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.

Fetal sex ratio in relation to maternal mass and age in reindeer

1997 ◽  
Vol 75 (4) ◽  
pp. 648-650 ◽  
Author(s):  
Eigil Reimers ◽  
Dag Lenvik
Keyword(s):  
Natural Selection ◽  
Sex Ratio ◽  
Parental Investment ◽  
Similar Condition ◽  
Rangifer Tarandus ◽  
Good Condition ◽  
Maternal Condition ◽  
Fetal Sex ◽  
Poor Condition ◽  
Parental Ability

Theory suggests that a male in good condition at the end of the period of parental investment will outproduce a sister in similar condition, while she will outproduce him if both are in poor condition. Accordingly, natural selection should favor parental ability to adjust the sex ratio of offspring produced according to parental ability to invest. As maternal condition declines from good to poor, the fetal sex ratio should decline from a high proportion of males to a high proportion of females. Data from 1525 domestic reindeer (Rangifer tarandus) in six different herds slaughtered during December and January in 1976 through 1979 do not support a relationship between the sex of the fetus and either the condition of the mother or her age.

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 Maternal condition and previous reproduction interact to affect offspring sex in a wild mammal

2016 ◽  
Vol 12 (8) ◽  
pp. 20160510 ◽  
Author(s):  
Mathieu Douhard ◽  
Marco Festa-Bianchet ◽  
Fanie Pelletier
Keyword(s):  
Sex Ratio ◽  
Empirical Studies ◽  
Good Condition ◽  
Ovis Canadensis ◽  
Maternal Condition ◽  
Paternal Effects ◽  
Offspring Sex Ratio ◽  
Fitness Consequences ◽  
Offspring Sex ◽  
Dimorphic Species

Trivers and Willard proposed that offspring sex ratio should vary with maternal condition when condition, meant as maternal capacity to care, has different fitness consequences for sons and daughters. In polygynous and dimorphic species, mothers in good condition should preferentially produce sons, whereas mothers in poor condition should produce more daughters. Despite its logical appeal, support for this hypothesis has been inconsistent. Sex-ratio variation may be influenced by additional factors, such as environmental conditions and previous reproduction, which are often ignored in empirical studies. We analysed 39 years of data on bighorn sheep ( Ovis canadensis ) that fit all the assumptions of the Trivers–Willard hypothesis. Production of sons increased with maternal condition only for mothers that weaned a son the previous year. This relationship likely reflects a mother's ability to bear the higher reproductive costs of sons. The interaction between maternal condition and previous weaning success on the probability of producing a son was independent of the positive effect of paternal reproductive success. Maternal and paternal effects accounted for similar proportions of the variance in offspring sex. Maternal reproductive history should be considered in addition to current condition in studies of sex allocation.

Do single point condition measurements predict fitness in female pronghorn (Antilocapra americana)?

2012 ◽  
Vol 90 (6) ◽  
pp. 729-735 ◽  
Author(s):  
E. Clancey ◽  
S.J. Dunn ◽  
J.A. Byers
Keyword(s):  
Reproductive Success ◽  
Empirical Test ◽  
Empirical Studies ◽  
Single Point ◽  
Antilocapra Americana ◽  
Maternal Condition ◽  
Poor Condition ◽  
Prenatal Growth ◽  
Female Condition ◽  
Point Condition

Condition is frequently used in evolutionary studies as an estimator of fitness. Broad theoretical interpretations of condition include many different attributes that can influence fitness, but in practice, researchers commonly employ condition measures (e.g., body-fat scores or size-adjusted body mass) that have uncertain relationships with reproductive success. In addition, researchers typically rely on condition estimates that are made once. Empirical studies investigating the relationship between condition and fitness are nearly absent. We examined the effect of maternal condition on current and future reproductive success in a wild population of pronghorn ( Antilocapra americana (Ord, 1852)). We used body condition scoring and date of annual molt to measure female condition, and mass–size residuals to measure offspring condition at birth. We found that current reproductive success lowered female condition, and that poor condition reduced subsequent prenatal growth rates. However, poor condition did not reduce postnatal offspring condition or future reproductive success. We suggest that the elapsed time should be taken into consideration when making predictions based on single point condition measures. The assumption that condition predicts fitness requires further empirical test.

