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.

Sperm counts and sperm sex ratio in male infertility patients

In recent years, investigators have noted a trend toward a declining proportion of male births in many industrialized nations. While men bear the sex-determining chromosome, the role of the female partner as it pertains to fertilization or miscarriage may also alter the gender ratio. We attempted to determine a man＇s secondary sex ratio （F1 generation） by directly examining the sex chromosomes of his sperm. We examined our male infertility clinic database for all men who had undergone a semen fluorescence in situ hybridization （FISH）. Patient demographic and semen parameters were recorded. Chi-squared analysis was used to compare gender ratios （Y chromosomes/total chromosomes）. Multivariable logistic regression was used to predict the odds of possessing a Y-bearing sperm after accounting for demographic and semen parameters. A total of 185 men underwent sperm FISH. For the entire cohort, the proportion of Y chromosome-bearing sperm was 51.5%. Men with less than five million motile sperm had a significantly lower proportion of Y chromosome-bearing sperm （50.8%） compared to men with higher sperm counts （51.6%; P= 0.02）. After multivariable adjustment, a higher sperm concentration, total motile sperm count and semen volume significantly increased the odds of having a Y chromosome-bearing sperm （P〈0.01）. As a man＇s sperm production declines, so does the proportion of Y chromosome-bearing sperm. Thus, a man＇s reproductive potential may predict his ability to sire male offspring.

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 for 30 days was studied using duplex PCR of certain fragments of sex chromosomes. Additional 894 dead embryos over a period of 21 days of incubation were also investigated to verify the sex ratio of the dead embryos. The sex of the early dead embryos was identified using this molecular sexing technique. The sex ratio of the hatch chicks and the total offspring of the hens investigated in this experiment did not differ from the expected sex ratio （i.e., 1：1）., However, the number of female dead embryos was significantly more than that of males. The data indicated that the different physiologic function of males and females contributed to female-biased mortality during incubation. It was also found by further analysis that the sex ratios of the offspring of some hens were significantly biased to female or male over the period investigated, which suggested that the sex ratio of offspring might be influenced by the maternal condition to some degrees.

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.

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.

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.

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.

Equal Sex Ratios of a Marine Green Alga, Bryopsis plumosa

By finding some important culture conditions as below, we succeeded in experimentally controlling the whole life history of a dioecious marine green alga, Bryopsis plumosa （Hudson） C. Agardh. In this study, we focused on the primary and secondary sex ratios （i.e. at inception and maturity） using these culture techniques. Gametogenesis was induced by culturing haploid gametophytes with Provasoli＇s enriched seawater （PES） medium under a 14：10 h light： dark cycle at 14 ℃. Formed zygotes grew into diploid sporophytes, which were cultured for 3 months with PES medium under a 14：10 h light ： nbsp;dark cycle at 18℃. Then they were transferred into Schreiber medium and cultured under a 10：14 h light： dark cycle at 22℃. Within 1 week, zoosporogenesis was observed. Zoospores were released within a couple of days. Each zoospore soon germinated and grew into a unisexual gametophyte. The primary sex ratio was examined in gametophytes that originated from a single sporophyte. The secondary sex ratio was studied in the field. Both were estimated as 1：1. Synchronized meiotic cell divisions might occur during zoosporogenesis dividing each sex-determining factor evenly among zoospores. Given the equal sex ratio at maturity, there seems to be no environmental factor that differentially affects the survival of male or female gametophytes in nature.

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.

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〈O. 01）. Sperm deformity rate in BPA group was increased by 9.65% compared with the control （P〈O.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.

Human semen quality and the secondary sex ratio

The aim of this study was to evaluate the association between semen quality and the secondary sex ratio （SSR）, defined as the ratio of male to female live births. Our study cohort comprised 227 male partners who were enrolled prior to conception in Michigan and Texas between 2005 and 2009, and prospectively followed through delivery of a singleton birth. The male partners provided a baseline and a follow-up semen sample a month apart. Semen analysis was conducted to assess 27 parameters including five general characteristics, six sperm head measures, 14 morphology measures, and two sperm chromatin stability assay measures. Modified Poisson regression models with a robust error variance were used to estimate the relative risk （RR） and 95% confidence interval （95% CI） of a male birth for each semen parameter, after adjusting for potential confounders. Of the 27 semen parameters, only the percentage of bicephalic sperm was significantly associated with the SSR （2nd VS Ist quartile, RR, 0.65, 95% CI, 0.45-0.95, P= 0.03; 4TM vs 1St quartile, RR, 0.61, 95% CI, 0.38-1.00, P 〈 0.05 before rounding to two decimal places）, suggestive of a higher percentage of bicephalic sperm being associated with an excess of female births. Given the exploratory design of the present study, this preconception cohort study suggests no clear signal that human semen quality is associated with offspring sex determination.

Pollinating fig wasp Ceratosolen solmsi adjusts the offspring sex ratio to other foundresses

Local mate competition theory predicts that offspring sex ratio in pollinating fig wasps is female-biased when there is only one foundress, and increased foundress density results in increased offspring sex ratio. Information of other foundresses and clutch size have been suggested to be the main proximate explanations for sex ratio adjustment under local mate competition. Our focus was to show the mechanism of sex ratio adjustment in a pollinating fig wasp, Ceratosolen solmsi Mayr, an obligate pollinator of the functionally dioecious fig, Ficus hispida Linn., with controlled experiments in the field. First, we obtained offspring from one pollinator and offspring at different oviposition sequences, and found that offspring sex ratio decreased with clutch size, and pollinators produced most of their male offspring at the start of bouts, followed by mostly females. Second, we found that offspring sex ratio increased with foundress density, and pollinators did adjust their offspring sex ratio to other females in the oviposition patches. We suggest that when oviposition sites are not limited, pollinators will mainly adjust their offspring sex ratio to other foundresses independent of clutch size changes, whereas adjusting clutch size may be used to adjust sex ratio when oviposition sites are limited.

Neither Biased Sex Ratio nor Spatial Segregation of the Sexes in the Subtropical Dioecious Tree Eurycorymbus cavaleriei(Sapindaceae)

Knowledge of sex ratio and spatial distribution of males and females of dioecious species is both of evolutionary interest and of crucial importance for biological conservation. Eurycorymbus cavaleriei, the only species in the genus Eurycorymbus （Sapindaceae）, is a dioecious tree endemic to subtropical montane forest in South China. Sex ratios were investigated in 15 natural populations for the two defined ages （young and old）. Spatial distribution of males and females was further studied in six large populations occurring in different habitats （fragmented and continuous）. The study revealed a slight trend of male- biased sex ratio in both ages of E. cavaleriei, but sex ratio of most populations （13 out of 15） did not display statistically significant deviation from equality. All of the four significantly male-biased populations in the young class shifted to equality or even female-biased, The Ripley＇s K analysis of the distribution of males with respect to females suggested that individuals of the opposite sexes were more randomly distributed rather than spatially structured. These results suggest that the male-biased sex ratio in E. cavaleriei may result from the precocity of males and habitat heterogeneity. The sex ratio and the sex spatial distribution pattern are unlikely to constitute a serious threat to the survival of the species.

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.