Biased Sex Ratios Research Articles

Endophytic colonization of sugar beet by Beauveria varroae and Beauveria bassiana reduces performance and host preference in army worm, Spodoptera littoralis

Spodoptera littoralis (Lepidoptera: Noctuidae) Boisduval 1833 is a voracious leaf feeder and major agricultural pest attacking numerous crops. Development of insecticide resistance hampers management efforts for S. littoralis and entomopathogenic fungi represent one possible alternative management tool. Here, we quantified colonization of sugar beet, Beta vulgaris L, with two fungal entomopathogens, Beauveria varroae Vuillemin 1912 and Beauveria bassiana (Balsamo) Vuillemin 1912 (Ascomycota: Hypocreales), and examined their endophytic effects on biological and reproductive parameters of S. littoralis. Two methods were used to inoculate sugar beet: soaking seeds in spore suspension and spray application of conidia onto leaves. For both methods, fungal suspensions with concentrations of 1 × 104 and 1 × 108 conidia/ml colonized roots, stems, and leaves of sugar beet. The colonization rate increased over time. Following inoculation of seeds, weight gain of S. littoralis larvae fed on leaves infected with endophytic fungi was reduced compared with controls. Furthermore, protease and lipase activities in the gut of S. littoralis decreased with increasing concentration of fungus applied to plants. An increase in phenol oxidase activity in the gut also indicated increased defense response of larvae feeding on Beauveria-infected leaves. Both B. bassiana and B. varroae decreased the duration of larval and pupal stages, adult emergence, and oviposition by females. Incubation of sugar beet seeds with B. varroae or B. bassiana decreased survival of pupae and egg laying by female moths on endophyte-infested treatments by 30 and 50%, respectively, compared with controls. Furthermore, an initially female biased sex ratio decreased toward 50:50 over time in populations of S. littoralis reared on sugar beet colonized by fungal endophytes as compared with controls, which remained female-biased. Endophyte inoculation increased growth of sugar beet compared with controls. Our results indicate that B. bassiana and B. varroae affect survival of S. littoralis and may be useful for management of this pest.

Male reproductive success is not strongly affected by phenological changes in mate availability in monoecious Sagittaria latifolia.

Many plants express their female and male sex roles at different times (dichogamy), with important consequences for mating. Dichogamy can yield mate limitation via biased floral sex ratios, particularly at the beginning and end of the flowering season when many plants simultaneously function as the same sex. This form of mate limitation should be reduced if plants adjust their allocations to female versus male sex functions in a manner that tracks seasonal variability in mating opportunities. For example, under protogyny (i.e. dichogamy with female function expressed first) plants with male-biased sex expression should have enhanced mating opportunities early in the flowering season as other plants begin to flower (in female sex phase). We quantified seasonal changes in sex allocation, patterns of mate availability and realized siring success in a population of protogynous Sagittaria latifolia. Our results were consistent with previous findings that seasonal changes in sex allocation should compensate for lost mating opportunities under the temporally variable mating environments caused by dichogamy. However, patterns of siring success in the population were inconsistent with this interpretation. We suggest that realized siring success might depend more strongly on spatial than on temporal aspects of mate availability.

Plasticity and the adaptive evolution of switchlike reaction norms under environmental change.

Phenotypic plasticity is often posited as an avenue for adaptation to environmental change, whereby environmental influences on phenotypes could shift trait expression toward new optimal values. Conversely, plastic trait expression may inhibit adaptation to environmental change by reducing selective pressure on ill-adapted traits. While plastic responses are often assumed to be linear, nonlinear phenotype-environment relationships are common, especially in thermally sensitive traits. Here we examine nonlinear plasticity in a trait with great ecological and evolutionary significance: sexual phenotype in species with environmental sex determination (ESD). In species with ESD, development switches between male and female at an environmental threshold (the inflection point). The inflection point is a key trait for adaptive responses to changing environments and should evolve toward the new optimum in order to maintain evolutionarily stable sex ratios. We used an individual-based theoretical model to investigate how two forms of plasticity in the ESD reaction norm-the nonlinear slope of the reaction norm and a linear shift in the inflection point-influence the evolution of the inflection point under climate warming. We found that steeper reaction norm slopes (high nonlinear plasticity) promoted evolution toward new optimal phenotypes (higher inflection points). In contrast, increased linear plasticity in the inflection point (shift) hindered adaptive evolution. Additionally, populations in moderate warming scenarios showed greater adaptive evolution of the inflection point compared with populations in extreme warming scenarios, suggesting that the proximity of existing phenotypes to new optimal phenotypes influences evolutionary outcomes. Unexpectedly, we found greater population persistence under high climate variability, due to the increased production of rare-sex individuals in unusually cold years. Our results demonstrate that different forms of phenotypic plasticity have crucially different effects on adaptive evolution. Plasticity that prevented sex ratio bias hindered the evolution of the inflection point, while plasticity that exacerbated sex ratio bias promoted adaptation to environmental change.

