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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    • "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.
    Journal of Evolutionary Biology 11/2015; DOI:10.1111/jeb.12787 · 3.23 Impact Factor
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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.
    PeerJ 10/2015; 3(1–4). DOI:10.7717/peerj.1308 · 2.11 Impact Factor
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    • "Reproduction success of most flowering plants depends on both their breeding system and pollination biology (Liu and Koptur, 2003). Mating systems play an essential role in shaping the spatial and temporal patterns of genetic diversity and the effective population size, with major consequences for the evolution and ecology of plants (Lloyd and Schoen, 1992; Barrett, 2003; Charlesworth, 2006). "
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    ABSTRACT: Helianthemum caput-felis is an endangered plant species growing in fragmented habitats in the western Mediterranean basin. Reproductive traits, breeding system and pollinator assemblage were studied in its largest known (mainland) European population to improve knowledge on the reproductive biology of the species. Hand-pollination experiments were carried out to determine the breeding system. Generalized linear mixed models (GLMM) were fitted to the data to evaluate the effect of treatment on fruit set and number of viable seeds per fruit. We also investigated the composition of the pollinator assemblage by direct observations, and studied their pollen load. Results were then compared to previous studies conducted in an island population. In the studied population, H. caput-felis is partially self-compatible, but mostly an outbreeder species, since outcrossed flowers produced many more fruits and seeds than self-pollinated ones. Conversely, pollination treatments did not affect reproductive output in the island population. We also found several differences between island and mainland composition of floral visitors, as it was expected. The study of pollen loads revealed that insects were mostly visiting H. caput-felis. Despite the low capacity to produce fruits with self-pollination, H. caput-felis presented no reproductive limitations in its main inland population. Reproductive characteristics along with differences among populations should be taken into account for adequate management and conservation practices.
    Flora - Morphology Distribution Functional Ecology of Plants 10/2015; 217:75-81. DOI:10.1016/j.flora.2015.10.001 · 1.47 Impact Factor
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