Sex Ratio In Response Research Articles

Brood size and sex ratio in response to host quality and wasp traits in the gregarious parasitoid Oomyzus sokolowskii (Hymenoptera: Eulophidae).

This laboratory study investigated whether the larval-pupal parasitoid Oomyzus sokolowskii females adjust their brood size and sex ratio in response to body size and stage of Plutella xylostella larval hosts, as well as to their own body size and the order of oviposition. These factors were analyzed using multiple regression with simultaneous entry of them and their two-way interactions. Parasitoids brood size tended to increase with host body size at parasitism when the 4th instar larval host was attacked, but did not change when the 2nd and 3rd instar larvae were attacked. Parasitoids did not vary in brood size according to their body size, but decreased with their bouts of oviposition on a linear trend from 10 offspring adults emerged per host in the first bout of oviposition down to eight in the third. Parasitoid offspring sex ratio did not change with host instar, host body weight, wasp body size, and oviposition bout. Proportions of male offspring per brood were from 11% to 13% from attacking the 2nd to 4th instar larvae and from 13% to 16% across three successive bouts of oviposition, with a large variation for smaller host larvae and wasps. When fewer than 12 offspring were emerged from a host, one male was most frequently produced; when more than 12 offspring were emerged, two or more males were produced. Our study suggests that O. sokolowskii females may optimize their clutch size in response to body size of mature P. xylostella larvae, and their sex allocation in response to clutch size.

Heat-induced masculinization in domesticated zebrafish is family-specific and yields a set of different gonadal transcriptomes

Understanding environmental influences on sex ratios is important for the study of the evolution of sex-determining mechanisms and for evaluating the effects of global warming and chemical pollution. Fishes exhibit sexual plasticity, but the underlying mechanisms of environmental effects on their reproduction are unclear even in the well-established teleost research model, the zebrafish. Here we established the conditions to study the effects of elevated temperature on zebrafish sex. We showed that sex ratio response to elevated temperature is family-specific and typically leads to masculinization (female-to-male sex reversal), resulting in neomales. These results uncovered genotype-by-environment interactions that support a polygenic sex determination system in domesticated (laboratory) zebrafish. We found that some heat-treated fish had gene expression profiles similar to untreated controls of the same sex, indicating that they were resistant to thermal effects. Further, most neomales had gonadal transcriptomes similar to that of regular males. Strikingly, we discovered heat-treated females that displayed a normal ovarian phenotype but with a "male-like" gonadal transcriptome. Such major transcriptomic reprogramming with preserved organ structure has never been reported. Juveniles were also found to have a male-like transcriptome shortly after exposure to heat. These findings were validated by analyzing the expression of genes and signaling pathways associated with sex differentiation. Our results revealed a lasting thermal effect on zebrafish gonads, suggesting new avenues for detection of functional consequences of elevated temperature in natural fish populations in a global warming scenario.

Altered sex ratios in response to climate change-Who will fall into the (epigenetic) trap? (Comment on DOI 10.1002/bies.201600058).

BioEssaysVolume 38, Issue 10 p. 939-939 Thoughts & Opinion Altered sex ratios in response to climate change—Who will fall into the (epigenetic) trap? (Comment on DOI 10.1002/bies.201600058) Francesc Piferrer, Corresponding Author Francesc Piferrer piferrer@icm.csic.es Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), Barcelona, Spain Corresponding author: Francesc Piferrer E-mail: piferrer@icm.csic.esSearch for more papers by this author Francesc Piferrer, Corresponding Author Francesc Piferrer piferrer@icm.csic.es Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas (CSIC), Barcelona, Spain Corresponding author: Francesc Piferrer E-mail: piferrer@icm.csic.esSearch for more papers by this author First published: 31 August 2016 https://doi.org/10.1002/bies.201600172Citations: 10Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume38, Issue10October 2016Pages 939-939 RelatedInformation

The Maternal Legacy: Female Identity Predicts Offspring Sex Ratio in the Loggerhead Sea Turtle.