Parental effects on offspring sex ratio in the Numbat (Myrmecobius fasciatus): does captivity influence paternal sex allocation?

Sex allocation theories predict that under different ecological conditions the production of sons and daughters will affect parental fitness differently. Skewed offspring sex ratios often occur under captive conditions where individuals are exposed to nutritional and social conditions that differ from nature. Here, we analyzed 29 years of offspring sex ratio data from a captive population of an endangered marsupial, the Numbat (Myrmecobius fasciatus). We partitioned variation in offspring sex ratio based on parental origin (captive- vs. wild-bred), parental weight, maternal age, and maternal reproductive history. Our analyses revealed no effect of parental weight or maternal origin on offspring sex ratio-however, there was a significant effect of paternal origin. Data visualization indicated that captive-bred males tended to produce male-biased litters. We discuss the result in relation to recent studies that have shown that male mammals have the capacity to be arbiters of sex allocation and highlight candidate mechanisms, but consider it with caution due to the small sample size from which the result was derived. We performed a population viability analysis (PVA) to explore the potential impact of a sex ratio skew on the sustainability of the captive Numbat population under hypothetical scenarios. Our PVA revealed that supplementation with wild individuals is critical to the persistence of the captive Numbat population and that a biased sex ratio will lead to extinction of the captive colony under certain conditions. Overall, our study demonstrates that covert sex ratio skews can persist undetected in captive populations, which have the potential to become impactful and compromise population sustainability under changed management processes.

Clonality, local population structure and gametophyte sex ratios in cryptic species of the Sphagnum magellanicum complex.

Sphagnum (peatmoss) comprises a moss (Bryophyta) clade with ~300-500 species. The genus has unparalleled ecological importance because Sphagnum-dominated peatlands store almost a third of the terrestrial carbon pool and peatmosses engineer the formation and microtopography of peatlands. Genomic resources for Sphagnum are being actively expanded, but many aspects of their biology are still poorly known. Among these are the degree to which Sphagnum species reproduce asexually, and the relative frequencies of male and female gametophytes in these haploid-dominant plants. We assess clonality and gametophyte sex ratios and test hypotheses about the local-scale distribution of clones and sexes in four North American species of the S. magellanicum complex. These four species are difficult to distinguish morphologically and are very closely related. We also assess microbial communities associated with Sphagnum host plant clones and sexes at two sites. Four hundred and five samples of the four species, representing 57 populations, were subjected to restriction site-associated DNA sequencing (RADseq). Analyses of population structure and clonality based on the molecular data utilized both phylogenetic and phenetic approaches. Multi-locus genotypes (genets) were identified using the RADseq data. Sexes of sampled ramets were determined using a molecular approach that utilized coverage of loci on the sex chromosomes after the method was validated using a sample of plants that expressed sex phenotypically. Sex ratios were estimated for each species, and populations within species. Difference in fitness between genets was estimated as the numbers of ramets each genet comprised. Degrees of clonality [numbers of genets/numbers of ramets (samples)] within species, among sites, and between gametophyte sexes were estimated. Sex ratios were estimated for each species, and populations within species. Sphagnum-associated microbial communities were assessed at two sites in relation to Sphagnum clonality and sex. All four species appear to engage in a mixture of sexual and asexual (clonal) reproduction. A single ramet represents most genets but two to eight ramets were dsumbers ansd text etected for some genets. Only one genet is represented by ramets in multiple populations; all other genets are restricted to a single population. Within populations ramets of individual genets are spatially clustered, suggesting limited dispersal even within peatlands. Sex ratios are male-biased in S. diabolicum but female-biased in the other three species, although significantly so only in S. divinum. Neither species nor males/females differ in levels of clonal propagation. At St Regis Lake (NY) and Franklin Bog (VT), microbial community composition is strongly differentiated between the sites, but differences between species, genets and sexes were not detected. Within S. divinum, however, female gametophytes harboured two to three times the number of microbial taxa as males. These four Sphagnum species all exhibit similar reproductive patterns that result from a mixture of sexual and asexual reproduction. The spatial patterns of clonally replicated ramets of genets suggest that these species fall between the so-called phalanx patterns, where genets abut one another but do not extensively mix because of limited ramet fragmentation, and the guerrilla patterns, where extensive genet fragmentation and dispersal result in greater mixing of different genets. Although sex ratios in bryophytes are most often female-biased, both male and female biases occur in this complex of closely related species. The association of far greater microbial diversity for female gametophytes in S. divinum, which has a female-biased sex ratio, suggests additional research to determine if levels of microbial diversity are consistently correlated with differing patterns of sex ratio biases.

