Influence Sex Ratio Research Articles

Janzen-Connell effects shape gene flow patterns and realized fitness in the tropical dioecious tree Spondias purpurea (ANACARDIACEAE)

Pollination and seed dispersal patterns determine gene flow within plant populations. In tropical forests, a high proportion of trees are dioecious, insect pollinated and dispersed by vertebrates. Dispersal vectors and density dependent factors may modulate realized gene flow and influence the magnitude of Fine Scale Genetic Structure (FSGS), affecting individual fitness. Spondias purpurea is a vertebrate-dispersed, insect-pollinated dioecious tropical tree. We assessed the influence of sex ratio, effective and realized gene flow on genetic diversity, FSGS and individual fitness within a 30 ha plot in the tropical dry forest reserve of Chamela-Cuixmala, Mexico. All individuals within the plot were tagged, geo-referenced and sampled for genetic analysis. We measured dbh and monitored sex expression during two reproductive seasons for all individuals. We collected seeds directly from maternal trees for effective pollen dispersal analysis, and analyzed established seedlings to assess realized pollen and seed dispersal. Nine microsatellite loci were used to describe genetic diversity parameters, FSGS and gene flow patterns among different size classes. A total of 354 individuals were located and classified into three size classes based on their dbh (<10, 10–20, and >20 cm). Population sex ratios were male biased and diametric size distributions differed among sexes, these differences may be the result of precocious male reproduction at early stages. Autocorrelation analyses indicate low FSGS (Fj <0.07) across all size classes. Long realized pollen and seed dispersal and differences among effective and realized gene flow were detected. In our study site low FSGS is associated with high gene flow levels. Effective and realized gene flow indicate a population recruitment curve indicating Janzen-Connell effects and suggesting fitness advantages for long-distance pollen and seed dispersal events.

Does operational sex ratio influence relative strength of purging selection in males versus females?

According to theory, sexual selection in males may efficiently purge mutation load of sexual populations, reducing or fully compensating 'the cost of males'. For this to occur, mutations not only need to be deleterious to both sexes, they also must affect males more than females. A frequently overlooked problem is that relative strength of selection on males versus females may vary between environments, with social conditions being particularly likely to affect selection in males and females differently. Here, we induced mutations in red flour beetles (Tribolium castaneum) and tested their effect in both sexes under three different operational sex ratios (1:2, 1:1 and 2:1). Induced mutations decreased fitness of both males and females, but their effect was not stronger in males. Surprisingly, operational sex ratio did not affect selection against deleterious mutations nor its relative strength in the sexes. Thus, our results show no support for the role of sexual selection in the evolutionary maintenance of sex.

Mechanisms that influence sex ratio variation in the invasive hymenopteran Sirex noctilio in South Africa.

Sirex noctilio is an economically important invasive pest of commercial pine forestry in the Southern Hemisphere. Newly established invasive populations of this woodwasp are characterized by highly male‐biased sex ratios that subsequently revert to those seen in the native range. This trend was not observed in the population of S. noctilio from the summer rainfall regions in South Africa, which remained highly male‐biased for almost a decade. The aim of this study was to determine the cause of this persistent male bias. As an explanation for this pattern, we test hypotheses related to mating success, female investment in male versus female offspring, and genetic diversity affecting diploid male production due to complementary sex determination. We found that 61% of females in a newly established S. noctilio population were mated. Microsatellite data analysis showed that populations of S. noctilio from the summer rainfall regions in South Africa are far less genetically diverse than those from the winter rainfall region, with mean Nei's unbiased gene diversity indexes of 0.056 and 0.273, respectively. These data also identified diploid males at low frequencies in both the winter (5%) and summer (2%) rainfall regions. The results suggest the presence of a complementary sex determination mechanism in S. noctilio, but imply that reduced genetic diversity is not the main driver of the male bias observed in the summer rainfall region. Among all the factors considered, selective investment in sons appears to have the most significant influence on male bias in S. noctilio populations. Why this investment remains different in frontier or early invasive populations is not clear but could be influenced by females laying unfertilized eggs to avoid diploid male production in populations with a high genetic relatedness.

