Effect Of Sex Ratio Research Articles

Impact of biased sex ratio on the genetic diversity, structure, and differentiation ofPopulus nigra(European black poplar)

Effective population size is a crucial concept of conservation biology. It is reduced by biased sex ratio, consequently causing loss of genetic variation. To evaluate genetic diversity related to gender, and investigate the possible effects of biased sex ratio, we analyzed available microsatellite DNA markers from 120 samples of Populus nigra L. (European black poplar) originating from five geographical regions in Turkey. Using 12 microsatellite markers, we detected 60 clones of the same genotype, out of 120 trees. The clone genotype was observed both in males and females, which might suggest that P. nigra deviates from dioecism. Three genetic clusters were detected, two of which possibly correspond to commercially available trees. Overall allelic richness was found to be similar for both genders, whereas heterozygosity was slightly higher in males. Additionally, a simulation software prototype was developed to see the effects of sex ratio on diversity and allele frequency trends in future generations, given the available molecular data. Results showed that if biased sex ratio persists, allele loss and fixation might occur in a higher rate, causing loss of variation.

Exploring the threat-sensitive predator avoidance hypothesis on mate competition in two wild populations of Trinidadian guppies

The intensity of mate competition is often influenced by predation pressure. The threat-sensitive predator avoidance hypothesis predicts that prey should precisely adjust their fitness-related activities to the level of perceived acute predation risk and this effect should be stronger under high background risk. Individuals should compensate during periods of moderate risk for lost opportunities during high risk. Our study examined the interaction between acute and background predation risk on mate competition. Under laboratory conditions, we explored the effects of acute risk (low vs. high) using chemical alarm cue (AC; control (results presented in Chuard et al. (2016)) The effects of adult sex ratio on mating competition in male and female guppies (Poecilia reticulata) in two wild populations. Behav Process 129:1−10), 25 % concentration, and 100 % concentration), and population of origin (low vs. high background risk) on mate competition in guppies (Poecilia reticulata). Surprisingly, males favored courtship over forced mating under acute predation risk irrespective of background risk, potentially benefiting from a female preference for bold males. We discuss our results in the context of chemical threat-sensitivity and resource differences in defendability (e.g. mates vs. food).

The influence of sex ratio and childhood harshness on male short-term mating preference

This research draws on Life History Theory to test the effect of sex ratio and childhood harshness on men's short-term mating preference. It applies three studies that: 1) manipulate perceived sex ratio by referring to two sets of profile photographs (Study 1); 2) require the participant to write an imaginative article that describes the potential situation of male or female-biased sex ratio (Study 2); 3) measure the participant's perception of sex distribution in a real situation (Study 3). The three studies consistently demonstrate that men who grew up in harsh environments are more likely to adopt short-term mating strategies when they see more women (than men) in their environment. But men who grew up in benign environments do not significantly differ in their short-term mating preference when responding to a male or female-biased sex ratio. The second and third study further demonstrate that when male resource acquirement capability is taken into account, it is childhood harshness, rather than ability to acquire resources, that performs a moderating role in the relationship between perceived sex ratio and men's short-term mating preference. Both studies also demonstrate that resource acquirement capability has the most significant effect on men's short-term mating preference.

Co-foundress confinement elicits kinship effects in a naturally sub-social parasitoid.