P-135 No difference in morphokinetic patterns between male and female preimplantation embryos

Abstract Study question Do morphokinetic parameters vary between male and female preimplantation embryos? Summary answer We observed no significant differences in morphokinetic characteristics between male and female preimplantation embryos What is known already Studies across various mammalian species, including humans, suggest that male and female embryos differ in their gene expression and metabolic phenotypes. These variations may inherently affect the timing and duration of key preimplantation events. In the context of ART, such developmental differences may ultimately bias embryo selection, leading to an unbalanced sex ratio in the resulting offspring. To date, only a few studies have explored the relationship between morphokinetic patterns and human embryo sex. While some suggest subtle sex-specific variations in human embryo growth dynamics, results have been conflicting and currently no clear consensus has been reached. Study design, size, duration Retrospective study of morphokinetic data obtained from 175 preimplantation embryos. The study included 175 cycles performed at two IVF centers, between March 2018 and June 2021. Only fresh oocyte donation cycles using intracytoplasmic sperm injection (ICSI) and fresh single embryo transfer (SET) were assessed. Sex of the embryos was obtained from live birth data. Overall, our analysis included 92 female and 83 male embryos. Participants/materials, setting, methods All embryos were cultured in a timelapse incubator in standardized conditions. The morphokinetic parameters assessed included: time to pronuclear fading (tPNf), times to 2–5 cells (t2, t3, t4, t5), time to 8 cells (t8), time to start of blastulation (tSB) and time to full blastocyst stage (tB). All parameters were measured in hours post insemination (hpi). A two-tailed Student’s t-test was used to compare morphokinetics between embryo sexes. A p<0.05 was considered statistically significant. Main results and the role of chance We observed no significant differences in morphokinetic parameters when comparing cycles resulting in female vs. male live births: tPNf (21.8 ± 3.3 vs. 22.3 ± 3.4 hpi; p > 0.39); t2 (24.6 ± 2.5 vs. 25.0 ± 2.5 hpi; p > 0.34); t3 (35.3 ± 3.3 vs. 35.8 ± 3.1 hpi; p > 0.28); t4 (36.3 ± 3.4 vs. 36.9 ± 3.7 hpi; p > 0.20); t5 (47.9 ± 4.7 vs. 48.0 ± 4.8 hpi; p > 0.88); t8 (54.0 ± 6.5 vs. 54.1 ± 6.5 hpi; p > 0.91); tSB (86.3 ± 14.6 vs 85.7 ± 15.5 hpi; p > 0.78) and tB (93.0 ± 16.9 vs. 93.2 ± 17.2 hpi; p > 0.94). These findings suggest that the timing of key developmental events does not vary between male and female ICSI-derived preimplantation embryos. Limitations, reasons for caution The main limitation of this study is its retrospective nature and sample size. We analyzed the data of embryos leading to a live birth; therefore, caution is warranted when generalizing results to non-implanting embryos. Wider implications of the findings Male and female human embryos display similar morphokinetic patterns throughout preimplantation development in our study. Accordingly, embryo selection in a timelapse setting based on developmental characteristics does not bias sex ratios in resulting live births. Trial registration number not applicable

Essential and recurrent roles for hairpin RNAs in silencing de novo sex chromosome conflict in Drosophila simulans.

