scholarly journals Female Chemical Warfare Drives Fitness Effects of Group Sex Ratio

2017 ◽  
Author(s):  
Imroze Khan ◽  
Arun Prakash ◽  
Swastika Issar ◽  
Mihir Umarani ◽  
Rohit Sasidharan ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Resource Competition ◽  
Sex Ratios ◽  
Interference Competition ◽  
Female Competition ◽  
Female Fitness ◽  
Female Fecundity ◽  
Individual Fitness ◽  
Flour Beetles ◽  
Group Sex

SUMMARYIn animals, skewed sex ratios can affect individual fitness either via sexual interactions (e.g. intersexual conflict or intrasexual mate competition) or non-sexual interactions (e.g. sex-specific resource competition). Because most analyses of sex ratio focus on sexual interactions, the relative importance of these mechanisms remains unclear. We addressed this problem using the flour beetle Tribolium castaneum, where male-biased sex ratios increase female fitness relative to unbiased or female-biased groups. Although flour beetles show both sexual and non-sexual (resource) competition, we found that sexual interactions did not explain female fitness. Instead, female fecundity was dramatically reduced even after a brief exposure to flour conditioned by other females. Earlier studies suggested that quinones (secreted toxins) might mediate density-dependent population growth in flour beetles. We identified ethyl- and methyl-benzoquinone (EBQ and MBQ) as the primary components of adult stink glands that regulate female fecundity. In female-biased groups (i.e. at high female density), females upregulated quinones and suppressed each other’s reproduction. In male-biased groups, low female density lead to low quinone levels, allowing higher fecundity. Thus, quinones serve both as indicators and mediators of female competition, resulting in the observed fitness decline in female-biased groups. Our results underscore the importance of non-sexual interference competition that may often underlie the fitness consequences of skewed sex ratios.

scholarly journals Recruitment sex ratios in gray-tailed voles (Microtus canicaudus) in response to density, sex ratio, and season

2003 ◽  
Vol 81 (8) ◽  
pp. 1306-1311 ◽  
Author(s):  
Monica L Bond ◽  
Jerry O Wolff ◽  
Sven Krackow
Keyword(s):  
Population Density ◽  
Sex Ratio ◽  
Resource Competition ◽  
Sex Ratios ◽  
Female Offspring ◽  
High Population ◽  
Reproductive Value ◽  
High Population Density ◽  
Adult Sex Ratio ◽  
Sex Ratio Adjustment

We tested predictions associated with three widely used hypotheses for facultative sex-ratio adjustment of vertebrates using eight enclosed populations of gray-tailed voles, Microtus canicaudus. These were (i) the population sex ratio hypothesis, which predicts that recruitment sex ratios should oppose adult sex-ratio skews, (ii) the local resource competition hypothesis, which predicts female-biased recruitment at low adult population density and male-biased recruitment at high population density, and (iii) the first cohort advantage hypothesis, which predicts that recruitment sex ratios should be female biased in the spring and male biased in the autumn. We monitored naturally increasing population densities with approximately equal adult sex ratios through the spring and summer and manipulated adult sex ratios in the autumn and measured subsequent sex ratios of recruits. We did not observe any significant sex-ratio adjustment in response to adult sex ratio or high population density; we did detect an influence of time within the breeding season, with more female offspring observed in the spring and more male offspring observed in the autumn. Significant seasonal increases in recruitment sex ratios indicate the capacity of female gray-tailed voles to manipulate their offspring sex ratios and suggest seasonal variation in the relative reproductive value of male and female offspring to be a regular phenomenon.

Competitive Motherhood from a Comparative Perspective

2016 ◽  
Author(s):  
Katherine A. Valentine ◽  
Norman P. Li ◽  
Jose C. Yong
Keyword(s):  
Reproductive Success ◽  
Sex Ratio ◽  
Nonhuman Primates ◽  
Resource Competition ◽  
Sex Ratios ◽  
Comparative Perspective ◽  
Future Directions ◽  
Competition Hypothesis ◽  
Resource Enhancement

Mothers play an important role in helping their children achieve maximal reproductive success. We explore how mothers across species manipulate birth sex ratios favoring the sex that will be best suited to their environments and how maternal competition affects offspring reproductive success in nonhuman mammals as well as humans. The Trivers-Willard hypothesis, resource competition hypothesis, resource enhancement hypothesis, and maternal dominance hypothesis are considered with respect to maternal birth sex ratio manipulation. Next, the primate literature is reviewed as inspiration for hypotheses on maternal competition for positive offspring outcomes. Nonhuman primates as well as humans are argued to compete for status, breeding opportunities, and allomothers (i.e., caregivers apart from the mother), and these factors have an impact on their reproductive success. Status is passed on from mother to offspring, amplifying the effects of competition for status. Future directions are delineated to fill in gaps in the existing literature.

