Biased Sex Ratios Research Articles

Covariations and trade‐offs of phosphorus (P) acquisition strategies in dioecious Populus euphratica as affected by soil water availability

Abstract Dioecious species may be particularly vulnerable to climate change because they often exhibit skewed sex ratios that are reinforced by the physiological and biological specialization of each sex to specific microhabitats. Yet, it is unclear how differences in functional traits between female and male plants lead to sex‐specific responses to drought and whether these responses are associated with phosphorus (P) acquisition diverge or converge. Here, we measured the morphological and physiological traits of roots, and the functional micro‐organisms related to P acquisition in Populus euphratica females and males in the rhizosphere under different water availability. The specific root length of females was greater than that of males, regardless of soil water availability. Therefore, the P concentration of females was significantly higher than that of males under well‐watered conditions. In contrast, the physiological adjustment to drought showed distinct sexual patterns: males significantly increased the foliar manganese concentration and maintained higher acid phosphatase activities in the rhizosphere. Moreover, the arbuscular mycorrhizal hyphal biomass reduced less in males than in females under water deficiency. Soil water shortage also decreased the α diversity of phosphate solubilizing bacteria (PSB) and changed the co‐occurrence network in the rhizosphere of females, but it had little effect on males. Consequently, the favourable physiological processes and effective maintenance of functional microbial homoeostasis in the rhizosphere were the reasons that enabled males to reduce P loss in leaves under water deficiency. Our study indicated that, within P. euphratica populations, covariations and trade‐offs simultaneously occurred among the three groups (root morphology, physiology and functional micro‐organisms) of functional traits evaluated. More generally, the assessment of variations in sex‐specific P acquisition strategies may help to understand the causes of sex ratio bias and how P. euphratica males and females mitigate resource shortage. Read the free Plain Language Summary for this article on the Journal blog.

High predation risk decimates survival during the reproduction season.

Predators attack conspicuous prey phenotypes that are present in the environment. Male display behavior of conspicuous nuptial coloration becomes risky in the presence of a predator, and adult males face higher predation risk. High predation risk in one sex will lead to low survival and sex ratio bias in adult cohorts, unless the increased predation risk is compensated by higher escape rate.Here, we tested the hypothesis that sand lizards (Lacerta agilis) have sex‐specific predation risk and escape rate. We expected the differences to manifest in changes in sex ratio with age, differences in frequency of tail autotomy, and in sex‐specific survival rate.We developed a statistical model to estimate predation risk and escape rate, combining the observed sex ratio and frequency of tail autotomy with likelihood‐based survival rate. Using Bayesian framework, we estimated the model parameters. We projected the date of the tail autotomy events from growth rates derived from capture–recapture data measurements.We found statistically stable sex ratio in age groups, equal frequency of tail regenerates between sexes, and similar survival rate. Predation risk is similar between sexes, and escape rate increases survival by about 5%. We found low survival rate and a low number of tail autotomy events in females during months when sand lizards mate and lay eggs, indicating high predator pressure throughout reproduction. Our data show that gravid females fail to escape predation.The risks of reproduction season in an ectotherm are a convolution of morphological changes (conspicuous coloration in males and body allometry changes in gravid females), behavior (nuptial displays), and environmental conditions which challenge lizard thermal performance. Performance of endotherm predators in cold spring months endangers gravid females more than displaying males in bright nuptial coloration.

Ecology of Indian wolf Canis lupus pallipes in the Great Indian Bustard Sanctuary, Nannaj, Solapur, Maharashtra, India