In organisms with temperature-dependent sex determination, the incubation environment plays a key role in determining offspring sex ratios. Given that global temperatures have warmed approximately 0.6 °C in the last century, it is necessary to consider how organisms will adjust to climate change. To better understand the degree to which mothers influence the sex ratios of their offspring, we use 24 years of nesting data for individual female loggerhead sea turtles (Caretta caretta) observed on Bald Head Island, North Carolina. We find that maternal identity is the best predictor of nest sex ratio in univariate and multivariate predictive models. We find significant variability in estimated nest sex ratios among mothers, but a high degree of consistency within mothers, despite substantial spatial and temporal thermal variation. Our results suggest that individual differences in nesting preferences are the main driver behind divergences in nest sex ratios. As such, a female’s ability to plastically adjust her nest sex ratios in response to environmental conditions is constrained, potentially limiting how individuals behaviorally mitigate the effects of environmental change. Given that many loggerhead populations already show female-biased offspring sex ratios, understanding maternal behavioral responses is critical for predicting the future of long-lived species vulnerable to extinction.

Patch exploitation strategies of parasitoids under indirect intra‐ and inter‐specific competition

1. Insect parasitoids are expected to evolve behavioural strategies to exploit resources in competitive environments optimally. Indirect competition between parasitoids is particularly common because exploited host patches remain available in the environment for other foraging individuals.2. The effects of indirect competition on the behaviour of two closely related generalist egg parasitoids were investigated: Trichogramma pintoi Voegelé and Trichogramma minutum Riley (Hymenoptera: Trichogrammatidae). Patch residence time, a patch‐leaving mechanism, and progeny sex allocation of females foraging were analysed: (i) alone, (ii) in patches partially parasitised by conspecifics, and (iii) in patches partially parasitised by heterospecifics.3. Each species responded differently to indirect competition. Trichogramma pintoi females shortened their patch residence times, but they did not adjust their progeny sex ratios. In contrast, T. minutum females did not modify their patch residence times, but they did increase their progeny sex ratios in response to competition. Both Trichogramma species used host rejection, either by antenna rejection or by ovipositor rejection, as a patch‐leaving mechanism.4. In agreement with a companion study of direct competition using the same model species, the present results indicate that even amongst closely related species, responses to competition can vary considerably.

Female mountain bluebirds (Sialia currucoides) paired to more colourful males produce male-biased broods

Sex allocation theory predicts that females should bias the sex ratio of their offspring in response to differences in the reproductive value of sons versus daughters. Consistent with this prediction, females of many species appear to bias offspring sex ratios in response to mate attractiveness and condition. Male mountain bluebirds (Sialia currucoides) display full body UV-blue structural plumage colouration, which is associated with attractiveness, condition, and reproductive success. Over four breeding seasons, we found females paired with more colourful males produced increasingly male-biased broods and provisioned offspring at a higher rate. Surprisingly, however, we also found females with duller plumage and those mated to first-year males produced more male-biased broods. These results provide support for sex allocation in mountain bluebirds and suggest female reproductive decisions may be influenced by the attractiveness of her mate. However, this system is clearly complex and more work is needed to understand the roles of male age and female colouration in the signalling systems of mountain bluebirds.

Territory Quality and Plumage Morph Predict Offspring Sex Ratio Variation in a Raptor.

Parents may adapt their offspring sex ratio in response to their own phenotype and environmental conditions. The most significant causes for adaptive sex-ratio variation might express themselves as different distributions of fitness components between sexes along a given variable. Several causes for differential sex allocation in raptors with reversed sexual size dimorphism have been suggested. We search for correlates of fledgling sex in an extensive dataset on common buzzards Buteo buteo, a long-lived bird of prey. Larger female offspring could be more resource-demanding and starvation-prone and thus the costly sex. Prominent factors such as brood size and laying date did not predict nestling sex. Nonetheless, lifetime sex ratio (LSR, potentially indicative of individual sex allocation constraints) and overall nestling sex were explained by territory quality with more females being produced in better territories. Additionally, parental plumage morphs and the interaction of morph and prey abundance tended to explain LSR and nestling sex, indicating local adaptation of sex allocation However, in a limited census of nestling mortality, not females but males tended to die more frequently in prey-rich years. Also, although females could have potentially longer reproductive careers, a subset of our data encompassing full individual life histories showed that longevity and lifetime reproductive success were similarly distributed between the sexes. Thus, a basis for adaptive sex allocation in this population remains elusive. Overall, in common buzzards most major determinants of reproductive success appeared to have no effect on sex ratio but sex allocation may be adapted to local conditions in morph-specific patterns.

