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68 results for “outcrossing”
High parasite virulence necessary for the maintenance of host outcrossing via parasite-mediated selection
<p>Biparental sex is widespread in nature, yet costly relative to uniparental reproduction. It is generally unclear why self-fertilizing or asexual lineages do not readily invade outcrossing populations. The Red Queen hypothesis predicts that coevolving parasites can prevent self-fertilizing or asexual lineages from invading outcrossing host populations. However, only highly virulent parasites are predicted to maintain outcrossing, which may limit the general applicability of the Red Queen hypothesis. Here, we tested whether the ability of coevolving parasites to prevent invasion of self-fertilization within outcrossing host populations was dependent on parasite virulence. We introduced wild-type <em>Caenorhabditis elegans</em> hermaphrodites, capable of both self-fertilization and outcrossing, into <em>C. elegans</em> populations fixed for a mutant allele conferring obligate outcrossing. Replicate <em>C. elegans</em> populations were exposed for 24 host generations to one of four strains of <em>Serratia marcescens</em> parasites that varied in virulence, under three treatments: a heat-killed (control, non-infectious) parasite treatment, a fixed-genotype (non-evolving) parasite treatment, and a copassaged (potentially coevolving) parasite treatment. As predicted, self-fertilization invaded <em>C. elegans</em> host populations in the control and fixed-parasite treatments, regardless of parasite virulence. In the copassaged treatment, selfing invaded host populations coevolving with low- to mid- virulent strains but remained rare in hosts coevolving with highly virulent bacterial strains. Therefore, we found that only highly virulent coevolving parasites can impede the invasion of selfing.</p>
High parasite virulence necessary for the maintenance of host outcrossing via parasite-mediated selection
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Data from: Bayesian quantification of ecological determinants of outcrossing in natural plant populations: computer simulations and the case study of biparental inbreeding in English yew
The mating system is a central parameter of plant biology because it shapes their ecological and evolutionary properties. Therefore, determining ecological variables that influence the mating system is important for a deeper understanding of the functioning of plant populations. Here, using old concepts and recent statistical developments, we propose a new statistical tool to make inferences about ecological determinants of outcrossing in natural plant populations. The method requires co-dominant genotypes of seeds collected from maternal plants within different locations. Using extensive computer simulations, we demonstrated that the method is robust to the issues expected for real-world data, including the Wahlund effect, inbreeding and genotyping errors such as allele dropout and allele misclassification. Furthermore, we showed that the estimates of ecological effects and outcrossing rates can be severely biased if genotyping errors and genetic differentiation are not treated explicitly. Application of the new method to the case study of a dioecious tree (Taxus baccata) allowed revealing that female trees that grow in lower local densities have a greater tendency towards mating with relatives. Moreover, we also demonstrated that biparental inbreeding is higher in populations that are characterised by a longer mean distance between trees and a smaller mean trunk perimeter. We found these results to agree with both the theoretical predictions and the history of English yew.
Data from: Pollen limitation and autonomous selfing ability interact to shape variation in outcrossing rate across a species range
Premise of the study: Hermaphroditic plants commonly reproduce through a mixture of selfing and outcrossing. The degree to which outcrossing rates reflect the availability of outcross pollen, genetic differentiation in the ability to autonomously self-fertilize, or both is often unclear. Despite the potential for autonomy and the pollination environment to jointly influence outcrossing, this interaction is rarely studied. Methods: We reviewed literature testing whether the pollination environment or floral traits causing autonomous selfing predict outcrossing rate variation among populations. We also measured outcrossing rates in 23 populations of Campanula americana and examined associations with the pollination environment, autonomy, and their interaction. Key Results: Our review revealed that traits facilitating selfing were often negatively associated with outcrossing rates while most aspects of the pollination environment poorly predicted outcrossing. Populations of C. americana varied from mixed mating to highly outcrossing but variation was unrelated to population size, density, pollen limitation, or autonomous selfing ability. Outcrossing rate was significantly influenced by an interaction between autonomous selfing ability and pollen limitation. In highly autonomous populations, elevated pollen limitation was associated with reduced outcrossing, while there was no relationship for less autonomous populations. Conclusions: Both the ability to self autonomously and pollen limitation interact to shape outcrossing rates in C. americana. This work suggests autonomy affords mating system flexibility, though it is not ubiquitous in all populations across the species range. Interactions between traits influencing autonomy and pollen limitation are likely to explain variation in outcrossing rates among populations of flowering plants.
