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Marc Stift - One of the best experts on this subject based on the ideXlab platform.
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no evidence for incipient speciation by selfing in north american arabidopsis lyrata
Journal of Evolutionary Biology, 2021Co-Authors: Courtney E. Gorman, Marcel E. Dorken, Marc StiftAbstract:Self-fertilization inherently restricts gene flow by reducing the fraction of offspring that can be produced by inter-population matings. Therefore, mating system transitions from Outcrossing to selfing could result in reproductive isolation between selfing and Outcrossing lineages and provide a starting point for speciation. In newly diverged lineages, for example after a transition to selfing, further reproductive isolation can be caused by a variety of prezygotic and post-zygotic mechanisms that operate before, during and after pollination. In animals, prezygotic barriers tend to evolve faster than post-zygotic ones. This is not necessarily the case for plants, for which the relative importance of post-mating, post-fertilization and early-acting post-zygotic barriers has been investigated far less. To test whether post-pollination isolation exists between populations of North American Arabidopsis lyrata that differ in breeding (self-incompatible versus self-compatible) and mating system (Outcrossing versus selfing), we compared patterns of seed set after crosses made within populations, between populations of the same mating system and between populations with different mating systems. We found no evidence for post-pollination isolation between plants from selfing populations (self-compatible, low Outcrossing rates) and Outcrossing populations (self-incompatible, high Outcrossing rates) via either prezygotic or early-acting post-zygotic mechanisms. Together with the results of other studies indicating the absence of reproductive barriers acting before and during pollination, we conclude that the transition to selfing in this study system has not led to the formation of reproductive barriers between selfing and Outcrossing populations of North American A. lyrata.
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Limited phenological and pollinator-mediated isolation among selfing and Outcrossing Arabidopsis lyrata populations
Proceedings. Biological sciences, 2020Co-Authors: Courtney E. Gorman, Lindsay Bond, Mark Van Kleunen, Marcel E. Dorken, Marc StiftAbstract: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.
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limited phenological and pollinator mediated isolation among selfing and Outcrossing arabidopsis lyrata populations
bioRxiv, 2019Co-Authors: Courtney E. Gorman, Lindsay Bond, Mark Van Kleunen, Marcel E. Dorken, Marc StiftAbstract:Mating system transitions from Outcrossing to selfing have been a frequent evolutionary shift in angiosperms 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 prezygotic 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 reproductively isolate selfing populations of Arabidopsis lyrata from conspecific Outcrossing populations, we conducted a common garden experiment in the native range with plants from selfing and Outcrossing populations as well as their F1 hybrids. Hybrid plants resulting from crosses between self-incompatible populations had the highest probability of flowering. Time of peak flowering differed among mating systems although the magnitude of the difference was small. Flowering duration and maximum flower number did not strongly differ between mating systems and hybrids, and these phenological traits had little influence on the frequency of pollinator visits of either solitary bees or hoverflies. Additionally, pollinators preferred to visit flowers on the same plant (~50% of the time) rather than exploring nearby plants, regardless of whether they were of an alternative mating system type or F1 hybrids, creating a large opportunity for geitonogamy. Finally, by modelling pollen-transfer probabilities, we found no significant differences in the opportunity for pollinations between selfing and Outcrossing plants. Overall, we found that selfing and Outcrossing A. lyrata populations show some phenological divergence but are likely only weakly prezygotically isolated via pre-pollination mechanisms.
