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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    • "Interestingly, although most plants exhibit high levels of local kinship, we know comparatively little about the effects of this local kinship on reproductive success (but see Jones and Comita, 2008). For example, dense patches of conspecific trees can receive greater visitation from pollinators but may receive poorer quality pollen from neighbours with shared kinship (Byers, 1995; Souto et al., 2002; Elam et al., 2007). Fruits resulting from matings between close relatives may exhibit higher levels of homozygosity or deleterious gene combinations that may result in embryos and endosperms with deficient maternal investment and, thus, increased abortion rates (Korbecka et al., 2002; Hufford and Hamrick, 2003; O'Connell et al., 2006). "
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    ABSTRACT: Background and aims: Global pollinator declines and continued habitat fragmentation highlight the critical need to understand reproduction and gene flow across plant populations. Plant size, conspecific density and local kinship (i.e. neighbourhood genetic relatedness) have been proposed as important mechanisms influencing the reproductive success of flowering plants, but have rarely been simultaneously investigated. Methods: We conducted this study on a continuous population of the understorey tree Miconia affinis in the Forest Dynamics Plot on Barro Colorado Island in central Panama. We used spatial, reproductive and population genetic data to investigate the effects of tree size, conspecific neighbourhood density and local kinship on maternal and paternal reproductive success. We used a Bayesian framework to simultaneously model the effects of our explanatory variables on the mean and variance of maternal viable seed set and siring success. Key results: Our results reveal that large trees had lower proportions of viable seeds in their fruits but sired more seeds. We documented differential effects of neighbourhood density and local kinship on both maternal and paternal reproductive components. Trees in more dense neighbourhoods produced on average more viable seeds, although this positive density effect was influenced by variance-inflation with increasing local kinship. Neighbourhood density did not have significant effects on siring success. Conclusions: This study is one of the first to reveal an interaction among tree size, conspecific density and local kinship as critical factors differentially influencing maternal and paternal reproductive success. We show that both maternal and paternal reproductive success should be evaluated to determine the population-level and individual traits most essential for plant reproduction. In addition to conserving large trees, we suggest the inclusion of small trees and the conservation of dense patches with low kinship as potential strategies for strengthening the reproductive status of tropical trees.
    Full-text · Article · Nov 2015 · Annals of Botany
    • "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.
    No preview · Article · Dec 2014 · Plant Biology
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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.
    Full-text · Article · Dec 2012 · Evolutionary Applications
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