Data from: Climate change is associated with increased allocation to potential outcrossing in a common mixed mating species
<p><strong>Premise:</strong> The balance between cross- and self-fertilization is driven by the environment. Yet no long-term study has documented whether anthropogenic climate change is affecting reproductive strategy allocation in species with mixed mating systems. Here, we test whether the common blue violet (<em>Viola sororia</em>; Violaceae) has altered relative allocation to the production of potentially outcrossing flowers as the climate has changed across the 20th century.</p> <p><strong>Methods:</strong> Using herbarium records spanning 1875 to 2015 from the central United States, we quantified production of obligately selfing cleistogamous (CL) flowers and potentially outcrossing chasmogamous (CH) flowers by <em>V. sororia</em>, coupled these records with historic temperature and precipitation data, and tested whether changes to the proportion of CL flowers correlate with temporal climate trends.</p> <p><strong>Results:</strong> We find that <em>V. sororia</em> progressively produced lower proportions of CL flowers across the past century and in environments with lower mean annual temperature and higher total annual precipitation. We also find that both CL and CH flower phenology has advanced across this time period.</p> <p><strong>Conclusions:</strong> Our results suggest that <em>V. sororia</em> has responded to lower temperatures and greater water availability by shifting reproductive strategy allocation away from selfing and toward potential outcrossing. This provides the first long term study of how climate change may affect relative allocation to potential outcrossing in species with mixed mating systems. By revealing that CL flowering is associated with low water availability and high temperature, our results suggest the production of obligately selfing flowers is favored in water limited environments.</p>
Outcrossing rates in an experimentally admixed population of self-compatible and self-incompatible Arabidopsis lyrata
AbstractThe transition to self-compatibility from self-incompatibility is often associated with high rates of self-fertilization, which can restrict gene flow among populations and cause reproductive isolation of self-compatible (SC) lineages. Secondary contact between SC and self-incompatible (SI) lineages might re-establish gene flow if SC lineages remain capable of outcrossing. By contrast, intrinsic features of SC plants that reinforce high rates of self-fertilization could maintain evolutionary divergence between lineages. Arabidopsis lyrata subsp. lyrata is characterized by multiple origins of self-compatibility and high rates of self-fertilization in SC-dominated populations. It is unclear whether these high rates of selfing by SC plants have intrinsic or extrinsic causes. We estimated outcrossing rates and examined patterns of pollinator movement for 38 SC and 40 SI maternal parents sampled from an admixed array of 1509 plants sourced from six SC and six SI populations grown under uniform density. Although plants from SI populations had higher outcrossing rates (mean tm = 0.78 ± 0.05 SE) than plants from SC populations (mean tm = 0.56 ± 0.06 SE), outcrossing rates among SC plants were substantially higher than previous estimates from natural populations. Patterns of pollinator movement appeared to contribute to lower outcrossing rates for SC plants; we estimated that 40% of floral visits were geitonogamous (between flowers of the same plant). The relatively high rates of outcrossing for SC plants under standardized conditions indicate that selfing rates in natural SC populations of A. lyrata are facultative and driven by extrinsic features of A. lyrata, including patterns of pollinator movement.
