Variation In Sex Ratio Research Articles

Study on the Influence of Sex Ratio on Ecology Based on Improved Lotka-Volterra Model

In a pioneering study of lamprey population dynamics, we employ an enhanced Lotka-Volterra model to illuminate the profound influence of sex ratio shifts on ecosystems. This exploration delves into how such changes affect resource availability, ecosystem equilibrium, and sustainability. We employ dynamic differential equations to simulate population fluctuations among males, females, and predators, incorporating elements like birth rate, mortality rate, competition coefficient, mating success rate, and predation rate. The differential equations are numerically resolved using the Runge-Kutta method, enabling us to analyze population dynamics across various scenarios. Concurrently, we construct Jacobian matrices to appraise ecosystem stability and equilibrium points. The refined Lotka-Volterra model effectively encapsulates the impact of sex ratio variations on reproductive and predation processes, offering profound insights into predator-prey interactions and ecosystem dynamics. Our pivotal discoveries underscore the influence of sex ratio modifications on reproductive capacity, population growth rates, social structure, genetic diversity, and predator-prey relationships. This study emphasizes the criticality of comprehending the repercussions of sex ratio shifts on ecosystems and communities.

Impacts of Sea Lamprey Sex Ratio Variation Analysis based on L-V Model and P-P Model

As an important animal model for the study of biological evolution and disease, lamprey has attracted the attention of many scholars. Its variable sex ratio is also becoming the focus of studying because of the impact of ecological system. This paper utilizes mathematical method, and establishes the Lotka-Volterra Model to simulate the variations of the sex ratio among lamprey larvae populations. Additionally, Holling II function and Weak Alley Effect are adopted to establish a Predator-Prey Model of adult lampreys in three-tiered food chain, predicting the population dynamics of adult lamprey. The result of model simulation finds that low environmental capacity leads to a unexpectedly high ratio of male lampreys, which is up to 74.51% and proably causes population extinction. The study offers a novel insight into the interaction between ecosystems and fish species with variable sex ratios such as the lampreys.

Socially plastic responses in females are robust to evolutionary manipulations of adult sex ratio and adult nutrition.

Socially plastic behaviours are widespread among animals and can have a significant impact on fitness. Here, we investigated whether the socially plastic responses of female Drosophila melanogaster can evolve in predictable ways following long-term manipulation of adult sex ratio and adult nutrient availability. Previous reports show that female D. melanogaster respond plastically to their same-sex social environment and lay significantly fewer eggs after mating when previously exposed to other females. In this study, we tested 2 hypotheses, using females drawn from lines with an evolutionary history of exposure to variation in adult sex ratio (male-biased, female-biased or equal sex ratio) and adult nutritional environment (high or low quality). The first was that a history of elevated competition in female-biased regimes would select for increased plastic fecundity responses in comparison to females from other lines. The second was that these responses would also be magnified under poor nutritional resource regimes. Neither hypothesis was supported. Instead, we found that plastic fecundity responses were retained in females from all lines and did not differ significantly across any of them. The lack of differences does not appear to be due to insufficient selection, as we did observe significant evolutionary responses in virgin egg-laying patterns according to sex ratio and nutritional regime. The lack of variation in the magnitude of predicted plasticity is consistent with the idea that the costs of maintaining plasticity are low, benefits high, and that plasticity itself can be relatively hard wired.