Effect of PPO-Inhibiting Herbicides on the Growth and Sex Ratio of a Dioecious Weed Species Amaranthus palmeri (Palmer Amaranth)

Amaranthus palmeri S. Watson (Palmer amaranth) is a fast-growing, dioecious, highly competitive agricultural weed species, which is spreading across the US Midwest. Population sex ratios are an important consideration in the management of A. palmeri populations as this species has become resistant to several herbicide sites of action, and there is need to minimize seed production by female plants. Environmental conditions, particularly stressors, may influence sex ratios, and herbicides act as major stressors and evolutionary filters in agricultural fields. Amaranthus spp. have shown a tendency for rapid evolution of herbicide resistance, with the frequency of protoporphyrinogen oxidase (PPO)-inhibitor resistance increasing across the Midwestern US. A greenhouse experiment was conducted to investigate the effect of two PPO-inhibiting herbicide treatments of either lactofen or fomesafen on four different Illinois populations (Cahokia, Collinsville, Rend Lake, and Massac). Plants raised from seed from the Massac population were tallest, and both males and females from this population also had the highest vegetative biomass. Female plants from the Collinsville population had more reproductive biomass than male plants. Control populations were male-biased (Cahokia, Collinsville), female-biased (Masaac), and 1:1 (Rend Lake). Lactofen shifted the male-biased populations to female-biased or 1:1 and the female-biased population to 1:1. Fomesafen-treated populations were male-biased or 1:1. This study suggests that PPO-inhibiting herbicide treatments may influence the growth and sex ratio of A. palmeri populations, which is an underlying factor in the rate of herbicide evolution in this species. An understanding of the underlying mechanisms of how external factors influence sex ratios may eventually provide an opportunity to reduce seed production in populations by shifting sex ratios towards a male bias.

Optimization of black soldier fly (Hermetia illucens) artificial reproduction.

The black soldier fly (BSF), Hermetia illucens (L., 1758) (Diptera: Stratiomyidae), is an endemic fly species from the tropical, subtropical and warm temperate zones of America. This saprophagous species relies on its environment where it finds the decomposing matter for the larvae to grow. The polyphagous diet and the macronutrient quality (mainly lipids and proteins) of these larvae make them excellent candidates for various applications such as waste and organic material management, incorporation in animal feed or alternative energy source. Although rearing development in temperate regions requires artificial processes to continuously produce high quality eggs and larvae, few studies have been conducted on the mating and oviposition processes governing H. illucens reproduction. Research conducted in semi-artificial rearing conditions showed that the number of mating varied according to the season. It has been speculated that this behavior could be due to differences in the intensity of sunlight caused by the change of seasons. This study aims at evaluating the influence of sex-ratio, density and nycthemeral cycle on H. illucens reproduction. In order to tackle this issue, an artificial set up for oviposition to collect eggs has been developed. This egg collection system aims at centralize oviposition and simplify eggs collection. Two populations with opposite sex-ratio (male-dominant and female-dominant) were selected. Their respective eggs productions have been evaluated for five breeding densities. Eggs weights varied significantly among the densities for each opposite sex-ratio population and female dominant population produced most eggs weight from 6500 individuals /m3. Finally, four nycthemeral cycles (2, 6, 12 and 18h of daily light) were simulated to evaluate the impact of light duration on reproduction. Early oviposition pic associated with a decrease of the oviposition period are shown when H. illucens are exposed to increasing light duration. These experiments enable improvement of the understanding on artificial reproduction of H. illucens.

Altered Sex Ratios in Offspring of U.S. Submariners Urban Legend or Fact - Do Submariners Have More Daughters?

