Manipulation Of Offspring Sex Ratio Research Articles

A possible case of offspring sex manipulation as result of a biased adult sex ratio

Although random meiosis should prevent the facultative adjustment of offspring sex ratio, theory predicts that females should produce more of the sex with the higher reproductive value. We reported a case of offspring sex ratio manipulation in grass wrens Cistothorus platensis. Males in better body condition would have higher reproductive value than females due to the potential for social polygyny and extra-pair fertilizations. On the other hand, local demography influences reproductive strategies in grass wrens as male abundance affects both social polygyny and extra-pair paternity frequencies. We evaluated whether females bias their brood sex ratio in response to adult sex ratio and nestling body condition (a proxy for female’s prospects of producing high-quality males). Females raised more male offspring when males were less abundant in the population (female-biased adult sex ratio). However, we found no relationship between nestling body condition and brood sex ratio, suggesting that females did not bias the brood sex ratio towards males when able to raise nestlings in better body condition. Taken together, our results provide the first suggestive evidence that female birds can manipulate their offspring sex ratio in response to the adult sex ratio.

Determinants of offspring sex in kangaroos: a test of multiple hypotheses

Abstract When the fitness costs and benefits of sons and daughters differ, offspring sex ratio manipulation could be an important reproductive tactic. We explored the effects of environment and maternal caring ability on offspring sex to test four adaptive sex ratio modification hypotheses: the extrinsic modification hypothesis (EMH), carrying capacity hypothesis (CCH), Trivers-Willard hypothesis (TWH), and cost-of-reproduction hypothesis (CRH). The EMH and CCH propose that environmental conditions shape offspring sex ratios, directly or in interaction with maternal condition. The TWH and CRH predict a positive relationship between maternal condition and production of the costlier sex. The TWH predicts that mothers with superior caring ability should produce more of the sex that can provide the greatest fitness returns from additional maternal allocation, and the CRH proposes that females with limited caring ability should reduce fitness costs by producing the cheaper sex. Repeated measures on 83 known-age eastern gray kangaroos, polygynous marsupials with strong sexual dimorphism, revealed that offspring sex ratio was independent of per capita forage, supporting neither the EMH nor CCH, but was dependent on maternal mass, consistent with the TWH and CCH. Our results, however, cannot clearly identify the ultimate cause of the relationship between maternal mass and greater production of sons. One of the three assumptions of the TWH could not be verified, and mothers of sons suffered only marginal additional fitness costs. Sex ratios in higher vertebrates are likely not solely explained by factors dependent on maternal control.

Exogenous Progesterone for Offspring Sex Ratio Manipulation in Arabic Chickens (Gallus turcicus) Leading to Increasing Female Chicks Proportion

Female birds of egg-laying hens are more valuable than males, because males bird have no commercial value. The opportunity to manipulate offspring sex ratio in poultry has been observed in female birds; hence, female birds have heterogametic ZW chromosomes. High progesterone concentration 2-5 h before ovulation is thought to affect the segregation of female sex chromosomes as the basis for determining the sex of offspring. This study aimed to investigate the effect of progesterone induction in Arabic hens, which was conducted 5 h before ovulation, along with the time of the first meiosis; therefore, segregation of sex chromosomes leading to an increase in female offspring. The study utilized on 60 Arabic hens divided into three treatment groups: Without injection (P0), progesterone injection 1 mg/hen, (P1), progesterone injection 2 mg/hen (P2). The results showed that the percentage of female offspring at P0 and P1 was 54.74 and 53.33%, respectively, while P2 hens resulted in 62.92% females, the highest female offspring rate than the other groups. Chi-square analysis of sex ratio showed that P0 and P1 hens had no significant effect (P>0.05) while P2 hens being significant (P<0.05) from the expected sex ratio (50:50). Progesterone concentration of hens produced female offspring in the P2 group was 7.15 ng/ml being highly significant (P<0.05) than that found in the hens produced male offspring (4.53 ng/ml). Progesterone 5 h preceding ovulation in the Arabic hens with a 2 mg/hen dose can increase the proportion of female offspring; therefore, an opportunity for sex ratio manipulation in Arabic chickens.

Revisiting the Trivers-Willard theory on birth sex ratio bias: Role of paternal condition in a Malagasy primate.