scholarly journals A comprehensive test of the Trivers–Willard hypothesis in pronghorn ( Antilocapra americana )

2015 ◽  
Vol 97 (1) ◽  
pp. 179-186 ◽  
Author(s):  
Erin Clancey ◽  
John A. Byers
Keyword(s):  
Empirical Studies ◽  
Good Condition ◽  
Social Rank ◽  
Investment Strategy ◽  
Female Offspring ◽  
Antilocapra Americana ◽  
Maternal Condition ◽  
Growth And Survival ◽  
Fawn Survival ◽  
Comprehensive Test

Abstract The Trivers–Willard hypothesis (TWH) predicts that in a polygynous mating system, when fitness of male offspring is more variable than fitness of female offspring, mothers should invest more heavily in the sex with the highest marginal fitness returns. Females in good condition or high social rank should benefit by investing in sons, and females in poor condition or low social rank should benefit by investing in daughters. Many empirical studies have tested different aspects of the TWH, but no study has tested the assumptions and predictions in a single polygynous species using measures of maternal condition and maternal social rank, while accounting for random effects that can also influence offspring growth and survival. Here, we followed individuals in an isolated population of pronghorn on the National Bison Range, Montana, over multiple generations and tested the assumptions and predictions of the TWH. Pronghorn females who were in good condition or were socially dominant weaned larger fawns that were in better condition, but this advantage did not increase male fawn survival or reproductive success. We detected a slight bias in birth sex ratios according to maternal social rank, but overall we did not detect any adaptive benefit to mothers adopting a sex-biased investment strategy.

scholarly journals Meta-analysis reveals that sexual signalling in animals is honest and resource-based

2020 ◽  
Author(s):  
Liam R. Dougherty
Keyword(s):  
Meta Analysis ◽  
Empirical Studies ◽  
Good Condition ◽  
Ecological Factors ◽  
Parasite Load ◽  
Positive Trend ◽  
Individual State ◽  
Poor Condition ◽  
State Dependent ◽  
Sexual Signalling

AbstractAnimals often need to signal to attract mates, and sexual signalling may impose significant energetic and fitness costs to signallers. Consequently, individuals should strategically adjust signalling effort in order to maximise the fitness payoffs of signalling. An important determinant of these payoffs is individual state, which can influence the resources available to signallers, the likelihood of mating, and the motivation to mate. However, empirical studies often find contradictory patterns of state-based signalling. For example, some studies find that individuals in poor condition signal less, in order to conserve resources (ability-based signalling). In other cases, individuals in poor condition signal more, in order to maximise short-term reproductive success (needs-based signalling). I used meta-analysis to examine animal sexual signalling behaviour in relation to six aspects of individual state: age, mated status, attractiveness, body size, condition, and parasite load. Across 228 studies and 147 species, individuals (who were overwhelmingly male) signalled significantly more when in good condition, and there was a strong positive trend for increased signalling for large, attractive individuals with a low parasite load. Overall, this suggests that animal sexual signalling behaviour is generally honest and ability-based. However, needs-based signalling (terminal investment) was found when considering age, with old virgins signalling more than young virgins. Sexual signalling was not significantly influenced by mated status. There was a large amount of heterogeneity across studies that remained unexplained, and therefore more work is needed to determine the ecological factors influencing the magnitude and direction of state-dependent sexual signalling.

An empirical review of gambling expansion and gambling-related harm

2018 ◽  
Vol 64 (5-6) ◽  
pp. 295-306 ◽  
Author(s):  
Debi A. LaPlante ◽  
Heather M. Gray ◽  
Pat M. Williams ◽  
Sarah E. Nelson
Keyword(s):  
Literature Review ◽  
Peer Review ◽  
Empirical Data ◽  
Empirical Studies ◽  
Expansion Method ◽  
Responsible Gambling ◽  
Review Literature ◽  
Evidence Based ◽  
Empirical Comparison ◽  
Related Harm