Meiotic drive loci distort the normally equal segregation of alleles, which benefits their own transmission even in the face of severe fitness costs to their host organism. However, relatively little is known about the molecular identity of meiotic drivers, their strategies of action, and mechanisms that can suppress their activity. Here, we present data from the fruitfly Drosophila simulans that address these questions. We show that a family of de novo, protamine-derived X-linked selfish genes (the Dox gene family) is silenced by a pair of newly emerged hairpin RNA (hpRNA) small interfering RNA (siRNA)-class loci, Nmy and Tmy. In the w[XD1] genetic background, knockout of nmy derepresses Dox and MDox in testes and depletes male progeny, whereas knockout of tmy causes misexpression of PDox genes and renders males sterile. Importantly, genetic interactions between nmy and tmy mutant alleles reveal that Tmy also specifically maintains male progeny for normal sex ratio. We show the Dox loci are functionally polymorphic within D. simulans, such that both nmy-associated sex ratio bias and tmy-associated sterility can be rescued by wild-type X chromosomes bearing natural deletions in different Dox family genes. Finally, using tagged transgenes of Dox and PDox2, we provide the first experimental evidence Dox family genes encode proteins that are strongly derepressed in cognate hpRNA mutants. Altogether, these studies support a model in which protamine-derived drivers and hpRNA suppressors drive repeated cycles of sex chromosome conflict and resolution that shape genome evolution and the genetic control of male gametogenesis.

The son-killer microbe Arsenophonus nasoniae is a widespread associate of the parasitic wasp Nasonia vitripennis in Europe

Heritable microbes that exhibit reproductive parasitism are common in insects. One class of these are the male-killing bacteria, which are found in a broad range of insect hosts. Commonly, our knowledge of the incidence of these microbes is based on one or a few sampling sites, and the degree and causes of spatial variation are unclear. In this paper, we examine the incidence of the son-killer microbe Arsenophonus nasoniae across European populations of its wasp host, Nasonia vitripennis. In preliminary work, we noticed two female N. vitripennis producing highly female biased sex ratios in a field study from the Netherlands and Germany. When tested, the brood from Germany was revealed to be infected with A. nasoniae. We then completed a broad survey in 2012, in which fly pupal hosts of N. vitripennis were collected from vacated birds’ nests from four European populations, N. vitripennis wasps allowed to emerge and then tested for A. nasoniae presence through PCR assay. We then developed a new screening methodology based on direct PCR assays of fly pupae and applied this to ethanol-preserved material collected from great tit (Parus major) nests in Portugal. These data show A. nasoniae is found widely in European N. vitripennis, being present in Germany, the UK, Finland, Switzerland and Portugal. Samples varied in the frequency with which they carry A. nasoniae, from being rare to being present in 50% of the pupae parasitised by N. vitripennis. Direct screening of ethanol-preserved fly pupae was an effective method for revealing both wasp and A. nasoniae infection, and will facilitate sample transport across national boundaries. Future research should examine the causes of variation in frequency, in particular testing the hypothesis that N. vitripennis superparasitism rates drive the variation in A. nasoniae frequency through providing opportunities for infectious transmission.

Inhibition of the NF-κB signaling pathway affects gonadal differentiation and leads to male bias in Paramisgurnus dabryanus

In recent years, sex-controlled breeding has emerged as an effective strategy to enhance the yields of economic animals with different growth characteristics, while increasing the economic benefits of aquaculture. It is known that the NF-κB pathway participates in gonadal differentiation and reproduction. Therefore, we used the large-scale loach as a research model for the present study and selected an effective inhibitor of the NF-κB signaling pathway (QNZ). This, to investigates the impacts of the NF-κB signaling pathway on gonadal differentiation during a critical period of gonad development and after maturation. Simultaneously, the sex ratio bias and the reproductive capacities of adult fish were analyzed. Our results indicated that the inhibition of the NF-κB signaling pathway influenced the expression of genes related to gonad development, regulated the gene expression related to the brain-gonad-liver axis of juvenile loaches, and finally impacted the gonadal differentiation of the large-scale loach and promoted a male-biased sex ratio. Meanwhile, high QNZ concentrations affected the reproductive abilities of adult loaches and inhibited the growth performance of offspring. Thus, our results deepened the exploration of sex control in fish and provided a certain research basis for the sustainable development of the aquaculture industry.