The Indian wolf, Canis lupus pallipes is an endangered carnivore of India listed in Schedule-1 of the Indian Wildlife (Protection) Act, 1972. There is not much information available on the species and with this perspective, the present study was initiated in the Great Indian Bustard Sanctuary in Maharashtra. Direct and indirect evidences were used to assess its population status and distribution, habitat use, feeding ecology, denning behaviour and wolf-human conflict emanating due to livestock depredation. Intensive ecological and behavioural studies were conducted at Nannaj on one pack between 1991 and 1994. The wolf survives all over the Sanctuary, which is densely populated by humans as elsewhere in its distribution range in India where wolf-human conflicts are common arising either due to livestock depredation or child-lifting. Usually, large packs were present in Blackbuck Antilope cervicapra areas whereas smaller packs inhabited areas not supporting healthy populations of Blackbuck. In Blackbuck poor areas, the wolf survived mainly on livestock. The Sanctuary supports 40-58 wolves. The wolves had a seasonal pattern of habitat use related to movement of prey and livestock. Wolves selected those areas as rendezvous sites which had higher prey density, vegetation cover, minimum human disturbance and were located close to water source. On an average wolves consumed 3.68 (S.E.=0.17) kg/wolf/kill and kill periodicity was 3.65 days (S.E.=0.58). Wolves preyed largely on blackbuck during the non-breeding period and livestock during denning period. Predation was higher on male blackbuck than females despite female biased sex ratio. The average litter size of three packs was recorded to be 5 (range 4-6). The dominant male and female wolves guarded the dens more often than the helpers. They used multiple dens for raising pups that were excavated and/or renewed during denning period. Important conservation problems of wolf have also been discussed in the paper.

Ecology of Indian wolf Canis lupus pallipes in the Great Indian Bustard Sanctuary, Nannaj, Solapur, Maharashtra, India

The Indian wolf, Canis lupus pallipes is an endangered carnivore of India listed in Schedule-1 of the Indian Wildlife (Protection) Act, 1972. There is not much information available on the species and with this perspective, the present study was initiated in the Great Indian Bustard Sanctuary in Maharashtra. Direct and indirect evidences were used to assess its population status and distribution, habitat use, feeding ecology, denning behaviour and wolf-human conflict emanating due to livestock depredation. Intensive ecological and behavioural studies were conducted at Nannaj on one pack between 1991 and 1994. The wolf survives all over the Sanctuary, which is densely populated by humans as elsewhere in its distribution range in India where wolf-human conflicts are common arising either due to livestock depredation or child-lifting. Usually, large packs were present in Blackbuck Antilope cervicapra areas whereas smaller packs inhabited areas not supporting healthy populations of Blackbuck. In Blackbuck poor areas, the wolf survived mainly on livestock. The Sanctuary supports 40-58 wolves. The wolves had a seasonal pattern of habitat use related to movement of prey and livestock. Wolves selected those areas as rendezvous sites which had higher prey density, vegetation cover, minimum human disturbance and were located close to water source. On an average wolves consumed 3.68 (S.E.=0.17) kg/wolf/kill and kill periodicity was 3.65 days (S.E.=0.58). Wolves preyed largely on blackbuck during the non-breeding period and livestock during denning period. Predation was higher on male blackbuck than females despite female biased sex ratio. The average litter size of three packs was recorded to be 5 (range 4-6). The dominant male and female wolves guarded the dens more often than the helpers. They used multiple dens for raising pups that were excavated and/or renewed during denning period. Important conservation problems of wolf have also been discussed in the paper.

Sex specificity of dispersal behaviour and flight morphology varies among tree hollow beetle species

BackgroundFlight performance and dispersal behaviour can differ between sexes, resulting in sex-biased dispersal. The primary sex ratio of populations may also explain dispersal bias between sexes, as this bias may evolve with the primary sex ratio to reduce intrasexual competition. Although dispersal bias between sexes is relevant to population dynamics, there are few studies on sex-biased dispersal in insects. We studied the flight performance and dispersal behaviour of seven saproxylic beetle species associated with tree hollows from a sex perspective. We also analysed the possible coevolution of flight performance with the primary sex ratio.MethodsWing loading and wing aspect ratio were used as measures of the flight performance of species and sexes. Dispersal behaviour was explored by analysing the frequency of each sex in interception traps versus the primary sex ratio obtained by tree hollow emergence traps using contingency tables and posthoc standardized residuals. A more active flight behaviour was expected for the sex with higher capture frequency in the interception traps. To explore the causes of flight performance bias between sexes, we searched for possible correlations between wing loading or wing aspect ratio and primary sex ratio using Pearson’s correlation coefficient.ResultsWing loading and wing aspect ratio differed between species and sexes, with flight performance being higher in males than in females for four of the seven species analysed. Dispersal behaviour and flight performance matched in the case of Elater ferrugineus; males showed higher flight performance and were the most collected sex in the interception traps (more active flyers). In contrast, the higher flight activity of Cetonia carthami aurataeformis females was not correlated with a higher flight performance than that of males. Moreover, we found that a bias in the primary sex ratio towards females is often correlated with a decrease in female flight performance.ConclusionsWe stress that flight performance and dispersal behaviour of sexes do not always go hand in hand. Moreover, the relationship between the sex ratio and flight performance bias between sexes is not driven by competition within the most abundant sex. The inclusion of a sex perspective in insect dispersal studies would be useful to detect dispersal bias between sexes and its causes and would allow for further analysis of its effects on population dynamics.

