Changes In Sex Ratio Research Articles

Sex determination in the oyster Crassostrea gigas - A large longitudinal study of population sex ratios and individual sex changes

Understanding sex determination in the Pacific oyster Crassostrea gigas, a sequential hermaphrodite, can provide prospective on the evolution of sex-determining systems for comparative reproduction from an evolutionary perspective. Surprisingly, this mechanism is still poorly understood. To date, sex ratio and sex change have never been studied at the individual level for a large size group and long-term monitoring. To this purpose, we performed an ambitious individual long-term follow-up (6 years) on a large population (cohort 1: 7488 oysters) produced from wild oysters, as well as for a second population produced from the cohort 1 (cohort 2: 4320 oysters). All oysters were individually sexed from 2014 to 2019. For the cohort 1, our results showed a significantly female-biased sex ratio each year, ranging from 61 to 73% for the cohort 1. The proportion of oysters exhibiting sex change between the first two breeding seasons was 34% and decreased each year, ending at 9% between years 5 and 6. From the initial population, 1386 oysters were sexed six years in a row. Among them, 58% were sequential hermaphrodites, within which 32% changed sex once (19% protandric and 13% protogynic), 19% twice, 5% three times, 1% four times and 0.1% five times. In contrast, 42% never exhibited a sex change, within which 34% were potentially true females and 8% potentially true males. However, a logistic regression model indicates that those oysters could experience one sex reversal in subsequent years resulting that all oysters of our population of C. gigas would be sequential hermaphrodites. Similar results were observed for the cohort 2, although the proportion of sequential hermaphrodite was higher than the one observed for cohort 1. It is supposed that a genetic basis exist for sex change in C. gigas. Our work participates to unravel the barriers existing about the sequential hermaphroditism, the protandry and the sexual system in C. gigas, still currently debated.

Development of gonads and evidence of protogyny in Spangled emperor (Lethrinus nebulosus) from the coastal waters off Negombo, Sri Lanka.

Gonad development and maturation of the spangled emperor Lethrinus nebulosus (Forsskål, 1775) inhabiting coastal waters off Negombo, Sri Lanka was investigated to understand the reproductive strategies. Sexual ontogeny was investigated using histological examinations of the gonads and changes in sex ratio with body size. Cellular characteristics and the most advanced germ cells presented in the gonads were considered for determining the sex and maturity stages. The transitional gonads were characterized by changes in internal gonad structure such as the appearance of spermatocyte and degenerated oocytes in the same developmental stage. Thick strands of stromal tissue within the lamellae and branched secondary strands were observed in transitional individuals. Increased blood vessels and sperm sinuses within the gonad wall were also an indications of sex transition. Therefore, L. nebulosus living in coastal waters off Negombo exhibited an early indication of protogynous hermaphroditism among adults. The sizes at 50% sexual maturity of males and females were estimated to be 29.5 cm and 39.5 cm respectively. A dramatic change in the sex ratio of the adult size classes suggested that female to male sex transition observed between 28.5- 40.4 cm body sizes. Sex ratios were 1.23: 0.46: 1 for female: transitional: males indicating slightly female-biased overall sex ratios. Female dominance in smaller size classes and male dominance in larger size classes were also evident Mean size at first capture recorded for L. nebulosus (19.6 cm) was well below the mean sizes of maturity for both male and female. Size-specific differences in sex ratios and reproductive potential indicate that conventional regulations that impose size limits for capture would not be very effective for the management of L. nebulosus.