Population dynamics and reproductive features of the Amazon River prawn Macrobrachium amazonicum (Heller, 1862) in Neotropical reservoirs under drought events

Here, we describe population and reproductive dynamics of four populations of Macrobrachium amazonicum in reservoirs during drought events. Additionally, we analyze possible phenotypic changes in this species promoted by fish predation. Two populations had a large-size phenotype (with large body proportions and morphotypes in males) while a small-size phenotype (with reduced sizes and no morphotypes) was found in the two other populations. Overall, females were larger than males and there were varying sex ratios among the four studied populations. All populations had bimodal or polymodal patterns in their monthly size-class frequency, suggesting a seasonal influence and a potentially great capacity of these populations to adapt to adverse environmental conditions. No major changes were found in the patterns of sex ratio, recruitment, frequency of (larger) male morphotypes and female ovarian development stages during drought events. Macrobrachium amazonicum is a resilient species and undergoes continuous reproduction. Females with immature ovaries were predominant in all populations, performing multiple spawns and exhibiting rapid ovarian development cycles. In males, the initial morphotype (TC - translucent claw) was predominant in populations with a social hierarchy. Males of dominant morphotypes (GC1 and GC2 - green claw 1 and 2) use more energy to carry out and maintain metabolic processes, which could probably one of the explanations why their number in populations are limited. We did not find any clear evidence that fish predation affected phenotypes, suggesting that phenotypic plasticity could be more related to intrinsic factors, which would have to be further investigated.

Testing secondary sex ratio bias hypotheses in white-tailed deer in Mississippi, USA.

Natural selection favors individuals with the highest inclusive fitness (i.e., total number of descendants). In cases where one sex is more productive, one or both parents may maximize their inclusive fitness by investing in the offspring of the more prolific sex. Such preferential production can lead to skewed sex ratios at various life history stages, including at birth, resulting in secondary sex ratio bias. Several competing hypotheses have been proposed to explain observed variation in secondary sex ratios including Fisher's frequency dependence and two hypotheses related to maternal condition: Trivers-Willard and the local resource hypotheses. Although it has been shown that maternal condition can influence the number of offspring produced in white-tailed deer, there is no consensus as to which of the hypotheses drives sex ratio bias in wild populations. Using a spatiotemporally extensive dataset of pregnant white-tailed deer from Mississippi, USA, we examined fetal sex ratio in relation to the Fisherian frequency-dependence hypothesis and hypotheses related to maternal condition. While there was a male-sex ratio bias in pregnant females that reduced in intensity with the number of offspring, there was no support for condition-related hypotheses. Instead, secondary sex ratios for white-tailed deer in Mississippi were nearly consistent with Fisherian frequency dependence. Our findings add to the body of literature on secondary sex biases in white-tailed deer and help inform sex bias ratios for a southern population of a cervid of management importance in the US.

Population structure, spatial aggregation, and sampling plan for the Texas citrus mite, Eutetranychus banksi (Acari: Tetranychidae) on citrus.

Eutetranychus banksi (McGregor) (Acari: Tetranychidae) is an invasive spider mite native to the Americas. In 2013 it invaded the main citrus-growing area in Spain producing significant damage and requiring chemical treatments. This work examines its population structure, spatial distribution and presents a sampling plan, which will assist in developing an integrated pest management (IPM) strategy. There were differences in the population structure on fruits and leaves, as well as between leaves from different flushes with fluctuations over time correlated with variations in sex ratio. No differences in aggregation at the different plant strata were found; however, immature stages showed a higher aggregation than adults, with females being the sex with the lowest aggregation. There was a high correlation between E. banksi motile forms and adult females with the total population, thus both were used as reference stages to develop sampling plans. We recommend binomial sampling of 100 leaves for female monitoring, sampling two leaves per tree on 25 trees per transect regularly spaced along two diagonal transects, the first oriented northeast to southwest and the second northwest to southeast. To be more accurate, it is possible to survey the presence/absence of motile forms. In this case, four leaves per tree in 50 trees per transect should be monitored. This study has resulted in the first sampling plan for E. banksi, one of the most damaging citrus mite species described so far. The binomial sampling plan involves monitoring reference developmental stages, as well as a reasonable sample size that makes it applicable in field sampling for decisions making based on a future intervention threshold. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Research on the Sex Ratio Variation of Lampetra japonica and Its Reciprocal Altruism Effects Based on the Logistic and Lotka-Volterra Models