Brood Sex Ratio in European Honey Buzzards Pernis apivorus is Related to Spring Phenology

In sexually size-dimorphic bird species, rearing costs of sons and daughters usually differ and may be important in the evolution of offspring sex ratio adjustment. Raptors have reversed sexual size dimorphism and the smaller males are sometimes found to be overrepresented in food-poor territories or years. As a raptor with small reversed sexual dimorphism (6% in body mass), the European Honey Buzzard Pernis apivorus is expected to show little or no brood sex ratio bias in relation to environmental conditions. We molecularly sexed 311 chicks of 195 broods in and around The Netherlands, during 1996–2014. We examined which environmental factors explained brood sex ratio variation best. Overall, sex ratio was not biased (all nests pooled: 50.8% females) but more females were produced in years when on average Honey Buzzards bred earlier (32% sex ratio change over a ten-day range in annual mean laying date). Within-year laying date variation, hatching order, abundance of wasp (Vespinae) nests (main food source) and summer weather did not explain sex ratio variation. In the Veluwe and Drenthe (1974–2014), Honey Buzzards laid eggs earlier when the spring was warmer, which resulted in a c. 9-day advance in laying date over 40 years. As warm spring weather was also a predictor of a higher density of wasp colonies, we expected female chicks to benefit more from growing up in wasp-rich years than males, if the sex ratio biases were adaptive. However, this differential growth benefit was not noticeable in chick body mass; chick body mass was best explained by negative effects of relative laying date (within a year) and hatching order. The potential benefit for female nestlings (compared to males) of growing up in years with warm springs, when egg laying occurs early and wasp colonies are more abundant, remains unknown.

The Use of Camera Traps and Auxiliary Satellite Telemetry to Estimate Jaguar Population Density in Northwestern Costa Rica.

Simple SummaryWe used data from a grid of camera traps, combined with satellite telemetry data from one female jaguar, to estimate jaguar population density in northwestern Costa Rica. Our estimate of 2.6 females and 5.0 males per 100 km2 was influenced by camera placement and sex of the jaguar, and indicated the importance of telemetry data to improve field design and parameter estimation. We recommend population assessments of at least 3 consecutive months, expanding the survey area to one several times the size of an individual’s home range, and including sex and camera placement considerations to reduce bias in jaguar density estimates.Regular evaluation of jaguar (Panthera onca) population status is an important part of conservation decision-making. Currently, camera trapping has become the standard method used to estimate jaguar abundance and demographic parameters, though evidence has shown the potential for sex ratio biases and density overestimates. In this study, we used camera trap data combined with satellite telemetry data from one female jaguar to estimate jaguar population density in the dry forest of Santa Rosa National Park in the Guanacaste Conservation Area of northwestern Costa Rica. We analyzed camera trap data collected from June 2016 to June 2017 using spatial capture-recapture methods to estimate jaguar density. In total, 19 individual jaguars were detected (11 males; 8 females) with a resulting estimated population density of 2.6 females (95% [CI] 1.7–4.0) and 5.0 male (95% [CI] 3.4–7.4) per 100 km2. Based on telemetry and camera trap data, camera placement might bias individual detections by sex and thus overall density estimates. We recommend population assessments be made at several consecutive 3-month intervals, that larger areas be covered so as not to restrict surveys to one or two individual home ranges, as in our case, and to carry out long-term camera monitoring programs instead of short-term studies to better understand the local population, using auxiliary telemetry data to adjust field designs and density estimations to improve support for jaguar conservation strategies.

