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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: 9.81). 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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    Evolutionary Applications 12/2012; 5(8):838-49. DOI:10.1111/j.1752-4571.2012.00261.x · 4.57 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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    • "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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