Research on the Sex Ratio Variation of Lampetra japonica and Its Reciprocal Altruism Effects Based on the Logistic and Lotka-Volterra Models

An ecological population study of lampreys in the Lotka-Volterra tertiary trophic level based on sex differences

This study examines the adaptive changes in sex ratio on animal populations and its effects on ecosystem stability and interactions. The effects of sex ratio dynamics on the ecosystem were analyzed through mathematical modeling using lampreys as the study population. In this study, a two-stage tertiary trophic Lotka-Volterra mathematical model of ecological dynamics was developed, taking into account food preferences, ecological roles, and sex interactions of lampreys. The simulation results showed that a rapid adjustment in sex ratio led to a reduction in environmental loads, which triggered an early rebound increase in lampreys and predator populations. To assess the ability of lampreys populations to adjust sex ratios, this study used a combination of fuzzy integrated evaluation and hierarchical analysis methods. The results of the study revealed the importance of sex-adaptive traits for population development, including increased resource utilization efficiency and population fitness, as well as decreased reproductive success and reduced genetic diversity. Based on the RRT (resistance, resilience and temporal stability) method, this study constructed an ecosystem stability assessment model and investigated the effects of changes in the sex ratio of lampreys on ecosystem stability. The experimental results showed that ecosystem stability was highest when the sex ratio was 0.6 and lowest when the sex ratio was 0.2. Variation in sex ratio may affect the behavior and abundance of lampreys, thereby directly influencing their interactions with other species. Variability in sex ratio provides more resources for predators and parasites of lampreys, promotes their growth, and positively affects ecosystem balance. Simulation results showed that the model was highly stable under different interactions. In summary, this study reveals the important effects of sex ratio on ecosystem stability and interactions, and provides important insights into the understanding of adaptive evolutionary traits of species, ecosystem stability and ecological interactions.

Dynamics of a goshawk population across half a century is driven by the variation of first-year survival.

Population dynamics are driven by stochastic and density-dependent processes acting on demographic rates. Individuals differ demographically, and to capture these differences, models of population dynamics are usually structured by age and stage, rarely by sex. An effect of sex on population dynamics is expected if the dynamics of males and females differ, requiring an unequal sex ratio at birth and/or sex-specific survival probabilities. Goshawks (Accipiter gentilis) show large sexual size dimorphism and differential survival, but it is unknown whether males and females contribute differently to population dynamics. We studied a goshawk population in northern Germany over 47 years using brood monitoring data, collected feathers and nestling ringing data. We jointly analyzed the data using a two-sex integrated population model and performed retrospective and prospective population analyses to understand whether the demographic drivers of population change differ between the sexes. The population showed large fluctuations, during which the number of breeding pairs doubled, but the long-term trend of the population was slightly negative. Female survival exceeded male survival during the first year of life. Females started to reproduce at a younger age than males, productivity increased with female age, the sex ratio of nestlings was male biased and there was moderate male immigration. Despite these differences, temporal variation in sex ratio did not contribute to population dynamics and the contribution of temporal variation in survival was similar for both sexes. Variation in first-year survival was the strongest driver in this population, regulated by a weak density-dependent feedback acting through female first-year survival. Overall, the contributions of the two sexes to population dynamics were similar in this monogamous species with strong sexual size dimorphism.

Does ecology shape geographical parthenogenesis? Evidence from the facultatively parthenogenetic stick insect Megacrania batesii.