The influence of sample size on two approaches to estimate Black Grouse Lyrurus tetrix population size using non‐invasive sampling methods

Population size is an important parameter to monitor for species conservation and management. This is especially important for rare and endangered species, as declines can give information about anthropogenic impacts and the need for new conservation measures. To estimate population size, various methods of analysis can be used, for which sample size is an important factor. Sample size is particularly important to consider when applying non‐invasive sampling strategies such as sampling faeces or feathers/hairs as a source of DNA, as a means to limit disturbance and stress for the species of concern. We investigated a Black Grouse Lyrurus tetrix population in the eastern part of the Alps, in East Tyrol (Austria), and estimated population size using two approaches: capture–recapture and rarefaction. With a set of 12 polymorphic microsatellite markers, we identified genotypes from faeces and feathers (backed up with 23 tissue samples) and checked for population substructure and gene flow among sampling sites. We estimated population size using four different models from the two approaches (molecular capture–recapture: TIRM, TIRMpart; rarefaction: hyperbolic function – Kohn, exponential function – Eggert). To evaluate the impact of sample size on the estimations, we used the full dataset of 500 samples (‘complete’ dataset) and half the dataset of 250 samples (‘half’ dataset). We also estimated the population size for each sex separately using complete and half datasets to check for sex‐specific differences in population size. We found similar results in three of four models (capture–recapture: capwire TIRM, capwire TIRMpart; rarefaction: rarefaction Kohn). Using just half of the data increased the uncertainties in the estimation of population size in all models used and deviations were particularly large in females, which indicated a sex bias. Only the complete dataset of males had an observation rate of more than two observations/individual, and this observation rate meets the recommendation for using the capwire models. This indicates that, for species with different sex‐specific detectability, larger sample sizes do not generally imply higher observation rates. We conclude that calculating the observation rates and population‐size estimations for each sex separately can improve overall population‐size estimation, especially in species with biased sex ratios and those that exhibit sex‐specific behaviour.

Variance components of sex determination in the copepod Tigriopus californicus estimated from a pedigree analysis.

Extensive theory exists regarding population sex ratio evolution that predicts equal sex ratio (when parental investment is equal). In most animals, sex chromosomes determine the sex of offspring, and this fixed genotype for sex has made theory difficult to test since genotypic variance for the trait (sex) is lacking. It has long been argued that the genotype has become fixed in most animals due to the strong selection for equal sex ratios. The marine copepod Tigriopus californicus has no sex chromosomes, multiple genes affecting female brood sex ratio, and a brood sex ratio that responds to selection. The species thus provides an opportune system in which to test established sex ratio theory. In this paper, we further our exploration of polygenic sex determination in T. californicus using an incomplete diallel crossing design for analysis of the variance components of sex determination in the species. Our data confirm the presence of extra-binomial variance for sex, further confirming that sex is not determined through simple Mendelian trait inheritance. In addition, our crosses and backcrosses of isofemale lines selected for biased brood sex ratios show intermediate phenotypic means, as expected if sex is a threshold trait determined by an underlying "liability" trait controlled by many genes of small effects. Furthermore, crosses between families from the same selection line had similar increases in phenotypic variance as crosses between families from different selection lines, suggesting families from artificial selection lines responded to selection pressure through different underlying genetic bases. Finally, we estimate heritability of an individual to be male or female on the observed binary scale as 0.09 (95% CI: 0.034-0.14). This work furthers our accumulating evidence for polygenic sex determination in T. californicus laying the foundation for this as a model species in future studies of sex ratio evolution theory.