Operational Sex Ratio and Female Competition

2014 ◽  
Author(s):  
Haley M. Dillon ◽  
Lora E. Adair ◽  
Gary L. Brase
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Intrasexual Competition ◽  
Operational Sex Ratio ◽  
Female Competition ◽  
Future Directions ◽  
Adaptive Changes ◽  
Mating Market ◽  
Mating Behaviors ◽  
Theoretical Foundations

When there is a surplus of one sex in a population, members of that sex often compete against each other for access to the scarcer sex. This chapter reviews the theoretical foundations for this phenomenon, focusing on the concept of operational sex ratio (OSR; the ratio of viable and available males to females in a given mating market) versus overall sex ratio, as well as the phylogenetic evidence of sex ratios as an important factor influencing mating behaviors. Research on human OSR and its effects is a fairly recent development but has already led to findings that are generally coherent and consistent with the nonhuman evidence. The evidence to date indicates that people who find themselves in female-disadvantaged mating markets show systematic and adaptive changes in their behaviors, including increased female intrasexual competition. The chapter concludes with discussions of additional issues and future directions for research on OSR.

scholarly journals Simultaneous failure of two sex-allocation invariants: implications for sex-ratio variation within and between populations

2015 ◽  
Vol 282 (1810) ◽  
pp. 20150570 ◽  
Author(s):  
António M. M. Rodrigues ◽  
Andy Gardner
Keyword(s):  
Sex Ratio ◽  
Sex Allocation ◽  
Resource Competition ◽  
Natural World ◽  
Female Fecundity ◽  
High Fecundity ◽  
Quantitative Evidence ◽  
Empirically Supported ◽  
Limited Dispersal ◽  
Female Dispersal

Local mate competition (LMC) occurs when male relatives compete for mating opportunities, and this may favour the evolution of female-biased sex allocation. LMC theory is among the most well developed and empirically supported topics in behavioural ecology, clarifies links between kin selection, group selection and game theory, and provides among the best quantitative evidence for Darwinian adaptation in the natural world. Two striking invariants arise from this body of work: the number of sons produced by each female is independent of both female fecundity and also the rate of female dispersal. Both of these invariants have stimulated a great deal of theoretical and empirical research. Here, we show that both of these invariants break down when variation in female fecundity and limited female dispersal are considered in conjunction. Specifically, limited dispersal of females following mating leads to local resource competition (LRC) between female relatives for breeding opportunities, and the daughters of high-fecundity mothers experience such LRC more strongly than do those of low-fecundity mothers. Accordingly, high-fecundity mothers are favoured to invest relatively more in sons, while low-fecundity mothers are favoured to invest relatively more in daughters, and the overall sex ratio of the population sex ratio becomes more female biased as a result.

scholarly journals Female Density-Dependent Chemical Warfare Underlies Fitness Effects of Group Sex Ratio in Flour Beetles

2018 ◽  
Vol 191 (3) ◽  
pp. 306-317 ◽  
Author(s):  
Imroze Khan ◽  
Arun Prakash ◽  
Swastika Issar ◽  
Mihir Umarani ◽  
Rohit Sasidharan ◽  
...  
Keyword(s):  
Sex Ratio ◽  
Chemical Warfare ◽  
Density Dependent ◽  
Fitness Effects ◽  
Flour Beetles ◽  
Group Sex

scholarly journals Parental Correlates of Offspring Sex Ratio in Eurasian Oystercatchers

The Auk ◽  
2000 ◽  
Vol 117 (4) ◽  
pp. 980-986 ◽  
Author(s):  
D. Heg ◽  
N. J. Dingemanse ◽  
C. M. Lessells ◽  
A. C. Mateman
Keyword(s):  
Sex Ratio ◽  
Resource Competition ◽  
Random Amplified Polymorphic Dna ◽  
Sex Ratios ◽  
Egg Laying ◽  
Laying Date ◽  
Territory Quality ◽  
Offspring Sex Ratio ◽  
Breeding Experience ◽  
Laying Sequence

Abstract We investigated hatchling and fledgling sex ratios in Eurasian Oystercatchers (Haematopus ostralegus) using random amplified polymorphic DNA markers. The overall hatchling (53% males, n = 374 hatchlings from 177 broods) and fledgling (49% males, n = 51) sex ratio did not differ significantly from unity. Hatchling and fledgling sex ratios were not correlated with laying date, clutch size, brood size, egg-laying sequence, territory quality, male age, or male breeding experience, but hatchling sex ratio was positively correlated with age and breeding experience of females (0.05 < P < 0.075, n = 71). Older females produced more sons irrespective of the position of the offspring in the egg-laying sequence. Fledging mass was not correlated with female age, so the Trivers and Willard (1973) hypothesis is unlikely to explain our results. Sons dispersed less than daughters, so the local resource competition hypothesis of Clark (1978) might apply. The adaptive significance of a male-biased sex ratio in clutches produced by older females is speculative because the costs and benefits of dispersing versus philopatric offspring to parents and offspring are largely unknown.

scholarly journals Sex Ratio Is Synergistically Modulated by Local Resource Competition and Enhancement: the Case of a Primitively Eusocial Wasp Under Female Philopatry