There is a widespread and long-held belief in the submarine community that submariners father more daughters than the general population. The U.S. Sex Ratio at birth (males/females) has remained around 1.05 since the early 2000s. Limited evidence exists that certain environmental exposures including chemicals, heavy metals, radiation and g-forces may influence sex ratio at birth. A reduction in male births in a population has been associated with lower male fertility. A 1970 single site study showed a higher ratio of female offspring in personnel serving aboard U.S. Navy nuclear submarines than the general population. A 2004 study concluded that this was probably not true. However, this study was small, and did not evaluate the difference between children conceived during sea duty versus shore duty. They did note a higher chance of female offspring correlated with a longer time in the community, as well as an increased ratio in sonar technicians. These findings warrant further investigation. An electronic survey was e-mailed to submariners, after receiving required IRB and Navy approvals. Participants were asked birth year, year they entered submarine service, and how many children they had. For each child they were asked sex, child's birth year, mother's birth year, and whether they were on sea duty or shore duty at the time of conception. Those who were on sea duty at the time of conception were asked what their job was, where they were stationed and what type of submarine they were on. Those who were on shore duty at the time of conception were asked whether they were in contact with submarines on a regular basis, whether they were officer or enlisted, and what region they were stationed in for shore duty. Four thousand eight hundred responses were received with a total of 6,958 children included in the analysis. Respondents had a SR of 0.95 compared to 1.05 U.S. population in 2015 (p < 0.0001). Submariners on sea duty had a SR of 0.88 compared to 1.02 on shore duty (p = 0.007). Those who had regular submarine contact on shore duty had a SR of 0.72 compared to 1.17 in those who did not (p < 0.001). Geographical location during shore duty did show differences that were statistically significant (p = 0.018). Geographical location during sea duty did not show significant differences. No significant differences were seen for paternal age, maternal age, job during sea duty, type of submarine assigned to or time in community. The submariners surveyed reported greater numbers of daughters than the general population, especially when on sea duty or in regular contact with submarines during shore duty. Further study should be done to confirm results and explore possible etiologies of differences in sex ratio.

Individual variation and the source-sink group dynamics of extra-group paternity in a social mammal.

Movement of individuals, or their genes, can influence eco-evolutionary processes in structured populations. We have limited understanding of the extent to which spatial behavior varies among groups and individuals within populations. Here, we use genetic pedigree reconstruction in a long-term study of European badgers (Meles meles) to characterize the extent of extra-group paternity, occurring as a consequence of breeding excursions, and to test hypothesized drivers of variation at multiple levels. We jointly estimate parentage and paternity distance (PD; distance between a cub’s natal and its father’s social group), and test whether population density and sex ratio influence mean annual PD. We also model cub-level PD and extra-group paternity (EGP) to test for variation among social groups and parental individuals. Mean PD varied among years but was not explained by population density or sex ratio. However, cub-level analysis shows strong effects of social group, and parental identities, with some parental individuals being consistently more likely to produce cubs with extra-group partners. Group effects were partially explained by local sex ratio. There was also a strong negative correlation between maternal and paternal social group effects on cub paternity distance, indicating source-sink dynamics. Our analyses of paternity distance and EGP indicate variation in extra-group mating at multiple levels—among years, social groups and individuals. The latter in particular is a phenomenon seldom documented and suggests that gene flow among groups may be disproportionately mediated by a nonrandom subset of adults, emphasizing the importance of the individual in driving eco-evolutionary dynamics.

How do long-term effects of temperature influence sex ratio, somatic and gonadal development in juvenile sterlet (Acipenser ruthenusL.)-An additional climate change consequence?

In this paper, the effects of temperature on the production performance values, as well as on sex differentiation and gonad development, of juvenile sterlet were investigated. For this purpose, fry were reared in the recirculating aquaculture system at three different temperatures (15, 20, and 25°C) in four replicate groups each for 140 days (10–150 dph). Fish were fed mainly with commercial diet. The growth rate in this period was significantly affected by temperature. The best performance values in terms of daily growth rate, thermal growth coefficient, and yield were registered at 20°C, indicating that this value to be near, or close to, the optimal for juvenile sterlet. Gonad samples were taken for histological analysis which revealed that the increased temperature did not cause significant differences in the sex ratio between treatments, but at 25°C resulted in significant deviation from the theoretically expected 1:1 gender ratio to favouring males. We have also found that increased temperature at 25°C accelerated germ cell development. These results indicate that rearing of sterlet juveniles at about 20°C temperature could be considered optimal both from aquaculture, as well as from species conservation viewpoints.

