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58 results for “population sex ratio”
Data from: Female-biased population sex ratios caused by genetic rather than ecological mechanisms in dwarf willow (Salix herbacea L.)
<p>Biased sex ratios among reproductive individuals are common in plants, but the underlying mechanisms, as well as the evolutionary consequences, are not well understood. The classical theory of Düsing and Fisher predicts an equal primary sex ratio at seed production, based on the selective advantage of the rare sex. Biased sex ratios among reproductive plants can arise from sexual dimorphism in survival and flowering. Sex ratio biases can also be present from the seed stage; in these cases, assumptions of Düsing's and Fisher's theory, for example, random mating or demographic equilibrium, are thought to be violated.</p> <p>We investigated mechanisms leading to female-biased sex ratios in the arctic-alpine dwarf willow <em>Salix herbacea</em> L. We studied sex ratios in three natural populations over three years as well as in 29 crosses (full-sib families) under controlled conditions over four growth periods. We tested whether sex ratio was associated with habitat parameters (elevation and snowmelt time), or with germination, survival or flowering, and whether females and males differed in size or flowering that may cause observation bias.</p> <p>We detected a strong and consistent female bias, both in natural populations (sex ratio [proportion of females]: 0.71-0.82) and in our controlled experiment (overall sex ratio: 0.70-0-72). Female bias became more pronounced with increasing elevation. Our data did not support sexual dimorphism in size or flowering. Family sex ratios varied largely (from 0.25 to 1), including many female-biased families, unbiased families and two male-biased families. Families with lower germination, seedling establishment, survival or flowering did not have stronger female bias, indicating that intrinsically higher survival or flowering in females does not explain overall female bias. </p> <p>Synthesis: Our results suggest that sex ratio bias in <em>S. herbacea</em> is already present in seeds and does not arise through intrinsic differences between sexes. Candidate mechanisms that can lead to both overall female bias and variation in sex ratio among families are meiotic drive or cyto-nuclear interactions. The pioneer habit of <em>Salix</em> may lead to non-equilibrium population dynamics that allow for the long-term persistence of variable genetic sex ratio distortion systems that arise from genetic conflict.</p>
FIG. 5 in Expressed sex ratio in populations of the moss Hamatocaulis vernicosus (Mitt.) Hedenäs (Scorpidiaceae) in the Czech Republic with consideration of its cryptic species
FIG. 5. — The sex ratio in mixed population at locality Zhůří 1. Unbordered pie charts refer to clade 1, bordered ones represent clade 2. The patch in the larger circle contained plants of both clades, so this patch must be excluded from evaluating sex ratio in separated clades.
FIG. 3 in Expressed sex ratio in populations of the moss Hamatocaulis vernicosus (Mitt.) Hedenäs (Scorpidiaceae) in the Czech Republic with consideration of its cryptic species
FIG. 3. — Rates of male (blue), female (red) and non-expressing (green) plants at studied localities of Hamatocaulis vernicosus (Mitt.) Hedenäs clade 1 and 2.
FIG. 2 in Expressed sex ratio in populations of the moss Hamatocaulis vernicosus (Mitt.) Hedenäs (Scorpidiaceae) in the Czech Republic with consideration of its cryptic species
FIG. 2. — The expressed sex ratio at studied localities of H. vernicosus (Mitt.) Hedenäs. In mixed populations,only single-clade patches were used for the assessment.
FIG. 4 in Expressed sex ratio in populations of the moss Hamatocaulis vernicosus (Mitt.) Hedenäs (Scorpidiaceae) in the Czech Republic with consideration of its cryptic species
FIG. 4.— Sex ratio at localities with co-occurring cryptic species. All, without distinguished clades; cl. 1, clade 1; cl. 2, clade 2; Šimanov, Šimanovské rašeliniště. Only barcoded shoots were used to create this graph.