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relatively weak inbreeding depression in selfing but also in Outcrossing populations of north american arabidopsis lyrata
Journal of Evolutionary Biology, 2017Co-Authors: Samuel Carleial, Mark Van Kleunen, Marc StiftAbstract:Hermaphroditic plants can potentially self-fertilize, but most possess adaptations that promote Outcrossing. However, evolutionary transitions to higher selfing rates are frequent. Selfing comes with a transmission advantage over Outcrossing, but self-progeny may suffer from inbreeding depression, which forms the main barrier to the evolution of higher selfing rates. Here, we assessed inbreeding depression in the North American herb Arabidopsis lyrata, which is normally self-incompatible, with a low frequency of self-compatible plants. However, a few populations have become fixed for self-compatibility and have high selfing rates. Under greenhouse conditions, we estimated mean inbreeding depression per seed (based on cumulative vegetative performance calculated as the product of germination, survival and aboveground biomass) to be 0.34 for six Outcrossing populations, and 0.26 for five selfing populations. Exposing plants to drought and inducing defences with jasmonic acid did not magnify these estimates. For Outcrossing populations, however, inbreeding depression per seed may underestimate true levels of inbreeding depression, because self-incompatible plants showed strong reductions in seed set after (enforced) selfing. Inbreeding-depression estimates incorporating seed set averaged 0.63 for Outcrossing populations (compared to 0.30 for selfing populations). However, this is likely an overestimate because exposing plants to 5% CO2 to circumvent self-incompatibility to produce selfed seed might leave residual effects of self-incompatibility that contribute to reduced seed set. Nevertheless, our estimates of inbreeding depression were clearly lower than previous estimates based on the same performance traits in Outcrossing European populations of A. lyrata, which may help explain why selfing could evolve in North American A. lyrata.
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evolution of the selfing syndrome in arabis alpina brassicaceae
PLOS ONE, 2015Co-Authors: Andrew Tedder, Samuel Carleial, Martyna Golebiewska, Kentaro K Shimizu, Christian Kappel, Marc StiftAbstract:Introduction The transition from cross-fertilisation (Outcrossing) to self-fertilisation (selfing) frequently coincides with changes towards a floral morphology that optimises self-pollination, the selfing syndrome. Population genetic studies have reported the existence of both Outcrossing and selfing populations in Arabis alpina (Brassicaceae), which is an emerging model species for studying the molecular basis of perenniality and local adaptation. It is unknown whether its selfing populations have evolved a selfing syndrome. Methods Using macro-photography, microscopy and automated cell counting, we compared floral syndromes (size, herkogamy, pollen and ovule numbers) between three Outcrossing populations from the Apuan Alps and three selfing populations from the Western and Central Alps (Maritime Alps and Dolomites). In addition, we genotyped the plants for 12 microsatellite loci to confirm previous measures of diversity and inbreeding coefficients based on allozymes, and performed Bayesian clustering. Results and Discussion Plants from the three selfing populations had markedly smaller flowers, less herkogamy and lower pollen production than plants from the three Outcrossing populations, whereas pistil length and ovule number have remained constant. Compared to allozymes, microsatellite variation was higher, but revealed similar patterns of low diversity and high Fis in selfing populations. Bayesian clustering revealed two clusters. The first cluster contained the three Outcrossing populations from the Apuan Alps, the second contained the three selfing populations from the Maritime Alps and Dolomites. Conclusion We conclude that in comparison to three Outcrossing populations, three populations with high selfing rates are characterised by a flower morphology that is closer to the selfing syndrome. The presence of Outcrossing and selfing floral syndromes within a single species will facilitate unravelling the genetic basis of the selfing syndrome, and addressing which selective forces drive its evolution.
Henrique Teotónio - One of the best experts on this subject based on the ideXlab platform.