Kinship among interacting individuals is often associated with sociality and also with sex ratio effects. Parasitoids in the bethylid genus Goniozus are sub-social, with single foundress females exhibiting post-ovipositional maternal care via short-term aggressive host and brood defence against conspecific females. Due to local mate competition (LMC) and broods normally being produced by a single foundress, sex ratios are female-biased. Contests between adult females are, however, not normally fatal, and aggression is reduced when competing females are kin, raising the possibility of multi-foundress reproduction on some hosts. Here, we screen for further life-history effects of kinship by varying the numbers and relatedness of foundresses confined together with a host resource and also by varying the size of host. We confined groups of 1-8 Goniozus nephantidis females together with a host for 5+days. Multi-foundress groups were either all siblings or all nonsiblings. Our chief expectations included that competition for resources would be more intense among larger foundress groups but diminished by both larger host size and closer foundress relatedness, affecting both foundress mortality and reproductive output. From classical LMC theory, we expected that offspring group sex ratios would be less female-biased when there were more foundresses, and from extended LMC theory, we expected that sex ratios would be more female-biased when foundresses were close kin. We found that confinement led to the death of some females (11% overall) but only when host resources were most limiting. Mortality of foundresses was less common when foundresses were siblings. Developmental mortality among offspring was considerably higher in multi-foundress clutches but was unaffected by foundress relatedness. Groups of sibling foundresses collectively produced similar numbers of offspring to nonsibling groups. There was little advantage for individual females to reproduce in multi-foundress groups: single foundresses suppressed even the largest hosts presented and had the highest per capita production of adult offspring. Despite single foundress reproduction being the norm, G.nephantidis females in multi-foundress groups appear to attune sex allocation according to both foundress number and foundress relatedness: broods produced by sibling foundresses had sex ratios similar to broods produced by single foundresses (ca. 11% males), whereas the sex ratios of broods produced by nonsibling females were approximately 20% higher and broadly increased with foundress number. We conclude that relatedness and host size may combine to reduce selection against communal reproduction on hosts and that, unlike other studied parasitoids, G.nephantidis sex ratios conform to predictions of both classical and extended LMC theories.

Female Self-Sexualization Covaries with Mate Value but Not Mate Availability

An array of literature spanning economics, sociology, biology, and psychology suggests that the availability of romantic partners has profound consequences for individuals and the societies in which they live. Here we build on this growing body of research to understand how variation in mate availability—operationalized via experimental imbalances in the ratio of men to women (the sex ratio)—affect women’s willingness to enhance their physical and sexual attractiveness to men. Using a series of three treatments, with four replicate stimuli nested within each treatment conditions, we experimentally manipulated the sex ratio of the dating environment for 334 women, giving them the impression that romantic partners were either abundant, scarce, or balanced relative to competitors. We measured women’s satisfaction with their body image, their interest in enhancing their sexual attractiveness to men, their acceptance of cosmetic surgery, and their overall belief that they were a high-quality romantic partner (their mate value; a potential moderator of the sex ratio effect). Contrary to expectations, we found no evidence that sex ratios affected women’s enhancement of their physical and sexual attractiveness, but we did find that individual differences in mate value robustly covaried with all three outcome variables. Results raise the possibility that female self-sexualization does not covary with the relative availability of mates, but that it is reliably associated with individual differences in mate value.

Operational sex ratio and paternal age sway mating and reproductive performance in Menochilus sexmaculatus (Coleoptera: Coccinellidae)

AbstractOperational sex ratio and paternal age are known to independently affect mating behaviour and reproductive performance. We conducted experiments to assess the effects of operational sex ratio and paternal age on mating, reproduction, and total development duration of Menochilus sexmaculatus (Fabricius) (Coleoptera: Coccinellidae). Three male-biased sex ratios, no (1:1), modest (1:2), and extreme (1:5) competition treatments, were formed using young, middle-aged, and old males. The reproductive performance of M. sexmaculatus at all ages under extreme competition (1:5) surpassed the other two treatments. More competition among males decreased the time of commencement of mating and increased the duration of copulation. Females laid a greater number of eggs in extreme competition treatments. The operational sex ratio (irrespective of age) had no significant effect on the total developmental duration of offspring. Among different age groups, older males took more time to commence mating and mated for longer durations in all the sex ratio treatments. The number of eggs in the first clutch was lowest when females were mated with older males with increased offspring development duration. Thus, it can be concluded that male-biased sex ratio elevates the performance of M. sexmaculatus. Among different age groups, older males were poor performers than young and middle-aged males.