FIG. 1 in Expressed sex ratio in populations of the moss Hamatocaulis vernicosus (Mitt.) Hedenäs (Scorpidiaceae) in the Czech Republic with consideration of its cryptic species
FIG. 1.— The sex expression of Hamatocaulis vernicosus (Mitt.) Hedenäs in the Czech Republic at individual localities assessed at two levels of pooling hierarchy ("shoots at localities" and "patches at localities").
Figure 2 in Population dynamics, age structure and sex ratio of the bromeliad-dwelling jumping spider, Psecas chapoda (Salticidae)
Figure 2. Mean number (¡SE) of Psecas chapoda per Bromelia balansae with no inflorescence, from May 1998 to April 2000 (N53516 spiders).
Figure 1 in Population dynamics, age structure and sex ratio of the bromeliad-dwelling jumping spider, Psecas chapoda (Salticidae)
Figure 1. Fluctuations in the number of Psecas chapoda and egg sacs (log) on bromeliads with and without inflorescence, and the frequency (%) of bromeliads in bloom (with inflorescence or infrutescence) between May 1998 and April 2000 (N53516 spiders and 314 egg sacs).
Figure 5 in Population dynamics, age structure and sex ratio of the bromeliad-dwelling jumping spider, Psecas chapoda (Salticidae)
Figure 5. Mean number (¡SE) of spiders Psecas chapoda on bromeliads that produced inflorescence between August and December and on bromeliads that did not produce inflorescence until December, in 1998 (A) and 1999 (B). The frequency (%) of bromeliads that bloomed up to December is also shown.
Figure 4 in Population dynamics, age structure and sex ratio of the bromeliad-dwelling jumping spider, Psecas chapoda (Salticidae)
Figure 4. Phenogram of the Psecas chapoda population on plants of Bromelia balansae without inflorescence, from May 1998 to April 2000 (N53516 spiders).
Data from: Potential drivers and implications of a balanced breeding sex ratio in a small population of an imperiled species with environmental sex determination
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Data from: Female-biased population sex ratios caused by genetic rather than ecological mechanisms in dwarf willow (Salix herbacea L.)
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Data from: Detecting the population dynamics of an autosomal sex-ratio distorter transgene in malaria vector mosquitoes
<p>1. The development of genetically modified mosquitoes and their subsequent field release offers innovative and cost-effective approaches to reduce mosquito-borne diseases, such as malaria. A sex-distorting autosomal transgene has been developed recently in G3 mosquitoes, a lab strain of the malaria vector Anopheles gambiae s.l. The transgene expresses an endonuclease called I-PpoI during spermatogenesis, which selectively cleaves the X chromosome to result in ~95% male progeny. Following the World Health Organization Guidance Framework for the testing of genetically modified mosquitoes, we assessed the dynamics of this transgene in large cages using a joint experimental-modelling approach.</p> <p>2. We performed a four-month experiment in indoor large cages to study the population genetics of the transgene. The cages were set up to mimic a simple tropical environment with a diurnal light-cycle, constant temperature, and constant humidity. We allowed the generations to overlap to engender a stable age structure in the populations. We constructed a model to mimic the experiments, and used the experimental data to infer the key model parameters.</p> <p>3. We identified two fitness costs associated to the transgene. First, transgenic adult males have reduced fertility and, second, their female progeny have reduced pupal survival rates. Our results demonstrate that the transgene is likely to disappear in less than three years under our confined conditions. Model predictions suggest this will be true over a wide range of background population sizes and transgene introduction rates.</p> <p>4. Synthesis and applications: Our semi-field indoor cage experiments are in line with WHO guidance recommendations in regards to the development and testing of self-limiting technologies. Since the transgenic strain (Ag(PMB)1) has been considered for genetic vector control of malaria, our results are fundamentally important for determining expectations on the persistence of the transgene post-release. Our results provide a demonstration of the self-limiting nature of the transgene, and indicate that longevity will be further reduced by fitness costs that were not previously identified. Finally, our study has showcased an alternative and effective method for characterising the phenotypic expression of a transgene in an insect pest population.</p>
Sex-specific patterns of senescence in artificial insect populations varying in sex-ratio to manipulate reproductive effort