Defensive mutualists affect outcross pollen transfer and male fitness in their host plant
<p>Ant guards can increase plant fitness by deterring herbivores, but they may also reduce it by interfering with pollination. While ant impacts on herbivory have been well-studied, much less is known about their impacts on pollinators and associated consequences for plant pollination, particularly pollen transfer dynamics and outcrossing/selfing rates. We used field experiments to quantify the effect of ant guards on pollinator community composition, frequency and duration of flower visits, and cascading effects on outcrossing pollen transfer and pollen exports in Turnera velutina (Passifloraceae). Although ant patrolling did not affect pollinator community composition or visitation frequency, it decreased flower visit duration and the time pollinators spent foraging inside flowers. Such behavioural changes resulted in reduced pollen deposition on stigmas, decreased pollen exports (a proxy for male fitness) and significantly doubled outcross pollen transfer. This study contributes to our understanding of how nonpollinator mutualists can shape plant reproductive processes. We discuss the downstream effects that variation in biotic defences, such as rewards for guarding ants, can have on plant pollen transfer patterns and fitness. In conclusion, guarding ants influence pollen transfer patterns in Turnera velutina, increasing outcrossing in a self-compatible species at the cost of male fitness. We show how non-pollinators, such as defensive ant mutualists, can shape plant reproductive traits and discuss the consequences these interactions may have for plant mating systems.</p>
Propensity for selfing varies within a population of hermaphroditic snails: coexistence of selfers, outcrossers, and mixed-mating individuals
<p class="MsoNormal">To understand mating-system evolution in self-compatible hermaphrodites, variation in selfing rates is highly relevant. Empirical studies are rarely designed to capture variation between individuals, instead often comparing species and populations. Yet, evolution primarily occurs within populations, rendering among-individual variation essential. </p> <p class="MsoNormal">Observed individual selfing rates depend on the environment (<em>e.g.</em>, differences in mate availability) and individuals' propensity for selfing. We quantified individual variation in selfing propensity in the snail <em>Radix balthica</em> by conducting laboratory mating trials that manipulated mate availability (low <em>vs.</em> moderate) and estimating selfing rates from progeny arrays. We also measured female lifetime fitness. We found substantial among-individual variation in selfing propensity, including pure selfers (32%), pure outcrossers (31%), and mixed-mating individuals that selfed and outcrossed (37%). Experimental levels of mate availability did not significantly affect selfing rates. Selfers had reduced female liftetime fitness.</p> <p class="MsoNormal">Our results show that the propensity for selfing can differ considerably among individuals, with similar proportions of selfers, outcrossers, and mixed maters. As mate availability did not affect selfing, our "moderate" level might still have been too low to prompt selfers to outcross. This and the observed fitness differences also cautiously suggest that investigating the heritability of selfing propensities might be worthwhile in this population.</p>
Data from: Shifts in outcrossing rates and changes to floral traits are associated with the evolution of herbicide resistance in the common morning glory
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Defensive mutualists affect outcross pollen transfer and male fitness in their host plant
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Outcrossing rates in an experimentally admixed population of self-compatible and self-incompatible Arabidopsis lyrata
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Data from: Pollen limitation and autonomous selfing ability interact to shape variation in outcrossing rate across a species range
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Data from: Outcrossing mating system of the early-divergent moonwort fern (Botrychium lunaria, Ophioglossaceae) revealed in the European Alps
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Data from: Climate change is associated with increased allocation to potential outcrossing in a common mixed mating species
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Data from: Bayesian quantification of ecological determinants of outcrossing in natural plant populations: computer simulations and the case study of biparental inbreeding in English yew
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'Disease-smart outcrossing can enhance individual fitness and increase survival via immune priming against pathogens: new approaches to strengthen genetic rescue efforts
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Propensity for selfing varies within a population of hermaphroditic snails: coexistence of selfers, outcrossers, and mixed-mating individuals
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Increased time sampling in an evolve-and-resequence experiment with outcrossing Saccharomyces cerevisiae reveals multiple paths of adaptive change