Abstract. Aims: To discuss and review the latest research related to gambling expansion. Method: We completed a literature review and empirical comparison of peer reviewed findings related to gambling expansion and subsequent gambling-related changes among the population. Results: Although gambling expansion is associated with changes in gambling and gambling-related problems, empirical studies suggest that these effects are mixed and the available literature is limited. For example, the peer review literature suggests that most post-expansion gambling outcomes (i. e., 22 of 34 possible expansion outcomes; 64.7 %) indicate no observable change or a decrease in gambling outcomes, and a minority (i. e., 12 of 34 possible expansion outcomes; 35.3 %) indicate an increase in gambling outcomes. Conclusions: Empirical data related to gambling expansion suggests that its effects are more complex than frequently considered; however, evidence-based intervention might help prepare jurisdictions to deal with potential consequences. Jurisdictions can develop and evaluate responsible gambling programs to try to mitigate the impacts of expanded gambling.

My Brother’s Reaper: Examining Officially Reported Siblicide Incidents in the United States, 2000–2007

2014 ◽  
Vol 29 (3) ◽  
pp. 523-540 ◽  
Author(s):  
Jeffrey A. Walsh ◽  
Jessie L. Krienert
Keyword(s):  
United States ◽  
Theoretical Foundation ◽  
Empirical Studies ◽  
The United States ◽  
Male And Female ◽  
Sibling Violence ◽  
Extreme Form ◽  
Older Brothers ◽  
Intrafamilial Violence ◽  
Frequent Offenders

With higher rates than any other form of intrafamilial violence, Hoffman and Edwards (2004) note, sibling violence “constitutes a pandemic form of victimization of children, with the symptoms often going unrecognized and the effect ignored” (p. 187). Approximately 80% of children reside with at least one sibling (Kreider, 2008), and in its most extreme form sibling violence manifests as siblicide. Siblicide is poorly understood with fewer than 20 empirical studies identified in the extant literature since 1980 (see Eriksen & Jensen, 2006). The present work employs 8 years of Supplemental Homicide Report (SHR) data, 2000–2007, with siblicide victims and offenders age 21 years and younger, to construct contemporary victim and offender profiles examining incident characteristics. Findings highlight the sex-based nature of the offense with unique victimization patterns across victims and offenders. Older brothers using a firearm are the most frequent offenders against both male and female siblings. Strain as a theoretical foundation of siblicide is offered as an avenue for future inquiry.

scholarly journals A State-of-the-Art Review on Empirical Data Collection for External Governed Pedestrians Complex Movement

2018 ◽  
Vol 2018 ◽  
pp. 1-42 ◽  
Author(s):  
Xiaomeng Shi ◽  
Zhirui Ye ◽  
Nirajan Shiwakoti ◽  
Offer Grembek
Keyword(s):  
Data Collection ◽  
Empirical Data ◽  
Empirical Studies ◽  
Movement Patterns ◽  
Simulation Models ◽  
Straight Line ◽  
Challenges And Opportunities ◽  
Pedestrian Traffic ◽  
Random Flows ◽  
Complex Movement

Complex movement patterns of pedestrian traffic, ranging from unidirectional to multidirectional flows, are frequently observed in major public infrastructure such as transport hubs. These multidirectional movements can result in increased number of conflicts, thereby influencing the mobility and safety of pedestrian facilities. Therefore, empirical data collection on pedestrians’ complex movement has been on the rise in the past two decades. Although there are several reviews of mathematical simulation models for pedestrian traffic in the existing literature, a detailed review examining the challenges and opportunities on empirical studies on the pedestrians complex movements is limited in the literature. The overall aim of this study is to present a systematic review on the empirical data collection for uni- and multidirectional crowd complex movements. We first categorized the complex movements of pedestrian crowd into two general categories, namely, external governed movements and internal driven movements based on the interactions with the infrastructure and among pedestrians, respectively. Further, considering the hierarchy of movement complexity, we decomposed the externally governed movements of pedestrian traffic into several unique movement patterns including straight line, turning, egress and ingress, opposing, weaving, merging, diverging, and random flows. Analysis of the literature showed that empirical data were highly rich in straight line and egress flow while medium rich in turning, merging, weaving, and opposing flows, but poor in ingress, diverging, and random flows. We put emphasis on the need for the future global collaborative efforts on data sharing for the complex crowd movements.

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