Evolution of Plant Breeding Systems

Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Ashworth Lab. King's Buildings, West Mains Road, Edinburgh EH9 3JT, UK.
Current Biology (Impact Factor: 9.57). 10/2006; 16(17):R726-35. DOI: 10.1016/j.cub.2006.07.068
Source: PubMed


Breeding systems are important, and often neglected, aspects of the natural biology of organisms, affecting homozygosity and thus many aspects of their biology, including levels and patterns of genetic diversity and genome evolution. Among the different plant mating systems, it is useful to distinguish two types of systems: 'sex systems', hermaphroditic versus male/female and other situations; and the 'mating systems' of hermaphroditic populations, inbreeding, outcrossing or intermediate. Evolutionary changes in breeding systems occur between closely related species, and some changes occur more often than others. Understanding why such changes occur requires combined genetical and ecological approaches. I review the ideas of some of the most important theoretical models, showing how these are based on individual selection using genetic principles to ask whether alleles affecting plants' outcrossing rates or sex morphs will spread in populations. After discussing how the conclusions are affected by some of the many relevant ecological factors, I relate these theoretical ideas to empirical data from some of the many recent breeding system studies in plant populations.

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    • "Information on the breeding system is essential to interpret ecological aspects and evolutionary dynamics of natural plant populations, and plan effective management practices for threatened species. The breeding system affects individual fitness, dependence on pollinators as well as levels and patterns of genetic variability (Charlesworth 2006; Fisogni et al. 2011; Berjano et al. 2013). The degree of selfing is modulated by physiological incompatibility (SI) and inbreeding depression (Lloyd and Schoen 1992; de Nettancourt 1997; Hiscock and McInnis 2003); in zoophilous species it is also affected by pollinator behaviour, flower display and intrinsic features (herkogamy and dichogamy). "
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    ABSTRACT: Background: Taxonomic analysis provides a basic understanding for taxon identification and contributes to preliminary information for several branches of applied biology, while studies on reproductive strategies and plant fitness are essential to interpret population status and dynamics. Aims: We tested the reliability of diagnostic characters for identification and to characterise sexual resource allocation, the breeding system and seed predation among subspecies of Gentiana lutea. Methods: We analysed morphological characters in 70 herbarium specimens. In five natural populations we counted pollen and ovule numbers, assessed reproductive output after pollination treatments and evaluated pre-dispersal predation. Results: Taxonomic traits previously indicated as diagnostic were not sufficient to discriminate among subspecies. The pollen number and pollen:ovule (P:O) ratio varied strongly among subspecies; self-pollinated flowers produced a signifi- cantly lower number of seeds than open-pollinated flowers. Retention of empty fruits and high levels of pre-dispersal seed predation were observed in every case. Conclusions: The variation of P:O ratios among subspecies suggests different efficiency in pollen transfer. The species is self-compatible, nevertheless all subspecies require pollen vectors to enhance cross pollination and viable seed production. Fruit retention may have evolved as a strategy to reduce predation, ensuring higher plant fitness.
    Plant Ecology & Diversity 08/2015; DOI:10.1080/17550874.2015.1074625 · 1.77 Impact Factor
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    • "On the other hand, already the loss of a single pollinator species can reduce plant reproduction (Brosi & Briggs, 2013). Third, a lower proportion of outcrossing species with land use intensification might simply reflect an increase in annual autogamous species that are better adapted to the disturbance regimes of agricultural and ruderal habitats than perennial plants (Charlesworth, 2006). Hence, the parallel decline of plants and pollinators might simply reflect a similar direct response of both taxonomic groups to changes of habitat quality and structure. "
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    ABSTRACT: AimParallel declines in plant and insect pollinator diversity under land use intensification may occur as a result of both taxonomic groups responding similarly, but independently, to habitat change or as a consequence of interdependence as insect-pollinated plants decline due to pollinator loss. Here, we explore the relative roles of independent and interdependent declines by comparing correlations of species richness and land use intensity for different functional groups of plants.LocationAustria.Methods Generalized linear and generalized linear mixed models were used to analyse trends in species richness of plant functional groups sampled along a land use intensity gradient across 100 agricultural landscapes (=625 × 625 m each). Plants were classified according to their pollination syndrome, breeding system and life span. Species numbers were related to the site-specific proportional area of semi-natural habitats as an indicator of land use intensity.ResultsOverall, as the level of agricultural intensification increased the proportion of outcrossing plants declined and the proportion of self-pollinating plants increased. However, while perennial plant species richness decreased under more intensive land use independently of pollination syndrome or breeding system, the richness of annuals only declined for outcrossing species requiring specialized insect pollinators but not for those pollinated by wind- or unspecialized insect pollinators.Main conclusionFrom these patterns we infer that land use intensification mainly drives plant species loss by excluding perennial species which suffer from the conversion of land to annually harvested crop fields. Hence, parallel declines in plant and insect richness largely result from a common response of perennials and pollinators to habitat change. Nevertheless, for annual plants with specialized pollinator requirements our data support a cascading effect of pollinator decline on species richness.
    Diversity and Distributions 07/2015; DOI:10.1111/ddi.12353 · 3.67 Impact Factor
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    • "Because most plants are hermaphrodite of certain selfing rates, it is of evolutionary significance to assess how selfing versus outcrossing alters the barrier to gene flow in a mixed mating system. Besides its direct effects on gene exchanges between species or populations, mating system has important effects on population ecology and evolution (Barrett 1995; Barrett and Harder 1996; Charlesworth 2006; Glémin 2007; Pannell 2010). The evolutionary transition to predominant inbreeding could mainly bring about the same directional consequences on the barrier to gene flow. "
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    ABSTRACT: Understanding mating system as one of reproductive isolating barriers remains important although this barrier is classified in a different sense from behavioral, ecological, and mechanical isolating barriers. Selfing enhances incipient speciation while outcrossing facilitates species integrity. Here, I study how mating system affects gene exchanges between genetically diverging species in a hybrid zone. Results show that a predominant selfing species has a greater barrier to selective gene flow than does a predominant outcrossing species. Barrier to neutral gene flow convexly changes with the selfing rate due to linkage disequilibrium, with a maximum at around intermediate selfing rate. Asymmetric transient or steady-state barriers to neutral gene flow occur between two sides of a hybrid zone when the neutral gene is affected by its linked selective gene whose alternative alleles are adaptive to heterogeneous habitats. Selfing interacts with both a physical barrier and a density-dependent ecological regulation (a logarithmic model) to strengthen the barriers to neutral and selective gene flow. This theory helps to interpret incipient speciation driven by selfing or to explain the asymmetric gene flow or unequal genomic mixtures between closely related species caused by their asymmetric mating systems in natural hybrid zones. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Evolution 04/2015; 69(5):1158-1177. DOI:10.1111/evo.12660 · 4.61 Impact Factor
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