Vertebrate endocrine disruptors induce sex-reversal in blue mussels.

Mollusks are the second most diverse animal phylum, yet little is known about their endocrinology or how they respond to endocrine disrupting compound (EDC) pollution. Characteristic effects of endocrine disruption are reproductive impairment, skewed sex ratios, development of opposite sex characteristics, and population decline. However, whether classical vertebrate EDCs, such as steroid hormone-like chemicals and inhibitors of steroidogenesis, exert effects on mollusks is controversial. In the blue mussel, Mytilus edulis, EDC exposure is correlated with feminized sex ratios in wild and laboratory mussels, but sex reversal has not been confirmed. Here, we describe a non-destructive qPCR assay to identify the sex of M. edulis allowing identification of males and females prior to experimentation. We exposed male mussels to 17α-ethinylestradiol and female mussels to ketoconazole, EDCs that mimic vertebrate steroid hormones or inhibit their biosynthesis. Both chemicals changed the sex of individual mussels, interfered with gonadal development, and disrupted gene expression of the sex differentiation pathway. Impacts from ketoconazole treatment, including changes in steroid levels, confirmed a role for steroidogenesis and steroid-like hormones in mollusk endocrinology. The present study expands the possibilities for laboratory and field monitoring of mollusk species and provides key insights into endocrine disruption and sexual differentiation in bivalves.

Analysis of the Factors Affecting the Male-Female Sex Ratio of Babies Born through Assisted Reproductive Technology.

BACKGROUND: Until now, the sex ratio in a population is believed to be relatively stable with no male/female preponderance. There has been an increasing amount of evidence to suggest that assisted conception may significantly impact on sex ratio (SR). Several factors have been suggested to affect SR such as parental variables (paternal race, maternal age, and body mass index-(BMI), methods of fertilisation (in-vitro fertilisation/intracytoplasmic sperm injection), stage of embryo transfer (cleavage/blastocyst), type of IVF cycle (fresh/cryopreserved), medications used for controlled ovarian stimulation, poor sperm motility, and even culture media. OBJECTIVES: This study aims to investigate the potential impact of the different ART procedures on sex ratio. It will also explore the relationship between paternal race, maternal age and body mass index BMI on sex ratio. METHODS: A retrospective cohort study from January 2017 to December 2023. Participants were women who had successful ART and delivery at Ninewells Assisted Conception Unit (NACU) Dundee and ART centre of Lagos University Teaching Hospital, Nigeria. RESULTS: Overall, 294 (66.2%) of the case records and 150 (33.8%) were evaluated from NACU and LUTH respectively. More male infants 244 (66.8%) were delivered following pregnancies conceived with blastocyst embryo stage transfer when compared with female infants which stood at 121 (33.2%). Concerning cleavage embryo stage transfer, 56 (70.9%) were in favour of female newborns while males accounted for 23 (29.1%). CONCLUSION: The study revealed that there is an increase in the proportion of male babies born following certain assisted conception techniques such as blastocyst stage embryo transfer and IVF while more female babies were born when cleavage stage embryos were transferred or when ICSI was used as a method of fertilisation.