Too Many Men, Too Short Lives: The Effect of the Male-Biased Sex Ratio on Mortality

Too Many Men, Too Short Lives: The Effect of the Male-Biased Sex Ratio on Mortality

Ecological Sex Ratios and Human Mating.

The ratio of men to women in a given ecology can have profound influences on a range of interpersonal processes, from marriage and divorce rates to risk-taking and violent crime. Here, we organize such processes into two categories - intersexual choice and intrasexual competition - representing focal effects of imbalanced sex ratios.

Effects of adult sex ratio on larvae number and survival of fry in Xiphophorus maculatus (Cyprinodontiformes: Poeciliidae)

In this study, differing adult sex ratios of the Southern platyfish, Xiphophorus maculatus were examined for fish larval number and the survival of fish fry. Sixty adult individuals of X. maculatus were randomly divided into 5 equal groups with various male to female sex ratios of 1:1, 1:2, 1:3, 2:1, and 3:1, respectively. After a month when the male and female fish were kept together in different experimental groups, all the female fish became pregnant. Four different factors in each group were recorded - notably the length of pregnancy, number of fry produced, number of live fry after 40 days, and final percentage survival. According to the analyzed data, the number of fry, the number of surviving fry after 40 days, and the percentage survival were significantly higher in the first group with a male to female sex ratio of 1:1 than the other experimental groups. Our results suggest that the best sex ratio for maximum efficiency is 1:1.

A Cock in the Henhouse

Abstract. The present study’s primary aim was to examine the effect of an imbalanced sex ratio on the Dark Triad traits, three types of jealousy, and their relations. For this purpose, data were collected in the Netherlands ( n = 297) and Curaçao ( n = 199). Curaçao is a constituent part of the Netherlands, but has, contrary to the Netherlands, a highly imbalanced sex ratio. We expected the Dark Triad traits to be positively related to anxious and preventive jealousy, but not to reactive jealousy (Hypothesis 1), and, in addition, these relations to be more pronounced in Curaçao than in the Netherlands (Hypothesis 2). Furthermore, it was expected that Curaçaoan men would score higher on the Dark Triad traits than Dutch men (Hypothesis 3), and that Curaçaoan men and women would, overall, report higher levels of jealousy than Dutch men and women (Hypothesis 4). Results largely supported Hypotheses 1, 2, and 4, but not Hypothesis 3. Results are discussed in relation to the role of sex ratio and the cultural beliefs that may accompany it. The current study’s findings may provide new insights into the role of the Dark Triad traits in mating psychology.

Fitness consequences of the selfish supergene Segregation Distorter.

Segregation distorters are selfish genetic elements that subvert Mendelian inheritance, often by destroying gametes that do not carry the distorter. Simple theoretical models predict that distorter alleles will either spread to fixation or stabilize at some high intermediate frequency. However, many distorters have substantially lower allele frequencies than predicted by simple models, suggesting that key sources of selection remain to be discovered. Here, we measured the fitness of Drosophila melanogaster adults and juveniles carrying zero, one or two copies of three different variants of the naturally occurring supergene Segregation Distorter (SD), in order to investigate why SD alleles remain relatively rare within populations despite being preferentially inherited. First, we show that the three SD variants differ in the severity and dominance of the fitness costs they impose on individuals carrying them. Second, SD-carrying parents produced less fit offspring in some crosses, independent of offspring genotype, indicating that SD alleles can have nongenetic, transgenerational costs in addition to their direct costs. Third, we found that SD carriers sometimes produce a biased offspring sex ratio, perhaps due to off-target effects of SD on the sex chromosomes. Finally, we used a theoretical model to investigate how sex ratio and transgenerational effects alter the population genetics of distorter alleles; accounting for these additional costs helps to explain why real-world segregation distorter alleles are rarer than predicted.