Reproductive Characteristics of the Flat Oyster Ostrea denselamellosa (Bivalvia, Ostreidae) Found on the Southern Coast of South Korea

In this study, we investigated the reproductive pattern of the commercially and ecologically important species, Ostrea denelamellosa, to inform stock management strategies in South Korea. Prior to the reproduction experiment, the complete mitochondrial (mt) genome of the flat oyster, Ostrea denselamellosa, was analyzed using next-generation sequencing technology. Then, to determine the reproductive pattern of Ostrea denselamellosa, we investigated monthly changes in the gametogenesis, reproductive cycle, and sex ratio from January to October 2021 in females. The total length of the mt genome sequence of O. denselamellosa was 16,225 bp and contained 37 genes (13 protein-coding genes, 22 tRNA genes, and 2 rRNA genes). Molecular phylogenetic comparison with 20 known species of Pteriomorphia showed that O. denselamellosa belongs to the family Ostreidae. In addition, O. denselamellosa clustered together with the O. denselamellosa Chinese strain, with a bootstrap value of 100%. Histological analysis indicated a discrepancy in gamete development of O. denselamellosa with synchronous maturation of oocytes and asynchronous development of spermatozoa in gonads. The spawning activity occurred between May and September with a temperature range gap of 6.5 °C. The spawning activity occurred from May when the temperature reached 16.7 °C until September when the temperature dropped below 23.2 °C. Furthermore, sex ratio bias was observed. This is the first study to report the complete mt genome sequence and examine the reproductive pattern in native O. denselamellosa in South Korea. Overall, these findings will help enhance the knowledge for the management and sustainable fishery of endangered oyster species including O. denselamellosa in the South Sea of Korea.

A morphologist, a modeler, and an endocrinologist consider sea turtle sex ratios in a changing climate. Some wine was involved

Because the sex of sea turtles is determined by temperature during embryonic development, many populations are vulnerable to increased bias in primary sex ratios as global temperatures rise. Higher temperatures produce more females, and some populations are already showing years with all-female offspring production. But because sea turtles take decades to mature and have long adult lifespans, these primary sex ratio biases can take years to impact adult sex ratios, and the males from cohorts that are produced during cooler years may compensate for the sex ratio bias if they can breed more frequently and with multiple females. To date, little is known about male sea turtle reproductive behavior, making predictions of sex ratio skew impacts highly speculative. We used data from southern Florida loggerhead sea turtle nests to parameterize a simple population model to explore the effects of an increase in the proportion of female hatchlings over time on population trends, effective population size (Ne), and quasi-extinction probability. We also tested the effects of increasing the frequency of relatively high male production years to simulate potential mitigation strategies. While heuristic rather than predictive, our results expectedly show a rise in nest counts due to the increase in females over time, followed by population decline as males become limiting. Population collapse due to increased female bias will take many decades to occur, but sex ratio skew can have large impacts on Ne, and thus increase the potential for inbreeding. An increase in the frequency of male production years, even just one additional “good male year” per decade, can help mitigate these outcomes if the rate of feminization is not too rapid. Male breeding frequency and mating success are critical drivers of the results and must be prioritized for research.

High temperature mortality of Wolbachia impacts the sex ratio of the parasitoid Ooencyrtus mirus (Hymenoptera: Encyrtidae).