Facultative adjustment of the offspring sex ratio and male attractiveness: a systematic review and meta-analysis.

Females can benefit from mate choice for male traits (e.g. sexual ornaments or body condition) that reliably signal the effect that mating will have on mean offspring fitness. These male-derived benefits can be due to material and/or genetic effects. The latter include an increase in the attractiveness, hence likely mating success, of sons. Females can potentially enhance any sex-biased benefits of mating with certain males by adjusting the offspring sex ratio depending on their mate's phenotype. One hypothesis is that females should produce mainly sons when mating with more attractive or higher quality males. Here we perform a meta-analysis of the empirical literature that has accumulated to test this hypothesis. The mean effect size was small (r = 0.064-0.095; i.e. explaining <1% of variation in offspring sex ratios) but statistically significant in the predicted direction. It was, however, not robust to correction for an apparent publication bias towards significantly positive results. We also examined the strength of the relationship using different indices of male attractiveness/quality that have been invoked by researchers (ornaments, behavioural displays, female preference scores, body condition, male age, body size, and whether a male is a within-pair or extra-pair mate). Only ornamentation and body size significantly predicted the proportion of sons produced. We obtained similar results regardless of whether we ran a standard random-effects meta-analysis, or a multi-level, Bayesian model that included a correction for phylogenetic non-independence. A moderate proportion of the variance in effect sizes (51.6-56.2%) was due to variation that was not attributable to sampling error (i.e. sample size). Much of this non-sampling error variance was not attributable to phylogenetic effects or high repeatability of effect sizes among species. It was approximately equally attributable to differences (occurring for unknown reasons) in effect sizes among and within studies (25.3, 22.9% of the total variance). There were no significant effects of year of publication or two aspects of study design (experimental/observational or field/laboratory) on reported effect sizes. We discuss various practical reasons and theoretical arguments as to why small effect sizes should be expected, and why there might be relatively high variation among studies. Currently, there are no species where replicated, experimental studies show that mothers adjust the offspring sex ratio in response to a generally preferred male phenotype. Ultimately, we need more experimental studies that test directly whether females produce more sons when mated to relatively more attractive males, and that provide the requisite evidence that their sons have higher mean fitness than their daughters.

Response of sex ratio to timing of breeding in the small cyprinid Gnathopogon caerulescens.

The influence of hatching date on the sex ratio of wild Gnathopogon caerulescens was examined. Cohorts reared from eggs collected in the early and middle parts of the spawning season showed almost balanced sex ratios, with female bias in some cohorts. Cohorts born later in the season mostly displayed male bias, and the mean proportion of males later in the season was significantly higher than in early- and mid-season cohorts. These results indicate that the sex ratio of G. caerulescens changes with the time of breeding, increasing along with the ambient water temperature of the lake.

Female Red-Breasted Flycatchers(Ficedula Parva) mated with older males produce male-biased broods

Recent avian studies suggest that offspring sex ratios can vary with environmental or parental characteristics. One example is that females may adjust brood sex ratio of fledglings in response to the sexual attractiveness of their mate and are expected to produce more sons when mated with older or more ornamented males. We determined offspring sex ratios at fledging (158 nestlings from 33 broods) in a population of migratory bird species, Red-breasted Flycatchers (Ficedula parva) that were breeding on the western edge of their geographic range, in the strictly protected part of the Białowieża Forest (north-eastern Poland). The ratio of individual broods ranged from all male to all female, but the average offspring sex ratio at the population level did not deviate significantly from the expected 50:50 sex ratio. Moreover, we found no evidence that sex ratio varied significantly with year, with the incidence of extra-pair paternity, with partial brood losses, or with brood size. However, females mated to older males (older males are also more ornamented) were significantly more likely to produce male-biased broods. Our data suggest that female Red-breasted Flycatchers manipulate sex ratio in response to their mate’s age.