Effects of culture conditions on growth and survival of Poecilia sphenops and Poecilia reticulata

Poecilia sphenops and P. reticulata are considered as two most popular and high demanding freshwater ornamental fish species globally. The effects of feeding frequency, feed protein level, photoperiod and salinity on growth and survival of these species and the effect of sex ratio on fecundity were studied under laboratory conditions from January to December 2016. Although there was no any significant impact of feeding frequency on growth and survival of these species, feed protein content affected significantly on their growth. Fry fed with newly hatched Artemia , commercial larval feeds and Chlorella sp. showed no significant impact on growth. Poecilia sphenops and P. reticulata could tolerate salinity up to 10 and 25 ppt, respectively. Fish exposed to 8 hrs photoperiod reported significantly lower growth than those who were exposed to 12 and 24 hrs photoperiods. The ideal female: male sex ratio for commercial stocking of P. sphenops and P. reticulata was 3:2.

Effects of sex ratio on adult fecundity, longevity and egg hatchability of Bradysia difformis Frey at different temperatures.

The fungus gnat Bradysia difformis Frey not only attacks edible and medicinal fungi, it also causes the damages to leek, green onion, garlic and other vegetable crops. To confirm the effects of temperature and sex ratio on adult fecundity, longevity and egg hatchability of B. difformis, we assayed the adults survival longevity and numbers of oviposition, as well as egg hatching rate under female-male ratios of 1:1, 1:2, 1:3, 2:1 and 3:1 at 10, 15, 20, 25 and 30°C. Female fecundity and egg hatchability were increased with temperature and peaked at 25°C, which, however, were adverse to adult longevity. Furthermore, female-male ratio of 1:1, 1:2 and 1:3 seemed suitable for female fecundity, of which the sex ratio of 1:1 was the most suitable ratio for its oviposition behavior. These results provide an insight for predicting the population density of B. difformis and offer a literature reference in the effective treatment of harmful insects by controlling and changing the sex ratio artificially.

The effects of sex-biased fisheries on crustacean sex ratios and reproductive output

ABSTRACTCrustacean fisheries often preferentially or exclusively harvest males, resulting in selection that alters sex ratios in fished populations. Sex-biased fisheries may occur when males are larger and fisheries are size-selective, or when regulations limit or prohibit harvest of females to protect sufficient spawning stock to maintain the population. This review explores the evidence for fishery-induced alterations in sex ratios in crustacean fisheries and the resulting effects on reproductive output at the level of the individual and population. Crustacean fisheries exhibit substantial spatial and temporal variation in exploitation, which could lead to hotspots of altered sex ratios. Experimental manipulations simulating the effects of selective harvest indicate that altered sex ratios can lead to sperm limitation and reduction in the reproductive output of individual females. The effects of altered sex ratios on reproduction at the population scale remain poorly understood. Future directions for improving our understanding of the effects of altered sex ratios on reproductive output include focused studies on sperm limitation at high fishery exploitation rates, model simulations of population scale reproductive output that account for individual variation in sperm quantity, and detailed studies of sperm storage and use during fertilization.

Joint effects of group sex-ratio and Wolbachia infection on female reproductive success in the terrestrial isopod Armadillidium vulgare

