Variation In Sex Ratio Research Articles

P-003 Sperm retrieved by microdissection testicular sperm extraction (MD-TESE) is associated with altered sex ratio of offspring after intracytoplasmic sperm injection in men with non-obstructive azoospermia

Abstract Study question Does the sperm retrieved surgically by MD-TESE of men with Non-Obstructive Azoospermia affect the live birth sex ratio? Summary answer Our data indicates that sperm retrieved in men with non-obstructive azoospermia alters the sex ratio in favor of female offspring. What is known already Non-Obstructive Azoospermia is the most severe form of male infertility and is the most common cause of Azoospermia. Among the different surgical techniques, MD-TESE gives the highest rate of sperm retrieval and when combined with intracytoplasmic sperm injection (ICSI), live births had been achieved with variable success, Sex ratio of offspring can vary substantially due to several variables, however no studies have investigated the resultant birth sex ratio in this setting. Study design, size, duration Retrospective Cohort study. Data were collected between May 2009 and December 2019. A total of 100 consecutive men with non-obstructive Azoospermia underwent MD-TESE for sperm retrieval. 46 couples underwent ICSI and live birth rate, cumulative live birth rate and sex ratio of offspring analysed. Participants/materials, setting, methods One-hundred men underwent MD-TESE out of which 46 proceeded with ICSI. Demographic data including male and female age, testicular volumes and serum hormone values are given as mean ± SD with a range (minimum and maximum). Fertility outcomes including sperm retrieval, fertilization rate, number of embryos transferred, and live birth rates and cumulative live birth rates were recorded. Chi-square test was performed to compare the proportions. Main results and the role of chance Sperm retrieval was successful in 58%(58/100). Testicular volume and hormonal parameters did not vary among patients with positive or negative sperm retrieval. Histology gave best correlation with sperm retrieval. Hypospermatogenesis yielded the highest sperm retrieval 93%(26/29), followed by Maturation arrest 78%(7/9), then Hyalinosis 46% (6/13) and lastly Sertoli cell only 38%(19/50). 46 couples underwent ICSI cycles where the mean age of patients and their wives were 36.4 ± 3.7y and 33.0 ± 4.3y. Fertilization rate and mean number of transferred embryos were 51.4 % and 1.7. Live birth rate and Cumulative Live Birth rate per Embryo transfer were 60.5% (26/43) and 74.4% (32/43) and per started ICSI cycle were 56.5% (26/46) and 69.6% (32/46), with a twin rate of 15.3%(4/26). Mean gestational length and mean body weight at birth were 39.0 ± 1.4w and 3228.5 ± 5.5 g. Number of live offspring were 36 (Female: Male = 26:10) giving rise to sex ratio of 2.6 to1 in favor of female offspring (P < 0.05). There were no neonatal death, and one baby had phenylketonuria. Limitations, reasons for caution This is the first study to test the hypothesis of sex ratio variation related to the source of sperm; the strength of our study is that all procedures were performed by the same surgeon, so there are no operator-dependent differences. This finding needs to be confirmed in larger cohort studies. Wider implications of the findings It has been demonstrated that different stressors may alter the sex of the offspring. While in the present study the stressor is the parental hypogonadism associated with non-obstructive azoospermia, We hypothesise that testicular environment may direct spermatogenesis in favor of X carrying sperm around the time of sperm retrieval. Trial registration number N/A

The effect of pregnancy on metabolic scaling and population energy demand in the viviparous fish Gambusia affinis.

