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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    • "Variation in mating system between ecotypes could be due to variation in inbreeding depression. Inbreeding depression is a major factor driving mating system evolution (Lande andSchemske, 1985;Goodwillie et al., 2005;Charlesworth, 2006), and it varies strongly with environmental conditions (Armbruster and Reed, 2005;Fox and Reed, 2011). Selfing rates were measured on adults collected in the field. "
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    ABSTRACT: Background and aims: The pseudometallophyte Noccaea caerulescens is an excellent model to study evolutionary processes, as it grows both on normal and on heavy-metal-rich, toxic soils. The evolution and demography of populations are critically impacted by mating system and, yet, information about the N. caerulescens mating system is limited. Methods: Mean selfing rates were assessed using microsatellite loci and a robust estimation method (RMES) in five metallicolous and five non-metallicolous populations of N. caerulescens in Southern France, and this measure was replicated for two successive reproductive seasons. As a part of the study, the patterns of gene flow among populations were analysed. The mating system was then characterized at a fine spatial scale in three populations using the MLTR method on progeny arrays. Key results: The results confirm that N. caerulescens has a mixed mating system, with selfing rates ranging from 0·2 to 0·5. Selfing rates did not vary much among populations within ecotypes, but were lower in the metallicolous than in the non-metallicolous ecotype, in both seasons. Effective population size was also lower in non-metallicolous populations. Biparental inbreeding was null to moderate. Differentiation among populations was generally high, but neither ecotype nor isolation by distance explained it. Conclusions: The consequences of higher selfing rates on adaptation are expected to be weak to moderate in non-metallicolous populations and they are expected to suffer less from inbreeding depression, compared to metallicolous populations.
    Full-text · Article · Jan 2016 · Annals of Botany
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    • "Therefore, selfing is selectively favoured when ID is less than the transmission advantage (Lande & Schemske, 1985; Goodwillie et al., 2005). A second alternative ecological force favouring selfing is reproductive assurance under gamete limitation (Charlesworth, 2006). These conditions may arise either due to reduced gamete exchange, reduced mate availability or a combination of both (Busch & Delph, 2012; Griffin & Willi, 2014). "
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    ABSTRACT: In hermaphroditic plants, theory for mating system evolution predicts that populations will evolve to either complete autonomous selfing or complete outcrossing, depending on the balance between automatic selection favouring self-fertilization and costs resulting from inbreeding depression (ID). Theory also predicts that selection for selfing can occur rapidly and is driven by purging of genetic load and the loss of ID. Therefore, selfing species are predicted to have low levels of ID or even to suffer from outbreeding depression (OD), whereas predominantly outcrossing species are expected to have high levels of ID. To test these predictions, we related the capacity of autonomous selfing to the magnitude of early acting inbreeding or outbreeding depression in both allogamous and autogamous species of the orchid genus Epipactis. For each species, the level of autonomous selfing was assessed under controlled greenhouse conditions, whereas hand-pollinations were performed to quantify early costs of inbreeding or outbreeding depression acting at the level of fruit and seed production. In the autogamous species, the capacity of autonomous selfing was high (> 0.72), whereas in the allogamous species autonomous selfing was virtually absent (< 0.10). Consistent with our hypothesis, allogamous Epipactis species had significantly higher total ID (average: 0.46) than autogamous species, which showed severe costs of OD (average: -0.45). Overall, our findings indicate that strong early-acting ID represents an important mechanism that contributes to allogamy in Epipactis, whereas OD may maintain selfing in species that have evolved to complete selfing. This article is protected by copyright. All rights reserved.
    Full-text · Article · Nov 2015 · Journal of Evolutionary Biology
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    • "Pollen vectors can drive plant evolution and diversification throughout their selection on floral traits (Darwin, 1859; Darwin, 1862; Thompson, 1994; Barrett & Harder, 1996; Charlesworth, 2006). Most angiosperms need vectors for pollen transfer between plants, which are mainly insects but can also be other animals and to a lesser extent wind or water (Harder & Barrett, 1996; Ackerman, 2000; Ollerton, Winfree & Tarrant, 2011). "
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    ABSTRACT: In Gentiana lutea two varieties are described: G. lutea var. aurantiaca with orange corolla colors and G. lutea var. lutea with yellow corolla colors. Both color varieties co-occur in NW Spain, and pollinators select flower color in this species. It is not known whether a hybridization barrier exists between these G. lutea color varieties. We aim to test the compatibility between flower color varieties in G. lutea and its dependence on pollen vectors. Within a sympatric population containing both flower color morphs, we analyzed differences in reproductive success (number, weight, viability and germinability of seeds) depending on fertilization treatments (autogamy and xenogamy within variety and among varieties). We found a 93% reduction in number of seeds and a 37% reduction in seed weight respectively of autogamy treatments compared to xenogamy crossings. Additionally, reproductive success is higher within color varieties than among varieties, due to a 45% seed viability reduction on hybrids from different varieties. Our results show that G. lutea reproductive success is strongly dependent on pollinators and that a partial hybridization barrier exists between G. lutea varieties.
    Full-text · Article · Oct 2015 · PeerJ
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