scholarly journals The Trivers–Willard hypothesis: sex ratio or investment?

2016 ◽  
Vol 283 (1830) ◽  
pp. 20160126 ◽  
Author(s):  
Carl Veller ◽  
David Haig ◽  
Martin A. Nowak
Keyword(s):  
Simple Model ◽  
Sex Ratio ◽  
Sex Allocation ◽  
Good Condition ◽  
The Other ◽  
Reproductive Value ◽  
Small Subset ◽  
Female Fitness ◽  
Male And Female ◽  
Fitness Functions

The Trivers–Willard hypothesis has commonly been considered to predict two things. First, that a mother in good condition should bias the sex ratio of her offspring towards males (if males exhibit greater variation in reproductive value). Second, that a mother in good condition should invest more per son than per daughter. These two predictions differ empirically, mechanistically and, as we demonstrate here, theoretically too. We construct a simple model of sex allocation that allows simultaneous analysis of both versions of the Trivers–Willard hypothesis. We show that the sex ratio version holds under very general conditions, being valid for a large class of male and female fitness functions. The investment version, on the other hand, is shown to hold only for a small subset of male and female fitness functions. Our results help to make sense of the observation that the sex ratio version is empirically more successful than the investment version.

scholarly journals Fitness Functions Determine Optimal Parental Allocation: Redefining Trivers–Willard Theory

2019 ◽  
Author(s):  
Jibeom Choi ◽  
Hyungmin Roh ◽  
Sang-im Lee ◽  
Hee-Dae Kwon ◽  
Myungjoo Kang ◽  
...  
Keyword(s):  
Parental Investment ◽  
Empirical Data ◽  
Empirical Studies ◽  
Good Condition ◽  
Maternal Condition ◽  
Female Fitness ◽  
Male And Female ◽  
Poor Condition ◽  
Fitness Functions ◽  
Parental Fitness

According to Trivers-Willard theory1, females in a good condition should carry more male offspring to maximize their fitness while should carry more females in a poor condition. Diverse theoretical and empirical studies has been performed to verify the validity of this claim2,3. Some portion of the empirical observations, however, exhibited contrary outcome to Trivers-Willard theory4. To resolve this problem, we computationally and mathematically show in here that reversed Trivers-Willard theory actually could be the outcome of the parental fitness optimization. In our models with identical fitness functions, we found that selective equitable care is optimal, and the number of the cared offspring should monotonically increase with maternal condition (or expendable parental investment). In some of our models with two distinguished male and female fitness functions, optimizations results were congruent with the conventional Trivers-Willard theory. In other models of ours, contrary to Trivers-Willard theory, it was optimal to invest in males when maternal condition was low. The results along with our hypothesis can explain the empirical observations that were previously thought to be the counterexample of Trivers-Willard theory. We propose that Trivers-Willard theory should be interpreted in multidimensional way, and more elaborate empirical data need to be collected to verify such propositions.

scholarly journals Flow cytometric sexing of spider sperm reveals an equal sperm production ratio in a female-biased species

2014 ◽  
Vol 10 (5) ◽  
pp. 20140159 ◽  
Author(s):  
B. Vanthournout ◽  
K. Deswarte ◽  
H. Hammad ◽  
T. Bilde ◽  
B. Lambrecht ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Sex Allocation ◽  
Evolutionarily Stable Strategy ◽  
General Rule ◽  
Sperm Cells ◽  
Sperm Production ◽  
Male And Female ◽  
Ratio Bias ◽  
Sex Ratio Bias ◽  
Production Ratio

Producing equal amounts of male and female offspring has long been considered an evolutionarily stable strategy. Nevertheless, exceptions to this general rule (i.e. male and female biases) are documented in many taxa, making sex allocation an important domain in current evolutionary biology research. Pinpointing the underlying mechanism of sex ratio bias is challenging owing to the multitude of potential sex ratio-biasing factors. In the dwarf spider, Oedothorax gibbosus , infection with the bacterial endosymbiont Wolbachia results in a female bias. However, pedigree analysis reveals that other factors influence sex ratio variation. In this paper, we investigate whether this additional variation can be explained by the unequal production of male- and female-determining sperm cells during sperm production. Using flow cytometry, we show that males produce equal amounts of male- and female-determining sperm cells; thus bias in sperm production does not contribute to the sex ratio bias observed in this species. This demonstrates that other factors such as parental genes suppressing endosymbiont effects and cryptic female choice might play a role in sex allocation in this species.

scholarly journals Investigating the interaction between inter-locus and intra-locus sexual conflict using hemiclonal analysis in Drosophila melanogaster