Metabolism is a fundamental attribute of all organisms that influences how species affect and are affected by their natural environment. Differences between sexes in ectothermic species may substantially alter metabolic scaling patterns, particularly in viviparous or live-bearing species where females must support their basal metabolic costs and that of their embryos. Indeed, if pregnancy is associated with marked increases in metabolic demand and alters scaling patterns between sexes, this could in turn interact with natural sex ratio variation in nature to affect population-level energy demand. Here, we aimed to understand how sex and pregnancy influence metabolic scaling and how differences between sexes affect energy demand in Gambusia affinis (Western mosquitofish). Using the same method, we measured routine metabolic rate in the field on reproductively active fish and in the laboratory on virgin fish. Our data suggest that changes in energy expenditure related to pregnancy may lead to steeper scaling coefficients in females (b=0.750) compared to males (b=0.595). In contrast, virgin females and males had similar scaling coefficients, suggesting negligible sex differences in metabolic costs in reproductively inactive fish. Further, our data suggest that incorporating sex differences in allometric scaling may alter population-level energy demand by as much as 20-28%, with the most pronounced changes apparent in male-biased populations due to the lower scaling coefficient of males. Overall, our data suggest that differences in energy investment in reproduction between sexes driven by pregnancy may alter allometric scaling and population-level energy demand.

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.

Experimental evolution under varying sex ratio and nutrient availability modulates male mating success in Drosophila melanogaster.

Biased population sex ratios can alter optimal male mating strategies, and allocation to reproductive traits depends on nutrient availability. However, there is little information on how nutrition interacts with sex ratio to influence the evolution of pre-copulatory and post-copulatory traits separately. To address this omission, we test how male mating success and reproductive investment evolve under varying sex ratios and adult diet in Drosophila melanogaster, using experimental evolution. We found that sex ratio and nutrient availability interacted to determine male pre-copulatory performance. Males from female-biased populations were slow to mate when they evolved under protein restriction. By contrast, we found direct and non-interacting effects of sex ratio and nutrient availability on post-copulatory success. Males that evolved under protein restriction were relatively poor at suppressing female remating. Males that evolved under equal sex ratios fathered more offspring and were better at supressing female remating, relative to males from male-biased or female-biased populations. These results support the idea that sex ratios and nutrition interact to determine the evolution of pre-copulatory mating traits, but independently influence the evolution of post-copulatory traits.

Sex reversal explains some, but not all, climate-mediated sex ratio variation within a viviparous reptile.

Evolutionary transitions in sex-determining systems have occurred frequently yet understanding how they occur remains a major challenge. In reptiles, transitions from genetic to temperature-dependent sex determination can occur if the gene products that determine sex evolve thermal sensitivity, resulting in sex-reversed individuals. However, evidence of sex reversal is limited to oviparous reptiles. Here we used thermal experiments to test whether sex reversal is responsible for differences in sex determination in a viviparous reptile, Carinascincus ocellatus, a species with XY sex chromosomes and population-specific sex ratio response to temperature. We show that sex reversal is occurring and that its frequency is related to temperature. Sex reversal was unidirectional (phenotypic males with XX genotype) and observed in both high- and low-elevation populations. We propose that XX-biased genotypic sex ratios could produce either male- or female-biased phenotypic sex ratios as observed in low-elevation C. ocellatus under variable rates of XX sex reversal. We discuss reasons why sex reversal may not influence sex ratios at high elevation. Our results suggest that the mechanism responsible for evolutionary transitions from genotypic to temperature-dependent sex determination is more complex than can be explained by a single process such as sex reversal.

Two-Sex Demography, Sexual Niche Differentiation, and the Geographic Range Limits of Texas Bluegrass (Poa arachnifera).

AbstractUnderstanding the mechanisms that generate biogeographic range limits is a long-standing goal of ecology. It is widely hypothesized that distributional limits reflect the environmental niche, but this hypothesis is complicated by the potential for intraspecific niche heterogeneity. In dioecious species, sexual niche differentiation may cause divergence between the sexes in their limits of environmental suitability. We studied range boundary formation in Texas bluegrass (Poa arachnifera), a perennial dioecious plant, testing the alternative hypotheses that range limits reflect the niche limits of females only versus the combined contributions of females and males, including their interdependence via mating. Common garden experiments across a longitudinal aridity gradient revealed female-biased flowering approaching eastern range limits, suggesting that mate limitation may constrain the species' distribution. However, a demographic model showed that declines in λ approaching range limits were driven almost entirely by female vital rates. The dominant role of females was attributable to seed viability being robust to sex ratio variation and to low sensitivity of λ to reproductive transitions. We suggest that female-dominant range limits may be common to long-lived species with polygamous mating systems and that female responses to environmental drivers may often be sufficient for predicting range shifts in response to environmental change.