Oviposition, Superparasitism, and Egg Load in the Solitary Parasitoid Diachasmimorpha longicaudata (Hymenoptera: Braconidae): Response to Host Availability

Parasitoid reproduction is often limited by disposable time for accessing hosts or egg availability. In the case of synovigenic parasitoids (which mature eggs during their lifetime), theory predicts that egg limitation is infrequent because they are able to replenish their egg supply throughout life. However, this theory does not contemplate the effect of superparasitism on egg load. If superparasitism is applied as a strategy for modulating offspring sex ratio, as extra eggs are normally deposited in each host, it is to be expected that females experience egg limitation, especially when host density is high. In this article, the effect of host density on egg load, oviposition, and sex ratio in the tephritid parasitoid Diachasmimorpha longicaudata (Ashmead) was investigated. Specifically we analyzed the rate of oviposition per host and adjustments in offspring sex ratio in response to changes in host density and how these affect egg load. Parasitoids maintained a similar rate of oviposition, independent of host densities, except when host density fluctuated between 25 and 5 hosts per day. Females increased their oviposition rate and parasitism when confronted with 5 hosts, after having experienced a density of 25 hosts. Offspring sex ratio was biased in favor of females at high host density and with increasing prevalence of superparasitism. Results suggest that parasitoids have a strategy for maintaining high egg load in order to mitigate egg limitation, and for adjusting oviposition rate and offspring sex ratio with reference to previous oviposition experience.

Loss of sex-allocation plasticity in the predatory mite Metaseiulus occidentalis and possible triggering cues

In two recent studies, we showed that females from a long-established Metaseiulus (Typhlodromus or Galendromus) occidentalis laboratory colony reared under crowded conditions for approximately 27years produced equal numbers of male and female progeny. This contrasts with our previous results that showed the females from the same colony produced progeny with a female-biased sex ratio. These discrepant findings raised the possibility that dense rearing conditions can affect the sex-allocation plasticity in this important biological control agent. In the current study, we show that females from a newly collected M. occidentalis colony initially were capable of producing progeny with a female-biased sex ratio, but lost this ability over a 12-month period (43 generations) when reared under dense rearing conditions and provided with damaged prey. We demonstrate that females from this newly collected colony initially could adjust offspring sex ratio in response to both conspecific cues and cues produced by their damaged prey. The results suggest that dense rearing conditions, which are often used in commercial rearing facilities, may have detrimental effects on the reproductive fitness of M. occidentalis and, possibly, other predatory mites.

Multiple queens and biased sex ratios in the independent‐founding Ropalidia Guérin‐Méneville, 1831 (Hymenoptera: Vespidae) wasps

AbstractThe social wasp genus Ropalidia includes both ‘swarm‐founding’ species with large, multi‐queen colonies, and ‘independent‐founding’ species that have smaller colonies and fewer queens. Swarm‐founding evolved from independent‐founding, and a key element of this transition was the evolution of queen cycling, which elevates relatedness despite high average queen numbers. Queen cycling is a form of split‐sex ratios; colonies with few queens specialise on new queen production, while colonies with many queens specialise on male production. This is consistent with worker preferences resulting from relatedness asymmetry (RA) to male and female brood but can also result from other factors. We characterised the demographic and genetic structure of colonies from three species of independent‐founding Ropalidia (R. excavata, R. revolutionalis and R. gregaria) to better understand the evolutionary origins of split‐sex ratios and queen cycling in their swarm‐founding relatives. We found that colonies of all three species varied in genetic structure, driving variation in RA. In colonies where the workers' RA was high (i.e. workers were more related to female than male brood), the proportion of males in the brood was lower, consistent with the relatedness‐based preferences of the workers. We also found that the proportion of males decreased in colonies with more mated and reproductively developed females. Our model explained 23% of the deviance in sex ratio across all three species and suggests that the workers manipulate the sex ratio in response to RA but that other factors are clearly important also. These results further suggest that split‐sex ratios and queen cycling in the swarm‐founding wasps are rooted in worker control of the colony sex ratio, and that such worker control may have occurred in their independent‐founding ancestors, enabling the subsequent evolution of large, multi‐queen societies.