Within current theories on potential adaptive manipulation of offspring sex ratio, giving birth to a male or to a female is assumed to depend on the capacity of the mother to invest in offspring to maximize her fitness. The active role of the father in sex ratio bias at birth has been neglected until recently. The human sex ratio at birth is biased towards sons, although in occidental populations, the ratio has decreased regularly for 30 years and could be the consequence of the adverse effects of environmental chemicals on male hormones. In a Malagasy primate, the lesser mouse lemur, the potential effect of paternal testosterone levels on sex ratio bias at birth was tested on 130 litters (278 babies) produced in 52 mixed-sex groups. For each group, social dominance among males was characterized based on aggressive interactions and sexual behaviours. Using a multi correspondence analysis, high testosterone levels in grouped males, particularly those of the dominant male, were significantly correlated with more infants produced in male-biased litters, independent of the female condition. According to these results, predictions for sex ratio bias towards one sex or the other in mouse lemurs were discussed considering the influence of both parents.

Annual variation in the offspring sex ratio of Saltmarsh Sparrows supports Fisher's hypothesis

ABSTRACT Evolutionary theory suggests that natural selection should favor the ability of animals to modify their offspring sex ratios when the fitness benefits of producing one sex over the other vary in relation to environmental conditions. The Saltmarsh Sparrow (Ammodramus caudacutus) is an extreme habitat specialist, with breeding behavior influenced by the tidal cycle. The challenges of nesting in the harsh environment of salt marshes and the unique promiscuous mating system of the Saltmarsh Sparrow provide a context for offspring sex ratio manipulation. We investigated adaptive sex ratio manipulation in this system across multiple sites and years using a mixed modeling approach. We collected data on nest initiation and nestling survival from 370 nests of 210 females during 2011–2015 in 4 marshes in the northeastern United States. Using molecular techniques, we determined the sex of 990 offspring and characterized variation in site- and population-level sex ratios. Using binomial linear mixed-effects ...

Offspring sex ratio of a woodland songbird is unrelated to habitat fragmentation

We assessed whether the sex ratio of nestling Marsh Tits (Poecile palustris) varied with habitat fragmentation by sampling broods from two British woodland areas with contrasting patch size, and comparing the data with published results from an extensive forest in Poland. We found no evidence for manipulation of offspring sex ratios, supporting findings from Poland, and suggesting that this trait may be typical of the species. The results are important in helping to understand the origin of biased sex ratios observed among adult Marsh Tits in the declining population in Britain.

No facultative manipulation of offspring sex ratio in relation to parental genetic characteristics in a bird with sex-specific heterozygosity-fitness correlation

Sex allocation theory predicts that parents should adjust their investment between female and male offspring when the fitness return of producing them differs. Genome-wide heterozygosity is related to many aspects of individual fitness, and an individual’s heterozygosity is usually determined by the genetic characteristics of its parents. When heterozygosity affects fitness differently for female and male offspring, parents may be expected to manipulate offspring sex ratio based on their own genetic characteristics. We examined whether parental genetic characteristics affected primary offspring sex ratios in a small passerine bird, the black-throated tit (Aegithalos concinnus). We found that offspring heterozygosity was significantly related to the heterozygosity of parents and the relatedness between parents. Importantly, genetic heterozygosity had a significantly negative effect on the survival of male but not female black-throated tits, implying higher variance in fitness in males than in females regarding the genetic heterozygosity inherited from parents. This sex-specific effect of heterozygosity on fitness provides black-throated tit parents with a potential reason to adjust offspring sex ratio in relation to their own genetic characteristics. However, although we found a seasonal decline of offspring sex ratio (proportion of males), offspring sex ratio was associated with neither the relatedness between parents nor the heterozygosity of parents. The results suggest that at least based on current data, there is a lack of evidence that black-throated tit parents manipulate offspring sex ratio with respect to their own genetic characteristics. The correlation between genome-wide heterozygosity and individual fitness has been extensively studied, but its potential role in mediating parental manipulation of offspring sex ratio has received attention only recently. If heterozygosity affects fitness differently for the two sexes of offspring, parents are likely to adjust their investment between female and male offspring based on their own genetic characteristics. This is because their own genetic characteristics determine their offspring’s heterozygosity and therefore fitness returns to parents. Existing studies have provided support to this hypothesized manipulation of offspring ratio, but studies in the area remain scarce. Our study shows that parents of a bird species do not manipulate offspring sex ratio with respect to their own genetic characteristics, even when there is a sex-specific heterozygosity-fitness correlation.