Environmental variation in sex ratios and sexual dimorphism in three wind‐pollinated dioecious plant species

Variation in plant sex ratios is often attributable to sex‐specific mortality in heterogeneous environments that differentially limit male and female plant reproduction. Yet sexual dimorphism and plastic responses to environmental heterogeneity are common and may co‐vary with variation in sex ratios. Here, we show that the sex ratio and the degree of sexual dimorphism for a number of plant traits varied along climatic and elevation gradients in three wind‐pollinated dioecious species, Rumex lunaria, Urtica dioica and Salix helvetica. Some of the observed sex‐specific responses to climatic variation are consistent with greater sensitivity of females to water scarcity, but most responses rather point to the greater sensitivity of males to ecological stress, consistent with larger male reproductive effort, as has been commonly reported for wind‐pollinated plants. In contrast, we found no evidence for variation in either sex ratios or sexual dimorphism expected under sexual selection. Interestingly, sex ratios and sexual dimorphism varied both along distinct and the same ecological axes of variation, suggesting that the evolution of sexual dimorphism in the measured traits was not sufficient to prevent sex‐specific mortality.

Evidence for a male-biased sex ratio in the offspring of a large herbivore: The role of environmental conditions in the sex ratio variation.

Numerous studies have examined whether the primary and/or secondary sex ratio in mammals, including humans, deviates from an equilibrium of 1:1. Although effect size in the sex ratio variation is expected to be low, a large sample size allows the identification of even small deviations from parity. In this study, we investigated whether the sex ratio of roe deer (Capreolus capreolus) offspring at birth approaches parity, using a large data set from roe deer offspring tagged in Baden‐Württemberg (Germany, 1972–2019, N = 12,437). In addition, a systematic re‐analysis of available data on the secondary sex ratios of roe deer was conducted to test whether our finding withstood the accumulation of further data. The null hypothesis that the sex ratio of roe deer (prenatal sex ratio and sex ratio at birth) approaches parity was rejected. Moreover, the secondary sex ratio of roe deer offspring deviated from the male‐biased mean for relatively cold or warm weather conditions during autumn and winter. Our study provides strong evidence for a male‐biased sex ratio in a large herbivore and weak evidence for variations in the secondary sex ratio owing to environmental conditions. The pattern is highly relevant in the context of climate change and its impact on the population dynamics of large herbivores.

Effect of maternal age on primary and secondary sex ratios in the ectoparasitoid wasp Pachycrepoideus vindemmiae

Sex allocation is defined as the allocation of resources to produce male and female offspring during reproduction, and it is an important topic in evolutionary biology. As organisms with special haplo‐diploid sex determination, parasitoid wasps are particularly suited for the study of sex allocation. However, most studies focused on the secondary sex ratio (i.e., the eclosion sex ratio) because the oviposition ratio (the primary sex ratio) is difficult to study, especially in parasitoid species. The primary sex ratio may differ from the secondary sex ratio due to larval mortality and self‐superparasitism. The present study used microsatellites to explore the effects of female age on the primary and secondary sex ratio (male proportion) of the solitary ectoparasitoid Pachycrepoideus vindemmiae (Rondani) (Hymenoptera: Pteromalidae). The primary sex ratio showed a significant decreasing trend as the oviposition days increased, and the secondary sex ratio significantly increased. Self‐superparasitism, i.e., laying more than one egg in a host, was the cause of the variation in the secondary sex ratio in P. vindemmiae. When females practiced self‐superparasitism, they tended to lay female eggs. The application of microsatellites helped explore and improve the understanding of the primary sex ratio and self‐superparasitism in this ectoparasitoid species.

Do Genetic Drift and Gene Flow Affect the Geographic Distribution of Female Plants in Gynodioecious Lobelia siphilitica?