2021 ◽  
Author(s):  
Manas Geeta Arun ◽  
Tejinder Singh Chechi ◽  
Rakesh Meena ◽  
Shradha Dattaraya Bhosle ◽  
Srishti ◽  
...  
Keyword(s):  
Drosophila Melanogaster ◽  
Sex Ratio ◽  
Genetic Correlation ◽  
Empirical Evidence ◽  
Sexual Conflict ◽  
Genetic Basis ◽  
Operational Sex Ratio ◽  
Female Fitness ◽  
Male And Female ◽  
Males And Females

Divergence in the evolutionary interests of males and females leads to sexual conflict. Traditionally, sexual conflict has been classified into two types: inter-locus sexual conflict (IeSC) and intra-locus sexual conflict (IaSC). IeSC is modeled as a conflict over outcomes of intersexual reproductive interactions mediated by loci that are sex-limited in their effects. IaSC is thought to be a product of selection acting in opposite directions in males and females on traits with a common underlying genetic basis. While in their canonical formalisms IaSC and IeSC are mutually exclusive, there is growing support for the idea that the two may interact. Empirical evidence for such interactions, however, is limited. Here, we investigated the interaction between IeSC and IaSC in Drosophila melanogaster. Using hemiclonal analysis, we sampled 39 hemigenomes from a laboratory-adapted population of D. melanogaster. We measured the contribution of each hemigenome to adult male and female fitness at three different intensities of IeSC, obtained by varying the operational sex-ratio. Subsequently, we estimated the intensity of IaSC at each sex-ratio by calculating the intersexual genetic correlation for fitness and the proportion of sexually antagonistic fitness-variation. Our results indicate a statistically non-significant trend suggesting that increasing the strength of IeSC ameliorates IaSC in the population.

scholarly journals Maternal effects obscure condition-dependent sex allocation in changing environments

2019 ◽  
Vol 6 (4) ◽  
pp. 181885 ◽  
Author(s):  
A. M. Edwards ◽  
E. Z. Cameron ◽  
E. Wapstra ◽  
J. McEvoy
Keyword(s):  
Climate Change ◽  
Sex Ratio ◽  
Environmental Change ◽  
Maternal Effects ◽  
Sex Allocation ◽  
Good Condition ◽  
Physiological Changes ◽  
Temperature Dependent ◽  
Changing Environments ◽  
Theoretical Predictions

Climate change increases environmental fluctuations which thereby impact population demography. Species with temperature-dependent sex determination may experience more extreme sex ratio skews, but this has not been considered in species with chromosomally determined sex. However, anticipatory maternal effects cause lifelong physiological changes impacting sex ratios. Here we show, in mice, that more sons were born to mothers in good condition when their breeding environment matched their gestational environment, consistent with theoretical predictions, but mothers in mismatched environments have no condition–sex ratio relationship. Thus, the predicted effect of condition on sex ratio was obscured by maternal effects when the environment changed. This may explain extreme sex ratio skews in reintroduced or translocated populations, and sex ratio skews may become more common and less predictable with accelerating environmental change.

Factors influencing the sex ratio at birth in Australia, 1902–65

1969 ◽  
Vol 1 (2) ◽  
pp. 125-144 ◽  
Author(s):  
G. N. Pollard
Keyword(s):  
Sex Ratio ◽  
Rural Areas ◽  
The Other ◽  
Multiple Births ◽  
Sex Ratio At Birth ◽  
Male And Female ◽  
Factors Influencing ◽  
Human Births ◽  
Mother’S Age ◽  
Urban And Rural Areas

SummaryUsing Australian records of human births for the first six decades of the twentieth century, the proportions of male and female births are studied in relation to the mother's age, the father's age, the parents' ages in combination, and certain other factors. The principal data used relate to the years 1931–55, during which over 3 million children were born, yet even so the significant features are not easy to discern.Masculinity tends to fall as the age of either parent increases. But it is only average or below if one parent is old while the other is young. For high masculinity, both parents must be young.The Australian data are available in a form which enables the sex ratio to be studied also in relation to (a) the season of the year; (b) urban and rural areas; (c) the different states of the Commonwealth; (d) births inside and outside marriage; and (e) single and multiple births. When the influence of the parents' ages is eliminated, however, it does not appear as though the sex ratio varies significantly with any of these factors.

scholarly journals Male-Biased Offspring Sex Ratio in the House Wren

The Condor ◽  
2002 ◽  
Vol 104 (4) ◽  
pp. 881-885
Author(s):  
Shannon M. Janota ◽  
Sheryl Swartz Soukup ◽  
Charles F. Thompson
Keyword(s):  
Sex Ratio ◽  
Breeding Season ◽  
Good Condition ◽  
Reproductive Value ◽  
Troglodytes Aedon ◽  
Offspring Sex Ratio ◽  
House Wren ◽  
House Wrens ◽  
Offspring Sex ◽  
Sex Ratio Adjustment