Hatchling sex ratio and female mating status in the great reed warbler, Acrocephalus arundinaceus (Aves, Passeriformes): further evidence for offspring sex ratio manipulation

Offspring sex in birds is maternally determined, thus females are expected to vary brood sex ratio adaptively in response to various environmental and/or genetic conditions preferring one sex to the other sex. However, recent studies provide controversial evidence showing mixed support for adaptive sex manipulation theory. One problem may lie in the fact that only sex ratios at fledging have been used in many of these studies, ignoring post-hatching sex-biased mortality. To validate these results, some authors call for replication of previous researches. Here we examined hatchling sex ratio variation in relation to female mating status in a local population of facultatively polygynous great reed warblers Acrocephalus arundinaceus in Central Europe. In agreement with results of previous works, we found that monogamous and primary females had a higher proportion of sons in their broods than secondary females. These results provide further evidence that great reed warbler females manipulate the sex ratio of their offspring in response to their social status.

A reliable method for sexing unincubated bird eggs for studying primary sex ratio

In birds, offspring sex ratio manipulation by mothers is now well established with potentially important consequences for evolution and animal breeding. In most studies on primary sex ratio of birds, eggs are sexed after incubation by the use of PCR methods targeted to the sex-linked CHD1 genes. Sexing of unincubated eggs would be preferred, but as fertile and infertile blastodiscs cannot be distinguished macroscopically, errors could arise from PCR amplifications of parental DNA associated with the vitelline membrane of infertile eggs. In this study, we stained blastodiscs without the vitelline membrane with Hoechst 33342. This allowed unequivocal distinction between fertile and infertile blastodiscs. Fertile blastodiscs contained thousands of fluorescent nuclei, whereas no nuclei were seen in infertile eggs. In addition, after nucleic acid analysis, fertile blastodiscs yielded much stronger chromosomal DNA and CHD1-targeted PCR bands on agarose gels compared with infertile blastodiscs. These findings indicate that fertile blastodiscs contain much more embryonic DNA than parental DNA, allowing reliable sexing of the fertile eggs. The differences between fertile and infertile blastodiscs in chromosomal DNA and CHD1 PCR banding intensities alone could also be used to distinguish fertile from infertile eggs without using Hoechst staining. We conclude that identifying fertile blastodiscs either by Hoechst staining or by analyzing the yield of chromosomal DNA and CHD1-PCR products, combined with CHD1-targeted PCR amplification, presents an easy and reliable method to sex unincubated eggs.

Female Control of Offspring Sex Ratios Based on Male Attractiveness in the Guppy

AbstractThe sex allocation hypothesis predicts that females manipulate the offspring sex ratios according to mate attractiveness. Although there is increasing evidence to support this prediction, it is possible that paternal effects may often obscure the relationship between female control of offspring sex ratios and male attractiveness. In the present study, we examined whether females played a primary role in the manipulation their offspring sex ratios based on male attractiveness, in the guppy Poecilia reticulata, a live‐bearing fish. We excluded the paternal effects by controlling the relative sexual attractiveness of the male by presenting them to the females along with a more attractive or less attractive stimulus male. The test male was perceived to be relatively more attractive by females when it was presented along with a less attractive stimulus male, or vice versa. Subsequently, test male was mated in two different roles (relatively more and less attractive) with two females. If females were responsible for offspring sex ratio manipulation, the sex ratio of the brood would be altered on the basis of the relative attractiveness of the test male. On the other hand, if males play a primary role in offspring sex ratio manipulation, the sex ratios would not differ with the relative attractiveness of the test male. We found that females gave birth to more male‐biased broods when they mated with test males in the attractive role than when they mated with males in the less attractive role. This finding suggests that females are responsible for the manipulation of offspring sex ratios based on the attractiveness of their mates.

Facultative Adjustment of Brood Sex Ratio in Response to Indirect Manipulation of Behaviour

AbstractSex allocation theory states that parents should adjust their offspring sex ratio according to the expected fitness returns from sons and daughters. Several recent studies indicate that such adaptive manipulation of offspring sex ratio is achievable, and that it may be influenced by e.g. morphological characters. Here we manipulate behaviour through interspecific cross‐fostering of great tits (Parus major) and blue tits (Cyanistes caeruleus), and investigate its effect on the offspring sex ratio of adults that were themselves cross‐fostered as chicks. The experience of being raised by a different species has previously been shown to result in aberrant species assortative behaviour and song, and a lowered dominance status during winter. Brood sex ratios of conspecifically breeding pairs with and without cross‐fostered members were compared. Broods with at least one cross‐fostered parent contained significantly more males than did control broods. Sex of cross‐fostered parents did not influence the brood sex ratio. We conclude that female great tits and blue tits seem to be able to adjust the sex ratio of their broods, and that changes in their own or their partners’ behaviour may elicit such adjustments.