BackgroundWolbachia bacteria are estimated to occur in more than half of all insect species. In Hymenoptera, Wolbachia often manipulates its host’s reproduction to its own advantage. Wolbachia is likely the reason that males are rare in the uniparental Ooencyrtus mirus Triapitsyn & Power (Hymenoptera: Encyrtidae). The likelihood of producing male offspring can be increased by giving mothers a continuous supply of Bagrada hilaris (Burmeister) (Heteroptera: Pentatomidae) host eggs to parasitize for 2–3 weeks, by feeding the parents antibiotics, or by rearing parent wasps at high temperatures; all variables that have been shown to correlate with depleting Wolbachia titers in other organisms. The purpose of the current study was to determine whether thelytoky in O. mirus is due to Wolbachia, and if so, at what time in development the sex change occurs. We also wished to determine if Wolbachia removal results in the production of intersexes, as in some other hymenopterans. Finally, mating behavior was observed to see if and where it breaks down as a result of the species becoming thelytokous.MethodsFemales were collected from parental lines of O. mirus reared at 26, 30, 31, 32, 33, 34, and 36 °C. The offspring of these females were reared at 26 °C, and their sex-ratio was determined. In a subsequent experiment, the parental generation was switched between 26 °C and 36 °C during development to narrow down the critical period at which changes occurred that subsequently affected the sex-ratio of their offspring.ResultsThe sex ratio was male biased in the offspring of O. mirus parents reared at 34 °C and 36 °C (high temperatures), even if the offspring themselves were reared at 26 °C. The constant temperature at which the percentage of males started to increase after two generations was 31 °C (10% males), rising to 39% males at 33 °C, and 100% males at 34 °C and 36 °C. Lasting more than 2 days, the critical period for the change toward a male biased sex ratio was during the second half of the parent’s development. Molecular diagnostic assays confirmed that O. mirus females contain Wolbachia and males do not. Examination of preserved males and male-female pairs under a dissecting microscope showed no signs of intersex characters. Observation of the mating behavior of live O. mirus showed that males initiate courtship by drumming their antennae on a female’s antennae, but after a few seconds, the females typically turn and walk away. However, a few instances of possible copulation were noted.ConclusionsAs hypothesized, the results indicated that thelytoky in O. mirus is likely mediated by Wolbachia bacteria. To maximize the population growth rate without generating males, the best temperature for mass rearing this species is 30 °C.

Thermal reaction norm for sexualization: The missing link between temperature and sex ratio for temperature-dependent sex determination

Species with temperature-dependent sex determination (TSD) can experience biased sex ratios in natural conditions, which raises questions the vulnerability of populations in the face of climate change. Studies addressing the adaptive significance TSD have been hampered by the difficulty of accurately estimating sex ratios under natural incubation conditions. Here we introduce the thermal reaction norm for sexualization, a novel concept measuring the strength of masculinization or feminization of temperatures, to model the effect of temperature for sex determination in TSD species. We use hatchling sex ratio data and field incubation temperatures collected between 2002 and 2018 at a globally important loggerhead turtle (Caretta caretta) nesting rookery. The new parametrization makes possible the understanding of how temperature-sensitive sex determination works. We show that the temperature could influence the sexualization of the gonad earlier than what is currently recognized. Additionally, we explore the results of several easy to implement proxies that have been used in literature. Our approach greatly outperforms previous ones in sex ratio prediction. Our results should help further studies to refine population-wide primary sex ratio estimates of reptiles with TSD to adapt current conservation strategies and develop them in the future.

Effects of Fluctuating Thermal Regimes on Life History Parameters and Body Size of Ophraella communa.

Simple SummaryThe ragweed is a global problem with its wide distribution and substantial economic and ecological cost. The ragweed beetle is an effective biological control agent for ragweed. With the increasing challenges of climate change, understanding the population responses of the ragweed beetle to thermal stress is essential to predict the impacts of climate change more accurately. Our study showed that Ophraella communa has stronger capabilities to adjust the development time with prolonged adult longevity, regulating sex differentiation and response to fluctuating temperatures. Taken together, the adaptation strategies of the ragweed beetle make it play a crucial role as an effective biological control agent for ragweed.The beetle Ophraella communa is an effective biological control agent against the invasive common ragweed spread across various ecosystems with variable temperature ranges. The trend in climate change attributed to fluctuating temperatures and abrupt rainfalls is expected to continue. This study aimed to better understand the effects of thermal fluctuation on O. communa by exposing all their life stages to heat stress under different treatments. Repeated exposure to high temperatures, relative to constant milder temperatures, increased the duration of immature development, mean generation time, and the adult longevity, decreased the intrinsic rate of increase, finite rate of population increase, net reproductive rate, survival rate, overall longevity, body length, and mass of adults and positively affected overall fecundity by prolonging the oviposition period, biasing sex ratio towards females. After exposure to heat stress, the mating success and production of viable offspring were higher in O. communa. Our findings demonstrate that exposure to heat stress negatively affects ragweed beetles, but they were able to survive and reproduce.

