Population size and relatedness affect fitness of a self-incompatible plant

California/Nevada Operations Office, U.S. Fish and Wildlife Service, 2800 Cottage Way, W-2606, Sacramento, CA 95825, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 02/2007; 104(2):549-52. DOI: 10.1073/pnas.0607306104
Source: PubMed


One of the lingering paradoxes in invasion biology is how founder populations of an introduced species are able to overcome the limitations of small size and, in a "reversal of fortune," proliferate in a new habitat. The transition from colonist to invader is especially enigmatic for self-incompatible species, which must find a mate to reproduce. In small populations, the inability to find a mate can result in the Allee effect, a positive relationship between individual fitness and population size or density. Theoretically, the Allee effect should be common in founder populations of self-incompatible colonizing species and may account for the high rate of failed introductions, but little supporting evidence exists. We created a field experiment to test whether the Allee effect affects the maternal fitness of a self-incompatible invasive species, wild radish (Raphanus sativus). We created populations of varying size and relatedness. We measured maternal fitness in terms of both fruit set per flower and seed number per fruit. We found that both population size and the level of genetic relatedness among individuals influence maternal reproductive success. Our results explicitly define an ecological genetic obstacle faced by populations of an exotic species on its way to becoming invasive. Such a mechanistic understanding of the invasions of species that require a mate can and should be exploited for both controlling current outbreaks and reducing their frequency in the future.

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    • "This corresponds to a genetic Allee effect (Courchamp et al. 2008). The Allee effect has been identified in the reproduction of some exotic and invasive plants that show lower seed production per fruit and reduced germination rate in individuals from small populations (Cappuccino 2004; Elam et al. 2007). However , these studies have not evaluated whether pollinator activity can lead to an Allee effect, although the reproduction of many exotic plants depends on mutualistic pollinators (Richardson et al. 2000). "
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    ABSTRACT: The component Allee effect has been defined as “a positive relationship between any measure of individual fitness and the number or density of conspecifics.” Larger plant populations or large patches have shown a higher pollinator visitation rate, which may give rise to an Allee effect in reproduction of the plants. We experimentally tested the effect of number of conspecifics on reproduction and pollinator visitation in Eschscholzia californica Cham., an invasive plant in Chile. We then built patches with two, eight and 16 flowering individuals of E. californica (11 replicates per treatment) in an area characterised by dominance of the study species. We found that E. californica exhibits a component Allee effect, as the number of individuals of this species has a positive effect on individual seed set. However, individual fruit production was not affected by the number of plants examined. Pollinator visitation rate was also independent of the number of plants, so this factor would not explain the Allee effect. This rate was positively correlated with the total number of flowers in the patches. We also found that the number of plants did not affect the seed mass or proportion of germinated seeds in the patches. Higher pollen availability in patches with 16 plants and pollination by wind could explain the Allee effect. The component Allee effect identified could lead to a weak demographic Allee effect that might reduce the rate of spread of E. californica. Knowledge of this would be useful for management of this invasive plant in Chile.This article is protected by copyright. All rights reserved.
    Plant Biology 12/2014; 17(3). DOI:10.1111/plb.12293 · 2.63 Impact Factor
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    • "Progressive increase in progeny fitness is expected with greater genetic distance between mating parents. This relationship results from the reduction of inbreeding depression caused by the increment in heterosis and hybrid vigor (Ellstrand and Schierenbeck 2000; Elam et al. 2007; Radosevich et al. 2007 "
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    ABSTRACT: Certain species of the Pooideae subfamily develop stress tolerance and herbivory resistance through symbiosis with vertically transmitted, asexual fungi. This symbiosis is specific, and genetic factors modulate the compatibility between partners. Although gene flow is clearly a fitness trait in allogamous grasses, because it injects hybrid vigor and raw material for evolution, it could reduce compatibility and thus mutualism effectiveness. To explore the importance of host genetic background in modulating the performance of symbiosis, Lolium multiflorum plants, infected and noninfected with Neotyphodium occultans, were crossed with genetically distant plants of isolines (susceptible and resistant to diclofop-methyl herbicide) bred from two cultivars and exposed to stress. The endophyte improved seedling survival in genotypes susceptible to herbicide, while it had a negative effect on one of the genetically resistant crosses. Mutualism provided resistance to herbivory independently of the host genotype, but this effect vanished under stress. While no endophyte effect was observed on host reproductive success, it was increased by interpopulation plant crosses. Neither gene flow nor herbicide had an important impact on endophyte transmission. Host fitness improvements attributable to gene flow do not appear to result in direct conflict with mutualism while this seems to be an important mechanism for the ecological and contemporary evolution of the symbiotum.
    Evolutionary Applications 12/2012; 5(8):838-49. DOI:10.1111/j.1752-4571.2012.00261.x · 3.90 Impact Factor
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    • "ulation dynamics and spread of this beetle, especially in low density, isolated populations, or both (Elam et al. 2007). In addition, the ability to efÞciently rear emerald ash borer in quarantine for the mass production of biological control agents will be crucial to any control efforts (Keena et al. 2009). "
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    ABSTRACT: The consequences of single versus multiple mating on the longevity, fecundity, and fertility of female emerald ash borers Agrilus planipennis (Fairmaire) were examined. In the first treatment, dissections of the common oviduct showed that 43 of 52 singly-mated females had received spermatophores. In the next two treatments, females were observed to mate one time, then housed either alone (observed separate) or with their mate (observed together). In the fourth treatment, females were paired with a randomly chosen male (unobserved together). Weight (0.0428 ± SE 0.0008 g) and longevity (50.5 ± SE 1.6 d) of female beetles did not differ among treatments. Fecundity, but not fertility, had a significant positive correlation with longevity in all treatments. Almost all of the females ‘Observed together’ laid eggs (87%, N = 31), while significantly fewer females ‘unobserved together’ (61%, N = 31) and ‘Observed separate’ (54%, N = 31) did. The fecundity of females that did lay eggs did not differ among treatments. Based on our results a single mating may be sufficient to ensure maximal fecundity for females, but there is potential for failure of any one mating, and no apparent cost to multiple mating. Thus, multiple mating is likely the best strategy for female emerald ash borers to maximize fecundity. The implications of results for laboratory rearing, and potential population level effects are discussed.
    Annals of the Entomological Society of America 01/2012; 105(Jan 2012):66-72. DOI:10.1603/AN11037 · 1.19 Impact Factor
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