CONTEXTE: Jusqu'à présent, le rapport de masculinité au sein d'une population est considéré comme relativement stable, sans prépondérance masculine/féminine. De plus en plus de preuves suggèrent que la procréation assistée peut avoir un impact significatif sur la sex-ratio (SR). Plusieurs facteurs ont été suggérés pour affecter la SR, tels que les variables parentales (race paternelle, âge maternel et indice de masse corporelle-IMC), les méthodes de fécondation (fécondation in vitro/injection intracytoplasmique de spermatozoïdes), le stade du transfert d'embryon (clivage/blastocyste), le type de Cycle de FIV (frais/cryoconservé), médicaments utilisés pour une stimulation ovarienne contrôlée, mauvaise motilité des spermatozoïdes et même milieux de culture. OBJECTIFS: Cette étude vise à étudier l'impact potentiel des différentes procédures de TAR sur le sex-ratio. Il explorera également la relation entre les variables parentales telles que la race paternelle, l'âge de la mère et l'indice de masse corporelle (IMC) sur le sex-ratio. Méthodes : Une étude rétrospective de janvier 2017 à décembre 2023. Les participantes étaient des femmes qui ont eu un TAR et un accouchement réussis à l'unité de conception assistée de Ninewells (NACU) de Dundee et au centre de TAR de l'hôpital universitaire de Lagos, au Nigeria. RESULTATS: Au total, 294 (66,2 %) des dossiers de cas et 150 (33,8 %) ont été évalués respectivement par le NACU et le LUTH. Un plus grand nombre de nourrissons de sexe masculin, 244 (66,8 %), ont accouché à la suite de grossesses conçues avec transfert de stade embryonnaire de blastocyste, par rapport aux nourrissons de sexe féminin, qui s'élevaient à 121 (33,2 %). Concernant le transfert de stades embryonnaires par clivage, 56 (70,9%) étaient en faveur des nouveau-nés de sexe féminin tandis que les mâles représentaient 23 (29,1%). CONCLUSION: L'étude a révélé qu'il y a une augmentation de la proportion de bébés mâles nés suite à certaines techniques de procréation assistée telles que le transfert d'embryons au stade blastocyste et la FIV, tandis qu'un plus grand nombre de bébés femelles sont nés lorsque des embryons au stade clivage ont été transférés ou lorsque l'ICSI a été utilisée comme méthode de fertilisation. MOTS-CLÉS: Ratio de sexes, ICSI, FIV, Blastocyste, Clivage, Race, IMC, Embryon congelé/frais.

In search of the genetic variants of human sex ratio at birth: was Fisher wrong about sex ratio evolution?

The human sex ratio (fraction of males) at birth is close to 0.5 at the population level, an observation commonly explained by Fisher's principle. However, past human studies yielded conflicting results regarding the existence of sex ratio-influencing mutations-a prerequisite to Fisher's principle, raising the question of whether the nearly even population sex ratio is instead dictated by the random X/Y chromosome segregation in male meiosis. Here we show that, because a person's offspring sex ratio (OSR) has an enormous measurement error, a gigantic sample is required to detect OSR-influencing genetic variants. Conducting a UK Biobank-based genome-wide association study that is more powerful than previous studies, we detect an OSR-associated genetic variant, which awaits verification in independent samples. Given the abysmal precision in measuring OSR, it is unsurprising that the estimated heritability of OSR is effectively zero. We further show that OSR's estimated heritability would remain virtually zero even if OSR is as genetically variable as the highly heritable human standing height. These analyses, along with simulations of human sex ratio evolution under selection, demonstrate the compatibility of the observed genetic architecture of human OSR with Fisher's principle and render it plausible that multiple OSR-influencing genetic variants segregate among humans.

Changes in seasonality and sex ratio of scrub typhus: a case study of South Korea from 2003 to 2019 based on wavelet transform analysis.

BACKGROUND: Scrub typhus (ST, also known as tsutsugamushi disease) is a common febrile vector-borne disease in South Korea and commonly known as autumn- and female-dominant disease. Although understanding changes in seasonality and sex differences in ST is essential for preparing health interventions, previous studies have not dealt with variations in periodicity and demographic characteristics in detail. Therefore, we aimed to quantify the temporal dynamics of seasonal patterns and sex differences in the incidence of ST in South Korea. METHODS: We extracted epidemiological week (epi-week)-based ST cases from 2003 to 2019 Korean National Health Insurance Service data (ICD-10-CM code: A75.3). To determine changes in seasonality and sex differences, year-, sex-, and age-group-stratified male-to-female ratios and wavelet transform analyses were conducted. RESULTS: Between 2003 and 2019, 213,976 ST cases were identified. The incidence per 100,000 population increased by 408.8% from 9.1 in 2003 to 37.2 in 2012, and subsequently decreased by 59.7% from 2012 to 15.0 in 2019. According to the continuous wavelet transform results, ST exhibited a dual seasonal pattern with dominant seasonality in autumn and smaller seasonality in spring from 2005 to 2019. Overall, the periodicity of seasonality decreased, whereas its strength decreased in autumn and increased in spring. With an overall male-to-female ratio being 0.68:1, the ratio has increased from 0.67:1 in 2003 to 0.78:1 in 2019 (Kendall's τ = 0.706, p < 0.001). However, interestingly, the ratio varied significantly across different age groups. CONCLUSIONS: Our findings quantitatively demonstrated changes in seasonality with dual seasonal pattern and shortened overall periodicity and a decrease in sex differences of ST in South Korea. Our study suggests the need for continuous surveillance on populations of vector and host to address ST dynamics to preemptively prepare against global warming.