Long-Term Resilience of Primary Sex Ratios in a Species with Temperature-Dependent Sex Determination after Decades of Climate Warming.

AbstractSpecies with environmental sex determination (ESD) have persisted through deep time, despite massive environmental perturbation in the geological record. Understanding how species with temperature-dependent sex determination (TSD), a type of ESD, persist through climate change is particularly timely given the current climate crisis, as highly biased sex ratios and extinction are predicted. Since 1982, we have studied primary sex ratios of a reptile with TSD (Chelydra serpentina). Primary sex ratios remained unchanged over time, despite warming in the environment. Resilience of the primary sex ratio occurred via a portfolio effect, realized through remarkable intra-annual variation in nest-level sex ratios, leading to a relatively consistent mean annual sex ratio. Intra-annual variation in nest-level sex ratios was related to variation in egg burial depth coupled with large clutch sizes, creating thermal gradients in the nest and promoting mixed-sex clutches. Furthermore, both locally and globally, sustained increases in nighttime air temperature contribute more to warming than increases in daily maximum temperature, but development rate was affected more strongly by maximum daily air temperature, conferring additional resilience to overall warming. Our study suggests that some TSD species may be resilient to warming and provides an example of how ESD may persist under environmental change.

Facultative and persistent offspring sex-ratio bias in relation to the social environment in cooperatively breeding red-winged fairy-wrens (Malurus elegans)

Females should facultatively bias offspring sex ratio when fitness returns vary among sexes. In cooperative breeders, where individuals help raise others’ young, overproducing the philopatric sex will be adaptive when helpers are absent, whereas overproducing the dispersive sex may be adaptive to reduce intrasexual competition. Thus, fitness returns are expected to vary with the social environment. However, any offspring sex-ratio biases may also result from consistent among-female differences (e.g. quality) and/or environmental variables (e.g. food availability). Yet, few studies have disentangled facultative from persistent biases. We investigated offspring sex-ratio biases in relation to the social environment in cooperatively breeding red-winged fairy-wrens (Malurus elegans). Repeated observations of the same females over nine years allowed for disentanglement of facultative from persistent biases. Females without help did not overproduce daughters, despite female helpers being associated with higher fledgling survival (resource enhancement hypothesis). Instead, females without helpers facultatively overproduced sons —the slower dispersing sex— thereby ensuring long-term helper availability. Furthermore, offspring sex ratio was not biased towards the rarer sex of helpers present in the group or population (resource competition hypothesis). However, females with sex-biased helping produced similarly skewed offspring sex ratios. This among-female association may not be surprising, because helpers are previous seasons’ offspring. Thus, in addition to facultative responses to prevailing social conditions, we found evidence for persistent biases among females. This could potentially explain previous evidence for resource competition/enhancement that have typically been interpreted as facultative responses, highlighting the need for a within-female approach to better understand the adaptiveness of sex-ratio biases.Significance statementUnder certain conditions, females may benefit from producing a biased offspring sex ratio, but evidence for such effects in vertebrates is weak and inconsistent. Here, using observations of the same females under different social conditions, we show that cooperatively breeding red-winged fairy-wrens facultatively biased offspring sex ratio towards sons when living in pairs, thereby ensuring the availability of a workforce to assist in raising future offspring. However, biased offspring sex ratio patterns may also be the result of consistent differences among females. Indeed, we also found evidence for such patterns and suggest that this could be an explanation for previous findings which are often interpreted as facultative responses.

How much does the unguarded X contribute to sex differences in life span?