Major global changes interact to cause male-biased sex ratios in a reptile with temperature-dependent sex determination

Habitat loss and pollution are two of the greatest global threats to biodiversity. Due to their widespread prevalence, these threats often co-occur, yet their interactive effects on organisms remain poorly understood. Some reptiles are vulnerable to these threats because they have specific microclimate requirements for embryonic development and because pollutants are maternally transferred to their eggs; both incubation temperature and pollutants affect reptile sex determination. In aquatic turtles, females often select nest sites in recently planted agricultural fields but the impact of nesting in polluted agricultural habitats is not understood. We examined the influences of crop agriculture and mercury pollution on nest microclimate and offspring sex ratios of Chelydra serpentina. We hypothesized that crop growth in agricultural fields would shade and cool turtle nests, decrease moisture levels, increase male offspring production, and interact with maternally-derived mercury to impact sex determination. As predicted, nests shaded by crops had lower average temperatures (−2.5 °C) and moisture levels (−107 kPa) than control nests. In field and laboratory experiments, agricultural thermal regimens increased the proportion of male offspring in clutches and this effect was intensified in the presence of mercury. Global temperatures are expected to rise within the 21st century and to have a feminizing effect on reptiles with temperature-dependent sex determination. That prediction should be refined to incorporate how the cooling effect of some local habitat conditions (e.g., agricultural fields), and interactions between anthropogenic land-use and common pollutants, will interact with climate change to influence sex ratios of reptiles with temperature-dependent sex determination.

The influence of sex ratio on the reproduction of pirarucu, Arapaima gigas, in captivity

ABSTRACT Because sex ratio in the broodstock can influence the reproductive behaviour of a species, the influence of sex ratio on the reproductive success of pirarucu, Arapaima gigas, in captivity was assessed. Pirarucu breeders were stocked in 0.10-0.13 ha earthen ponds at three sex ratios in quadruplicate: one male to one female (1M1F); one male to two females (1M2F); and two males to one female (2M1F). Eight spawning events occurred, seven of them with the 1M1F sex ratio, which was the most successful of the three tested sex ratios.

Reprint to: Phosphate starvation during the transition phase increases the sex ratio and 12-oxo-phytodienoic acid contents in females of Urtica dioica

The transition phase in plants, which is marked by the onset of flowering and seed production, is very sensitive to the physical environment. Moreover, dimorphic plant species can show important sex-related differences in the response to nutrient availability. How availability of inorganic phosphate (Pi) during the transition phase influences sex ratios and whether or not male and female plants respond differently to nutrient stress is still however very poorly understood. Here, we examined whether contrasting Pi availability during the transition phase may influence sexual differentiation in stinging nettle (U. dioica L.) plants. We also evaluated to what extent males and females respond differently to varying Pi concentrations in terms of nutrient accumulation, C and N isotopic composition, photo-oxidative stress and hormone profiling. Results showed that reduced Pi availability delays plant maturation in males, causing as well an increase in the sex ratio towards females. Females showed enhanced lipid peroxidation (as indicated by higher lipid hydroperoxide contents) compared to males under Pi starvation, but sexes did not differ in photosystem II efficiency. Furthermore, reduced Pi availability led to enhanced 12-oxo-phytodienoic acid contents, the immediate precursor of jasmonic acid, particularly in females. This increase was, however, not accompanied by increases in other jasmonates, neither free nor conjugated jasmonic acid, thus suggesting a specific role for 12-oxo-phytodienoic acid in chemical defense in females under Pi starvation. Sex biased ratios in favour of females over males and enhanced 12-oxo-phytodienoic acid contents in the former under Pi starvation illustrate the great adaptive capacity of dimorphic species to reduced nutrient availability.

