 13 and 20 compared to that at 35(25%). Total longevity of females was not af fected by salinity increment. Based on our results, for mass culture we recommend that a salinity of 35 be adopted due to higher reproductive performances, better feeding, and faster development of A. tonsa.

Can overexpression of TGF-β1 gene change the sex ratio in transgenic mice?

Mouse TGF-β1 gene was microinjected into male pronuclei of F2 hybrid fertilized eggs obtained by mating CSJLF1 and C57BL/6J inbred strains to generate transgenic mice with over-expressed TGF-β1 gene. The rate of founder production is 31% and Southern blot analysis of founder mice tail DNAS gave an integration efficiency of 33%. TGF-β1 gene could be stably integrated to the chromosomes of transgenic mice and transmitted to their progeny at a rate of 33% in the second generation. Dot blot analysis of tail RNA of some transgenic mice indicated a moderate expression of the transgene. The most interesting finding of the present work is the striking deviation from the normal male:female sex ratio in transgenic mice,with an average ratio of 6.7:1. The possible nature of the predominance of male sex in transgenic mice overexpressing TGF-β1 is discussed.

Sex Ratio and Sexual Size Dimorphism in a Toad-headed Lizard, Phrynocephalus guinanensis

Phrynocephalus guinanensis has sexual dimorphism in abdominal coloration, but its ontogenetic development of sexual size dimorphism(SSD) is unknown. Using mark-recapture data during four days each year from August from 2014 to 2016, we investigated the development of sex ratios, SSD, sex-specific survivorship and growth rates in a population of P. guinanensis. Our results indicated that the sex ratio of males to females was 1:2.8. Males had a lower survival rate(6%) than females(14%) across the age range from hatchling to adult, which supported the discovered female-biased sex ratio potentially associated with the low survival rate of males between hatchlings and juveniles. Male-biased SSD in tail length and head width existed in adults rather than in hatchling or juvenile lizards. The growth rates in body dimensions were undistinguishable between the sexes during the age from hatchling to juvenile, but the growth rate in head length from juvenile to adult was significantly larger in males than females. Average growth rate of all morphological measurements from hatchling to juvenile were larger compared with corresponding measurements from juvenile to adult, but only being significant in tail length, head width, abdomen length in females and snout-vent length in males. We provided a case study to strengthen our understanding of the important life history traits on how a viviparous lizard population can survive and develop their morphology in cold climates.

Nestling sex ratio is unaffected by individual and population traits in the griffon vulture

Variation in offspring sex ratios is a central topic in animal demography and population dynamics.Most studies have focused on bird species with marked sexual dimorphism and multiple-nestling broods,where the offspring sex ratio is often biased due to different individual or environmental variables.However,biases in offspring sex ratios have been far less investigated in monomorphic and single-egg laying species,and few studies have evaluated long-term and large-scale variations in the sex ratio of nestling vultures.Here,we explore individual and environmental factors potentially affecting the secondary sex ratio of the monomorphic griffon vulture Gyps fulvus.We used information collected at three breeding nuclei from central Spain over a 30-year period(1990–2020)to analyse the effects of nestling age,parental age,breeding phenology,conspecific density,population reproductive parameters,and spatial and temporal variability on nestling sex.Sex ratio did not differ from parity either at the population or the nuclei level.No significant between-year differences were detected,even under highly changing conditions of food availability associated with the mad-cow crisis.We found that tree nesting breeders tend to have more sons than daughters,but as this nesting behavior is rare and we consequently have a small sample size,this issue would require additional examination.Whereas further research is needed to assess the potential effect of breeder identity on nestling sex ratio,this study contributes to understanding the basic ecology and population dynamics of Griffon Vultures,a long-lived species with deferred maturity and low fecundity,whose minor deviations in the offspring sex ratio might imply major changes at the population level.