AbstractThe sex-ratio adjustment hypothesis predicts that females should modify offspring sex ratios according to the potential reproductive success of their offspring under existing ecological conditions. We tested this hypothesis in the polygynous, sexually size-monomorphic House Wren (Troglodytes aedon). Typically, nestling House Wrens that hatch in the first half of the three-month breeding season are heavier and have higher rates of survival and recruitment than those that hatch in the second half of the season. Therefore, the sex-ratio adjustment hypothesis predicts that early broods should be more male biased than later broods, because males in good condition have higher reproductive value than females. As conditions deteriorate, broods should become less male biased because female offspring have higher reproductive value than males in poor condition. Contrary to expectation, there was no seasonal decrease in offspring condition, and the sex ratio of broods was consistently male biased throughout the breeding season. We conclude that the results are consistent with the sex-ratio adjustment hypothesis, because in the year of this study female House Wrens were able to produce offspring in similar (and presumably good) condition throughout the breeding season; therefore, they continued to produce broods that were significantly male biased.Sesgo hacia Machos en el Cociente de Sexos de la Prole en Troglodytes aedonResumen. La hipótesis sobre el ajuste del cociente de sexos predice que las hembras deberían modificar el cociente de sexos de la prole en relación al éxito potencial reproductivo de la prole bajo las condiciones ecológicas existentes. Evaluamos esta hipótesis en Troglodytes aedon, especie polígina y sin diferencias sexuales de tamaño. Típicamente, los pichones de T. aedon que eclosionan en la primera mitad de la estación reproductiva (que dura tres meses) son más pesados y presentan tasas de supervivencia y reclutamiento más altas que aquellos que eclosionan en la segunda mitad de la estación. De este modo, la hipótesis sobre el ajuste del cociente de sexos predice que las camadas tempranas deberían estar más sesgadas hacia los machos que las camadas más tardías, ya que los machos en buena condición tienen un valor reproductivo más alto que las hembras. A medida que la condición se deteriora, las camadas deberían estar menos sesgadas hacia los machos debido a que los vástagos de sexo femenino tienen un valor reproductivo más alto que los machos en mala condición. Contrariamente a lo esperado, no hubo una disminución estacional en la condición de la prole, y el cociente de sexos de las camadas estuvo consistentemente sesgado hacia los machos a lo largo de la estación de cría. Concluimos que los resultados son consistentes con la hipótesis sobre el ajuste del cociente de sexos, ya que durante el año de este estudio las hembras de T. aedon fueron capaces de producir proles en condiciones similares (y presumiblemente buenas) a lo largo de la estación de cría. De este modo, las hembras continuaron produciendo camadas que estuvieron significativamente sesgadas hacia los machos.

scholarly journals Caste development and sex ratio of the Ryukyu drywood termite Neotermes sugioi and its potential mechanisms

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Y. Miyaguni ◽  
A. Agarie ◽  
K. Sugio ◽  
K. Tsuji ◽  
K. Kobayashi
Keyword(s):  
Sex Ratio ◽  
Evolutionary Biology ◽  
Sex Allocation ◽  
Reproductive Value ◽  
Total Biomass ◽  
Theoretical Predictions ◽  
Total Investment ◽  
Biased Sex Ratio ◽  
Caste Development ◽  
Female Bias

AbstractSex allocation is one of the most studied traits in evolutionary biology because its theoretical predictions match the empirical data. Here, using the Ryukyu dry-wood termite Neotermes sugioi, we investigated several factors that could bias the sex allocation in three populations (Okinawa, Ishigaki/Iriomote, and Yonaguni). Our survey showed that there were more queen-only colonies than king-only colonies in these populations, suggesting a longer lifespan of the queens than that of the kings. In this condition, sex-asymmetric reproductive value (SRV) theory predicts female bias, because even after the short-lived kings die, the long-lived queens can continue reproduction with their sons. However, sex allocation in this species seemed to be biased toward males. Furthermore, we examined the possibility of intrasexual competition among siblings (ICS). If ICS is the cause of the bias, the allocation is expected to change depending on the total investment in sexual offspring. However, the biomass of both male and female alates increased linearly with the increase in the total biomass of the alates in these populations. Thus, neither the SRV nor the ICS theory could explain the male-biased sex ratio of N. sugioi. On the basis of these results, we discuss the remaining possibilities in this species.

