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37 results for “sex ratio bias”
Male biased sex ratio in the offspring of roe deer
<p>The file "metafor_roe_sex.csv" was used for the meta-analysis regarding the sex ratio of roe deer juveniles. It contains the columns: </p> <p>Author (author(s) of the publication, Country (country were the study was publised), Location (specific location, in case that the data set contains several different locations the term "divers" is used), Year (year(s) were the sex of roe deer offspring were documented), Pub-Year (Year of publication) , N (number of offspring), N_female (number of female offspring), Sex ratio (primary - P or secondary - S sex ratio), Habitat conditions (F - free ranging, I - Island conditions, C - captive), Proportion female (proportion of female juveniles), Low_95 (lower boundary for the proportion of females using an exact binomial test with a 95% confidence interval), High_95 (upper boundary for the proportion of females using an exact binomial test with a 95% confidence interval), d (effect size), d_se (standard error of the effect size), North (Latitude), East (Longitude)</p> <p>The file "sex_bw.csv" contains information about roe deer juveniles tacked in Baden-Württemberg. The columns read as: Year (year were the juvenile was tacked), sex (the sex of the juvenile, m- male; f- female), and Hasl (elevation in m)</p> <p>The file "temp_data_comma_sep.csv" contains the montly mean values for temperature (Temp) and precipitation (NDS) for the months January, February, March, ..., December for the German federal state Baden-Württemberg (Source German Weather Service).</p> <p>All data sets were used for analysis presented in: Evidence for a male-biased sex ratio in the offspring of a large herbivore: the role of environmental conditions in the sex ratio variation.</p> <p> </p> <p> </p>
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>
Data for: Five decades of data yield no support for adaptive biasing of offspring sex ratio in wild baboons (Papio cynocephalus)
<p>Over the past 50 years, a wealth of testable, often conflicting, hypotheses has been generated about the evolution of offspring sex ratio manipulation by mothers. Several of these hypotheses have received support in studies of invertebrates and some vertebrate taxa. However, their success in explaining sex ratios in mammalian taxa, and especially in primates, has been mixed. Here, we assess the predictions of four different hypotheses about the evolution of biased offspring sex ratios in the well-studied baboons of the Amboseli basin in Kenya: the Trivers-Willard, female rank enhancement, local resource competition, and local resource enhancement hypotheses. Using the largest sample size ever analyzed in a primate population (n = 1372 offspring), we test the predictions of each hypothesis. Overall, we find no support for adaptive biasing of sex ratios. Offspring sex is not consistently related to maternal dominance rank or biased towards the dispersing sex, nor it is predicted by group size, population growth rates, or their interaction with maternal rank. Because our sample size confers power to detect even subtle biases in sex ratio, including modulation by environmental heterogeneity, these results suggest that adaptive biasing of offspring sex does not occur in this population.</p>
Data for: Five decades of data yield no support for adaptive biasing of offspring sex ratio in wild baboons (Papio cynocephalus)
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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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Adult sex-ratio bias does not lead to detectable adaptive offspring sex allocation via nest-site choice in a turtle with temperature-dependent sex determination
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Sperm limitation produces male biased family sex ratios
<p>Haplo-diploid sex determination in the parasitoid wasp, <em>Nasonia vitripennis</em> (Walker), allows females to adjust their brood sex ratios. Females influence whether ova are fertilized, producing diploid females, or remain unfertilized, producing haploid males. Females appear to adjust their brood sex ratios to minimize "local mate competition," <em>i.e.</em>, competition among sons for mates. Because mating occurs between siblings, females may optimize mating opportunities for their offspring by producing only enough sons to inseminate daughters when ovipositing alone and producing more sons when superparasitism is likely. Although widely accepted, this hypothesis makes no assumptions about gamete limitation in either sex. Because sperm is used to produce daughters, repeated oviposition could reduce sperm supplies, causing females to produce more sons. In contrast, if egg-limited females produce smaller broods, they might use fewer sperm, making sperm limitation less likely. To investigate whether repeated oviposition and female fertility influence gamete limitation within females, we created two treatments of six mated female wasps, which received a series of six hosts at intervals of 24 or 48 hrs. All females produced at least one mixed-sex brood (63 total broods; 3,696 offspring). As expected, if females became sperm limited, in both treatments, brood sex ratios became increasingly male-biased with increasing host number. The interhost interval did not affect brood size, total offspring number or sex ratio, indicating females did not become egg limited. Our results support earlier studies showing sperm depletion affects sex allocation in <em>N. vitripennis</em>¸ and could limit adaptive sex ratio manipulation in these parasitoid wasps.</p>
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>
Operational sex ratio bias due to sex-specific cohort splitting in response to predation
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Sperm limitation produces male biased family sex ratios
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Female biased offspring sex ratios of eastern wild turkeys across the southeastern United States
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Data for: Mechanisms that can cause population decline under heavily skewed male-biased adult sex ratios