Sheep grazing causes shift in sex ratio and cohort structure of Brandt’s vole:Implication of their adaptation to food shortage

Livestock grazing has been demonstrated to affect the population abundance of small rodents in grasslands,but the causative mechanism of grazing on demographic parameters,particularly the age structure and sex ratio,is rarely investigated.In this study,we examined the effects of sheep grazing on the cohort structure and sex ratio of Brandt’s vole(Lasiopodomys brandtii)in Inner Mongolia of China by using large manipulative experimental enclosures during 2010-2013.Our results indicated that sheep grazing significantly decreased the proportion of the spring-born cohort,but increased the proportion of the summer-born cohort.Grazing increased the proportion of males in both spring and summer cohorts.In addition,we found a negative relation between population density and the proportion of the overwinter cohort.Our results suggest that a shift in the cohort structure and the sex ratio may be an important strategy for small rodents to adapt to changes in food resources resulting from livestock grazing.

Effects of social and climatic factors on birth sex ratio in Macaca mulatta in Mount Taihangshan area

Sex allocation theory predicts the optimal investment to male and female offspring.However,a biased sex ratio requires explanations as to why the deviation occurs.Rhesus macaque(Macaca mulatta)is the most widely distributed nonhuman primate species and the Taihangshan macaque(Macaca mulatta tcheliensis)occupies the northern limit of all rhesus macaque natural populations worldwide.We observed one macaque troop(Wangwu-1[WW-1])inhabiting Taihangshan Macaque National Nature Reserve and recorded all birth events and the sex of newborn macaques from 2004 to 2013.Our aim was to apply the Trivers–Willard hypothesis to this free-ranging rhesus macaque troop,and to understand the relationship between climatic parameters(precipitation and temperature)and birth sex ratio.We found that the total newborn macaques showed a female-biased sex ratio at birth in the WW-1 troop,but there were no significant biased birth sex ratios in all matriarchs and in high-ranking and middle-ranking matrilineal units.However,the low-ranking macaque matrilineal unit was significantly female-biased.Moreover,we found that the annual precipitation of the previous year was positively associated with the birth sex ratio,and there was an interactive effect of troop size and current winter temperature on the birth sex ratio.The underlying mechanisms for the effects of social and climatic factors on birth sex ratio could be complex,and we discuss several plausible explanations.

Sex ratio variation and sex determination in the mallee dragon Ctenophorus fordi

Recent evidence suggests that many Australian agamids show temperature-dependent sex determination(TSD)with variation in sex determining mechanisms among closely related taxa.However,as shown in other vertebrates,sex ratios can also be influenced by genetic or phenotypic differences among females in their propensity to produce sons or daughters,and these influences might confound any thermal effects of incubation per se.To address these issues,we investigated the determinants of sex ratios in the mallee dragon Ctenophorus fordi,together with a detailed analysis of karyotypes.There was no detectable variation in sex ratios arising from variation among females,clutches or incubation temperatures,which might indicate genetic sex determination for this species.However,there was no evidence of cytologically distinct sex chromosomes using standard banding techniques.The sex ratio pattern in C.fordi strongly contrasts with the results for the congener Ctenophorus pictus,where sex ratios show variation among females.Thus,Australian agamids offer promising opportunities to address fundamental issues in sex ratio biology.

Geographic segregation and evidence of density-dependent changes in sex ratios in an abundant colonial waterbird

Demographic information,such as geographic segregation of sexes and sex ratio data,is needed to develop,model and evaluate conservation and management strategies for wildlife.A variety of physiological,behavioral and environmental factors can influence segregation of sexes and sex ratios,many of which originate with den­sity-dependent processes.Departure from 50:50 sex ratios of double-crested cormorants(Phalacrocorax auri­tus)collected during control efforts in breeding and wintering areas across their eastern range of the USA were evaluated using using a Z-test as well as Stouffer’s weighted Z-tests.In addition,a specifically-designed ran­domization test was used to evaluate density-dependent effects on primary sex ratios in cormorants from egg collections and colony nest count data over a 21-year period.Cormorants collected from breeding colonies were strongly male-biased,whereas cormorants collected from feeding flocks were slightly biased toward females.Cormorants were partly segregated by sex on the wintering grounds,with significantly more males found in ar­eas with intensive channel catfish aquaculture.The null hypothesis that females produced a balanced sex ra­tio independent of number of nesting cormorants was rejected:more male embryos were produced during rapid population growth,whereas at maximum nesting number more female embryos were produced.Once popula­tions stabilized,the sex ratio was more equal.This examination of sex ratios indicates that different manage­ment methods and locations result in sex-biased culling of cormorants.Sex-biased culling in cormorants could make population reduction efforts more efficient and reduce overall take.We suggest further research to exam­ine density-dependent effects on primary sex ratios documented here.