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reproductive assurance drives transitions to self fertilization in experimental caenorhabditis elegans
BMC Biology, 2014Co-Authors: Ioannis Theologidis, Henrique Teotónio, Ivo M Chelo, Christine GoyAbstract:Evolutionary transitions from Outcrossing between individuals to selfing are partly responsible for the great diversity of animal and plant reproduction systems. The hypothesis of `reproductive assurance’ suggests that transitions to selfing occur because selfers that are able to reproduce on their own ensure the persistence of populations in environments where mates or pollination agents are unavailable. Here we test this hypothesis by performing experimental evolution in Caenorhabditis elegans. We show that self-compatible hermaphrodites provide reproductive assurance to a male-female population facing a novel environment where Outcrossing is limiting. Invasions of hermaphrodites in male-female populations, and subsequent experimental evolution in the novel environment, led to successful transitions to selfing and adaptation. Adaptation was not due to the loss of males during transitions, as shown by evolution experiments in exclusively hermaphroditic populations and in male-hermaphrodite populations. Instead, adaptation was due to the displacement of females by hermaphrodites. Genotyping of single-nucleotide polymorphisms further indicated that the observed evolution of selfing rates was not due to selection of standing genetic diversity. Finally, numerical modelling and evolution experiments in male-female populations demonstrate that the improvement of male fitness components may diminish the opportunity for reproductive assurance. Our findings support the hypothesis that reproductive assurance can drive the transition from Outcrossing to selfing, and further suggest that the success of transitions to selfing hinges on adaptation of obligate Outcrossing populations to the environment where Outcrossing was once a limiting factor.
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hermaphrodite life history and the maintenance of partial selfing in experimental populations of caenorhabditis elegans
BMC Evolutionary Biology, 2014Co-Authors: Sara Carvalho, Henrique Teotónio, Patrick C. PhillipsAbstract:Background Classic population genetics theory predicts that mixed reproductive systems, where self reproduction (selfing) and Outcrossing co-exist, should not be as common as they are in nature. One means of reconciling theory with observations is to recognize that sexual conflict between males and hermaphrodites and/or constraints in the allocation of resources towards sex functions in hermaphrodites can balance the fitness components of selfing and Outcrossing.
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GENETIC VARIATION FOR Outcrossing AMONG CAENORHABDITIS ELEGANS ISOLATES
Evolution; international journal of organic evolution, 2006Co-Authors: Henrique Teotónio, Diogo Manoel, Patrick C. PhillipsAbstract:The evolution of breeding systems results from the existence of genetic variation and selective forces favoring different Outcrossing rates. In this study we determine the extent of genetic variation for characters directly related to Outcrossing, such as male frequency, male mating ability, and male reproductive success, in several wild isolates of the nematode Caenorhabditis elegans. This species is characterized by an androdioecious breeding system in which males occur with hermaphrodites that can either self-fertilize or outcross with males. We find genetic variation for all characters measured, but also find that environmental variation is a large fraction of the total phenotypic variance. We further determine the existence of substantial genetic variation for population competitive performance in several laboratory environments. However, these measures are uncorrelated with Outcrossing characters. The data presented here contribute to an understanding of male maintenance in natural populations through their role in Outcrossing.
Patrick C. Phillips - One of the best experts on this subject based on the ideXlab platform.
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Coevolutionary interactions with parasites constrain the spread of self-fertilization into Outcrossing host populations.
Evolution; international journal of organic evolution, 2016Co-Authors: Samuel P. Slowinski, Levi T. Morran, Raymond C. Parrish, Eric R. Cui, Amrita Bhattacharya, Curtis M. Lively, Patrick C. PhillipsAbstract:Given the cost of sex, Outcrossing populations should be susceptible to invasion and replacement by self-fertilization or parthenogenesis. However, biparental sex is common in nature, suggesting that cross-fertilization has substantial short-term benefits. The Red Queen hypothesis (RQH) suggests that coevolution with parasites can generate persistent selection favoring both recombination and Outcrossing in host populations. We tested the prediction that coevolving parasites can constrain the spread of self-fertilization relative to Outcrossing. We introduced wild-type Caenorhabditis elegans hermaphrodites, capable of both self-fertilization, and Outcrossing, into C. elegans populations that were fixed for a mutant allele conferring obligate Outcrossing. Replicate C. elegans populations were exposed to the parasite Serratia marcescens for 33 generations under three treatments: a control (avirulent) parasite treatment, a fixed (nonevolving) parasite treatment, and a copassaged (potentially coevolving) parasite treatment. Self-fertilization rapidly invaded C. elegans host populations in the control and the fixed-parasite treatments, but remained rare throughout the entire experiment in the copassaged treatment. Further, the frequency of the wild-type allele (which permits selfing) was strongly positively correlated with the frequency of self-fertilization across host populations at the end of the experiment. Hence, consistent with the RQH, coevolving parasites can limit the spread of self-fertilization in Outcrossing populations.
