Population size and relatednes affect fitness of a self-compatible invasive 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

ABSTRACT 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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    • "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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    • "It may provide an alien species with a competitive advantage over native species due to differences in the timing of germination (Moravcová et al. 2005, Fisher et al. 2009) and/or seed persistence, and from the saturation of available microsites (Brown & Fridley 2003), which could subsequently limit the recruitment of native species (Thomsen et al. 2006, Ens & French 2008, Fisher et al. 2009, French et al. 2011). The formation of a seed bank may also allow an alien species to overcome densitydependent effects and/or Allee effects (Allee 1931, Taylor & Hastings 2005), which may play a central role in the establishment of a species, particularly during the introduction phase and for self-incompatible founder populations (Elam et al. 2007). Recent studies showed the significance of Allee effects in determining the establishment of the invasive grass Spartina alterniflora (Davis et al. 2004a, b), as well as the maternal fitness of the self-incompatible invasive radish Raphanus sativus (Elam et al. 2007). "
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    ABSTRACT: Invasions by alien plant species significantly affect biodiversity and ecosystem functioning. Investigations of the soil seed banks of invasive plant species and changes in the composition and structure of resident seed banks following plant invasions can provide valuable insight into the long-term implications of plant invasions. Soil seed banks play a major role as reservoirs of species and genetic diversity and allow for the persistence of a species at a locality, buffering environmental changes that may occur over time. Despite the emerging body of literature on ecological impacts of invasive plants on the diversity of resident communities, the long-term implications of impoverished soil seed banks for vegetation dynamics and ecosystem functioning have only recently begun receiving attention. Evidence has so far indicated that there is a correlation between the invasiveness of a species and the characteristics of its seed bank, and that changes in the seed banks of resident communities associated with plant invasions affect their biotic resistance to primary and secondary invasions. To promote the study of soil seed banks in the context of invasive species, we (i) summarize the functional roles of soil seed banks; (ii) describe how the capacity to form a seed bank may contribute to a species' invasiveness using data from the flora of the Czech Republic, showing an increasing representation of species capable of forming long-term persistent seed bank from casual to naturalized to invasion stage; (iii) assess the impact of invasive plants on seed banks of resident communities, including the potential creation of conditions that favour secondary invasions by other alien species or native weeds, and long-term implications of such impact; and (iv) describe the potential effects of climate change on the soil seed bank in the context of plant invasions. We conclude with highlighting promising avenues for future research on invaded soil seed banks, and emphasize the importance of this knowledge in the development of control programs and restoration strategies.
    Preslia -Praha- 01/2012; 84:327-350. · 4.10 Impact Factor
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