Variation in population sex ratio is particularly pronounced in gynodioecious angiosperms. Extremely high female frequencies in gynodioecious populations cannot be readily explained by selective forces alone. To assess the contributions of drift and gene flow to extreme sex-ratio variation, we documented sex ratio and population size in 92 populations of Lobelia siphilitica across its range and genotyped plants using plastid and nuclear genetic markers. Similarity in spatial patterns of genetic and demographic variables may suggest that drift and/or gene flow have contributed to population sex-ratio variation in L. siphilitica. We found strong spatial structuring of extremely high female frequencies: populations with >50% female plants are restricted to the south–central portion of the range. However, we did not detect any spatial structuring in population size nor metrics of genetic diversity, suggesting that extreme variation in female frequency is not strongly affected by drift or gene flow. Extreme sex-ratio variation is frequently observed in gynodioecious plants, but its causes are difficult to identify. Further investigation into mechanisms that create or maintain the spatial structure of sex ratios in gynodioecious species will provide much needed insight.

Evaluation of Epidermal Growth Factor Receptor Gene Mutations in an Iranian Population with Non-Small Cell Lung Carcinoma.

Background:Mutations of the epidermal growth factor receptor (EGFR) gene, predominantly in exons 18–21, have been highlighted to function as the crucial predictors of the response rate of patients with non-small cell lung cancer (NSCLC) to EGFR tyrosine kinase inhibitors (TKIs).Methods:This study was performed at Tehran University of Medical Sciences. Data and information were retrospectively collected from the period between Dec 2010 and Apr 2014. Exons 18 to 21 of the EGFR were analyzed for any potential mutation by PCR, accompanied by DNA sequencing on 160 with pathological confirmation of NSCLC.Results:Demographically, the male to female ratio was approximately 2:1, and a substantial difference in age between sexes was not observed (P=0.065), but a noticeable difference was found in the smoking variable, where 77.8% of males were smokers compared to 17.3% of women (odds ratio (OR) (95% CI) = 16.72 (7.15–39.11)). We found a frequency of 10.63% (17/160) for mutations found in exons 19 and 21, nonetheless, no mutations in exon 18 and exon 20 were observed. The most frequently observed mutations were c.2235_2249, del and c.2240_2257, del in exon 19 and p. L858R in exon 21. The c.2253A>G was found as a novel mutation that was the rarest mutation detected in this work. Interestingly, a remarkable negative association was revealed between smoking and mutation rates in NSCLC patients (OR (95% CI) = 0.13 (0.04–0.46).Conclusion:The occurrence of EGFR mutations is largely varied among the different states of Iran, probably due to variations in ethnicity, smoking rate, and sex ratio of participants.

Sex in the city: Uncovering sex-specific management of equine resources from prehistoric times to the Modern Period in France

Sex identification from fragmentary archeozoological assemblages is particularly challenging in the Equid family, including for horses, donkeys and their hybrids. This limitation has precluded in-depth investigations of sex-ratio variation in various temporal, geographic and social contexts. Recently, shallow DNA sequencing has offered an economical solution to equine sex determination, even in environments where DNA preservation conditions is not optimal. In this study, we applied state-of-the-art methods in ancient DNA-based equine sex determination to 897 osseous remains in order to assess whether equal proportions of males and females could be found in a range of archeological contexts in France. We found Magdalenian horse hunt not focused on isolated bachelors, and Upper Paleolithic habitats and natural traps equally balancing sex ratios. In contrast, Iron Age sacrificial rituals appeared to have been preferentially oriented to male horses and this practice extended into the Roman Period. During Antiquity, the Middle Ages and the Modern Period, cities emerged as environments largely dominated by horse males. This strong sex-bias was considerably reduced, and sometimes even absent, in various rural contexts. Combined with previous archaeozoological work and textual evidence, our results portray an urban economy fueled by adult, often old, males, and rural environments where females and subadults of both sexes were maintained to sustain production demands.