Information use and plasticity in the reproductive decisions of malaria parasites.

BackgroundInvestment in the production of transmissible stages (gametocytes) and their sex ratio are malaria parasite traits that underpin mosquito infectivity and are therefore central to epidemiology. Malaria parasites adjust their levels of investment into gametocytes and sex ratio in response to changes in the in-host environment (including red blood cell resource availability, host immune responses, competition from con-specific genotypes in mixed infections, and drug treatment). This plasticity appears to be adaptive (strategic) because parasites prioritize investment (in sexual versus asexual stages and male versus female stages) in manners predicted to maximize fitness. However, the information, or ‘cues’ that parasites use to detect environmental changes and make appropriate decisions about investment into gametocytes and their sex ratio are unknown.MethodsSingle genotype Plasmodium chabaudi infections were exposed to ‘cue’ treatments consisting of intact or lysed uninfected red blood cells, lysed parasitized RBCs of the same clone or an unrelated clone, and an unmanipulated control. Infection dynamics (proportion of reticulocytes, red blood cell and asexual stage parasite densities) were monitored, and changes in gametocyte investment and sex ratio in response to cue treatments, applied either pre- or post-peak of infection were examined.Results and conclusionsA significant reduction in gametocyte density was observed in response to the presence of lysed parasite material and a borderline significant increase in sex ratio (proportion of male gametocytes) upon exposure to lysed red blood cells (both uninfected and infected) was observed. Furthermore, the changes in gametocyte density and sex ratio in response to these cues depend on the age of infection. Demonstrating that variation in gametocyte investment and sex ratio observed during infections are a result of parasite strategies (rather than the footprint of host physiology), provides a foundation to investigate the fitness consequences of plasticity and explore whether drugs could be developed to trick parasites into making suboptimal decisions.

The evolution of sex ratio differences and inflorescence architectures in Begonia (Begoniaceae)

A major benefit conferred by monoecy is the ability to alter floral sex ratio in response to selection. In monoecious species that produce flowers of a given sex at set positions on the inflorescence, floral sex ratio may be related to inflorescence architecture. We studied the loci underlying differences in inflorescence architecture between two monoecious Begonia species and related this to floral sex ratios. We performed trait comparisons and quantitative trait locus (QTL) mapping in a segregating backcross population between Central American Begonia plebeja and B. conchifolia. We focused on traits related to inflorescence architecture, sex ratios, and other reproductive traits. The inflorescence branching pattern of B. conchifolia was more asymmetric than B. plebeja, which in turn affects the floral sex ratio. Colocalizing QTLs of moderate effect influenced both the number of male flowers and the fate decisions of axillary meristems, demonstrating the close link between inflorescence architecture and sex ratio. Additional QTLs were found for stamen number (30% variance explained, VE) and pollen sterility (12.3% VE). One way in which Begonia species develop different floral sex ratios is through modifications of their inflorescence architecture. The potential pleiotropic action of QTL on inflorescence branching and floral sex ratios may have major implications for trait evolution and responses to selection. The presence of a single QTL of large effect on stamen number may allow rapid divergence for this key floral trait. We propose candidate loci for stamen number and inflorescence branching for future characterization.

Hormone-Mediated Adjustment of Sex Ratio in Vertebrates

The ability to adjust sex ratios at the individual level exists among all vertebrate groups studied to date. In many cases, there is evidence for facultative adjustment of sex ratios in response to environmental and/or social cues. Because environmental and social information must be first transduced into a physiological signal to influence sex ratios, hormones likely play a role in the adjustment of sex ratio in vertebrates, because the endocrine system acts as a prime communicator that directs physiological activities in response to changing external conditions. This symposium was developed to bring together investigators whose work on adjustment of sex ratio represents a variety of vertebrate groups in an effort to draw comparisons between species in which the sex-determination process is well-established and those in which more work is needed to understand how adjustments in sex ratio are occurring. This review summarizes potential hormone targets that may underlie the mechanisms of adjustment of sex ratio in humans, non-human mammals, birds, reptiles, and fishes.