Cooperatively breeding superb fairy-wrens show no facultative manipulation of offspring sex ratio despite plausible benefits

We report a long-term study of offspring sex ratios in the cooperatively breeding superb fairy-wren Malurus cyaneus. Detailed study of this species had revealed a suite of potentially strong selection pressures on the sex ratio. First, females gain substantial fitness benefits from the presence of helpers; so females without male helpers would benefit from any strategy that increased the probability of recruiting help, such as overproduction of sons (local resource enhancement hypothesis), but large numbers of helper males compete among themselves, favouring the production of daughters (local resource competition). Second, daughters fledged early in the season have far greater chances of recruitment to the breeding population than late-fledged daughters, so mothers would benefit from production of daughters early in the breeding season (early bird hypothesis). Third, extra-group mate choice imposes strong sexual selection on males, suggesting that females mating with attractive sires could benefit from investing in sons (sexual selection hypothesis). However, the predictions from these and other sex ratio hypotheses were rejected. The only convincing evidence for manipulation of the sex ratio was a slight bias towards sons (11 sons to 10 daughters) that occurred regardless of context. This result does not support current theory.

Manipulating sex ratio to increase population growth: the example of the Lesser Kestrel

AbstractSmall or decreasing populations call for emergency actions like, for example, captive breeding programs. Such programs aim at rapidly increasing population sizes in order to reduce the loss of genetic variability and to avoid possible Allee effects. The Lesser Kestrel Falco naumanni is one of the species that is currently supported in several captive breeding programs at various locations. Here, we model the demographic and genetic consequences of potential management strategies that are based on offspring sex ratio manipulation. Increased population growth could be achieved by manipulating female conditions and/or male attractiveness in the captive breeders and consequently shifting the offspring sex ratio towards more female offspring, which are then used for reintroduction. Fragmenting populations into wild‐breeding and captive‐breeding demes and manipulating population sex ratio both immediately increase the inbreeding coefficient in the next generation (i.e. decrease Ne) but may, in the long term, reduce the loss of genetic variability if population growth is restricted by the number of females. We use the Lesser Kestrel and the wealth of information that is available on this species to predict the long‐term consequences of various kinds of sex‐ratio manipulation. We find that, in our example and possibly in many other cases, a sex‐ratio manipulation that seems realistic could have a beneficial effect on the captive breeding program. However, the possible long‐term costs and benefits of such measures need to be carefully optimized.

Sex ratio response to conspecifics in a parasitoid wasp: test of a prediction of local mate competition theory and alternative hypotheses

Maternal manipulation of offspring sex ratio in response to conspecifics is considered in relation to sex ratio theory using the parasitoid wasp Spalangia endius. Females produced a greater proportion of sons in response to mated but not virgin females. This is the first demonstration of a differential sex ratio response to virgin versus mated females and provides support for local mate competition theory. More recent sex ratio models that predict sex ratio responses to conspecifics, specifically constrained, perturbation, and crowding models, were not supported. An increased proportion of sons in response to another mated female occurred on the second day of oviposition but not on the first, and the day effect resulted from experience not age. When females oviposited alone after 2 days' exposure to another female, they still produced a greater proportion of sons than if they had always been alone, but only if the other female was mated, not if she was virgin. Females do not seem to assess the presence of virgin versus mated females indirectly by using a low density of males or a long latency to mate as an indicator for virgin females: neither affected offspring sex ratio. That mated females adjusted their sex ratios in response to other mated females, but not virgin females or males, may be due proximally to mated females not often encountering the latter. Virgin females and males are not located as deep in the oviposition substrate as mated females.

Manipulation of offspring sex ratio by second-mated female house wrens.

In 1973, Trivers and Willard proposed that offspring sex ratio should be associated with the quality of parental care likely to be provided to the offspring. We tested this hypothesis by comparing fledgling sex ratios in nests of first- and second-mated female house wrens (Troglodytes aedon). In our Wyoming population, second-mated females typically receive little or no male parental assistance and fledge fewer and lower-quality young compared with first-mated females. Assuming that being of lower quality has stronger negative effects on the future reproductive success of males than that of females in this polygynous population, we predicted that fledgling sex ratios in the nests of second-mated females would be female-biased compared with the fledgling sex ratios of first-mated females. Additionally, we asked whether any sex bias at fledging could have resulted from male-biased nestling mortality caused by sex-biased parental provisioning. As predicted, mean fledgling sex ratios in nests of second-mated females were more female-biased than fledgling sex ratios in nests of first-mated females. However, we found no evidence of either sex-biased nestling mortality or sex-biased parental provisioning. These findings suggest that females are responding to their status as second-mated females and to the associated low-quality parental care that their young are likely to receive by producing female-biased clutches rather than manipulating the offspring sex ratio through sex-biased nestling mortality.