Using Mediterranean Mussel Bio-Indicators to Assess the Initial Health State of Ecosystems Receiving Desalination Plant Effluents in Agadir Bay (Morocco)

Elazzaoui, A.; Kalla, Y.; Lefrere, L.; Bouhaimi, A., and Moukrim, A., 2022. Using Mediterranean mussel bio-indicators to assess the initial health state of ecosystems receiving desalination plant effluents in Agadir Bay (Morocco). Journal of Coastal Research, 38(1), 154–167. Coconut Creek (Florida), ISSN 0749-0208. Mussels are often used as a biological bio-indicator for the quality assessment of marine ecosystems. Adopting this approach, the present work aims to study the initial health status of two ecosystems in Agadir Bay, Morocco expected to receive seawater desalination plant effluents. This study was conducted between February 2015 and March 2017 in two stations, Tifnit-Douira and Cap Ghir. In addition to the gametic development, variations of sex ratio and gonadal index were also determined. The reproductive cycle of Mytilus galloprovincialis is spread throughout the year. Under natural conditions, three collective spawning periods were observed. The main one was during the spring and the two other periods were optional and were in winter and summer. Variations of seawater temperature can make some changes in mussel spawning, with one principal period lasting during spring and summer and the optional one during winter. In both studied stations, sexual rest was manifested by a small percentage of the population particularly during summer, and could not reach the whole population at the same time. This finding is consistent with the gonadal index that never reached the value of 1. A unique hermaphroditism case was revealed in Tifnit-Douira mussels, and it remained statistically insignificant. The sex ratio was perfectly balanced in both stations and was in favour of males. The gonad histology did not show any cellular abnormalities in the germinal tissue. These results are of great importance since they characterize the current state of the studied stations area before the installation of the desalination plant. This state must be maintained after installation in order to preserve the typical halieutic resources of these ecosystems. The present findings confirm the good environmental health status and the aquaculture potential of Agadir Bay, especially in the north ecosystems (Cap Ghir) due to upwelling-nutritional intake and optimum seawater temperature.

Trends and seasonal variations in human secondary sex ratio in Southwest Nigeria: A 10-year survey

Introduction: Secondary sex ratio is the number of live male births per 100 female births. In humans, the primary sex ratio, which is the sex ratio at conception, is expected to be 1:1 in natural populations based on the law of independent assortment of the X and Y chromosomes. This is not the case with the sex ratio at birth as it is largely affected by various social and cultural practices that it tends to bias towards one sex, with profound implications for population and demographic dynamics. Materials and Methods: We collected retrospective data of records of live births from three Southwestern Nigerian states, covering 10 years. The data were obtained from different Hospitals/Birth Centres from three states, i.e., Lagos, Ondo and Osun, between 2006 and 2017. Data analysis was performed to determine the monthly, quarterly, yearly and seasonal variation in sex ratios. Chi-square analysis was used to determine the significance of differences in sex ratios at P < 0.05. Results: Annual average sex ratios of 99.7, 105.6 and 106.0 were obtained for Lagos, Osun and Ondo, respectively, while the pooled data had a sex ratio of 104.2, indicating male preponderance. Sex ratios differ significantly according to season. Differences in sex ratio were significant during the dry season in Lagos and Osun states and in Ondo during the rainy season. Conclusions: Sex ratios from Southwest Nigeria are as diverse as other populations, with ratios ranging between 99.7 and 106.0.

Aspectos reprodutivos do camarão Desmocaris trispinosa (Aurivillius, 1898) em um riacho suburbano de Abidjan (riacho Banco, Costa do Marfim)