Population structure and dynamics of the Mediterranean Pond Turtle Mauremys leprosa (Schweigger, 1812) in contrasted polluted aquatic environments

Pollution contributes to the degraded state of continental aquatic ecosystems and biodiversity. Some species appear to be tolerant to aquatic pollution, yet little is known about the effects of such pollution on population structure and dynamics. Here, we investigated how wastewater treatment plant (WWTP) effluents of the Cabestany City, in southern France, contribute to the pollution levels of the Fosseille River, and we tested how they could affect population structure and medium-term dynamics of the native freshwater turtle, the Mediterranean Pond Turtle Mauremys leprosa (Schweigger, 1812). Amongst the 68 pesticides surveyed from water samples collected along the river in 2018 and 2021, a total of 16 pesticides were detected, among which eight were found in the upstream section of the river, 15 in the river section located downstream of the WWTP, and 14 in the outfall of the WWTP, exhibiting the contribution of effluents to the river pollution. From 2013 to 2018 and in 2021, capture-mark-recapture protocols were carried out on the freshwater turtle population living in the river. Using robust design and multi-state models, we showed a stable population throughout the study period, with high year-dependent seniority, and a bidirectional transition occurring primarily from the upstream to the downstream river sections of the WWTP. The freshwater turtle population consisted mostly of adults, with a male biased sex ratio detected downstream of the WWTP neither related to sex-dependent survival, recruitment, nor transition, suggesting a male bias in the hatchlings or primary sex ratio. Also, the largest immatures and females were captured downstream of the WWTP, with females having the highest body condition, whereas no such differences were observed in males. This study highlights that population functioning of M. leprosa is driven primarily by effluents induced resources, at least over the medium-term.

Population genetics of Glossina fuscipes fuscipes from southern Chad

In Subsaharan Africa, tsetse flies (genus Glossina) are vectors of trypanosomes causing Human African Trypanosomiasis (HAT) and Animal African Trypanosomosis (AAT). Some foci of HAT persist in Southern Chad, where a program of tsetse control was started against the local vector Glossina fuscipes fuscipes in the Mandoul focus in 2014, and in Maro in 2018. Flies were also sampled in 2018 in Timbéri and Dokoutou. We analyzed the population genetics of G. fuscipes fuscipes from the four tsetse-infested zones. The trapping samples were characterized by a strong female biased sex-ratio, except in Timbéri and Dokoutou that had high tsetse densities. Apparent density and effective population density appeared smaller in the main foci of Mandoul and Maro and the average dispersal distance (within the spatial scale of each zone) was as large as or larger than the total length of each respective zone. The genetic signature of a population bottleneck was found in the Mandoul and Timbéri area, suggesting a large ancient interconnected metapopulation that underwent genetic subdivision into small, isolated pockets due to adverse environmental conditions. The long-range dispersal and the existence of genetic outliers suggest a possibility of migration from remote sites such as the Central African Republic in the south (although the fly situation remains unknown there) and/or a genetic signature of recent exchanges. Due to likely isolation, an eradication strategy may be considered for sustainable HAT control in Mandoul focus. Another strategy will probably be required in Maro focus, which probably experiences much more exchanges with its neighbors.

The evolutionarily stable strategy, animal contests, parasitoids, pest control and sociality.

The evolutionarily stable strategy, ESS, concept was first used in biology to understand sex ratio bias and, shortly afterwards, to explore the logic of contests over essential and indivisible resources. ESS models formed the basis of much subsequent research on animal behaviour and placed game-theoretic thinking firmly within the behavioural ecology approach. Among behavioural ecologists studying parasitoids, it was those asking questions about the evolution of sex ratios who first made extensive use of the game-theoretic approach. A later growth of interest in parasitoid host defence and fighting behaviour made use of these tractable study species to explore contests and their connections to further aspects of life-history evolution plus some pest control applications. Our aims are to (i) introduce the topic of contests, which are engaged in by a very wide array of animal taxa, and the importance, both historical and conceptual, of the game-theoretic approach to their study, and (ii) review recent studies of parasitoid contests, including those that have considered the context of social evolution and the performance of parasitoids as agents of biological control. We consider that game-theoretic models are eminently testable and applicable and will likely endure as valuable tools in studies of parasitoid biology. This article is part of the theme issue 'Half a century of evolutionary games: a synthesis of theory, application and future directions'.