Females and males often have markedly different mortality rates and life spans, but it is unclear why these forms of sexual dimorphism evolve. The unguarded X hypothesis contends that dimorphic life spans arise from sex differences in X or Z chromosome copy number (i.e., one copy in the “heterogametic” sex; two copies in the “homogametic” sex), which leads to a disproportionate expression of deleterious mutations by the heterogametic sex (e.g., mammalian males; avian females). Although data on adult sex ratios and sex‐specific longevity are consistent with predictions of the unguarded X hypothesis, direct experimental evidence remains scant, and alternative explanations are difficult to rule out. Using a simple population genetic model, we show that the unguarded X effect on sex differential mortality is a function of several reasonably well‐studied evolutionary parameters, including the proportion of the genome that is sex linked, the genomic deleterious mutation rate, the mean dominance of deleterious mutations, the relative rates of mutation and strengths of selection in each sex, and the average effect of mutations on survival and longevity relative to their effects on fitness. We review published estimates of these parameters, parameterize our model with them, and show that unguarded X effects are too small to explain observed sex differences in life span across species. For example, sex differences in mean life span are known to often exceed 20% (e.g., in mammals), whereas our parameterized models predict unguarded X effects of a few percent (e.g., 1–3% in Drosophila and mammals). Indeed, these predicted unguarded X effects fall below statistical thresholds of detectability in most experiments, potentially explaining why direct tests of the hypothesis have generated little support for it. Our results suggest that evolution of sexually dimorphic life spans is predominantly attributable to other mechanisms, potentially including “toxic Y” effects and sexual dimorphism for optimal investment in survival versus reproduction.

Maternal cortisol level around conception is associated with offspring sex ratio in captive European wild rabbit (Oryctolagus cuniculus)

The sex ratio of the offspring at birth is usually 1: 1 established by natural selection. The sex allocation model predicts that if parents have adequate resources, they would benefit from differentially allocating maternal investment to that sex having higher fittness under the particular environmental conditions. However, little is known about what mechanisms would result in biased sex ratio. One such mechanism could be the interaction of of stress reactivity and progesterone levels in the mothers around conception. In the present investigation the fecal cortisol and progesterone levels at the day of conception were measured in fifteen European wild rabbit does kept in cages. The does were clustered to low and high cortisol response groups and the sex ratio of their progeny was determined. We found a significant correlation between the progesterone levels of mothers and their stress status measured at the mating. This correlation was also reflected in the sex ratio bias in their litters. Even though the litter size was not different, we found higher progesterone levels and more female offspring in the does with higher cortisol levels indicating that maternal status around conception may affect the litter sex ratio.

Current and historical factors drive variation of reproductive traits in unisexual mosses in Europe: A case study

AbstractUnisexual bryophytes provide excellent models to study the mechanisms that regulate the frequency of sexual versus asexual reproduction in plants, and their ecological and evolutionary implications. Here, we determined sex expression, phenotypic sex ratio, and individual shoot traits in 242 populations of the cosmopolitan moss Pseudoscleropodium purum spanning its whole distributional range. We tested whether niche differentiation, sex‐specific differences in shoot size, and biogeographical history explained the spatial variation of reproductive traits. We observed high levels of sex expression and predominantly female‐biased populations, although both traits showed high intraspecific variation among populations. Sex expression and sex ratio were partly explained by current macroscale environmental variation, with male shoots being less frequent at the higher end of the environmental gradients defined by the current distribution of the species. Female bias in population sex ratio was significantly lower in areas recolonized after the last glacial maximum (recent populations) than in glacial refugia (long‐term persistent populations). We demonstrated that reproductive trait variation in perennial unisexual mosses is partially driven by macroscale and historical environmental variation. Based on our results, we hypothesize that sexual dimorphism in environmental tolerance and vegetative growth contribute to sex ratio bias over time, constraining the chances of sexual reproduction, especially in long‐term persistent populations. Further studies combining genetic analyses and population monitoring should improve our understanding of the implications of the intraspecific variation in the frequency of sexual versus asexual reproduction in bryophyte population fitness and eco‐evolutionary dynamics.

Epigenetic Regulation of Phenotypic Sexual Plasticity Inducing Skewed Sex Ratio in Zebrafish.