Closely related sexual and parthenogenetic species often show distinct distribution patterns, known as geographical parthenogenesis. Similar patterns, characterized by the existence of separate sexual and parthenogenetic populations across their natural range, can also be found in facultative parthenogens - species in which every female is capable of both sexual and parthenogenetic reproduction. The underlying mechanisms driving this phenomenon in nature remain unclear. Features of the habitat, such as differences in host-plant phenotypes or niche breadth, could favour sexual or asexual reproductive modes and thus help to explain geographical parthenogenesis in natural insect populations. Megacrania batesii is a facultatively parthenogenetic stick insect that displays geographical parthenogenesis in the wild. We aimed to explore whether sexual and parthenogenetic populations of M. batesii displayed niche differentiation or variations in niche breadth that could explain the separation of the two population types. To do this, we sampled host plants from across the range of M. batesii and quantified phenotypic traits that might affect palatability or accessibility for M. batesii, including leaf thickness, toughness, spike size and density, plant height, and chemical composition. We also quantified host-plant density, which could affect M. batesii dispersal. We found little evidence of phenotypic differences between host plants supporting sexual versus asexual M. batesii populations, and no difference in host-plant density or niche breadth between the two population types. Our results suggest that habitat parameters do not play a substantial role in shaping patterns of geographical parthenogenesis in wild populations of M. batesii. Instead, population sex ratio variation could result from interactions between the sexes or dispersal dynamics.

Research on the Sex Ratio Variation of Sea Lampreys and Its Ecological Impact Based on the Lotka-Volterra Competition Model

Research on the Sex Ratio Variation of Sea Lampreys and Its Ecological Impact Based on the Lotka-Volterra Competition Model

Study on the relationship between Lampreys and ecosystem with variable sex ratio based on cellular automata

Study on the relationship between Lampreys and ecosystem with variable sex ratio based on cellular automata

OFFSPRING SEX RATIO IS RELATED WITH LAYING DATE AND HATCHING SEQUENCE IN THE MAGELLANIC PENGUIN SPHENISCUS MAGELLANICUS

We analyzed the variation in the secondary sex ratio of Magellanic Penguin Spheniscus magellanicus breeding in six colonies on the Patagonian coast of Argentina. We tested the effects of laying date and hatching sequence on the probability of producing sons and daughters. The global secondary sex ratio did not differ from equality, and there were no differences among the colonies. However, regardless of the colony, laying date, and hatching sequence, there was a significant effect on the proportion of males and females reared. Pairs that were laid early in the breeding season were more likely to raise a male. In addition, offspring that hatched first were more likely to be male than those that hatched second. Our results are consistent with the adaptive importance of producing males, likely the costliest sex, early in the breeding season or early in the brood when food resources are still abundant.

Female‐biased population sex ratios caused by genetic rather than ecological mechanisms in dwarf willow (Salix herbacea L.)

Abstract 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. We investigated mechanisms leading to female‐biased sex ratios in the arctic‐alpine dwarf willow Salix herbacea L. We studied sex ratios in three natural populations over 3 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. 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. Synthesis. Our results suggest that sex ratio bias in S. herbacea 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 Salix 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.

The Impact of Biologically Adaptive Sex Ratio Variation in Lamprey Population on Ecosystem Stability: Based on Lotka-Volterra Model

The Impact of Biologically Adaptive Sex Ratio Variation in Lamprey Population on Ecosystem Stability: Based on Lotka-Volterra Model

Understanding the Effects of Sex Ratio Variations on Ecosystem Sustainability and Environmental Quality

Understanding the Effects of Sex Ratio Variations on Ecosystem Sustainability and Environmental Quality

Reproductive biology of Lepidocephalichthys guntea: a key conservation approach considering environmental factors in Payra River, Bangladesh.

