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 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.

Density-dependent aggression, courtship, and sex ratio in a fishing spider

Arachnology ◽  
2019 ◽  
Vol 18 (3) ◽  
pp. 295 ◽  
Author(s):  
Adam M. Fisher ◽  
Tom A. R. Price
Keyword(s):  
Sex Ratio ◽  
Density Dependent ◽  
Fishing Spider

scholarly journals Parental care and adaptive brood sex ratio manipulation in birds

2002 ◽  
Vol 357 (1419) ◽  
pp. 363-372 ◽  
Author(s):  
D. Hasselquist ◽  
B. Kempenaers
Keyword(s):  
Sex Ratio ◽  
Parental Care ◽  
Statistical Power ◽  
Molecular Techniques ◽  
Fitness Effects ◽  
Primary Sex Ratio ◽  
Brood Sex Ratio ◽  
Power Studies ◽  
High Statistical Power

Under many circumstances, it might be adaptive for parents to bias the investment in offspring in relation to sex. Recently developed molecular techniques that allow sex determination of newly hatched offspring have caused a surge in studies of avian sex allocation. Whether females bias the primary brood sex ratio in relation to factors such as environmental and parental quality is debated. Progress is hampered because the mechanisms for primary sex ratio manipulation are unknown. Moreover, publication bias against non–significant results may distort our view of adaptive sex ratio manipulation. Despite this, there is recent experimental evidence for adaptive brood sex ratio manipulation in birds. Parental care is a particularly likely candidate to affect the brood sex ratio because it can have strong direct effects on the fitness of both parents and their offspring. We investigate and make predictions of factors that can be important for adaptive brood sex ratio manipulation under different patterns of parental care. We encourage correlational studies based on sufficiently large datasets to ensure high statistical power, studies identifying and experimentally altering factors with sex–differential fitness effects that may cause brood sex ratio skew, and studies that experimentally manipulate brood sex ratio and investigate fitness effects.

scholarly journals Can't live with them, can't live without them? Balancing mating and competition in two-sex populations

2017 ◽  
Vol 284 (1865) ◽  
pp. 20171999 ◽  
Author(s):  
Aldo Compagnoni ◽  
Kenneth Steigman ◽  
Tom E. X. Miller
Keyword(s):  
Sex Ratio ◽  
Mating Success ◽  
Sex Ratios ◽  
Structured Populations ◽  
Allee Effects ◽  
Mate Finding ◽  
Frequency Dependent ◽  
Density Dependent ◽  
Positive Effects ◽  
Demographic Processes

Two-sex populations are usually studied through frequency-dependent models that describe how sex ratio affects mating, recruitment and population growth. However, in two-sex populations, mating and recruitment should also be affected by density and by its interactions with the sex ratio. Density may have positive effects on mating (Allee effects) but negative effects on other demographic processes. In this study, we quantified how positive and negative inter-sexual interactions balance in two-sex populations. Using a dioecious grass ( Poa arachnifera ), we established experimental field populations that varied in density and sex ratio. We then quantified mating success (seed fertilization) and non-mating demographic performance, and integrated these responses to project population-level recruitment. Female mating success was positively density-dependent, especially at female-biased sex ratios. Other demographic processes were negatively density-dependent and, in some cases, frequency-dependent. Integrating our experimental results showed that mate-finding Allee effects dominated other types of density-dependence, giving rise to recruitment that increased with increasing density and peaked at intermediate sex ratios, reflecting tension between seed initiation (greater with more females) and seed viability (greater with more males). Our results reveal, for the first time, the balance of positive and negative inter-sexual interactions in sex-structured populations. Models that account for both density- and sex ratio dependence, particularly in mating, may be necessary for understanding and predicting two-sex population dynamics.

Large-scale spatiotemporal variation in calf sex ratio in moose (Alces alces): an effect of density-dependent decrease in maternal condition?

2009 ◽  
Vol 87 (4) ◽  
pp. 346-355 ◽  
Author(s):  
K. Bjørneraas ◽  
E. J. Solberg ◽  
I. Herfindal ◽  
B.-E. Sæther
Keyword(s):  
Sex Ratio ◽  
Large Scale ◽  
Alces Alces ◽  
Recruitment Rate ◽  
Spatiotemporal Variation ◽  
Adult Males ◽  
Maternal Condition ◽  
Density Dependent ◽  
Postnatal Mortality

The harvest of Norwegian moose ( Alces alces (L., 1758)) is directed towards certain sex and age classes to maximize yield in terms of meat or number of animals. Observed side effects are declining numbers of calves per female and proportions of adult males, which may affect other demographic variables. Using long-term data, we examined whether spatiotemporal variation in the calf sex ratio was related to changes in (i) density of harvested moose, (ii) recruitment rate, and (or) (iii) the composition of the adult segment of the population. We found declining proportions of male calves in the autumn harvest over time associated with decreasing recruitment rates. Similarly, the proportion of male calves was lower when density of harvested moose was high. We suggest that the decrease in proportion of male calves was caused by increased prenatal or postnatal mortality rates of males, possibly owing to a density-dependent decline in maternal body condition. Proportion of male calves increased with the proportion of adult males in the population the previous year, indicating that low proportions of adult males may lead to lower male recruitment, particularly at high densities. Further declines in proportions of male calves recruited may be avoided by reducing the population density and changing the demographic composition of the harvest.

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