2021 ◽  
Author(s):  
Koji Tsuchida ◽  
Norio Ishiguro ◽  
Fuki Saito-Morooka ◽  
Jun-Ichi Kojima ◽  
Philip Spradbery
Keyword(s):  
Sex Ratio ◽  
Resource Competition ◽  
Female Competition ◽  
Offspring Sex Ratio ◽  
Local Resource Competition ◽  
Local Resource ◽  
Female Philopatry ◽  
Primitively Eusocial Wasp ◽  
Before And After ◽  
Biased Sex Ratio

Abstract BackgroundIn animals, the offspring sex ratio is modulated by kin conflict and cooperation, and determining the ratio is a main concern in evolutionary biology. Male competition for access to local mates is predictive of a female-biased sex ratio in the offspring (local mate competition; LMC). Conversely, female competition for access to local resources is predictive of a male-biased sex ratio in the offspring (local resource competition; LRC). However, several factors other than competition should synergistically operate in real-world populations. In the Australian paper wasp Ropalidia plebeiana, LRC and local resource enhancement (LRE) may operate simultaneously. To determine whether this is the case, we evaluated colony sex ratios and examined whether competition and/or enhancement operates at the population level in this species. ResultsIn spring, many foundress queens started their colonies by comb-cutting, in which nest combs from the previous season were divided into several combs to be reused. Genetic relatedness among foundresses did not differ before and after comb-cutting. Relatedness among foundresses was 0.339, whereas relatedness among new foundresses was 0.589, revealing nearly functional monogyny. The global FST value calculated with mtDNA markers was higher than that calculated with microsatellite markers, even after we corrected for differences in effective population sizes between sexes. This finding indicates female philopatry, which was also confirmed by mark–release–recapture before and after the hibernation of new foundresses. The colony sex ratio of reproductives became slightly biased toward males in larger colonies. In addition, both the number of foundresses and number of workers were positively associated with the number of reproductives, which indicates that LRE was also operating.ConclusionsOur results suggest that although the population structure seems to meet the requirements of LRC, the sex ratio is not modulated solely by LRC. Instead, the availability of female helpers at the founding stage likely mitigates the sex ratio predicted by LRC through LRE. Thus, LRC at the founding stage and LRE at the reproductive stage synergistically modulate the colony sex ratio in R. plebeiana.

scholarly journals Problems with primate sex ratios

2000 ◽  
Vol 355 (1403) ◽  
pp. 1627-1635 ◽  
Author(s):  
Craig Packer ◽  
D. Anthony Collins ◽  
Lynn E. Eberly
Keyword(s):  
Sex Ratio ◽  
Environmental Conditions ◽  
National Park ◽  
Resource Competition ◽  
Sex Ratios ◽  
Adaptive Variation ◽  
Gombe National Park ◽  
Local Resource Competition ◽  
Local Resource ◽  
Complex Processes

Birth sex ratios of baboons in Gombe National Park, Tanzania, show an overall male bias of ca . 20%, but there is no obvious explanation for this trend. Individual females did not alter their sex ratios according to persistent levels of local resource competition. Sex ratios showed an unexpected relationship between age and rank: subordinate females had more sons when they were young; dominant females had more sons when they were old. The sex ratio of low–ranking females also varied with the severity of environmental conditions during pregnancy. Our findings suggest that mammalian sex ratios might be the product of more complex processes than is generally recognized or that sex–determining mechanisms impose sufficient constraints to prevent adaptive variation in all contexts.

scholarly journals Sex-specific deaths in Norway and Sweden during the COVID-19 pandemic: Did mandates make a difference?

2021 ◽  
pp. 140349482110100
Author(s):  
Ralph Catalano
Keyword(s):  
Sex Ratio ◽  
Infection Control ◽  
Temporal Variation ◽  
Risky Behavior ◽  
Control Strategies ◽  
Sex Ratios ◽  
Female Mortality ◽  
All Cause Mortality ◽  
Societal Expectations ◽  
Male To Female

Aims: To determine whether differences between Norway’s and Sweden’s attempts to contain SARS-CoV-2 infection coincided with detectably different changes in their all-cause mortality sex ratios. Measuring temporal variation in the all-cause mortality sex ratio before and during the pandemic in populations exposed to different constraints on risky behavior would allow us to better anticipate changes in the ratio and to better understand its association with infection control strategies. Methods: I apply time Box–Jenkins modeling to 262 months of pre-pandemic mortality sex ratios to arrive at counterfactual values of 10 intra-pandemic ratios. I compare counterfactual to observed values to determine if intra-pandemic ratios differed detectably from those expected as well as whether the Norwegian and Swedish differences varied from each other. Results: The male to female mortality sex ratio in both Norway and Sweden increased during the pandemic. I, however, find no evidence that the increase differed between the two countries despite their different COVID-19 containment strategies. Conclusion: Societal expectations of who will die during the COVID-19 pandemic will likely be wrong if they assume pre-pandemic mortality sex ratios because the intra-pandemic ratios appear, at least in Norway and Sweden, detectably higher. The contribution of differences in policies to reduce risky behavior to those higher ratios appears, however, small.

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