BackgroundIn species that reproduce with sexual reproduction, males and females often have opposite strategies to maximize their own fitness. For instance, males are typically expected to maximize their number of mating events, whereas an excessive number of mating events can be costly for females. Although the risk of sexual harassment by males and resulting costs for females are expected to increase with the proportion of males, it remains unknown whether and how parasitic distorters of a host population’s sex-ratio can shape this effect on the fitness of females. Here, we addressed this question using Armadillidium vulgare and its parasite Wolbachia that alters the sex-ratio of a population. We set up Wolbachia-free and Wolbachia-infected females in experimental groups exhibiting 100, 80, 50% or 20% females for 1 year, during which we measured changes in survival, fertility and fecundity.ResultsWolbachia infection shaped the effects of both population sex-ratio and reproductive season on female fecundity. Compared to Wolbachia-free females, Wolbachia-infected females were less likely to be gravid in populations exhibiting an excess of females and did not exhibit the otherwise negative effect of seasons on this likelihood. Group sex-ratio and Wolbachia infection have independent effects on other measured traits. Male-biased populations had females both exhibiting the lowest survival rate after 6 months and producing the smallest number of offspring, independent of Wolbachia infection. Conversely, Wolbachia-infected females had the lowest likelihood of producing at least one offspring, independent of group sex-ratio. Wolbachia infection had no effect on female survival rate.ConclusionsWe demonstrated that male-biased sex-ratio and the presence of Wolbachia are costly for females due to sexual harassment by males and bacterial infection, respectively. Interestingly, Wolbachia infection triggers another negative effect. This effect does not come from an excess of males and its associated sexual harassment of females but instead from a lack of males and the associated risk for females of remaining unmated. Overall, these findings highlight the importance of social pressures and infection on female fitness and provide insights into our general understanding of the joint and opposite effects of these two parameters in the evolution of reproductive strategies.

Effect of sex ratio, storage time and temperature on hatching rate, fertility and embryonic mortality in Chukar partridge (Alectoris chukar)

Chukar partridges (Alectoris chukar) are frequently reared in captivity with the aim of producing fertile eggs and chicks. The aims of the present study were to evaluate the effect of male to female sex ratio on hatching rate and fertility and to determine the optimal temperature and time for egg storage and its effect on hatching rate and embryonic mortality in Chukar partridges. Maximum hatching rate and fertility rate were affected by male:female ratios during breeding (P < 0.05). The greatest embryonic mortality rate was with eggs that were stored at 25 °C for 15–20 d, however, the greatest hatching rate was when eggs were stored at 10 and 15 °C for 5 days. Storage time of Chukar partridge eggs can be extended for as long as 5 d, but longer storage periods can negatively affect hatching rate. In conclusion, a reduction of storage temperature and duration of time of storage in combination with reducing the sex ratio of the egg producing females and males during the breeding period might improve fertility, hatching rate and fertility of Chukar partridge eggs.

Evolving social dynamics prime thermal tolerance during a poleward range shift

Cold tolerance plays a critical role in determining species geographical range limits. Previous studies have found that range shifts in response to climate warming are facilitated by cold acclimation capacities, due to increasingly colder and variable weather at high latitudes, and that cold tolerance can also be influenced by social factors. In this study we combined experiments and field studies to investigate the climatic and social factors affecting cold tolerances in range- shifting populations of the female-polymorphic damselfly Ischnura elegans in northeast Scotland. In the field, we observed both environmental (measured via habitat suitability) and social (sex ratio and density) effects on cold tolerance (CTmin). Androchrome females (male-like females) were less susceptible to beneficial social effects on cold tolerance than gynochromes (female- like females), and correspondingly, gynochrome frequency increased at colder, environmentally- limiting sites towards the range margin. Our manipulations of density in the laboratory further provide novel, experimental evidence that social interactions directly impact cold tolerance n this species. These results suggest that reciprocal effects of social environments on thermal acclimation may be an important but commonly overlooked aspect of allee effects which contribute to the formation of range margins. Moreover, our results point to a wider need to consider the role of population and social dynamics to shape both the thermal physiology of individuals and the thermal niches of species.

Effect of flower sex ratio on fruit set in pumpkin (Cucurbita maxima)

Flower sex expression and sex ratio are the two plant functional traits likely to explain pollination efficiency in monoecious animal-pollinated plants. Cucurbitaceae crop plants are staminate flower-biased, but, relatively little is known about the natural variation in flower sex expression and the effect of flower sex ratio on fruit set. To address these, 325 plants of Cucurbita maxima were monitored for the entire flowering cycle and studied fruit set in 1515 pistillate flowers under open conditions for two years. The flower sex ratio of the fields and the plants and the flowering age (=phase) of the plants were used as the predictors of fruit set. The blooming in C. maxima started with the staminate flowers; 67% of the plants produced a staminate flower first, which continued for about ten days. The number of staminate flowers produced in the plants strongly predicted the number of pistillate flowers bloomed later. The sex ratio of the fields, rather than that of an individual plant, predicted the fruit set. Although pollinators are vital for pollination in animal-pollinated monoecious plants, our results suggest that flower sex ratio is also a crucial predictor of pollination efficiency. Monitoring flower sex expression in fields may be required to predict realistic fruit set and to take necessary measures, including facilitated pollination to improve fruit set.