Women’s Political Status and the Sex Ratio at Birth:An Empirical Study Based on 1950-2020 County-Level Data

Women’s emancipation is an important part of the people’s liberation movement led by the Communist Party of China.Improving women’s political status is the basic condition for improving their social welfare rights and interests.Based on the data from county gazetteers covering more than 1,700 counties,the censuses of 1990 and 2000,and other representative surveys,we conducted an empirical study on the long-term effect of women’s political status on the sex ratio at birth.Our research found that the higher the ratio of female Communist Party members in each county in 1950,the more normal was the sex ratio at birth in the following 50 years.The improved political status of women aged 16-20 significantly raised the proportion of girls among surviving children,especially in the era of family planning.This demographic study provides empirical historical evidence for the first time on one aspect of the long-term social impact of the mission of the Chinese people’s liberation.

Existing theories do not explain sex ratio variation at birth in monomorphic roe deer (Capreolus capreolus)

The phenomenon of skewed sex ratios at birth has been reported in many ungulate species.So far,no consistent trend has emerged for roe deer(Capreolus capreolus),because male-biased,female-biased and equal sex ratios at birth have all been found.Nevertheless,both the Trivers–Willard hypothesis and the theory of local resource competition have gained support.Despite the great number of studies carried out regarding the ecology of roe deer,too many aspects remain unclear,and contradictory results have been produced with respect to several crucial elements.Without further research,the discussion on which theory applies will therefore remain inconclusive.We put forward the argument that eventually the theories of Trivers–Willard and local resource competition can be considered as being not essentially different.After all,both theories explain the observed skewed sex ratios as being due to the effect of the progeny s sex on the mother s body condition and hence her reproductive success in subsequent years.Furthermore,neither theory is likely to prove to be suitable for roe deer,as several assumptions are unlikely to be met.In roe deer,skewed ratios probably only have a temporal character.As a matter of fact,several observations of skewed sex ratios in birds and mammals did not withstand the accumulation of further data,as sex ratios that were initially believed to be biased turned out to be equal in the long term.This is likely to be the case in roe deer as well.We hypothesize that roe deer,as r-strategists,will produce as many offspring as possible,regardless of sex.

Addressing skewed sex ratio at birth in China:practices and challenges

The sex ratio at birth(SRB)in China began to rise rapidly in the 1980s and declined after 2009.The ratio has maintained a downward trend since 2009,but is still higher than the normal level.The government of China has committed to redress the distortions in SRB and has initiated multiple actions to accomplish that end.Against a background of economic development,accelerating modernization and the empowerment of women,China has strengthened governance and made significant progress in balancing the sex ratio at birth.This paper examines the trend for SRB in China,summarizes the practices that address gender imbalance at birth,and analyzes the challenges ahead.

Noninvasive genetic assessment of the population trend and sex ratio of the Shennongjia population of Sichuan snub-nosed monkeys(Rhinopithecus roxellana)

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.

Pubertal exposure to bisphenol A affects the reproduction of male mice and sex ratio of offspring

Objective To study the effects of pubertal exposure to bisphenol A(BPA)on the reproduction of male mice in adulthood and subsequent generation mice.Methods Male mice aged 21 d were exposed to BPA at a dose of 50 mg/kg per day for 7 d by intraperitoneal injection.Sperm count,sperm deformity rate and testis histology were evaluated 35 d after exposure.Male fertility index and newborns were further observed by mating with the normal female mice.Results The epididymal sperm number was decreased by 20.6%in BPA exposure group compared with the control(P<0.01).Sperm deformity rate in BPA group was increased by 9.65%compared with the control(P<0.05).Testis seminiferous tubules were abnormal with sloughing of germ cells;BPA exposure had no significant effects on the fertility of male mice in adulthood;sex ratio of male to female offspring was increased.Conclusion Pubertal exposure to BPA disrupted spermatogenesis in adult mice,and the proportion of male offspring was increased compared with the control.