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.

scholarly journals Cooperative interactions among females and even more extraordinary sex ratios

2020 ◽  
Author(s):  
Ryosuke Iritani ◽  
Stuart A West ◽  
Jun Abe
Keyword(s):  
Sex Ratio ◽  
Sex Ratios ◽  
Structured Populations ◽  
Local Mate Competition ◽  
Mate Competition ◽  
Wasp Species ◽  
Cooperative Interactions ◽  
Competition Theory ◽  
Local Mate ◽  
Biased Sex Ratio

AbstractHamilton’s local mate competition theory provided an explanation for extraordinary female biased sex ratios in a range of organisms. When mating takes place locally, in structured populations, a female biased sex ratio is favoured to reduce competition between related males, and to provide more mates for males. However, there are a number of wasp species where the sex ratios appear to more female biased than predicted by Hamilton’s theory. We investigated theoretically the extent to which cooperative interactions between related females can interact with local mate competition to favour even more female biased sex ratios. We found that: (i) cooperative interactions between females can lead to sex ratios that are more female biased than predicted by local competition theory alone; (ii) sex ratios can be more female biased when the cooperative interactions are offspring helping parents before dispersal, rather than cooperation between siblings after dispersal. Our results can be applied to a range of organisms, and provide an explanation for the extreme sex ratio biases that have been observed in Sclerodermus and Melittobia wasps.

scholarly journals Experimental evolution under varying sex ratio and nutrient availability modulates male mating success in Drosophila melanogaster

2021 ◽  
Author(s):  
Irem Sepil ◽  
Jennifer C. Perry ◽  
Alice Dore ◽  
Tracey Chapman ◽  
Stuart Wigby
Keyword(s):  
Drosophila Melanogaster ◽  
Sex Ratio ◽  
Nutrient Availability ◽  
Mating Success ◽  
Experimental Evolution ◽  
Sex Ratios ◽  
Male Mating ◽  
Male Mating Success ◽  
Restricted Diet ◽  
Protein Restricted Diet

AbstractBiased population sex ratios can alter optimal male mating strategies, and allocation to reproductive traits depends on nutrient availability. However, there is little information on how nutrition interacts with sex ratio to influence the evolution of pre-copulatory and post-copulatory traits separately. To address this omission, here we test how male mating success and reproductive investment evolve under varying sex ratios and adult diet in Drosophila melanogaster using an experimental evolution approach. We found that sex ratio and nutrient availability interacted to determine male pre-copulatory performance. Males from female-biased populations were slow to mate when they evolved on a protein-restricted diet. On the other hand, we found direct and non-interacting effects of sex ratio and nutrient availability on post-copulatory success, without interactions between them. Males that evolved on a protein-restricted diet were poor at suppressing female remating. Males that evolved under equal sex ratios fathered more offspring and were better at supressing female remating, relative to males from male-biased or female-biased populations. These results support the idea that sex ratios and nutrition interact to determine the evolution of pre-copulatory mating traits, but independently influence the evolution of post-copulatory traits.

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.

scholarly journals Sex Ratios in a Warming World: Thermal Effects on Sex-Biased Survival, Sex Determination, and Sex Reversal

2021 ◽  
Vol 112 (2) ◽  
pp. 155-164
Author(s):  
Suzanne Edmands
Keyword(s):  
High Temperature ◽  
Sex Ratio ◽  
Sex Determination ◽  
Heat Tolerance ◽  
Sex Ratios ◽  
Sex Reversal ◽  
Survival Sex ◽  
Ratio Distortion ◽  
Warming World ◽  
Sex Ratio Distortion