Dietary fat supplements influence weight gain and egg production, but not offspring sex ratios in Japanese quail, Coturnix coturnix japonica

Sex ratio theory suggests that females should bias offspring sex ratios based on maternal condition and the availability of critical food resources. Work in birds indicates that females do, indeed, bias sex ratios according to maternal condition and food quality and quantity. Yet it is unknown whether these sex ratio skews occur due to fluctuations in particular micro‐ or macro‐nutrients, caloric content overall or even the perception of food availability. We hypothesized that dietary fats may drive biases in offspring sex ratios, because measures of maternal condition often reflect fat reserves, and fats are critical for the process of egg‐laying in birds. To test this, we provided breeding Japanese quail, a species that biases sex ratios in response to maternal condition, with either a control breeding diet or a diet supplemented with two oils (safflower oil and flaxseed oil). These oils were chosen for their high omega‐3 and omega‐6 fatty acid content as well as their importance in mammalian sex allocation. We then measured influences of these diets on the sex ratio of offspring, the change in maternal weight, and the laying rates of female quail. The dietary oil supplements increased weight gains in quail but decreased the number of eggs laid during the experiment. There was no influence of the oil supplements on offspring sex ratios. This indicates that fat may not be a macro‐nutrient involved in the process of sex ratio adjustment in quail.

Widespread sex ratio polymorphism inCaenorhabditisnematodes

Although equal sex ratio is ubiquitous and represents an equilibrium in evolutionary theory, biased sex ratios are predicted for certain local conditions. Cases of sex ratio bias have been mostly reported for single species, but little is known about its evolution above the species level. Here, we surveyed progeny sex ratios in 23 species of the nematode genus Caenorhabditis, including 19 for which we tested multiple strains. For the species with multiple strains, five species had female-biased and two had non-biased sex ratios in all strains, respectively. The other 12 species showed polymorphic sex ratios across strains. Female-biased sex ratios could be due to sperm competition whereby X-bearing sperm outcompete nullo-X sperm during fertilization. In this model, when sperm are limited allowing all sperm to be used, sex ratios are expected to be equal. However, in assays limiting mating to a few hours, most strains showed similarly biased sex ratios compared with unlimited mating experiments, except that one C. becei strain showed significantly reduced female bias compared with unlimited mating. Our study shows frequent polymorphism in sex ratios within Caenorhabditis species and that sperm competition alone cannot explain the sex ratio bias.

Male’s influence on the primary sex ratio bias in Ryukyu drywood termite

Selfish genetic elements (SGEs) increase their transmission efficiency relative to the rest of the individual genome, which is often deleterious to individual fitness. Theoretical studies have suggested that intragenomic conflict over the sex ratio distortion between SGEs and the rest of the genome should lead to the evolution of sex-determining systems. However, in insects, there are relatively few studies other than those on Dipterans, which makes it difficult to understand the role of SGEs in the evolution of insect sex determination. This is partially due to the difficulties in observing SGEs under field conditions. The effect of SGEs is often masked by the counter-evolution of the resistance genes. Interpopulation cross-breeding experiments are effective to detect the SGEs and their resistance genes. If these populations have different SGEs and resistance genes, cross-breeding experiments reveal their existence by collapsing the evolutionary antagonistic state. The Ryukyu drywood termites Neotermes sugioi, distributed in the Ryukyu Islands, show male-biased sex ratios in pseudergates, nymphs, alates and soldiers both in Okinawa and Ishigaki Islands, but different degrees of bias have been reported between the islands. Male-specific microsatellite alleles have been reported in this species, which allowed us to identify the sex of the eggs and young larvae. In this study, we used the microsatellite locus with male-specific alleles to investigate the primary sex ratio of field colonies on Okinawa and Ishigaki islands and the sex ratio of offspring obtained through cross-breeding experiments between the islands. The primary sex ratios of field colonies were male-biased in Okinawa but not in Ishigaki. Cross-breeding experiments showed that Okinawa males tend to have a male-biased sex ratio in their offspring, but Ishigaki males do not. This result is consistent with the hypothesis that the male bias in this species is caused by SGEs, even though termites are phylogenetically distant from Diptera. Accumulation of knowledge on genetic conflicts in a wide range of taxa might be an important step toward elucidating the mechanisms of diversification of sex determination systems in insects.