Parasitism, sexual dimorphism and effect of host size on Apocephalus attophilus offspring, a parasitoid of the leaf-cutting ant Atta bisphaerica.

Atta bisphaerica (Forel) is a leaf-cutting ant that specializes on grass and causes productivity losses in sugar cane fields and pastures. Three phorid species, Apocephalus attophilus (Borgmeier), Myrmosicarius grandicornis (Borgmeier) and Eibesfeldtphora bragancai (Brown), have been found parasitizing A. bisphaerica workers. These parasitoids can reduce plant material transported into the nests and ant traffic on the trails. Therefore, phorid flies have been considered potential biological control agents for leaf-cutting ants. Here, we evaluated which parasitoid species attack the leaf-cutting ant A. bisphaerica in pasture areas of a Brazilian Savannah-Atlantic Forest ecotone, parasitism rate, effect of host size, sexual dimorphism and sex ratio of the emerged parasitoids. Four nests of A. bisphaerica were selected in pasture areas from August 2016 to August 2017, with 400 workers collected from each colony monthly. A total of 23,714 A. bisphaerica workers were collected during the study, of which 236 (0.99%) were parasitized by phorid parasitoids. Apocephalus attophilus, E. bragancai and M. grandicornis parasitized 217, 17 and 2 ants, respectively. The higher parasitism rate was found in the hottest/rainy season of the year. Non-parasitized ants survived longer than those parasitized by A. attophilus. The larval and pupal periods of this parasitoid were 2.2 ± 0.8 and 16 ± 1.4 days, respectively, and the number of pupae per parasitized ant ranged from 1 to 7. The number of A. attophilus pupae per host increased with the host head size. Likewise, the size of the adult parasitoids also increased according to the host ant. Apocephalus attophilus females were larger than males and the sex ratio (male: female) did not differ from 1: 1. Our results showed that A. attophilus would be a potential biocontrol agent of leaf-cutting ants because it produces multiple larvae per host, allowing a great production of parasitoids with short developmental time and kills the host ant faster than other phorids.

Complex interaction of resource availability, life-history and demography determines the dynamics and stability of stage-structured populations

The dynamics of stage-structured populations facing stage-specific variability in resource availability and/or demographic factors like unequal sex-ratios, remains poorly understood. We addressed these issues using a stage-structured individual-based model that incorporates life-history parameters common to many holometabolous insects. The model was calibrated using time series data from a 49-generation experiment on laboratory populations of Drosophila melanogaster, subjected to four different combinations of larval and adult nutritional levels. The model was able to capture multiple qualitative and quantitative aspects of the empirical time series across three independent studies. We then simulated the model to explore the interaction of various life-history parameters and nutritional levels in determining population stability. In all nutritional regimes, constancy stability of the populations was reduced upon increasing egg-hatchability, critical mass, and proportion of body resource allocated to female fecundity. However, the effects of increasing sensitivity of female-fecundity to adult density on constancy stability varied across nutrition regimes. The effects of unequal sex-ratio and sex-specific culling were greatly influenced by fecundity but not by levels of juvenile nutrition. Finally, we investigated the implications of some of these insights on the efficiency of the widely-used pest control method, the Sterile Insect Technique (SIT). We show that increasing the amount of juvenile food had no effects on SIT efficiency when the density-independent fecundity is low, but reduces SIT efficiency when the density-independent fecundity is high.