Elevated pCO2 is less detrimental than increased temperature to early development of the giant kelp, Macrocystis pyrifera (Phaeophyceae, Laminariales)

:Global climate change is increasing ocean temperature and partial pressure of CO2 (pCO2) in coastal and marine ecosystems. Research in this field has largely focused on how limited CO32− availability and low pH adversely affect early development of calcifying organisms, but noncalcareous organisms are comparatively understudied despite their prevalence in many coastal communities. We investigated how present-day and future levels of ocean temperature (12°C vs 15°C, respectively) and pCO2 (400 μatm vs 1500 μatm, respectively) influence successful germling production, gametophyte survival, growth, and sex ratio, and embryonic sporophyte production and growth in the habitat-forming kelp Macrocystis pyrifera over a 15-wk period in San Diego, California, USA. Our results indicate that relative to present-day conditions, successful germling production was reduced fourfold under elevated temperature alone, and fivefold under combined elevated temperature and pCO2 (i.e. “future conditions”). Similarly, survival and growth of male and female gametophytes were lower under elevated temperature alone than under either present-day, elevated pCO2 alone, or future conditions. Gametophyte sex ratios skewed slightly toward males across all treatments. Sporophyte recruitment and growth were greatest and occurred earliest under elevated pCO2 alone, but were delayed under elevated temperature alone. Although elevated pCO2 and temperature adversely affected germling production independently and cumulatively, elevated pCO2 enhanced gametophyte and sporophyte survival under both present-day and elevated temperatures. Thus, under projected climate change conditions, elevated pCO2 may be less detrimental than increased temperature for development beyond germling production. Given that M. pyrifera is globally distributed and provides numerous ecosystem services including the potential to mitigate ocean acidification, impacts of climate change on its complex life history merit further exploration.

Fertility behaviors in South Korea and their association with ultrasound prenatal sex screening

Imbalances in the sex ratio at birth in Southeast and East Asia increased especially after the mid-1980s. We study how ultrasonic technology affected sex ratios at birth in South Korea, a country with a strong son preference. Between 1985 and 1995 fetal screenings and abortion services were widely available, though not available in the years before, and prohibited in the years after. Using the 1985, 1995, and 2005 Census microdata, we examine changes in sex ratios of newborns by birth year. We then study periodic effects on the fertility stopping rule, using the 2006 Korean Longitudinal Study of Aging, which provides birth years for all children. Between 1985 and 1995 there was a large increase in the fraction of boy babies at birth orders of three or more. Despite these fractions falling in the subsequent time period when fetal screening became illegal, they remained above plausible biological levels. Supporting earlier findings in the literature, the increase in sex ratios was especially large when prior sibling composition was entirely female. We also find that having only daughters significantly increases the probability of parents having another child, and this effect is greater for parents with any child born after 1985 than the parents with all children born before 1985. There exist significant period effects, suggesting that sex ratios at birth became imbalanced when ultrasound technology became available. The availability of ultrasound technology also influenced parents’ fertility decisions, seen especially in parents with only daughters deciding to have another child. Our study provides new evidence for how the availability of ultrasound technology influenced sex ratios at birth and influenced fertility behaviors in Korea.

Phosphate starvation during the transition phase increases the sex ratio and 12-oxo-phytodienoic acid contents in females of Urtica dioica

The transition phase in plants, which is marked by the onset of flowering and seed production, is very sensitive to the physical environment. Moreover, dimorphic plant species can show important sex-related differences in the response to nutrient availability. How availability of inorganic phosphate (Pi) during the transition phase influences sex ratios and whether or not male and female plants respond differently to nutrient stress is still however very poorly understood. Here, we examined whether contrasting Pi availability during the transition phase may influence sexual differentiation in stinging nettle (U. dioica L.) plants. We also evaluated to what extent males and females respond differently to varying Pi concentrations in terms of nutrient accumulation, C and N isotopic composition, photo-oxidative stress and hormone profiling. Results showed that reduced Pi availability delays plant maturation in males, causing as well an increase in the sex ratio towards females. Females showed enhanced lipid peroxidation (as indicated by higher lipid hydroperoxide contents) compared to males under Pi starvation, but sexes did not differ in photosystem II efficiency. Furthermore, reduced Pi availability led to enhanced 12-oxo-phytodienoic acid contents, the immediate precursor of jasmonic acid, particularly in females. This increase was, however, not accompanied by increases in other jasmonates, neither free nor conjugated jasmonic acid, thus suggesting a specific role for 12-oxo-phytodienoic acid in chemical defense in females under Pi starvation. Sex biased ratios in favour of females over males and enhanced 12-oxo-phytodienoic acid contents in the former under Pi starvation illustrate the great adaptive capacity of dimorphic species to reduced nutrient availability.