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RESEARCH ARTICLE Reproductive Mode and the Evolution of Genome Size and Structure in Caenorhabditis
2016Co-Authors: Janna L. Fierst¤a, Cristel G Thomas, Asher D Cutter, Wei Wang, John H. Willis, Rose M. Reynolds¤b, Timothy E. Ahearne, Patrick C. PhillipsAbstract:The self-fertile nematode worms Caenorhabditis elegans, C. briggsae, and C. tropicalis evolved independently from Outcrossing male-female ancestors and have genomes 20-40 % smaller than closely related Outcrossing relatives. This pattern of smaller genomes for selfing species and larger genomes for closely related Outcrossing species is also seen in plants. We use comparative genomics, including the first high quality genome assembly for an Outcrossing member of the genus (C. remanei) to test several hypotheses for the evolu-tion of genome reduction under a change in mating system. Unlike plants, it does not appear that reductions in the number of repetitive elements, such as transposable elements, are an important contributor to the change in genome size. Instead, all functional genomic catego-ries are lost in approximately equal proportions. Theory predicts that self-fertilization should equalize the effective population size, as well as the resulting effects of genetic drift, between the X chromosome and autosomes. Contrary to this, we find that the self-fertile C. briggsae and C. elegans have larger intergenic spaces and larger protein-coding genes on the X chromosome when compared to autosomes, while C. remanei actually has smalle
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hermaphrodite life history and the maintenance of partial selfing in experimental populations of caenorhabditis elegans
BMC Evolutionary Biology, 2014Co-Authors: Sara Carvalho, Henrique Teotónio, Patrick C. PhillipsAbstract:Background Classic population genetics theory predicts that mixed reproductive systems, where self reproduction (selfing) and Outcrossing co-exist, should not be as common as they are in nature. One means of reconciling theory with observations is to recognize that sexual conflict between males and hermaphrodites and/or constraints in the allocation of resources towards sex functions in hermaphrodites can balance the fitness components of selfing and Outcrossing.
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mutation load and rapid adaptation favour Outcrossing over self fertilization
Nature, 2009Co-Authors: Levi T. Morran, Michelle D Parmenter, Patrick C. PhillipsAbstract:One of the oldest questions in biology is, why are there separate sexes? More animals reproduce by cross-fertilization than by 'selfing', despite the cost of producing males and finding mates. Two advantages of cross-fertilization or Outcrossing that could outweigh its cost are commonly suggested: the ability to evolve rapidly and avoidance of inbreeding, but it is hard to test for these experimentally. An experiment in which 'selfing' and 'Outcrossing' variants of Caenorhabditis elegans nematodes were subjected to selective pressures now provides a practical test, and both potential standard explanations appear to have a role in promoting Outcrossing. The tendency of organisms to reproduce by cross-fertilization, despite the advantages of self-fertilization and particularly the cost of males, is one of the oldest puzzles of evolutionary biology. Two advantages of Outcrossing that could outweigh this cost have been suggested: the avoidance of inbreeding and an enhanced ability to adapt to environmental change. Here, the study of Outcrossing in populations of Caenorhabditis elegans suggests that both of these explanations are correct. The tendency of organisms to reproduce by cross-fertilization despite numerous disadvantages relative to self-fertilization is one of the oldest puzzles in evolutionary biology. For many species, the primary obstacle to the evolution of Outcrossing is the cost of production of males1, individuals that do not directly contribute offspring and thus diminish the long-term reproductive output of a lineage. Self-fertilizing (‘selfing’) organisms do not incur the cost of males and therefore should possess at least a twofold numerical advantage over most Outcrossing organisms2. Two competing explanations for the widespread prevalence of Outcrossing in nature despite this inherent disadvantage are the avoidance of inbreeding depression generated by selfing3,4,5 and the ability of Outcrossing populations to adapt more rapidly to environmental change1,6,7. Here we show that Outcrossing is favoured in populations of Caenorhabditis elegans subject to experimental evolution both under conditions of increased mutation rate and during adaptation to a novel environment. In general, fitness increased with increasing rates of Outcrossing. Thus, each of the standard explanations for the maintenance of Outcrossing are correct, and it is likely that Outcrossing is the predominant mode of reproduction in most species because it is favoured under ecological conditions that are ubiquitous in natural environments.