EFFECT OF SOIL WATER DEFICITS ON ANNUAL FRESH FRUIT BUNCH PRODUCTION IN CENTRAL KALIMANTAN

The soil water deficits have an after-effect over the time lagged fruiting activities of palms, which subsequently affects the annual fresh fruit bunch (FFB) production in the oil palm plantation. Field data from 2014 to 2018 in a reasonably well managed oil palm estate with three soils of the greater groups of Typic Dystrudept (lnceptisol), Typic Haplohumod (Spodosol) and Typic Haplohemist (Histosol) were analysed. The palms were planted in the years 2004 and 2005, and were producing FFB at its prime plateau age of yield life cycle. The amount of monthly water deficits that results in single or multiple fruiting activities responded quadratically to subsequent annual FFB production in all three soils. With two consecutive total soil water deficits in the years 2014 and 2015, the multiple time lagged fruiting activities from bunch failure to sex differentiation with change in sex ratio favouring male inflorescences resulted in reduced yield in 2016 in all three soils. Typic Haplohumod soils being sandy achieved the lowest yield in 2016. The palms planted on Typic Haplohemist showed rapid decline in crop with the slightest water deficit. The soil derived from Typic Dystrudept gave relatively high FFB production at low water deficit. Keywords: Water deficit, fruiting activity, fresh fruit bunch production, El nino, drought.

Endangered species protection and evidence-based decision-making: Case study of a quarry proposal in endangered turtle habitat

Surface mining practices can negatively impact turtles through degradation of wetlands and surrounding upland habitat, alteration of movement corridors, increased risk of nest and turtle predation, and direct mortality. These impacts, in turn, can cause changes in sex ratios and population demography, which may ultimately lead to population declines and extirpation. Using radio-telemetry, GPS data loggers, and capture-mark-recapture surveys over two field seasons, we described the demography of, and identified critical habitat for, a population of endangered Blanding's turtles (Emydoidea blandingii) inhabiting an area of interest for development of a trap rock quarry in Ontario, Canada. We captured 56 turtles and estimated population size to be 80±18 turtles, and density to be 1.84 turtles/ha, which is among the highest reported densities for the species. Daily distances moved and home range sizes were generally smaller than conspecific values reported in the literature, suggesting that habitat quality was high as turtles did not need to move much to acquire necessary resources. We identified 15 nesting sites and 12 wetlands that housed overwintering turtles, both considered by government to be critical habitats with lowest tolerance to destruction. We mapped our spatial data based on the application of legislated provincial and federal recovery guidelines, and the results indicate that the quarry proposal should be rejected if the spirit of the law is upheld given that at least 63% and at most 100% of the proposed quarry area is categorized as endangered species habitat.

The sex‐determination pattern in crocodilians: A systematic review of three decades of research

Sex in crocodilians is not determined by chromosomes, but by egg incubation temperature, where different temperatures produce different clutch sex ratios. Two patterns have been proposed to describe these changes in sex ratios: a 100% female proportion at low and high temperatures with male predominance at intermediate ones (FMF) or a simpler pattern with a single female-to-male transition (FM). Over the last three decades, researchers have provided empirical information to support either of these two patterns in different species; however, no consensus has been reached partly because data have not been analysed as a whole. Here, we aimed at gathering the existing data on these patterns to provide models of temperature-dependent sex determination in those crocodilians studied so far. Potentially relevant publications were searched on Web of Knowledge, Scopus, Scielo and Science Direct. Studies that reported results on the sexual identity of crocodilian hatchlings obtained from constant temperature incubation treatments were considered. Using statistical models varying in their underlying assumptions, we evaluated which sex-determination pattern was best supported for the studied crocodilians and constructed species-specific and latitude-specific models. Based on the 8,458 sexed hatchlings studied throughout 31 studies, we show that the evidence supports a shared FMF pattern in all the crocodilian species for which enough data are available. We find that such pattern changes between species and at different latitudes. These results suggest a lability of the FMF crocodilian sex-determination pattern, a key feature under the present climate change scenario.

Skewed sex ratios in a newly established osprey population

With recent increases in the numbers of reintroduction projects, it has become crucial to know the main factors that allow colonization of new areas and prevent the extinction of small and reintroduced populations. Dispersal is one of the most important phenomena in population biology with consequences to the proportion of individuals that keep breeding in the natal population and the number of individuals that move to other populations to breed. We studied changes in offspring sex ratio and differences in dispersal patterns between the sexes in a reintroduced population of osprey (Pandion haliaetus). Results showed that at the beginning of the colonization process breeding pairs produced more males, which dispersed shorter distances and were more philopatric than females. However, with increasing breeding population size over the years, the offspring production was skewed to females, which dispersed longer distances from their natal area and tended to breed in different areas. Here we suggest that changes in offspring sex ratio during colonization processes, together with differences in dispersal pattern between sexes, could influence colonization rate and the probability of success of future reintroduction projects.