The plasticity of sexual phenotype in response to environmental conditions results in biased sex ratios, and their variation has an effect on population dynamics. Epigenetic modifications can modulate sex ratio variation in species, where sex is determined by genetic and environmental factors. However, the role of epigenetic mechanisms underlying skewed sex ratios is far from being clear and is still an object of debate in evolutionary developmental biology. In this study, we used zebrafish as a model animal to investigate the effect of DNA methylation on sex ratio variation in sex-biased families in response to environmental temperature. Two sex-biased families with a significant difference in sex ratio were selected for genome-wide DNA methylation analysis using reduced representation bisulfite sequencing (RRBS). The results showed significant genome-wide methylation differences between male-biased and female-biased families, with a greater number of methylated CpG sites in testes than ovaries. Likewise, pronounced differences between testes and ovaries were identified within both families, where the male-biased family exhibited a higher number of methylated sites than the female-biased family. The effect of temperature showed more methylated positions in the high incubation temperature than the control temperature. We found differential methylation of many reproduction-related genes (e.g., sox9a, nr5a2, lhx8a, gata4) and genes involved in epigenetic mechanisms (e.g., dnmt3bb.1, dimt1l, hdac11, h1m) in both families. We conclude that epigenetic modifications can influence the sex ratio variation in zebrafish families and may generate skewed sex ratios, which could have a negative consequence for population fitness in species with genotype-environment interaction sex-determining system under rapid environmental changes.

Nestling sex ratio is unaffected by individual and population traits in the griffon vulture.

Variation in offspring sex ratios is a central topic in animal demography and population dynamics. Most studies have focused on bird species with marked sexual dimorphism and multiple-nestling broods, where the offspring sex ratio is often biased due to different individual or environmental variables. However, biases in offspring sex ratios have been far less investigated in monomorphic and single-egg laying species, and few studies have evaluated long-term and large-scale variations in the sex ratio of nestling vultures. Here, we explore individual and environmental factors potentially affecting the secondary sex ratio of the monomorphic griffon vulture Gyps fulvus. We used information collected at three breeding nuclei from central Spain over a 30-year period (1990-2020) to analyse the effects of nestling age, parental age, breeding phenology, conspecific density, population reproductive parameters, and spatial and temporal variability on nestling sex. Sex ratio did not differ from parity either at the population or the nuclei level. No significant between-year differences were detected, even under highly changing conditions of food availability associated with the mad-cow crisis. We found that tree nesting breeders tend to have more sons than daughters, but as this nesting behavior is rare and we consequently have a small sample size, this issue would require additional examination. Whereas further research is needed to assess the potential effect of breeder identity on nestling sex ratio, this study contributes to understanding the basic ecology and population dynamics of Griffon Vultures, a long-lived species with deferred maturity and low fecundity, whose minor deviations in the offspring sex ratio might imply major changes at the population level.

Population structure and morphology of Canarium (Canarium) incisum and Canarium (Canarium) esculentum (Mollusca: Neostromboidae: Strombidae) from the Philippines with preliminary notes on aperture colouration based on DArTseq data

AbstractCanarium (Canarium) incisum and Canarium (Canarium) esculentum are small members of the molluscan Strombidae family. Little is known of their population structure. Therefore, we explored this using samples from a population of each. The first sample from Corong Corong Beach, El Nido, Philippines, consisted of 81 adult C. incisum, of which 33 were female and 48 were male. The second sample from Olango Island, Philippines consisted of 73 adult C. esculentum, of which 40 were female and 33 were male. Bias in sex ratio between species was not significant. However, there was bias in sex ratio within species, where males from both species were smaller in axial length than females. We found no evidence of pseudohermaphroditism. The black colouration of the aperture is a phenotype shared by many stromboidians, and 7.4% of C. incisum population exhibited this trait, while the C. esculentum population contained 50.1% black apertures specimens. Preliminary DArTseq analysis indicates that organisms with the black aperture colouration are nested within the populations. Our study fills a knowledge gap on C. incisum and C. esculentum population structure, and gives greater insights to size dynamics of stromboidian taxa in general.