Abstract Rising global temperatures threaten to disrupt population sex ratios, which can in turn cause mate shortages, reduce population growth and adaptive potential, and increase extinction risk, particularly when ratios are male biased. Sex ratio distortion can then have cascading effects across other species and even ecosystems. Our understanding of the problem is limited by how often studies measure temperature effects in both sexes. To address this, the current review surveyed 194 published studies of heat tolerance, finding that the majority did not even mention the sex of the individuals used, with <10% reporting results for males and females separately. Although the data are incomplete, this review assessed phylogenetic patterns of thermally induced sex ratio bias for 3 different mechanisms: sex-biased heat tolerance, temperature-dependent sex determination (TSD), and temperature-induced sex reversal. For sex-biased heat tolerance, documented examples span a large taxonomic range including arthropods, chordates, protists, and plants. Here, superior heat tolerance is more common in females than males, but the direction of tolerance appears to be phylogenetically fluid, perhaps due to the large number of contributing factors. For TSD, well-documented examples are limited to reptiles, where high temperature usually favors females, and fishes, where high temperature consistently favors males. For temperature-induced sex reversal, unambiguous cases are again limited to vertebrates, and high temperature usually favors males in fishes and amphibians, with mixed effects in reptiles. There is urgent need for further work on the full taxonomic extent of temperature-induced sex ratio distortion, including joint effects of the multiple contributing mechanisms.

scholarly journals Sex Chromosome Meiotic Drive in Stalk-Eyed Flies

Genetics ◽  
1997 ◽  
Vol 147 (3) ◽  
pp. 1169-1180 ◽  
Author(s):  
Daven C Presgraves ◽  
Emily Severance ◽  
Gerald S Willrinson
Keyword(s):  
Sex Ratio ◽  
Sex Chromosome ◽  
Sex Ratios ◽  
Natural Populations ◽  
Meiotic Drive ◽  
Operational Sex Ratio ◽  
Genetic Modifiers ◽  
Ratio Distortion ◽  
The Impact ◽  
Sex Ratio Distortion

Meiotically driven sex chromosomes can quickly spread to fixation and cause population extinction unless balanced by selection or suppressed by genetic modifiers. We report results of genetic analyses that demonstrate that extreme female-biased sex ratios in two sister species of stalk-eyed flies, Cyrtodiopsis dalmanni and C. whitei, are due to a meiotic drive element on the X chromosome (Xd). Relatively high frequencies of Xd in C. dalmanni and C. whitei (13–17% and 29%, respectively) cause female-biased sex ratios in natural populations of both species. Sex ratio distortion is associated with spermatid degeneration in male carriers of Xd. Variation in sex ratios is caused by Y-linked and autosomal factors that decrease the intensity of meiotic drive. Y-linked polymorphism for resistance to drive exists in C. dalmanni in which a resistant Y chromosome reduces the intensity and reverses the direction of meiotic drive. When paired with Xd, modifying Y chromosomes (Ym) cause the transmission of predominantly Y-bearing sperm, and on average, production of 63% male progeny. The absence of sex ratio distortion in closely related monomorphic outgroup species suggests that this meiotic drive system may predate the origin of C. whitei and C. dalmanni. We discuss factors likely to be involved in the persistence of these sex-linked polymorphisms and consider the impact of Xd on the operational sex ratio and the intensity of sexual selection in these extremely sexually dimorphic flies.

scholarly journals Frequency-dependent interactions determine outcome of competition between two breast cancer cell lines

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Audrey R. Freischel ◽  
Mehdi Damaghi ◽  
Jessica J. Cunningham ◽  
Arig Ibrahim-Hashim ◽  
Robert J. Gillies ◽  
...  
Keyword(s):  
Breast Cancer ◽  
Cancer Cell ◽  
Critical Density ◽  
Low Ph ◽  
Breast Cancer Cell Lines ◽  
Frequency Dependent ◽  
Density Dependent ◽  
Low Glucose ◽  
Competition Assays ◽  
Mcf 7