Breeding sex ratios in two declining diving duck species: between-year variation and changes over six decades

Sex ratio variation has important consequences for population dynamics and viability. Adult sex ratio is male biased in many duck species, and data from wintering areas suggest male bias has been increasing in some European duck species. However, the reasons for changes in sex ratios remain poorly understood, and information on sex ratio variation among breeding ducks is limited. We studied long-term changes in breeding sex ratios and breeding numbers in Common Pochard Aythya ferina and Tufted Duck Aythya fuligula in southern Finland, the former species being currently assessed as critically endangered and the latter as endangered in Finland. In addition, we tested the hypothesis that between-year variation in breeding sex ratios is affected by the severity of weather conditions in the wintering areas. The proportion of females among breeding Tufted Ducks decreased from 42.9% in 1951–1970 to 36.9% in 1996–2015, while no statistically significant change was observed in Common Pochard (41.8% and 39.5%, respectively). Both species showed a decline in breeding numbers over the same period. Severity of the preceding winter did not affect the proportion of females in the breeding area.

Distribution of and associated factors for dengue burden in the state of Odisha, India during 2010\u20132016

This study is aimed to estimate the epidemiological burden of dengue in Odisha, India using the disability adjusted life year (DALY) methods and to explore the associated factors in the year 2010–2016. During the period of 2010–2016, 27 772 cases (68.4% male) were reported in the state. Mean age (years) of male and female was 31.63 and 33.82, respectively. Mean district wise disability adjusted life years (DALY) per 100 000 people was higher in the year 2016 (0.45) and mean DALY lost per person was highest in the year 2015 (34.90 years). Adjusted regression model indicates, every unit increase in humidity and population density increases DALY by 1.05 and 1.02 units respectively. Whereas, unit change in sex ratio (females per 1000 males) and forest coverage increases the DALY by 0.98 units. Our results indicate geographical variation of DALY in Odisha, which is associated with population density, humidity and forest cover. Discrepancies identified between standard incidence and DALY maps suggests, latter can be used to present disease burden more effectively. More prevalence among young males suggests the need of strengthening the targeted prevention and control measures.

The Effects of Conflict on Fertility: Evidence From the Genocide in Rwanda.

Our study analyzes the fertility effects of the 1994 genocide in Rwanda. We study the effects of violence on both the duration time to the first birth in the early post-genocide period and on the total number of post-genocide births per woman up to 15 years following the conflict. We use individual-level data from Demographic and Health Surveys, estimating survival and count data models. This article contributes to the literature on the demographic effects of violent conflict by testing two channels through which conflict influences fertility: (1) the type of violence exposure as measured by the death of a child or sibling, and (2) the conflict-induced change in local demographic conditions as captured by the change in the district-level sex ratio. Results indicate the genocide had heterogeneous effects on fertility, depending on the type of violence experienced by the woman, her age cohort, parity, and the time horizon (5, 10, and 15 years after the genocide). There is strong evidence of a child replacement effect. Having experienced the death of a child during the genocide increases both the hazard of having a child in the five years following the genocide and the total number of post-genocide births. Experiencing sibling death during the genocide significantly lowers post-genocide fertility in both the short-run and the long-run. Finally, a reduction in the local sex ratio negatively impacts the hazard of having a child in the five years following the genocide, especially for older women.

Swift declines predicted following mating system changes driven by an introduced predator.