Abstract Aim Characterize habitats and determine the reproductive parameters of the prawn Desmocaris trispinosa (Aurivillius, 1898) from Banco stream, a periurban stream of Abidjan (Côte d'Ivoire, West Africa). Methods Sampling was conducted monthly, from July 2020 to June 2021 at four stations. Environmental characteristics were measured before prawn sampling. The sampling was made with a dipnet during five-minute active fishing conducted by a single operator at each station. Results According to environmental variables, sampling stations were divided into three groups: almost undamaged (B4), slightly disturbed (B1) and disturbed (B2 and B3). In total, 467 specimens of D. trispinosa were captured in which 127 males, 275 females and 65 juveniles. Overall, the sex ratio (1:2.1) was in favour of females. Considering stations, the sex ratio was also in favour of females. But, only in the almost undamaged station (B4), the difference was significant (χ2 = 70.20; P&lt;0.001). At this station, a variation of sex-ratio was observed in two seasons. In total, 116 ovigerous females were analysed on all stations. Fecundity varies from 5 to 16 oocytes with an average of 11.03 ± 2.18. First maturity size was estimated at 4.82 mm carapace length for the combined data. Females from the station free from human activities (B4) reached sexual maturity (4.23 mm) before those of the other stations (4.97 in B1 and 5.70 mm in B2). D. trispinosa from Banco stream reproduces continuously year-round with two peaks in the rainy season. The oocyte volume was negatively influenced by temperature and positively by dissolved oxygen. Conclusions D. trispinosa reproduces year-round in undisturbed stations and reaches sexual maturity faster at these stations compared to disturbed stations. The sex ratio was in favour of females. Consequently, this species would be naturally polygamous.

Integrating climate change and management scenarios in population models to guide the conservation of marine turtles

The globally significant green turtle (Chelonia mydas) population in the northern Great Barrier Reef is threatened by anthropogenic pressures, including climate change, habitat degradation, and indigenous harvest. Evidence suggesting the population is producing an extreme proportion of females due to increasing temperatures, coupled with temperature-dependent sex determination, is concerning. In response, and to explore management options, we developed two density-independent, stochastic stage-structured metapopulation models: a “Moderate Climate Model” and an “Extreme Climate Model”. The models differ based on climate change projections by incorporating increased female hatchling sex ratios due to global warming and loss of nesting habitat due to sea level rise. The models were based on demographic data from field studies at major rookeries and regional foraging grounds and allowed for variation in operational sex ratios, management actions, and levels of indigenous harvest. Under the Moderate Climate Model, population size increased but could be vulnerable to overharvest of adult females. If overharvest was indicated, the harvest of a proportion of subadults rather than only adult females reduced population declines. Under the Extreme Climate Model, there was a steep population decline even without any harvest, and harvesting subadults accelerated population decline due to the inclusion of subadult males. In the Extreme Climate Model, reversal of population decline depended on male turtles mating with an increased number of females, or management actions to substantially increase the number of male hatchlings produced.

Sex ratio, floral traits, and genetic variation of androdioecious &lt;i&gt;Osmanthus fragrans&lt;/i&gt; L. (Oleaceae) and the implications for maintenance of high male frequency

Several examples of androdioecy appear to have evolved from dioecy and have low male frequency (&lt; 0.5). However, the evolutionary pathway to androdioecy in Oleaceae may come from hermaphroditism. <italic>Osmanthus fragrans</italic> L. has a 1:1 sex ratio in nature populations. Significant differences are observed not only in flowering phenology but also in some floral traits between males and hermaphrodites. The protandry in the same population and the protogyny in the same plant will promote the xenogamy between genders. The majority of flower traits that related with the pollen production are different between males and hermaphrodites. Males bear more flowering nodes, and more flowers per node, and larger anther in all three populations. This characteristic demonstrated that males have more male advantage than hermaphrodites. Population genetic structure of <italic>O. fragrans</italic> is genetically homogeneous at the species level, and most variations exist within population. The percentage of variation among populations (13%) and between males and hermaphrodites (0%) is low. Moreover, genetic differentiation was very low between genders not only among populations but also in the same population. This genetic variation could be attributed to the occurrence of high levels of xenogamy between genders. Therefore, high male frequency and more male fitness advantage in males are the essential conditions for this mating system, which plays an important role during population reproduction and regeneration. The 1:1 sex ratio could be the result of integrative effects of sexual system, mating system, and reproductive success.

Spatiotemporal variation in the adult sex ratio, male aggregation, and movement of two tropical cloud forest dung beetles.