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Causes and consequences of an unusually male-biased adult sex ratio in an unmanaged feral horse population
<p>1. The adult sex ratio (ASR) is important within ecology due to its predicted effects on behaviour, demography, and evolution, but research examining the causes and consequences of ASR bias have lagged behind studies of sex ratios at earlier life stages. Although ungulate ASR is relatively well-studied, exceptions to the usual female-biased ASR challenge our understanding of the underlying drivers of biased ASR, and provide an opportunity to better understand its consequences.</p> <p>2. Some feral ungulate populations, including multiple horse populations, exhibit unusually male-biased ASR. For example, research suggests that the feral horse (Equus ferus caballus) population on Sable Island, Nova Scotia, Canada, may exhibit a male-biased ASR. Such exceptions to the rule provide a valuable opportunity to reveal the contributions of environmental context and trait differences to ASR bias.</p> <p>3. We aimed to test for bias in Sable Island horse ASR, identify the demographic drivers of bias, and explore its demographic and social consequences. To do this, we used life-history, movement, and group membership information for hundreds of horses followed through a long-term individual-based study between 2007 and 2018.</p> <p>4. Sable Island horse ASR is male-biased, and this skew has increased over time, reaching 62% male in 2018. Our life table response experiment suggested that ASR skew was driven predominantly by male-biased adult survival. Further analyses pointed to sex-biased survival being driven by reduced female survival post-reproduction. Male-biased ASR was associated with reduced harem sizes, an increase in the number of social groups on the island, and reduced reproduction in young females.</p> <p>5. Our results support the idea that male-biased ASR in feral ungulate populations may be caused by a combination of high population density and high reproductive output. We suggest that female-biased mortality may be caused by females continuing to reproduce at high density, and thus being more susceptible to resource shortages. Thus, our results highlight the strong context-dependence of ASR. Furthermore, our work indicates the potential for ASR to substantially alter a population's social organisation. Such changes in social structure could have knock-on consequences for demography by altering the formation/stability of social relationships, or competition for matings.</p>
Data from: Slower senescence in a wild insect population in years with a more female-biased sex ratio
Life-history theories of senescence are based on the existence of a trade-off in resource allocation between body maintenance and reproduction. This putative trade-off means that environmental and demographic factors affecting the costs of reproduction should be associated with changes in patterns of senescence. In many species, competition among males is a major component of male reproductive investment, and hence variation in the sex ratio is expected to affect rates of senescence. We test this prediction using nine years of demographic and behavioural data from a wild population of the annual field cricket Gryllus campestris. Over these generations the sex ratio at adulthood varied substantially, from years with an equal number of each sex to years with twice as many females as males. Consistent with the predictions of theory, we found that in years with a greater proportion of females, both sexes experienced a slower increase in mortality rate with age. Additionally, phenotypic senescence in males was slower in years when there were more females. Sex ratio did not affect the baseline mortality rate in males, but females suffered higher age-independent mortality rates when males were in short supply.
Data from: Is biasing offspring sex ratio adaptive? a test of Fisher's principle across multiple generations of a wild mammal in a fluctuating environment
Fisher's principle explains that population sex ratio in sexually reproducing organisms is maintained at 1:1 due to negative frequency-dependent selection, such that individuals of the rare sex realize greater reproductive opportunity than individuals of the more common sex until equilibrium is reached. If biasing offspring sex ratio towards the rare sex is adaptive, individuals that do so should have a higher number of grandoffspring. In a wild population of North American red squirrels (Tamiasciurus hudsonicus) that experiences fluctuations in resource abundance and population density, we show that overall across 26 years, the secondary sex ratio was 1:1; however, stretches of years during which adult sex ratio was biased did not yield offspring sex ratios biased towards the rare sex. Females that had litters biased towards the rare sex did not have more grandoffspring. Critically, adult sex ratio was not temporally autocorrelated across years, thus the population sex ratio experienced by parents was independent of the population sex ratio experienced by their offspring by the time of their primiparity. Expected fitness benefits of biasing offspring sex ratio may be masked or negated by fluctuating environments across years, which limit the predictive value of the current sex ratio.
Data from: Is biasing offspring sex ratio adaptive? a test of Fisher’s principle across multiple generations of a wild mammal in a fluctuating environment
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Data from: The male handicap: male-biased mortality explains skewed sex ratios in brown trout embryos
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Data from: Unexpected consequences of a drier world: evidence that delay in late summer rains biases the population sex ratio of an insect
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Data from: A father effect explains sex-ratio bias
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Data from: Natal habitat and sex-specific survival rates result in a male-biased adult sex ratio
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