English

Many studies have demonstrated that many species of parasitoid wasps can control offspring sex ratio in response to environmental variables. This article tests the effects of temperature, relative humidity, photoperiod, foundress number, foundress age, host number, interval time of host supplying, species of food, species of host and symbiotic bacterium (Wolbachia) on sex ratio of&nbsp;Trichogramma ostriniae. Results showed that the sex ratio of&nbsp;T. ostriniae&nbsp;was affected significantly by temperature (35&deg;C), number of foundress (&gt;2 number), age of foundress (3-day-old) and&nbsp;Wolbachia. Through transmitted&nbsp;Wolbachia&nbsp;from&nbsp;Trichogramma embryophagum&nbsp;to&nbsp;Trichogramma dendrolimi, even the reproductive mode of&nbsp;T. dendrolimi&nbsp;was changed from gamogenesis to thelytoky. Our work verifies the sex ratio theory and implies that the potential effectiveness ofTrichogramma&nbsp;spp. as a biological control agent can be further improved. &nbsp; Key words:&nbsp;Environmental factors, biological factors, sex ratio,&nbsp;Wolbachia,&nbsp;Trichogramma ostriniae.

THE COMPLEX INTERPLAY OF SEX ALLOCATION AND SEXUAL SELECTION

It is well recognized that sex allocation strategies can be influenced by sexual selection, when females adjust offspring sex ratios in response to their mates' attractiveness. Yet the reciprocal influence of strategic sex allocation on processes of sexual selection has only recently been revealed. Recent theoretical work demonstrates that sex allocation weakens selection for female preferences, leading to the decline of male traits. However, these results have been derived assuming that females have perfect knowledge of mate attractiveness and precise control over cost-free allocation. Relaxing these assumptions highlights the importance of another feedback: that adaptive sex allocation must become difficult to maintain as traits and preferences decline. When sex allocation strategies erode not only traits and preferences but also their own selective advantage, predictions can no longer be expressed as a simple linear correlation between ornament exaggeration and adaptive sex allocation. Instead, strongest sex ratio biases may be found at intermediate trait levels.

Sex-ratio adjustment in response to local mate competition is achieved through an alteration of egg size in a haplodiploid spider mite.

Sex-ratio adjustments are commonly observed in haplodiploid species. However, the underlying proximate mechanisms remain elusive. We investigated these mechanisms in Tetranychus urticae, a haplodiploid spider mite known to adjust sex ratio in response to the level of local mate competition (LMC). In this species, egg size determines fertilization probability, with larger eggs being more likely to be fertilized, and thus become female. We explored the hypothesis that sex-ratio adjustment is achieved through adjustment of egg size. By using spider mites from a large population, we found that females produced not only a higher proportion of daughters under high levels of LMC, but also larger eggs. Moreover, in populations experimentally evolving under varying levels of LMC, both the proportion of females and the egg size increased with LMC intensity. These results suggest that sex-ratio adjustment in spider mites is mediated by egg size, although the causal relationship remains to be tested.

Mothers adjust offspring sex to match the quality of the rearing environment

Theory predicts that mothers should adjust offspring sex ratios when the expected fitness gains or rearing costs differ between sons and daughters. Recent empirical work has linked biased offspring sex ratios to environmental quality via changes in relative maternal condition. It is unclear, however, whether females can manipulate offspring sex ratios in response to environmental quality alone (i.e. independent of maternal condition). We used a balanced within-female experimental design (i.e. females bred on both low- and high-quality diets) to show that female parrot finches (Erythrura trichroa) manipulate primary offspring sex ratios to the quality of the rearing environment, and not to their own body condition and health. Individual females produced an unbiased sex ratio on high-quality diets, but over-produced sons in poor dietary conditions, even though they maintained similar condition between diet treatments. Despite the lack of sexual size dimorphism, such sex ratio adjustment is in line with predictions from sex allocation theory because nutritionally stressed foster sons were healthier, grew faster and were more likely to survive than daughters. These findings suggest that mothers may adaptively adjust offspring sex ratios to optimally match their offspring to the expected quality of the rearing environment.