Socioeconomic status influences sex ratios in a Chinese rural population

According to the logic of the Trivers–Willard hypothesis, in a human population, if socioeconomic status is transmitted across generations to some extent, and if sons of high-status parents tend to have higher reproductive success than daughters, while daughters of low-status parents tend to have higher reproductive success than sons, then we should expect that offspring sex ratio is positively associated with socioeconomic status. This study examines whether the assumptions and prediction of this hypothesis apply to a rural population in northern China. Results show that (1) current family socioeconomic status is positively related to family head’s father’s socioeconomic status in around 1950, (2) low-status family heads have more grandchildren through their daughters than their sons, whereas high- or middle-status family heads have more grandchildren through sons, and (3) as family heads’ status increases, they tend to produce a higher offspring sex ratio. Therefore, the assumptions and prediction of the hypothesis are met in the study population. These results are discussed in reference to past studies on sex ratio manipulation among humans.

Sex Ratios, Single Motherhood, and Gendered Structural Relations: Examining Female-Headed Families Across Racial-Ethnic Populations

ABSTRACTSex ratio research often ignores how structural inequalities influence sex ratio effects. Employing decomposition analysis and using standardized U.S. Census tract data from 1970 to 2000, this research investigates how adult sex ratio effects predict the proportion of single parenting women among White, Black, and Hispanic/Latino populations, examining both main and conditional effects of sex ratios on female-headed families. Analyses reveal that main sex ratio effects consistently predict the proportion of single mothers across all racial-ethnic groups, but the conditional effect of gender-distributed labor force participation differentially influences sex ratio effects across race-ethnicities. Specifically, relative labor force participation consistently weakens the sex ratio effects on female headship among Whites. However, the relative female employment alters sex ratio effects among Blacks only when examining the same area over time, and it does not alter sex ratio effects among Hispanic/Latino populations. Findings underscore the importance of understanding family as a sociopolitical phenomenon.

Live birth sex ratios and father's geographic origins in Jerusalem, 1964-1976.

To examine whether ancestry influenced sex ratios of offspring in a birth cohort before parental antenatal sex selection influenced offspring sex. We measured the sex ratio as the percent of males according to countries of birth of paternal and maternal grandfathers in 91,459 live births from 1964 to 1976 in the Jerusalem Perinatal Study. Confidence limits (CI) were computed based on an expected sex ratio of 1.05, which is 51.4% male. Of all live births recorded, 51.4% were male. Relative to Jewish ancestry (51.4% males), significantly more males (1,761) were born to Muslim ancestry (54.5, 95% CI = 52.1-56.8, P = 0.01). Among the former, sex ratios were not significantly associated with paternal or maternal age, education, or offspring's birth order. Consistent with a preference for male offspring, the sex ratio decreased despite increasing numbers of births over the 13-year period. Sex ratios were not affected by maternal or paternal origins in North Africa or Europe. However, the offspring whose paternal grandfathers were born in Western Asia included fewer males than expected (50.7, 50.1-51.3, P = 0.02), whether the father was born abroad (50.7) or in Israel (50.8). This was observed for descendents of paternal grandfathers born in Lebanon (47.6), Turkey (49.9), Yemen & Aden (50.2), Iraq (50.5), Afghanistan (50.5), Syria (50.6), and Cyprus (50.7); but not for those from India (51.5) or Iran (51.9). The West Asian group showed the strongest decline in sex ratios with increasing paternal family size. A decreased sex ratio associated with ancestry in Western Asia is consistent with reduced ability to bear sons by a subset of Jewish men in the Jerusalem cohort. Lower sex ratios may be because of pregnancy stress, which may be higher in this subgroup. Alternatively, a degrading Y chromosome haplogroup or other genetic or epigenetic differences on male germ lines could affect birth ratios, such as differential exposure to an environmental agent, dietary differences, or stress. Differential stopping behaviors that favor additional pregnancies following the birth of a daughter might exacerbate these lower sex ratios.

Local population density and group composition influence the signal-preference relationship in Enchenopa treehoppers (Hemiptera: Membracidae).