The 'Goldilocks Grub': reproductive responses to leafroller host development in Goniozus jacintae, a parasitoid of the light brown apple moth.

Many parasitoids alter their reproductive behaviour in response to the quality of encountered hosts. They make adaptive decisions concerning whether to parasitise a potential host, the number of eggs laid on an accepted host, and the allocation of sex to their offspring. Here we present evidence that Goniozus jacintae Farrugia (Hymenoptera: Bethylidae), a gregarious ectoparasitoid of larval tortricids, adjusts its reproductive response to the size and developmental stage of larvae of the light brown apple moth (LBAM), Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae). Goniozus jacintae parasitises instars 3-6 of LBAM, but most readily parasitises the later, larger, instars. Brood sizes were bigger on larger hosts and brood sex ratios were female biased (proportion of males = 0.23) with extremely low variance (never >1 male in a brood at emergence), perhaps the most precise of all studied bethylids. Host size did not influence brood development time, which averaged 19.64 days, or the body size of male offspring. However, the size of females was positively correlated with host size and negatively correlated with brood size. The sizes of individual males and females were positively related to the average amount of host resource available to individuals within each brood, suggesting that adult body size is affected by scramble competition among feeding larvae. Average brood sizes were: 3rd instar host, 1.3 (SE ± 0.075); 4th instar, 2.8 (SE ± 0.18); 5th instar, 4.7 (SE ± 0.23); 6th instar, 5.4 (SE ± 0.28). The largest brood size observed was 8 individuals (7 females, 1 male) on the 6th instar of LBAM. These results suggest that later instars would give the highest yield to optimise mass-rearing of G. jacintae if used for augmentative biological pest control.

Hexafluoropropylene oxide trimer acid (HFPO-TA) disrupts sex differentiation of zebrafish (Danio rerio) via an epigenetic mechanism of DNA methylation.

Hexafluoropropylene oxide trimer acid (HFPO-TA), an alternative to perfluorooctanoic acid, has been shown to have estrogenic effects. However, its potential to disrupt fish sex differentiation during gonadal development remains unknown. Therefore, this study exposed zebrafish to HFPO-TA from approximately 2 hours post fertilization (hpf) to 60 days post fertilization (dpf) to investigate its effects on sex differentiation. Results indicated that HFPO-TA disrupted steroid hormone homeostasis, delayed gonadal development in both sexes, and resulted in a female-skewed sex ratio in zebrafish. HFPO-TA exposure up-regulated gene expressions of cyp19a1a, esr1, vtg1 and foxl2, while down-regulated those of amh, sox9a and dmrt1. These suggested that HFPO-TA dysregulated the expressions of key genes related to sex differentiation of zebrafish, promoted the production and activation of estrogen, and further induced the feminization. Interestingly, we observed promoter hypomethylation of cyp19a1a and promoter hypermethylation of amh in male zebrafish, which were negatively associated with their gene expressions. These suggested that HFPO-TA dysregulated these key genes through DNA methylation in their promoters. Therefore, the HFPO-TA disrupted the sex differentiation of zebrafish through an epigenetic mechanism involving DNA methylation, ultimately skewing the sex ratio towards females. Overall, this study demonstrated adverse effects of HFPO-TA on fish sex differentiation and provided novel insights into the underlying epigenetic mechanism.

Long-term exposure to environmental concentration of dinotefuran disrupts ecdysis and sex ratio by dysregulating related gene expressions in Chironomus kiinensis.