Cultural inheritance as a mechanism for population sex-ratio bias in reptiles.

Although natural populations of most species exhibit a 1:1 sex ratio, biased sex ratios are known to be associated with non-Mendelian inheritance, as in sex-linked meiotic drive and cytoplasmic inheritance (Charnov 1982; Hurst 1993). We show how cultural inheritance, another type of non-Mendelian inheritance, can favor skewed primary sex ratios and propose that it may explain the female-biased sex ratios commonly observed in reptiles with environmental sex determination (ESD). Like cytoplasmic elements, cultural traits can be inherited through one sex. This, in turn, favors skewing the primary sex allocation in favor of the transmitting sex. Female nest-site philopatry is a sex-specific, culturally inherited trait in many reptiles with ESD and highly female-biased sex ratios. We propose that the association of nest-site selection with ESD facilitates the maternal manipulation of offspring sex ratios toward females.

Offspring sex ratio response to host size in the parasitoid wasp Spalangia endius

The host size model, an adaptive model for maternal manipulation of offspring sex ratio, was examined for the parasitoid wasp Spalangia endius. In a Florida strain, as the model predicts, daughters emerged from larger hosts than sons, but only when mothers received both small and large hosts simultaneously. The pattern appeared to result from the mother's ovipositional choice and not from differential mortality of the sexes during development. If sex ratio manipulation is adaptive in the Florida strain, it appears to be through a benefit to daughters of developing on large hosts rather than through a benefit to sons of developing on small hosts. Both female and male parasitoids were larger when they developed on larger hosts. For females, developing on a larger host (1) increased offspring production, except for the largest hosts, (2) increased longevity, (3) lengthened development, and (4) had no effect on wing loading. For males, development on a larger host had no effect on any measure of male fitness – mating success, longevity, development duration, or wing loading. In contrast, a strain from India showed no difference in the size of hosts from which daughters versus sons emerged, although both female and male parasitoids were larger when they developed on larger hosts. These results together with previous studies of Spalangia reveal no consistent connection between host-size-dependent sex ratio and host-size-dependent parasitoid size among strains of S. endius or among species of Spalangia.

Skewed Brood Sex Ratio and Sex-Biased Hatching Sequence in Harris's Hawks

Nestling sex ratios in Harris's hawks show a significant bias toward males at the age of sexing, as predicted by Fisher's equilibrium hypothesis. Our data, however, do not support current hypotheses of parental manipulation of offspring sex ratios in response to varying environmental or social cues. The overall bias in offspring sex ratios was due to a highly significant skew toward males in first-hatched nestlings. We propose that sex-dependent hatching sequence may represent a proximal mechanism that upholds an adaptive sex-ratio skew toward males, the less expensive sex. If this mechanism were not employed by Harris's hawks, we submit that the dimorphic-size advantage of female nestlings added to the developmental advantage of hatching first might result in maladaptive brood reduction. Our observations show that nests in which males hatch first fledged significantly more young than nests in which females hatch first. Therefore, we suggest that female breeders may enhance their fitness by skewing the sex ratio of the first-hatched offspring toward males

SEX-RATIO MANIPULATION IN RESPONSE TO HOST SIZE BY THE PARASITOID WASP SPALANGIA CAMERONI: A LABORATORY STUDY.

The prediction of Charnov et al.'s (1981) host-size model that there should be a negative relationship between host size and wasp sex ratio (proportion sons) was supported for Spalangia cameroni, a solitary parasitoid wasp. The relationship was shown to be a result of offspring sex manipulation by females in response to host size rather than a result of differential mortality of the sexes. A major assumption of the host-size model is that host size has a greater effect on the ultimate reproductive success of emerging female wasps than of males. This assumption was not supported. Host size had a positive effect on the size of both male and female S. cameroni. However, neither host size nor wasp size affected longevity, production of offspring by females, or ability of males to compete for mates. Host size may differentially affect the reproductive success of female and male wasps through effects on other aspects of reproductive success. Tests of the assumptions of offspring sex-ratio manipulation hypotheses are scarce but critical, not only for parasitoid wasps, but also for other organisms.