Many animals exhibit social plasticity - changes in phenotype or behaviour in response to experience with conspecifics that change how evolutionary processes like sexual selection play out. Here, we asked whether social plasticity arising from variation in local population density in male advertisement signals and female mate preferences influences the form of sexual selection. We manipulated local density and determined whether this changed how the distribution of male signals overlapped with female preferences - the signal preference relationship. We specifically look at the shape of female mate preference functions, which, when compared to signal distributions, provide hypotheses about the form of sexual selection. We used Enchenopa binotata treehoppers, a group of plant-feeding insects that exhibit natural variation in local densities across individual host plants, populations, species and years. We measured male signal frequency and female preference functions across the density treatments. We found that male signals varied across local social groups, but not according to local density. By contrast, female preferences varied with local density - favouring higher signal frequencies in denser environments. Thus, local density changes the signal-preference relationship and, consequently, the expected form of sexual selection. We found no influence of sex ratio on the signal-preference relationship. Our findings suggest that plasticity arising from variation in local group density and composition can alter the form of sexual selection with potentially important consequences both for the maintenance of variation and for speciation.

Genetic markers provide insight on origins of immature green turtles Chelonia mydas with biased sex ratios at foraging grounds in Sabah, Malaysia

An understanding of population dynamics is needed to assess the viability of migra- tory species. Monitoring of marine turtles at foraging grounds may detect changes in population trends that would take decades to be seen at nesting beaches. Mixed Stock Analysis using molec- ular markers provides a tool for estimating the origin of turtles sampled at foraging grounds. Here, we analysed mitochondrial DNA sequences of 90 immature green turtles at 2 foraging grounds in northwestern Sabah, Malaysia. We used data from 30 Indo-Pacific green turtle rookeries as the baseline for tracing the origin of turtles at the 2 foraging grounds. The inferred origins of turtles at the 2 locations were not different and indicated that the majority originated from 3 major popula- tions in Southeast Asia, the Turtle Islands of Sarawak in northwestern Borneo (29%), the Turtle Islands Heritage Protected Area (TIHPA) (28%) and Peninsular Malaysia (25%). Previous analy- ses indicated a 1:4 female-biased sex ratio at the foraging grounds, and based on our results, this largely reflects the use of unshaded beach hatcheries at some of the source rookeries for decades, which resulted in mostly female hatchlings. This result is supported by differences in the origins of male and female turtles. The result suggests a greater proportion of males originating from Peninsular Malaysia and fewer males originating from Sarawak and possibly the TIHPA com- pared to females. We discuss the implications of hatchery practices that influence sex ratios of hatchlings and recommend future research to improve the management of marine turtles in the region.

Incomplete offspring sex bias in Australian populations of the butterfly Eurema hecabe.

Theory predicts unified sex ratios for most organisms, yet biases may be engendered by selfish genetic elements such as endosymbionts that kill or feminize individuals with male genotypes. Although rare, feminization is established for Wolbachia-infected Eurema butterflies. This paradigm is presently confined to islands in the southern Japanese archipelago, where feminized phenotypes produce viable all-daughter broods. Here, we characterize sex bias for E. hecabe in continental Australia. Starting with 186 wild-caught females, we reared >6000 F1-F3 progeny in pedigree designs that incorporated selective antibiotic treatments. F1 generations expressed a consistent bias across 2 years and populations that was driven by an ~5% incidence of broods comprising ⩾80% daughters. Females from biased lineages continued to overproduce daughters over two generations of outcrossing to wild males. Treatment with antibiotics of differential strength influenced sex ratio only in biased lineages by inducing an equivalent incomplete degree of son overproduction. Brood sex ratios were nevertheless highly variable within lineages and across generations. Intriguingly, the cytogenetic signature of female karyotype was uniformly absent, even among phenotypic females in unbiased lineages. Molecular evidence supported the existence of a single Wolbachia strain at high prevalence, yet this was not clearly linked to brood sex bias. In sum, we establish an inherited, experimentally reversible tendency for incomplete offspring bias. Key features of our findings clearly depart from the Japanese feminization paradigm and highlight the potential for more subtle degrees of sex distortion in arthropods.