Introduction: Currently, although there have been a few reports on the endocrine-disrupting effects of neonicotinoids, the effect on Chironomidae during long-term exposure remains unknown. Methods: Ecdysis and sex ratio, along with ecdysone-relevant gene expressions of representative neonicotinoid dinotefuran on Chironomus kiinensis were investigated at different environmental concentrations by long-term exposure. Results: A low dose of dinotefuran delayed pupation and emergence via inhibiting ecdysis. Sex ratios of adults shifted toward male-dominated populations with the concentration of dinotefuran increasing. The corresponding transcriptions of ecdysis genes ecr, usp, E74, and hsp70 were significantly downregulated in the midge. For estrogen effects, the vtg gene expression was upregulated, but there was no significant change for the err gene. Discussion: These results would improve our understanding of the endocrine-disrupting mechanisms of neonicotinoid insecticides to Chironomidae and provide data support for assessing their potential environmental risks.

Reproduction in the spider mite Oligonychus yothersi (Acari: Tetranychidae).

In this work we reported injuries caused by the spider mite Oligonychus yothersi on Vitis vinifera leaves and we also investigate the sex ratio of this species under laboratory conditions. To access the aspects regarding reproduction, females were placed individually in arenas made of V. vinifera leaves to oviposit and all progeny were mounted on slides when they reached adulthood to confirm the offspring sex. Our study showed that O. yothersi reproduces by thelytokous /arrhenotokous parthenogenesis, generating low number of males. Additionally, we found vine plants with leaf browning, particularly on the adaxial surface, where mites were usually found.

No place for young women? The impact of internal migration on adult sex ratios in rural East Germany.

Shortages of women in rural areas occur in many highly urbanized countries. Rural East Germany is an ideal case for studying this phenomenon because of its low adult sex ratio (ASR)-men greatly outnumber women-coupled with high outmigration among young adults. This study identifies how internal migration between rural and urban areas contributes to the shortage of young adult women. We use data on inter-county migration flows (for years 2002-21) to decompose the impacts of migration flows on ASRs. We find that the low ASRs in rural East Germany have been driven by sex-selective migration. In the early 2000s the main destination of sex-selective outflows was West Germany, while in the 2010s urban areas in East Germany were the key destinations. We find that moves among 18-24-year-olds increased the shortage of women in the rural population, whereas moves among 25-29-year-olds contributed to more balanced ASRs.

Two World Wars and Belgium: Missing Births and Birth Sex Ratio Changes.

INTRODUCTION: The sex ratio at birth (male/total births, M/T) is expected to approximate 0.515. M/T is influenced by many factors including stress. Both World Wars have been implicated as influencing birth rates and M/T. This study was carried out to analyse the effects of two World Wars on Belgium vis-à-vis missing births as well as M/T changes. METHODS: Belgian male and female births were available for 1830-2019 and annual population was available from Statista. ARIMA models were used to estimate and project birth losses. The effect of wars was assumed to begin in the years following the commencement of each war and extend to the year after cessation of hostilities i.e., 1915-1919 and 1940-1946 for the First and Second World Wars respectively. RESULTS: This study included 27,346,178 live births for 1830-2019, M/T 0.5124. There was a decreasing trend in births for 1830-2019, significant for 1950-2019. There were dips in births in association with both Wars resulting in over 440,000 missing births, 3.80% of the Belgian population for the First World War and 1.91% for the Second World War. M/T rose non-significantly for the First World War and significantly for the Second World War. DISCUSSION: The declining birth rate and M/T in developed countries is a recognised phenomenon. The missing births in relation to wars are of demographic importance but are often overlooked with emphasis usually on casualties and deaths. M/T may rise in wars, possibly due to increased coital activity as well as other factors.

Sons Shorten Mother's Lifespan in Preindustrial Families with a High Level of Infant Mortality.

AbstractIn dimorphic vertebrates where males are larger than females, the energetic costs of producing and rearing sons can exceed those of daughters. In humans, differences in maternal energy intake suggest that sons require 10% and 7% more energy than daughters during pregnancy and lactation, respectively. Due to a trade-off between reproduction and somatic maintenance, having sons is expected to have a more pronounced detrimental impact on a mother's lifespan than having daughters. A limitation of previous studies investigating this hypothesis is that the increased mortality cost of having sons was assumed to affect all mothers equally. Using a dataset from a preindustrial Quebec population monitored over two centuries, we found that the number of sons decreased postmenopausal lifespan only in mothers experiencing high infant mortality. Our study highlights the importance of interindividual variation in environmental conditions and maternal health when studying effects of offspring sex on reproductive costs.