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mutation load and rapid adaptation favour Outcrossing over self fertilization
Nature, 2009Co-Authors: Levi T. Morran, Michelle D Parmenter, Patrick C. PhillipsAbstract:The tendency of organisms to reproduce by cross-fertilization despite numerous disadvantages relative to self-fertilization is one of the oldest puzzles in evolutionary biology. For many species, the primary obstacle to the evolution of Outcrossing is the cost of production of males, individuals that do not directly contribute offspring and thus diminish the long-term reproductive output of a lineage. Self-fertilizing ('selfing') organisms do not incur the cost of males and therefore should possess at least a twofold numerical advantage over most Outcrossing organisms. Two competing explanations for the widespread prevalence of Outcrossing in nature despite this inherent disadvantage are the avoidance of inbreeding depression generated by selfing and the ability of Outcrossing populations to adapt more rapidly to environmental change. Here we show that Outcrossing is favoured in populations of Caenorhabditis elegans subject to experimental evolution both under conditions of increased mutation rate and during adaptation to a novel environment. In general, fitness increased with increasing rates of Outcrossing. Thus, each of the standard explanations for the maintenance of Outcrossing are correct, and it is likely that Outcrossing is the predominant mode of reproduction in most species because it is favoured under ecological conditions that are ubiquitous in natural environments.
Weidong Chen - One of the best experts on this subject based on the ideXlab platform.
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inferring Outcrossing in the homothallic fungus sclerotinia sclerotiorum using linkage disequilibrium decay
Heredity, 2014Co-Authors: R N Attanayake, Vidhura Tennekoon, Dennis A Johnson, Lyndon D Porter, L E Del Riomendoza, D Jiang, Weidong ChenAbstract:The occurrence and frequency of Outcrossing in homothallic fungal species in nature is an unresolved question. Here we report detection of frequent Outcrossing in the homothallic fungus Sclerotinia sclerotiorum. In using multilocus linkage disequilibrium (LD) to infer recombination among microsatellite alleles, high mutation rates confound the estimates of recombination. To distinguish high mutation rates from recombination to infer Outcrossing, 8 population samples comprising 268 S. sclerotiorum isolates from widely distributed agricultural fields were genotyped for 12 microsatellite markers, resulting in multiple polymorphic markers on three chromosomes. Each isolate was homokaryotic for the 12 loci. Pairwise LD was estimated using three methods: Fisher's exact test, index of association (IA) and Hedrick's D′. For most of the populations, pairwise LD decayed with increasing physical distance between loci in two of the three chromosomes. Therefore, the observed recombination of alleles cannot be simply attributed to mutation alone. Different recombination rates in various DNA regions (recombination hot/cold spots) and different evolutionary histories of the populations could explain the observed differences in rates of LD decay among the chromosomes and among populations. The majority of the isolates exhibited mycelial incompatibility, minimizing the possibility of heterokaryon formation and mitotic recombination. Thus, the observed high intrachromosomal recombination is due to meiotic recombination, suggesting frequent Outcrossing in these populations, supporting the view that homothallism favors universal compatibility of gametes instead of traditionally believed haploid selfing in S. sclerotiorum. Frequent Outcrossing facilitates emergence and spread of new traits such as fungicide resistance, increasing difficulties in managing Sclerotinia diseases.