Prevalence of the scuticociliate Orchitophrya stellarum in seastars from the Pacific and Atlantic oceans

As part of a study to investigate the use of the scuticociliate Orchitophrya stellarum as a biological control for the invasive seastar Asterias amurensis in Australia, we collected prevalence data for O. stellarum from 3 seastar species (A. amurensis, A. rubens, Pisaster ochraceus) between 1996 and 1999 from the Pacific (Australia, Japan, Korea, Canada) and Atlantic (France, Netherlands, Canada) oceans. In the Pacific Ocean, for the first time, we found O. stellarum in male A. amurensis in Korea and female A. amurensis in Japan. The parasite was not detected in the invasive A. amurensis from Australia. There was no significant difference between size of infected and uninfected male seastars, nor a correlation between biased sex ratio and parasite prevalence in populations in the Pacific or Atlantic oceans. Therefore, unlike other studies, we found size and sex ratio in seastar populations in the field are unreliable indicators of parasite impacts. Regular monitoring of infected seastar populations in the field would be useful to better understand how sex ratio varies with parasite prevalence. We recommend laboratory studies under controlled conditions to determine the effect of O. stellarum on seastar populations.

Responses of dioecious Populus to heavy metals: a meta-analysis.

A total of 946 sets of comparative data were collected from 20 publications and a meta-analysis performed to evaluate the responses of growth, photosynthetic capacity, oxidative stress and antioxidants in Populus females and males under exposure to heavy metals, like Cu, Mn, Zn, Pb and Cd. It was found that heavy metals have negative effects on Populus growth and photosynthetic capacity, as the average total biomass, leaf biomass, stem biomass, root biomass and height decreased by 29.78%, 33.41%, 27.22%, 35.30% and 34.83%, respectively. Furthermore, total chl, P n, g s, E, C i decreased by 23.30%, 26.03%, 40.49%, 23.76% and 18.24%, respectively. In addition, heavy metals increased oxidative stress and antioxidant enzyme activities: the average values of TBARS, H2O2, [Formula: see text] and MDA increased by 51.39%, 55.79%, 64.67% and 48.92%, respectively, and proline, APX, NPT, POD, CAT and SOD increased by 68.91%, 64.81%, 68.40%, 57.34%, 77.30% and 49.01%, respectively. However, there were sex-specific responses to heavy metals: females suffered more negative effects, as they had significantly greater decreases in root biomass, R/S ratio, height and total chl, and significantly smaller increases in NPT and POD activities than males. The present meta-analysis shows the responses of Populus females and males to heavy metals on a regional scale, which is crucial for understanding the patterns of sexual dimorphism and sex ratio biases in Populus with increasing heavy metal pollution in the future.

Female mate choice in the fat-tailed dunnart (Sminthopsis crassicaudata) influences offspring sex ratio, but not fecundity

Obtaining a suitable mate is an integral part of reproduction, with sexual selection processes such as female mate choice resulting in both direct and/or indirect benefits. Here, we investigated whether olfactory driven female mate choice influenced reproductive success in captive fat-tailed dunnarts (Sminthopsis crassicaudata). Although females spent 67% more time with a preferred male’s scent, reproductive success was not influenced by assigned mate choice. Of the 10 (of 12) litters that survived to weaning, average litter size was higher for non-preferred pairings (3 ± 0.83) compared with preferred pairings (1.6 ± 0.60), with weaning success equal for both pairings. Analyses suggested that offspring sex ratios were influenced by mate choice, with females paired with their preferred mate having more daughters (81%) in comparison to non-preferred pairings (44%) and by paternal body condition, whereby females paired with males in better body condition produced more sons. In this species, altering offspring sex ratios in favour of daughters may be achieved by pairing with preferred males, and towards sons by pairing with males in better body condition. With the increasing need for captive breeding programs, these techniques may provide opportunities to correct sex ratio biases and incorporate natural mating systems into conservation programs.