In Focus: Heinsohn, R., Olah, G., Webb, M., Peakall, R., & Stojanovic, D. (2019). Sex ratio bias and shared paternity reduce individual fitness and population viability in a critically endangered parrot. Journal of Animal Ecology, 88, 502-510. While the effects of variation in the sex ratio of offspring have been thoroughly explored over the last century, the sex ratio of adults has received far less attention. A paper by Heinsohn and colleagues in this issue shows that changes in the adult sex ratio can have striking effects on mating systems, reproductive success and population viability. These impacts are all the more dramatic because they occur in a critically endangered species, the swift parrot, Lathamus discolor, of Tasmania. This species suffers heavy predation from the introduced sugar glider, Petaurus breviceps, which kills nesting females and their clutches, resulting in strongly male-biased adult sex ratios. The authors combined demographic and genetic data to show that, at sites with heavier predation, the remaining females were more likely to mate with multiple males. This shift in the mating system also led to lower overall nesting success, with fewer chicks fledged per nest at sites with higher levels of mixed paternity. Population viability models based on these data predicted steep population declines, with models using the highest observed rates of mixed paternity showing the sharpest declines. These results demonstrate that changes in the adult sex ratio can have far-reaching impacts, including on the fitness of populations themselves.

Gender dysphoria in adolescent population: A 5-year replication study.

The aim of this study was to explore whether there has been an increase in prevalence and changes in sex ratio in feelings of gender dysphoria (GD) in an adolescent population in Northern Europe, and to study the impact of invalid responding on this topic. We replicated an earlier survey among junior high school students in Tampere, Finland. All first and second year students, aged 16-18, in the participating schools were invited to respond to an anonymous classroom survey on gender experience during the 2012-2013 school year and in the spring and autumn terms of 2017. Gender identity/GD was measured using the GIDYQ-A. A total of 318 male and 401 female youth participated in 2012-2013, and 326 male and 701 female youth in 2017. In the earlier survey, the GIDYQ-A scores, both among males and females, were strongly skewed toward a cis-gender experience with very narrow interquartile ranges. Of males, 2.2%, and of females, 0.5% nevertheless reported possibly clinically significant GD. The 2017 GIDYQ-A distribution was similarly skewed. The proportion of those reporting potentially clinically significant GD was 3.6% among males and 2.3% among females. Validity screening proved to have a considerable impact on conclusions. GD seems to have increased in prevalence in the adolescent population.

Plasticity of Mating Duration in Response to Slightly Biased Operational Sex Ratios in the Water Strider (Aquarius remigis): The Effect of Cohabitation Under Standard Laboratory Conditions

In polygynandrous species, males face the trade-off between the pursuit of increased mating opportunities and securing paternity. Within such systems, males need to accurately assess the social composition of the local environment to maximize fitness. Here, we investigated this capability in the water strider (Aquarius remigis), a semi-aquatic insect known to exhibit a broad spectrum of mating behaviors and inhabit a socially diverse and changing environment. Using a combination of methodological designs to track both within- and between-subject effects, individuals remained in same-sex housing prior to being exposed to slightly biased operational sex ratios (2:1 vs. 1:2) with or without prior cohabitation to determine the effects on mating duration. Results show that males were sensitive to these subtle differences in social conditions, mating for longer periods within male-biased environments, but this was true only under conditions with prior cohabitation. In particular, when individuals could acclimate to the testing environment, mating duration dropped precipitously in female-biased conditions. These findings do not support the view that male water striders have consistent behavioral syndromes, and instead show that individuals are able to differentiate between, and adaptively respond to, small changes in the local sex ratio. In addition to improving our understanding of the plasticity of male mating behavior in this species, this study offers new insights for future laboratory research studying reproductive competition across a diverse range of polygynandrous animals.

Changes in adult sex ratio in wild bee communities are linked to urbanization

Wild bees are indispensable pollinators, supporting global agricultural yield and angiosperm biodiversity. They are experiencing widespread declines, resulting from multiple interacting factors. The effects of urbanization, a major driver of ecological change, on bee populations are not well understood. Studies examining the aggregate response of wild bee abundance and diversity to urbanization tend to document minor changes. However, the use of aggregate metrics may mask trends in particular functional groups. We surveyed bee communities along an urban-to-rural gradient in SE Michigan, USA, and document a large change in observed sex ratio (OSR) along this gradient. OSR became more male biased as urbanization increased, mainly driven by a decline in medium and large bodied ground-nesting female bees. Nest site preference and body size mediated the effects of urbanization on OSR. Our results suggest that previously documented negative effects of urbanization on ground-nesting bees may underestimate the full impact of urbanization, and highlight the need for improved understanding of sex-based differences in the provision of pollination services by wild bees.