Mark Van Kleunen - One of the best experts on this subject based on the ideXlab platform.
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Limited phenological and pollinator-mediated isolation among selfing and Outcrossing Arabidopsis lyrata populations
Proceedings. Biological sciences, 2020Co-Authors: Courtney E. Gorman, Lindsay Bond, Mark Van Kleunen, Marcel E. Dorken, Marc StiftAbstract: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.
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limited phenological and pollinator mediated isolation among selfing and Outcrossing arabidopsis lyrata populations
bioRxiv, 2019Co-Authors: Courtney E. Gorman, Lindsay Bond, Mark Van Kleunen, Marcel E. Dorken, Marc StiftAbstract:Mating system transitions from Outcrossing to selfing have been a frequent evolutionary shift in angiosperms 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 prezygotic 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 reproductively isolate selfing populations of Arabidopsis lyrata from conspecific Outcrossing populations, we conducted a common garden experiment in the native range with plants from selfing and Outcrossing populations as well as their F1 hybrids. Hybrid plants resulting from crosses between self-incompatible populations had the highest probability of flowering. Time of peak flowering differed among mating systems although the magnitude of the difference was small. Flowering duration and maximum flower number did not strongly differ between mating systems and hybrids, and these phenological traits had little influence on the frequency of pollinator visits of either solitary bees or hoverflies. Additionally, pollinators preferred to visit flowers on the same plant (~50% of the time) rather than exploring nearby plants, regardless of whether they were of an alternative mating system type or F1 hybrids, creating a large opportunity for geitonogamy. Finally, by modelling pollen-transfer probabilities, we found no significant differences in the opportunity for pollinations between selfing and Outcrossing plants. Overall, we found that selfing and Outcrossing A. lyrata populations show some phenological divergence but are likely only weakly prezygotically isolated via pre-pollination mechanisms.
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relatively weak inbreeding depression in selfing but also in Outcrossing populations of north american arabidopsis lyrata
Journal of Evolutionary Biology, 2017Co-Authors: Samuel Carleial, Mark Van Kleunen, Marc StiftAbstract:Hermaphroditic plants can potentially self-fertilize, but most possess adaptations that promote Outcrossing. However, evolutionary transitions to higher selfing rates are frequent. Selfing comes with a transmission advantage over Outcrossing, but self-progeny may suffer from inbreeding depression, which forms the main barrier to the evolution of higher selfing rates. Here, we assessed inbreeding depression in the North American herb Arabidopsis lyrata, which is normally self-incompatible, with a low frequency of self-compatible plants. However, a few populations have become fixed for self-compatibility and have high selfing rates. Under greenhouse conditions, we estimated mean inbreeding depression per seed (based on cumulative vegetative performance calculated as the product of germination, survival and aboveground biomass) to be 0.34 for six Outcrossing populations, and 0.26 for five selfing populations. Exposing plants to drought and inducing defences with jasmonic acid did not magnify these estimates. For Outcrossing populations, however, inbreeding depression per seed may underestimate true levels of inbreeding depression, because self-incompatible plants showed strong reductions in seed set after (enforced) selfing. Inbreeding-depression estimates incorporating seed set averaged 0.63 for Outcrossing populations (compared to 0.30 for selfing populations). However, this is likely an overestimate because exposing plants to 5% CO2 to circumvent self-incompatibility to produce selfed seed might leave residual effects of self-incompatibility that contribute to reduced seed set. Nevertheless, our estimates of inbreeding depression were clearly lower than previous estimates based on the same performance traits in Outcrossing European populations of A. lyrata, which may help explain why selfing could evolve in North American A. lyrata.