The guntea loach, Lepidocephalichthys guntea, is categorically common freshwater fish in Southeast Asia. Current study is the first elucidation on the reproductive feature of L. guntea including population structure, sex ratio (SR), size at first maturity (Lm), breeding period, and condition factor, emphasizing on the effect of environmental factors on reproduction of this fish in the Payra River (Southern Bangladesh) during July 2021 to June 2022. Using various conventional gears, 1128 individuals (534 males and 594 females) have been collected. Total length (TL), standard length (SL), and body weight (BW) of each fish were measured. Ovaries were cautiously dissected, removed, and precisely weighed. TL ranges from 4.6 to 9.7cm (BW = 0.7-9.27g) for male and 4.6-10.3cm (BW = 0.8-10.75g) for female. Both male (47.34%) and female (52.66%) populations were the leading group in 7.00-7.99cm TL. Overall SR was not notably altered from anticipated value of 1:1 (male:female = 1:1.11). Nonetheless, monthly variations of SR specified females were considerably outnumbered males in each month excluding March-May. Lm range was 6.4-7.0cm, so larger than Lm is recommended to exploit. Monthly changes in GSI indicated that the main spawning season was from March to June. The spawning season was substantially correlated with rainfall, nonetheless with temperature. Additionally, relative weight indicated that habitat was imbalanced with higher predators. A fishing ban is recommended during peak spawning to protect L. guntea in the Payra River and its surroundings based on current research.

Successive stamen movement in Saxifraga candelabrum is responsive to weather and pollinator visits

BackgroundSuccessive stamen movement is a complex plant behavior involving successive uplift of stamens and pollen release, which plays a role in reducing sexual interference, increasing pollen deposition and promoting pollen export. Although reported from several taxa, studies on whether the movement can be influenced by abiotic and biotic factors are scarce.MethodsIn this study, we here for the first time described a pattern of successive stamen movement in Saxifraga candelabrum (Saxifragaceae). We then compared the rates of stamen movement in S. candelabrum under different weather and varying pollinator visits. Pollen packaging and presentation schedule of S. candelabrum were also investigated.ResultsThe results showed that the number of stamens bent per day in sunny days was significantly higher than overcast and rain. Flowers that receive more pollinator visits (control treatment) had significantly higher number of stamen movement than those that received fewer (removal treatment) and none (bagging treatment). Throughout the staminate phase of a flower, there was a progressive increase in both pollen quantity of individual stamens and pollen presentation during each day.ConclusionOur research demonstrates that successive stamen movement in S. candelabrum was accelerated by favorable weather and increased pollinator visits, which may promote pollen export. Moreover, incremental pollen packaging is likely an adaptation to seasonal regularity in variations of sex ratio resulting from protandry.

Life strategies of pacific salmon. Communication 2. Formation of life-history forms. Variability in sex ratio

Conditions determining the vector of ontogenetic development and factors influencing the sex ratio for various life-history forms of pacific salmon (gen. Oncorhynchus) are discussed on the basis of cited data.

Effects of broodstock sex pairing ratios and rest periods of the nile tilapia <i>Oreochromis</i> <i>niloticus</i> on fry production

This study evaluated the effects of varying male to female brood stock pairing ratios of 1:1, 1:2 and 1:3 with resting intervals of 0, 3 and 7 days on fry production of the Nile tilapia at the Aquaculture Demonstration Centre (ADC), Ashaiman, Ghana. Nine (9) treatments were arranged according to a 3 x 3 factorial design with three replicates giving a total of 27 spawning hapas (1 m3). Male and female brooders of mean body weight (229 ± 5.43 g and 171.6 ± 21.7 g respectively) were paired at the different sex ratios. Water temperature and DO were taken daily whiles pH, salinity and ammonia were measured weekly. All the water quality parameters were within suitable range for Nile tilapia fry production. The total mean fry output for the sex pairing ratios (1:1, 1:2, 1:3) were 716 ± 344, 973 ± 325 and 723 ± 577 respectively. The total fry output for 0, 3 and 7 days of resting were 1503 ± 868, 2030 ± 637 and 3051 ± 1054 respectively with an observed 35% (3 days rest) and 103% (7 days rest) fry production increment over the 0-resting treatment. With respect to the combined effect of varying sex ratios and resting periods, the highest mean fry production (701 ± 405) was attained under the 7 days resting period at a pairing ratio of 1:2. The high reproductive performance of broodstock pairing ratio 1:2 and resting period of 7 days under this study confirms its efficient as a broodstock management technique for an increased Nile tilapia fry production.