Phosphorylation of GATA4 serine 105 but not serine 261 is required for testosterone production in the male mouse.

GATA4 is a transcription factor essential for male sex determination, testicular differentiation during fetal development, and male fertility in the adult. GATA4 exerts part of its function by regulating multiple genes in the steroidogenic enzyme pathway. In spite of these crucial roles, how the activity of this factor is regulated remains unclear. Studies in gonadal cell lines have shown that GATA4 is phosphorylated on at least two serine residues-serine 105 (S105) and serine 261 (S261)-and that this phosphorylation is important for GATA4 activity. The objective of the present study is to characterize the endogenous role of GATA4 S105 and S261 phosphorylation in the mouse testis. We examined both previously described GATA4 S105A mice and a novel GATA4 S261A knock-in mouse that we generated by CRISPR/Cas9 gene editing. The male phenotype of the mutants was characterized by assessing androgen-dependent organ weights, hormonal profiles, and expression of multiple testicular target genes using standard biochemical and molecular biology techniques. The fecundity of crosses between GATA4 S105A mice was reduced but without a change in sex ratio. The weight of androgen-dependent organs was smaller when compared to wild-type controls. Plasma testosterone levels showed a 70% decrease in adult GATA4 S105A males. This decrease was associated with a reduction in Cyp11a1, Cyp17a1, and Hsd17b3 expression. GATA4 S261A mice were viable and testis morphology appeared normal. Testosterone production and steroidogenic enzyme expression were not altered in GATA4 S261A males. Our analysis showed that blocking GATA4 S105 phosphorylation is associated with decreased androgen production in males. In contrast, S261 phosphorylation by itself is dispensable for GATA4 function. These results confirm that endogenous GATA4 action is essential for normal steroid production in males and that this activity requires phosphorylation on at least one serine residue.

Developmental Dioxin Exposure Alters the Methylome of Adult Male Zebrafish Gonads.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a persistent environmental toxicant and endocrine disrupting compound with reproductive and developmental effects in humans and model organisms, including zebrafish. Our previous microarray and histological studies found defects in spermatogenesis and fertility of zebrafish in response to acute developmental TCDD exposure. These effects are apparent following exposure during reproductive development, modeling fetal basis of adult-onset disease. Some outcomes of these previous studies (reduced fertility, changes in sex ratio, transcriptomic alterations) are also transgenerational – persisting to unexposed generations – through the male germline. We hypothesized that DNA methylation could be a possible mechanism for these reproductive effects and performed whole genome bisulfite sequencing (WGBS), which identifies whole genome DNA methylation status at the base pair level, on testes of adult zebrafish exposed to TCDD (two separate hour-long exposures to 50 pg/mL TCDD at 3 and 7 weeks post fertilization). In response to TCDD exposure, multiple genes were differentially methylated; many of which are involved in reproductive processes or epigenetic modifications, suggesting a role of DNA methylation in later-life health outcomes. Additionally, several differentially methylated genes corresponded with gene expression changes identified in TCDD-exposed zebrafish testes, indicating a potential link between DNA methylation and gene expression. Ingenuity pathway analysis of WGBS and microarray data revealed genes involved in reproductive processes and development, RNA regulation, the cell cycle, and cellular morphology and development. We conclude that site-specific changes in DNA methylation of adult zebrafish testes occur in response to acute developmental TCDD exposure.