<p>"Evolve and resequence" (E&R) studies combine experimental evolution and whole-genome sequencing to interrogate the genetics underlying adaptation. Due to ease of handling, E&R work with asexual organisms like bacteria can employ optimized experimental design, with large experiments and many generations of selection. By contrast, E&R experiments with sexually reproducing organisms are more difficult to implement, and design parameters vary dramatically among studies. Thus, efforts have been made to assess how these differences, such as number of independent replicates, or size of experimental populations, impact inference. We add to this work by investigating the role of time sampling – the number of discrete timepoints sequence data is collected from evolving populations. Using data from an E&R experiment with outcrossing <i>Saccharomyces cerevisiae </i>in which populations were sequenced 17 times over ~540 generations, we address the following questions: (i) do more timepoints improve the ability to identify candidate regions underlying selection? And (ii) does high-resolution sampling provide unique insight into evolutionary processes driving adaptation? We find that while time sampling does not improve the ability to identify candidate regions, high-resolution sampling does provide valuable opportunities to characterize evolutionary dynamics. Increased time sampling reveals three distinct trajectories for adaptive alleles: one consistent with classic population genetic theory (i.e. models assuming constant selection coefficients), and two where trajectories suggest more context-dependent responses (i.e. models involving dynamic selection coefficients). We conclude that while time sampling has limited impact on candidate region identification, sampling 8 or more timepoints has clear benefits for studying complex evolutionary dynamics.</p>
Simulated pollinator declines intensify selection on floral traits that facilitate selfing and outcrossing in Impatiens capensis
<p>PREMISE OF THE STUDY: Anthropogenic environmental change is causing pollinator populations to decline. These declines should intensify selection for floral traits that facilitate outcrossing by making plants more attractive to pollinators and/or for floral traits that facilitate selfing in the absence of pollinators. However, the effect of pollinator declines on selection on floral traits could be modified by other environmental factors such as herbivores. <br> METHODS: We studied the effect of simulated pollinator declines on selection on floral traits of Impatiens capensis, a mixed-mating species that produces both obligately selfing cleistogamous flowers and primarily outcrossing chasmogamous flowers. We measured directional selection differentials via seeds per plant on two traits that facilitate outcrossing (chasmogamous flower size and number) and one trait that facilitates selfing (cleistogamous flower number) in ambient, reduced pollinator access, and reduced pollinator access + increased foliar herbivory treatments.<br> RESULTS: Reduced pollinator access intensified selection for larger chasmogamous flowers and more cleistogamous flowers. In contrast, increased herbivory did not affect selection on any floral trait. <br> CONCLUSIONS: Reduced pollinator access intensified selection for a trait that facilitates outcrossing, suggesting that even species such as I. capensis that can autonomously self-pollinate have the potential to respond to pollinator declines by evolving floral traits that reinforce interactions between plants and pollinators. However, reduced pollinator access also intensified selection for a trait that facilitates selfing, suggesting that I. capensis could adapt to pollinator declines by evolving floral traits that maintain the production of both selfed and outcrossed seeds.<br> </p>
Limited phenological and pollinator-mediated isolation among selfing and outcrossing Arabidopsis lyrata populations
<p>Transitions from outcrossing to selfing have been a frequent evolutionary shift in plants and clearly play a role in species divergence. However, many questions remain about the initial mechanistic basis of reproductive isolation during the evolution of selfing. For instance, how important are pre-zygotic pre-pollination mechanisms (e.g. changes in phenology and pollinator visitation) in maintaining reproductive isolation between newly arisen selfing populations and their outcrossing ancestors? To test whether changes in phenology and pollinator visitation isolate selfing populations of Arabidopsis lyrata from outcrossing populations, we conducted a common garden experiment with plants from selfing and outcrossing populations as well as their between-population hybrids. Specifically, we asked whether there was isolation between outcrossing and selfing plants and their between-population hybrids through differences in (1) the timing or intensity of flowering; and/or (2) pollinator visitation. We found that phenology largely overlapped between plants from outcrossing and selfing populations. There were also no differences in pollinator preference related to mating system. Additionally, pollinators preferred to visit flowers on the same plant rather than exploring nearby plants, creating a large opportunity for self-fertilization. Overall, this suggests that pre-zygotic pre-pollination mechanisms do not strongly reproductively isolate plants from selfing and outcrossing populations of Arabidopsis lyrata.</p>
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Allen Brain Atlas
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DANDI Archive for NWB datasets
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International Brain Laboratory public data
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OpenNeuro
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