While theory suggests that at conception the sex ratio should be balanced (1:1), this can be variable across space and time in wild populations. Currently, studies of the environmental factors that regulate adult sex ratio (ASR) in species with different life history traits are scarce. Using capture-recapture over a year, we analyzed the influence of habitat type (forest and nonforest) and season (rainy and dry) on variation in ASR, male aggregation and the trajectory movement of 2 dung beetle species with different life history traits: Deltochilum mexicanum (a hornless roller species) and Dichotomius satanas (a tunneler species with horns on its head and thorax). We found opposite tendencies. The D. mexicanum population tends to be female-biased, but the population of D. satanas tends to be predominantly male, and observed values were not related to habitat type or season. However, the 95% confidence intervals estimated were highly variable between seasons depending on habitat. On examining the monthly variation in ASR for both habitats, we found that it depends on the species. In addition, male aggregation differed between species depending on habitat type and season, and species movement patterns were closely related to their habitat preferences. Based on our results, we argue that comparative population studies of species with different life history traits are necessary to understand the variation in demographic parameters as well as its ecological and evolutionary implications in the face of spatial and climatic environmental variation.

Observable variations in human sex ratio at birth.

The human sex ratio at birth (SRB), defined as the ratio between the number of newborn boys to the total number of newborns, is typically slightly greater than 1/2 (more boys than girls) and tends to vary across different geographical regions and time periods. In this large-scale study, we sought to validate previously-reported associations and test new hypotheses using statistical analysis of two very large datasets incorporating electronic medical records (EMRs). One of the datasets represents over half (∼ 150 million) of the US population for over 8 years (IBM Watson Health MarketScan insurance claims) while another covers the entire Swedish population (∼ 9 million) for over 30 years (the Swedish National Patient Register). After testing more than 100 hypotheses, we showed that neither dataset supported models in which the SRB changed seasonally or in response to variations in ambient temperature. However, increased levels of a diverse array of air and water pollutants, were associated with lower SRBs, including increased levels of industrial and agricultural activity, which served as proxies for water pollution. Moreover, some exogenous factors generally considered to be environmental toxins turned out to induce higher SRBs. Finally, we identified new factors with signals for either higher or lower SRBs. In all cases, the effect sizes were modest but highly statistically significant owing to the large sizes of the two datasets. We suggest that while it was unlikely that the associations have arisen from sex-specific selection mechanisms, they are still useful for the purpose of public health surveillance if they can be corroborated by empirical evidences.

Sex-Biased Mortality and Sex Reversal Shape Wild Frog Sex Ratios

Population sex ratio is a key demographic factor that influences population dynamics and persistence. Sex ratios can vary across ontogeny from embryogenesis to death and yet the conditions that shape changes in sex ratio across ontogeny are poorly understood. Here, we address this issue in amphibians, a clade for which sex ratios are generally understudied in wild populations. Ontogenetic sex ratio variation in amphibians is additionally complicated by the ability of individual tadpoles to develop a phenotypic (gonadal) sex opposite their genotypic sex. Because of sex reversal, the genotypic and phenotypic sex ratios of entire cohorts and populations may also contrast. Understanding proximate mechanisms underlying phenotypic sex ratio variation in amphibians is important given the role they play in population biology research and as model species in eco-toxicological research addressing toxicant impacts on sex ratios. While researchers have presumed that departures from a 50:50 sex ratio are due to sex reversal, sex-biased mortality is an alternative explanation that deserves consideration. Here, we use a molecular sexing approach to track genotypic sex ratio changes from egg mass to metamorphosis in two independent green frog (Rana clamitans) populations by assessing the genotypic sex ratios of multiple developmental stages at each breeding pond. Our findings imply that genotypic sex-biased mortality during tadpole development affects phenotypic sex ratio variation at metamorphosis. We also identified sex reversal in metamorphosing cohorts. However, sex reversal plays a relatively minor and inconsistent role in shaping phenotypic sex ratios across the populations we studied. Although we found that sex-biased mortality influences sex ratios within a population, our study cannot say at this time whether sex-biased mortality is responsible for sex ratio variation across populations. Our results illustrate how multiple processes shape sex ratio variation in wild populations and the value of testing assumptions underlying how we understand sex in wild animal populations.