AbstractTumors are highly dynamic ecosystems in which diverse cancer cell subpopulations compete for space and resources. These complex, often non-linear interactions govern continuous spatial and temporal changes in the size and phenotypic properties of these subpopulations. Because intra-tumoral blood flow is often chaotic, competition for resources may be a critical selection factor in progression and prognosis. Here, we quantify resource competition using 3D spheroid cultures with MDA-MB-231 and MCF-7 breast cancer cells. We hypothesized that MCF-7 cells, which primarily rely on efficient aerobic glucose metabolism, would dominate the population under normal pH and low glucose conditions; and MDA-MB-231 cells, which exhibit high levels of glycolytic metabolism, would dominate under low pH and high glucose conditions. In spheroids with single populations, MCF-7 cells exhibited equal or superior intrinsic growth rates (density-independent measure of success) and carrying capacities (density-dependent measure of success) when compared to MDA-MB-231 cells under all pH and nutrient conditions. Despite these advantages, when grown together, MCF-7 cells do not always outcompete MDA-MB-231 cells. MDA-MB-231 cells outcompete MCF-7 cells in low glucose conditions and coexistence is achieved in low pH conditions. Under all conditions, MDA-MB-231 has a stronger competitive effect (frequency-dependent interaction) on MCF-7 cells than vice-versa. This, and the inability of growth rate or carrying capacity when grown individually to predict the outcome of competition, suggests a reliance on frequency-dependent interactions and the need for competition assays. We frame these results in a game-theoretic (frequency-dependent) model of cancer cell interactions and conclude that competition assays can demonstrate critical density-independent, density-dependent and frequency-dependent interactions that likely contribute to in vivo outcomes.

scholarly journals Fisher vs. The Worms: Extraordinary Sex Ratios in Nematodes and the Mechanisms That Produce Them

Cells ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1793
Author(s):  
Justin Van Goor ◽  
Diane C. Shakes ◽  
Eric S. Haag
Keyword(s):  
Sex Ratio ◽  
Sperm Competition ◽  
Sex Chromosomes ◽  
Sex Ratios ◽  
Environmental Sex Determination ◽  
Fitness Advantage ◽  
Selection For ◽  
Facultative Parthenogenesis ◽  
Multicellular Organisms ◽  
Inbred Populations

Parker, Baker, and Smith provided the first robust theory explaining why anisogamy evolves in parallel in multicellular organisms. Anisogamy sets the stage for the emergence of separate sexes, and for another phenomenon with which Parker is associated: sperm competition. In outcrossing taxa with separate sexes, Fisher proposed that the sex ratio will tend towards unity in large, randomly mating populations due to a fitness advantage that accrues in individuals of the rarer sex. This creates a vast excess of sperm over that required to fertilize all available eggs, and intense competition as a result. However, small, inbred populations can experience selection for skewed sex ratios. This is widely appreciated in haplodiploid organisms, in which females can control the sex ratio behaviorally. In this review, we discuss recent research in nematodes that has characterized the mechanisms underlying highly skewed sex ratios in fully diploid systems. These include self-fertile hermaphroditism and the adaptive elimination of sperm competition factors, facultative parthenogenesis, non-Mendelian meiotic oddities involving the sex chromosomes, and environmental sex determination. By connecting sex ratio evolution and sperm biology in surprising ways, these phenomena link two “seminal” contributions of G. A. Parker. 

A new male-killing parasitism:Spiroplasmabacteria infect the ladybird beetleAnisosticta novemdecimpunctata(Coleoptera: Coccinellidae)

Parasitology ◽  
2006 ◽  
Vol 132 (6) ◽  
pp. 757-765 ◽  
Author(s):  
M. C. TINSLEY ◽  
M. E. N. MAJERUS
Keyword(s):  
Phylogenetic Analysis ◽  
Sex Ratio ◽  
High Efficiency ◽  
Sex Ratios ◽  
Egg Hatch ◽  
Hatch Rate ◽  
Male Killing ◽  
Offspring Sex ◽  
Novel Host ◽  
Males And Females

Whilst most animals invest equally in males and females when they reproduce, a variety of vertically transmitted parasites has evolved the ability to distort the offspring sex ratios of their hosts. One such group of parasites are male-killing bacteria. Here we report the discovery of females of the ladybirdAnisosticta novemdecimpunctatathat produced highly female-biased offspring sex ratios associated with a 50% reduction in egg hatch rate. This trait was maternally transmitted with high efficiency, was antibiotic sensitive and was infectious following experimental haemolymph injection. We identified the cause as a male-killingSpiroplasmabacterium and phylogenetic analysis of rDNA revealed that it belongs to theSpiroplasma ixodetisclade in which other sex ratio distorters lie. We tested the potential for interspecific horizontal transfer by injection from an infectedA. novemdecimpunctataline into uninfected individuals of the two-spot ladybirdAdalia bipunctata. In this novel host, the bacterium was able to establish infection, transmit vertically and kill male embryos.

Sign in / Sign up

Export Citation Format

Share Document