The Effects of Conflict on Fertility: Evidence from the Genocide in Rwanda

This paper analyzes the effects of the 1994 genocide in Rwanda on fertility outcomes. We study the effects of violence on both the timing of the first birth after the genocide and the total number of post-genocide births. We analyze individual-level data from several Demographic and Health Surveys, using event history and count data models. The paper contributes to the literature on the demographic effects of violent conflict by testing two channels through which conflict influences subsequent fertility. First, the type of violence exposure as measured by child death as well as by the death of a woman’s sibling. Second, the conflict-induced change in local demographic conditions as captured by the change in the commune-level sex ratio. Results indicate that the genocide has heterogeneous effects on fertility, depending on the type of violence experienced by the woman, her age cohort, parity, and the time horizon (5, 10, and 15 years after the genocide). There is strong evidence of a replacement effect. Having experienced the death of a child during the genocide reduces the time to the first birth after the genocide and increases the total number of births in the post-genocide period. Experiencing a sibling death during the genocide significantly lowers fertility in the long run. The effect is strongest if a woman loses a younger sister. Finally, the genocide-induced reduction in the sex ratio has a strong negative impact on fertility, both in terms of the timing of the first birth and the total number of births after the genocide.

Effects of the maternal and current social environment on female body mass and reproductive traits in Japanese quail (Coturnix japonica).

The social environment of breeding females can affect their phenotype, with potential adaptive maternal effects on offspring that experience a similar environment. We housed Japanese quail (Coturnix japonica) females in two group sizes (pairs versus groups of four) and studied the effects on their offspring under matched and mismatched conditions. We measured F1 body mass, reproduction, and plasma levels of androgens and corticosterone. F1 group housing led to an increase in body mass. In addition, F1 group housing had a positive effect on mass in daughters of pair-housed P0 females only, which were heaviest under mismatched conditions. At the time of egg collection for the F2 generation, F1 group-housed females were heavier, irrespective of the P0 treatment. F1 females in groups laid heavier eggs, with higher hatching success, and produced heavier offspring, most likely a maternal effect of F1 mass. F1 plasma hormones were affected by neither the P0 nor the F1 social environment. These results contrasted with effects in the P0 generation (reported previously), in which plasma hormone levels, but not mass, differed between social environments. This may be due to changes in adult sex ratios as P0 females were housed with males, whereas F1 females encountered males only during mating. Our study demonstrates potentially relevant mismatch effects of the social environment on F1 body mass and maternal effects on F2 offspring, but further study is needed to understand their adaptive significance and physiological mechanisms.

Assessing long-term changes in sex ratios of Pacific herring in Prince William Sound, Alaska

The Pacific herring (Clupea pallasii) population in Prince William Sound, Alaska suffered a sudden collapse in 1993 and has failed to recover. No consensus has been reached for the causes of the collapse, but hypotheses span a range of ecological, environmental, and anthropogenic drivers. During the course of investigations into changes in PWS herring and salmon population dynamics and fisheries we discovered that the observed percentage of male herring in spawning biomass estimates appeared to increase since the mid-1980s. Using available data (1983–2015) we analysed sex ratios of herring caught in close proximity to the spring spawn using various gear types. In recent years, the overall sex ratio of Pacific herring in PWS has been skewed towards males (>60%), but only if samples from cast nets are included, which generally catch spawning fish. In contrast, purse seine samples, generally collected days to weeks prior to the spawn, had relatively equal sex ratios. Age also affected the sex ratio, with a higher proportion of older fish being females. Using an age-structured simulation model, we illustrate that overestimating the number of males in the population can lead to biases in estimated model parameters (such as vulnerability at age) and as a result, biases in the inferred age composition of the population, and other derived quantities. After accounting for differences in sampling gears to improve estimated sex ratios, we recommend that future work focus attention on separating spatial and temporal differences in sex ratios of this otherwise much-studied population.

The population structure and sex ratios of Bursaphelenchus xylophilus under α-pinene stress

Pine wood nematode (PWN), Bursaphelenchus xylophilus, is a serious pathogen of pines throughout the world. Previous work indicated that different concentrations of α-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 α-pinene, we investigated different aspects of population changes of B. xylophilus under two concentrations of α-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 α-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 α-pinene. This study has provided a theoretical basis for the prevention and control of pine wilt disease caused by the pine wood nematode.

Influence of Monensin, Yeast, Selenoproteinand S odium Selenite Supplement on change of Offspring Sex Ratio at Birthof Sheep

Influence of Monensin, Yeast, Selenoproteinand S odium Selenite Supplement on change of Offspring Sex Ratio at Birthof Sheep