First sexual maturity and type of spawning of the fish Conodon nobilis (Linnaeus, 1758) from the Amazon coast - Brazil.

The study of reproductive biology is an important tool in identifying protective measures to preserve fish stocks, providing essential data for a reliable management system that ensures a balance between the environment and the economy. This study aims to analyze the first sexual maturity and type of spawning of the fish Conodon nobilis (Linnaeus, 1758) on the Amazon coast, specifically in the Gulf Maranhense region. 360 specimens were obtained from commercial fishing activity in the community of Raposa-MA during the period from January to December 2021. Biometric data were recorded, and the gonadal maturation stages were determined through macro (maturation scale) and microscopic (histology) analyzes. Sex ratio, mean length of first sexual maturation and type of spawning were determined. Negative allometric growth was recorded for both sexes, indicating a greater increase in length than in weight, and the length varied from 11 to 31.8 cm and the sex ratio was 1 male:1.5 female. Individuals in all stages of maturation were observed throughout the year, with a predominance of individuals in spawning capacity and reproductive peaks in January, April and May, indicating that the species presents multiple spawning. The length at first sexual maturity (L50) for females was 18.41 cm and for males was 18.91 cm. Knowledge of the mean size at sexual maturity can help define appropriate regulations for fishing, ensuring that individuals have the opportunity to reproduce at least once before being captured.

Maternal Folic Acid and Dietary Folate Intake in Relation to Sex Ratio at Birth and Sex-Specific Birth Weight in China.

BACKGROUND: It is well-established that prenatal folic acid supplements can reduce neural tube defects. However, the associations between folic acid supplementation, dietary folate intake, and overall folate intake with sex-specific birth outcomes are not yet fully understood. OBJECTIVES: This study aims to investigate the association of periconceptional folic acid supplement, dietary folate, and total folate intake with the sex ratio at birth and sex-specific birth weight. METHODS: Data were sourced from a cross-sectional survey conducted between August and December 2013 in Northwest China, involving 7318 infants and their mothers, recruited using a stratified multistage random sampling method. Folic acid supplements (400 µg/d) were ascertained via a retrospective in-person interview. Dietary folate was evaluated using a validated food frequency questionnaire. Birth outcomes, including sex and weight at birth, were obtained from the Medical Certificate of Birth. Generalized linear models were employed to calculate relative risks (RRs) or differences with 95% confidence intervals (CIs). RESULTS: No association or dose-response relationship was observed between folic acid supplement, dietary folate, and total folate intake during periconception and the likelihood of male births. However, women who took folic acid supplements during pre- and post-conception were associated with an increased male birth weight by 52.8 (8.1 to 97.5) g. Additionally, the total folate intake during periconception was associated with birth weight for males (upper vs. lower tertile: ß = 38.8, 95%CI: 5.0 to 72.5 g, p-trend = 0.024) and females (upper vs. lower tertile: ß = 42.4, 95%CI: 6.7 to 78.1; p-trend = 0.022). CONCLUSIONS: Our findings indicate that periconceptional total folate intake does not correlate with sex ratio at birth but was positively linked to infant birth weights, regardless of gender. These findings offer novel insights into potential benefits of total folate intake, beyond the prevention of neural tube defects, for policymakers and public health.

Evaluation of levamlodipine benzenesulfonate compound I for embryo-fetal developmental toxicity in SD rats and genotoxicity.