<p><strong>Background:</strong> The disposable soma theory of ageing assumes that organisms optimally trade-off limited resources between reproduction and longevity to maximize fitness. Early reproduction should especially trade-off against late reproduction and longevity because of reduced investment into somatic protection, including immunity. Moreover, as optimal reproductive strategies of males and females differ, sexually dimorphic patterns of senescence may evolve. In particular, as males gain fitness through mating success, sexual competition should be a major factor accelerating male senescence. In a single experiment, we examined these possibilities by establishing artificial populations of the mealworm beetle, <em>Tenebrio molitor</em>, in which we manipulated the sex-ratio to generate variable levels of investment into reproductive effort and sexual competition in males and females.</p> <p><strong>Results:</strong> As predicted, variation in sex-ratio affected male and female reproductive efforts, with contrasted sex-specific trade-offs between lifetime reproduction, survival and immunity. High effort of reproduction accelerated mortality in females, without affecting immunity, but high early reproductive success was observed only in balanced sex-ratio condition. Male reproduction was costly on longevity and immunity, mainly because of their investment into copulations rather than in sexual competition.</p> <p><strong>Conclusions:</strong> Our results suggest that <em>T. molitor</em> males, like females, maximize fitness through enhanced longevity, partly explaining their comparable longevity. </p>
Figure 3 in Population dynamics, age structure and sex ratio of the bromeliad-dwelling jumping spider, Psecas chapoda (Salticidae)
Figure 3. Climatic data from Itauna farm (5 km from the study site), from May 1998 to April 2000.
Data for: Mechanisms that can cause population decline under heavily skewed male-biased adult sex ratios
<ol> <li><span>While adult sex ratio (ASR) is a crucial component for population management, there is still a limited understanding of how its fluctuation affects population dynamics. To demonstrate mechanisms that hinder population growth under a biased ASR, we examined changes in reproductive success with ASR using a decapod crustacean exposed to female-selective harvesting. </span></li> <li> <span>We examined the effect of ASR on the spawning</span><span> success </span><span>of females. A laboratory experiment showed that the number of eggs carried by females decreased as the proportion of males in the mating groups increased. Although the same result was not observed in data collected over 25 years in the wild, the negative effect of ASR was suggested when success in carrying eggs was considered as a spawning success. These results indicate that a surplus of males results in females failing to carry eggs, probably due to sexual coercion, and</span> <span>the negative effect of ASR can be detected at the population level only when the bias increases because failure in spawning success occurs in part of population.</span> </li> <li><span>We experimentally examined how male-biased sex ratios affected the maintenance of genetic diversity in a population. The diversity of paternity in a clutch increased with the number of candidate fathers. However, over 50% of a clutch was fertilised by a single male regardless of the sex ratio, and the degree of diversity was less than half of the highest diversity expected in each mating group. </span></li> <li><span>We also experimentally examined the mating ability of males during the breeding season. The experiment showed that multiple mating by males could not compensate for the risk that their genotypes would be lost when multiple males competed for one female. These results suggest that a male-biased ASR could trigger a decline of genetic diversity in a population.</span></li> <li><span>We show that ASR skewed by female-selective harvesting decreases reproductive success not only of males that have few mating opportunities but also of females. We discuss that we may still underestimate the significance of ASR on population persistence due to the difficulty of revealing the effect of ASR.</span></li> </ol>
Data from: Clonality, local population structure, and gametophyte sex ratios in cryptic species of the Sphagnum magellanicum complex
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Sex-specific patterns of senescence in artificial insect populations varying in sex-ratio to manipulate reproductive effort
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Data from: Detecting the population dynamics of an autosomal sex-ratio distorter transgene in malaria vector mosquitoes
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Data for: Mechanisms that can cause population decline under heavily skewed male-biased adult sex ratios
Open the record for dataset details and reuse information.
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International Brain Laboratory public data
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