Sex Ratios and Sex Allocation

2001 ◽  
Author(s):  
Steven Hecht Orzack
Keyword(s):  
Sex Ratio ◽  
Sex Allocation ◽  
Female Flower ◽  
Reproductive Organs ◽  
Evolutionary Analysis ◽  
Male And Female ◽  
Sex Ratio Theory ◽  
Males And Females ◽  
Descent Of Man ◽  
Evolutionary Aspects

Understanding the allocation of energy is the goal of the evolutionary analysis of sex allocation. Whether one is concerned with the relative sizes of male and female flower parts in plants like those discussed by Campbell (1998), the ratio of males and females in insects like those discussed by Orzack et al. (1991), or the relative sizes of male and female reproductive organs in hermaphroditic fish like those discussed by Leonard (1993), one is concerned with how energy allocated toward reproduction is apportioned into one sex as opposed to the other (or more in the case of some kinds of organisms). Here, the sexes are entities that at regular or irregular intervals produce gametes, some of which come together to produce zygotes. The abstract nature of this description underscores the degree to which there are common evolutionary aspects to all of these problems, despite the fact that the biological details involved are so diverse. One of the most influential and important agendas for evolutionary studies of sex allocation was laid out by Charnov (1982). He described the underlying evolutionary similarities between phenomena as diverse as sex change in shrimp and sex ratio in vertebrates like us. Even more important, he promoted sex allocation as a central evolutionary problem by describing how seemingly unrelated allocation problems could all be analyzed with a kind of mathematical approach elaborated by Shaw and Mohler (1953). I consider in turn four important examples of this approach. Shaw and Mohler’s goal was to understand the evolution of the proportions of males and females. This problem of the sex ratio was most famously addressed by Darwin in his 1871 book, The Descent of Man, and Selection in Relation to Sex, as well as by others in the subsequent decades. The most influential analysis is that of Fisher (1930); however, Carl Düsing, who worked in the 1880s, can rightly be regarded as the progenitor of modern sex ratio theory (see Edwards 1998).

scholarly journals Can mammalian mothers influence the sex of their offspring peri-conceptually?

Reproduction ◽  
2010 ◽  
Vol 140 (3) ◽  
pp. 425-433 ◽  
Author(s):  
Valerie J Grant ◽  
Lawrence W Chamley
Keyword(s):  
Evolutionary Biology ◽  
Sex Allocation ◽  
Molecular Mechanisms ◽  
Good Condition ◽  
The Other ◽  
Proximate Mechanisms ◽  
High Fat Diets ◽  
Fat Diets ◽  
To Receive ◽  
Maternal Glucose

Although controversial, growing evidence from evolutionary biology suggests that the mammalian mother may have a role in influencing the sex of her offspring. However, there is competing information on the molecular mechanisms by which such influence could be manifested. The new initiatives are based on hypotheses from evolutionary biology: the ‘good condition’ hypothesis, which suggests that post conception, higher levels of maternal glucose may differentially promote the development of male embryos; and the ‘maternal dominance’ hypothesis, which proposes that before conception, higher follicular testosterone may influence the development of the ovum so that it emerges already adapted to receive an X- or a Y-chromosome-bearing spermatozoon. Now, it seems these hypothesised mechanisms could be operating in synchrony, each complementing and reinforcing the other. On the other hand, there are continuing problems in identifying a precise sequence of mechanisms as evidenced from research in sperm-sorting. Research on high-fat diets and the sex ratio in polytocous species may indicate important differences in proximate mechanisms for sex allocation between polytocous and monotocous mammals.

Items’ Cross-Category Associations as a Confounding Factor in the Implicit Association Test

2001 ◽  
Vol 48 (2) ◽  
pp. 123-134 ◽  
Author(s):  
Melanie C. Steffens ◽  
Inga Plewe
Keyword(s):  
Implicit Association Test ◽  
Confounding Factor ◽  
Reaction Times ◽  
Association Test ◽  
The Other ◽  
Reaction Time Difference ◽  
Implicit Association ◽  
Male And Female ◽  
Research Activities ◽  
Degree Of Association

Abstract. The introduction of the Implicit Association Test (IAT; Greenwald, McGhee, & Schwartz, 1998 ) has stimulated numerous research activities. The IAT is supposed to measure the degree of association between concepts. Instances have to be assigned to these concepts by pressing appropriate keys as quickly as possible. The reaction time difference between certain conditions, termed the IAT effect, is used as an indicator of the degree of the concepts’ association. We tested the hypothesis that the degree of association between one concept (or category) and the instances of the other presented concept also influences reaction times. In our experiment, the instances in the target categories, male and female names, were kept constant. The adjectives in the evaluative categories were manipulated: Either the pleasant adjectives were female-associated and the unpleasant adjectives were male-associated, or vice versa. These stereotypic associations were indeed found to exert a substantial influence on the size of the IAT effect. This finding casts doubt on the assumption that the IAT effect may be interpreted as a pure measure of the degree of association between concepts.

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