In the present study, the effects of levamlodipine benzenesulfonate on the development of fertile Sprague-Dawley (SD) rats, their embryos, and littermates were assessed using an embryo-fetal developmental toxicity test. Maternal body weight reduction was observed at a dose of 20 mg/kg, but it recovered after treatment cessation. The 20 mg/kg dose group showed a skewed sex ratio in fetal rats, with a higher proportion of males. While some effects on fetal sternum development were observed at 20 mg/kg, no skeletal malformations were observed. No significant gross morphological abnormalities were detected in the dams (mothers), no significant embryotoxicity or foetotoxicity in fetal rats and no significant effects on fetal length and weight development at doses of 5 and 10 mg/kg. Genotoxicity was evaluated using a combination of the Ames test, the Chinese hamster ovary (CHO) cell chromosome aberration assay, and the ICR mouse bone marrow micronucleus test. The Ames test results indicated substantial bacteriostatic effects at doses of 500 and 5000 mg/dish, with no mutagenicity observed at doses of 0.5, 5, and 50 mg/dish. No significant effect on the aberration rate of CHO cell chromosomes was found at doses of 2.8, 5.6, and 11.2 mg/mL. In the ICR mouse micronucleus test, no micronucleus-inducing effect was observed at doses of 3.125, 6.25, and 12.5 mg/kg in each treatment group. In conclusion, under the conditions of this experiment, the no-observed-adverse-effect level (NOAEL) for developmental toxicity of levamlodipine benzenesulfonate in fertile SD rats, their embryos, and littermates was established to be 10 mg/kg/day. Levamlodipine benzenesulfonate did not exhibit significant genotoxicity.

Ancestral lineages of dietary exposure to an endocrine disrupting chemical drive distinct forms of transgenerational subfertility in an insect model.

Across the globe, many species of insects are facing population decline. This is largely driven by anthropogenic changes to the environment, including the widespread exposure of invertebrates to endocrine disrupting chemicals (EDCs), which impair fertility. To test whether generations of Drosophila melanogaster born from parents exposed to a common dietary EDC, equol, could recover reproductive function, we quantified the reproductive capacity of the two subsequent generations. Using a novel suite of flow cytometry assays to assess sperm functionality in real time, we find that sperm function is compromised across three generations, even after non-exposed in individuals contribute to the breeding population. Though the sex ratio alters in response to EDC exposure, favouring the survival of female offspring, most lineages with ancestral EDC exposure exhibit persistent subfertility in both the male and female. Male offspring with ancestral EDC exposure present with reduced fertility and dysfunctional spermatozoa, whereby spermatozoa are metabolically stressed, lack DNA integrity and present with permanent epigenetic alterations. Across generations, male and female offspring demonstrate distinct patterns of reproductive characteristics, depending upon the specific lineage of EDC exposure. Our results illustrate how dietary EDCs present in agricultural plants could promote transgenerational subfertility and contribute to declining insect populations.

Reproductive parameters of Oreochromis mossambicus in Laguna de Los Patos, Cumaná, Venezuela.

A total of 381 specimens of the tilapia Oreochromis mossambicus collected monthly from May 2017 to May 2018 in the Laguna de Los Patos, Cumaná, Venezuela, to evaluate reproductive parameters of this non-native species. Significant differences were found in relation to average height and weight between males and females, with the highest values in males. The sex ratio was 1:1.5 (males:females), which deviates significantly from the expected 1:1 ratio. The mean length of sexual maturity (Lm50) was 18.0 cm in females and 20.1 cm in males, reflecting that females mature at smaller sizes than males. The monthly variations of the gonadosomatic index (GSI) and the stages of sexual maturity show two reproductive peaks during the study, in October 2017 and April 2018, coinciding with the rainy and dry seasons in the region respectively. The condition factor (CF) showed significant differences between months, but not between sexes, with an average of 1.87 in females and 1.84 in males. The average absolute fecundity was 921 ± 604.6 eggs per fish, with a relative fecundity of 8.36 ± 3.09 eggs per gram of fish. Differences in oocyte size in mature females confirm that the species can spawn repeatedly over a period, which is considered an important factor for the establishment of tilapia in non-native environments.

The life history consequences of host switching in Ooencyrtus egeria (Hymenoptera: Encyrtidae), a parasitoid of stink bug eggs.

The stink bugs Acrosternum arabicum Wagner and Brachynema germari Kolenati (Hemiptera: Pentatomidae) damage developing pistachio nuts in Iran. Ooencyrtus egeria Huang and Noyes (Hymenoptera: Encyrtidae) parasitizes eggs of both species, alternating between them seasonally. We compared the biological and life history attributes of O. egeria reared for 3 generations on each host species with those that had been transferred to the alternate host for 2 generations. We also tested female responses to host egg density. Eggs of B. germari were parasitized at higher rates and yielded faster wasp development, heavier female progeny with greater fecundity, and a more female-biased sex ratio, than eggs of A. arabicum. Rearing on A. arabicum did not diminish wasp fitness on B. germari, and the F1 progeny of wasps switched to A. arabicum inherited some beneficial parental effects from rearing on B. germari. Regardless of host species, females parasitized fewer eggs in 8 h as density increased from 10 to 30 eggs, but progeny sex ratio (% female) increased. The anomalous response to host density appears to arise from a combination of behavioral and egg load constraints. Females mature only 10-12 eggs per day. Carefully inspect egg clusters before selecting the most suitable eggs for oviposition, a more time-consuming process for large clusters. Our results indicate that rearing O. egeria on eggs of A. arabicum, which are more convenient and cost-effective to produce than those of B. germari, will not diminish its performance on B. germari following augmentative release, beyond a slight reduction in female fecundity.

Non-Mendelian transmission of X chromosomes: mechanisms and impact on sex ratios and population dynamics in different breeding systems.

The non-Mendelian transmission of sex chromosomes during gametogenesis carries significant implications, influencing sex ratios and shaping evolutionary dynamics. Here we focus on known mechanisms that drive non-Mendelian inheritance of X chromosomes during spermatogenesis and their impact on population dynamics in species with different breeding systems. In Drosophila and mice, X-linked drivers targeting Y-bearing sperm for elimination or limiting their fitness, tend to confer unfavourable effects, prompting the evolution of suppressors to mitigate their impact. This leads to a complex ongoing evolutionary arms race to maintain an equal balance of males and females. However, in certain insects and nematodes with XX/X0 sex determination, the preferential production of X-bearing sperm through atypical meiosis yields wild-type populations with highly skewed sex ratios, suggesting non-Mendelian transmission of the X may offer selective advantages in these species. Indeed, models suggest X-meiotic drivers could bolster population size and persistence under certain conditions, challenging the conventional view of their detrimental effects. Furthering our understanding of the diverse mechanisms and evolutionary consequences of non-Mendelian transmission of X chromosomes will provide insights into genetic inheritance, sex determination, and population dynamics, with implications for fundamental research and practical applications.

Socially plastic responses in females are robust to evolutionary manipulations of adult sex ratio and adult nutrition.

Socially plastic behaviours are widespread among animals and can have a significant impact on fitness. Here, we investigated whether the socially plastic responses of female Drosophila melanogaster can evolve in predictable ways following long-term manipulation of adult sex ratio and adult nutrient availability. Previous reports show that female D. melanogaster respond plastically to their same-sex social environment and lay significantly fewer eggs after mating when previously exposed to other females. In this study, we tested 2 hypotheses, using females drawn from lines with an evolutionary history of exposure to variation in adult sex ratio (male-biased, female-biased or equal sex ratio) and adult nutritional environment (high or low quality). The first was that a history of elevated competition in female-biased regimes would select for increased plastic fecundity responses in comparison to females from other lines. The second was that these responses would also be magnified under poor nutritional resource regimes. Neither hypothesis was supported. Instead, we found that plastic fecundity responses were retained in females from all lines and did not differ significantly across any of them. The lack of differences does not appear to be due to insufficient selection, as we did observe significant evolutionary responses in virgin egg-laying patterns according to sex ratio and nutritional regime. The lack of variation in the magnitude of predicted plasticity is consistent with the idea that the costs of maintaining plasticity are low, benefits high, and that plasticity itself can be relatively hard wired.

Transformation of meiotic drive into hybrid sterility in Drosophila.

Hybrid male sterility is one of the fastest evolving intrinsic reproductive barriers between recently isolated populations. A leading explanation for the evolution of hybrid male sterility involves genomic conflicts with meiotic drivers in the male germline. There are, however, few examples directly linking meiotic drive to hybrid sterility. In this study, we report that the Sex-Ratio chromosome of Drosophila pseudoobscura, which causes X-chromosome drive within the USA subspecies, causes near-complete male sterility when it is moved into the genetic background of the Bogota subspecies. In addition, we show that this new form of sterility is genetically distinct from the sterility of F1 hybrid males in crosses between USA males and Bogota females. Our observations provide a tractable study system where noncryptic drive within species is transformed into strong hybrid sterility between very young subspecies.