Ecological and Genetic Associations in an Iris Hybrid Zone

Cruzan, Mitchell B.; Arnold, Michael L.

doi:10.2307/2410158

Cited by 161 publications

(220 citation statements)

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“…Hybrids may also perform better than both parents in a novel environment that parental types do not colonize. This is the case for hybrids between I. hexagona and I. fulva: The fulvatype hybrids were found most frequently in an environment not used by either parent (Cruzan and Arnold 1993).…”

Section: Selection Against F 1 Hybrids In the Parental Environmentsmentioning

confidence: 93%

Reproductive Isolation Between Divergent Races of Pea Aphids on Two Hosts. Ii. Selection Against Migrants and Hybrids in the Parental Environments

Bouck²,

2000

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Abstract. Sympatric races of pea aphids on alfalfa and red clover are highly ecologically specialized and significantly reproductively isolated. Much of the restriction of gene flow between the specialized populations is due to habitat choice behavior of the winged colonizers (Via 1999). Here, we document additional pre-and postmating reproductive isolation through selection against migrants and hybrids in the parental environments. First, a group of randomly chosen genotypes from each race that were experimentally migrated between hosts had very low survival and reproduction on the alternate host relative to genotypes originating from that host (natives). Such selection against crosshost migrants forms a premating barrier to gene flow because it is likely to reduce migrant frequencies before the sexual forms are induced in the fall. Our reciprocal transplant experiment also shows that natural selection acts directly on individual migrants between the crops to favor host choice behavior: genotypes from each host suffered large losses of fitness when forced to migrate to the alternate host plant relative to the fitness they would have enjoyed had they been able to choose their native host. In a companion field study, sequential sampling throughout the summer in newly colonized fields of both alfalfa and clover revealed a decrease in the frequency of host-specific marker alleles characteristic of the alternate crop. These field data further support the hypothesis that selection disfavors migrants that cross between crops. Second, when two sets of F 1 hybrids between the races were reciprocally tested on alfalfa and clover, both sets had significantly lower average fitness than the specialized parent in each of the two environments. This demographic selection against hybrids in the parental environments is a source of postmating reproductive isolation between the specialized races. Finally, significant genetic variation in fitness traits was seen among F 1 hybrid genotypes from both crosses between alfalfa and clover specialists. Although this variation suggests that a generalized pea aphid could evolve, such generalists are not seen in field collections of these populations.

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Section: Selection Against F 1 Hybrids In the Parental Environmentsmentioning

confidence: 93%

Reproductive Isolation Between Divergent Races of Pea Aphids on Two Hosts. Ii. Selection Against Migrants and Hybrids in the Parental Environments

Bouck²,

2000

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“…Second, studies that describe fertility, viability, or other fitness parameters in hybrids almost invariably report the presence of a small fraction of hybrid genotypes that are as fit or fitter than parental individuals, even if the hybrids on average exhibit reduced fitness (Heiser, 1947 ;Valentine, 1947 ;. Third, significant genotype-habitat associations are often reported for hybrid swarms (Stebbins & Daly, 1961 ;Potts & Reid, 1985 ;Cruzan & Arnold, 1993, 1994Arnold, 1997). Presumably, this indicates that a selective advantage accrues for certain hybrid genotypes when found in favourable habitats, although these correlations could also result from historical factors (Barton & Hewitt, 1985).…”

Section: The Fitness Of Different Classes Of Hybridsmentioning

confidence: 99%

Plant hybridization

1998

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Summary 599 I. Introduction 599 II. Concepts and terminology 600 III. Historical background 600 IV. Studies of experimental hybrids 601 1. Isolating mechanisms 601 2. Prezygotic barriers 602 (a) Gametic barriers to hybridization 602 3. Postzygotic barriers 603 (a) Chromosomal rearrangements 604 (b) Genic sterility or inviability 604 4. Hybrid vigour 605 5. Introgression 606 6. Hybrid speciation 607 V. Experimental manipulations of natural hybrid populations 609 1. Hybrid‐zone formation 610 2. Pollinator‐mediated selection 610 3. Habitat selection 612 VI. The biology of different classes of hybrids 612 1. Character expression 613 (a) Morphological characters 613 (b) Chemical characters 613 (c) Molecular characters 613 2. The fitness of different classes of hybrids 614 (a) The importance of variance 614 (b) Estimating hybrid fitness 615 3. Interactions with parasites and herbivores 616 4. Patterns of mating 617 (a) Outcrossing rate 617 (b) Hybridization frequency 618 (c) Mate choice 618 VII. Conclusions and future research 619 Acknowledgements 620 References 620 Most studies of plant hybridization are concerned with documenting its occurrence in different plant groups. Although these descriptive, historical studies are important, the majority of recent advances in our understanding of the process of hybridization are derived from a growing body of experimental microevolutionary studies. Analyses of artificially synthesized hybrids in the laboratory or glasshouse have demonstrated the importance of gametic selection as a prezygotic isolating barrier; the complex genetic basis of hybrid sterility, inviability and breakdown; and the critical role of fertility selection in hybrid speciation. Experimental manipulations of natural hybrid zones have provided critical information that cannot be obtained in the glasshouse, such as the evolutionary conditions under which hybrid zones are formed and the effects of habitat and pollinator‐mediated selection on hybrid‐zone structure and dynamics. Experimental studies also have contributed to a better understanding of the biology of different classes of hybrids. Analyses of morphological character expression, for example, have revealed transgressive segregation in the majority of later‐generation hybrids. Other studies have documented a high degree of variability in fitness among different hybrid genotypes and the rapid response of such fitness to selection – evidence that hybridization need not be an evolutionary dead end. However, a full accounting of the role of hybridization in adaptive evolution and speciation will probably require the integration of experimental and historical approaches.

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“…As an important mechanism of speciation, especially in plants, the resulting novel genetic variation will be subjected to natural selection from divergent ecological pressures (see Gross et al 2004 and references therein). In some cases, such as irises and sunflowers, hybrids have a fitness advantage in habitats substantially different from that of either parental species (Cruzan & Arnold 1993;Rieseberg et al 2003). Another widely recognized mechanism of speciation is polyploidy, which can be a major source of increased genetic diversity and concomitant adaptability (Wendel 2000).…”

Section: Introductionmentioning

confidence: 99%

Convergent adaptation to a marginal habitat by homoploid hybrids and polyploid ecads in the seaweed genusFucus

et al. 2006

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Hybridization and polyploidy are two major sources of genetic variability that can lead to adaptation in new habitats. Most species of the brown algal genus Fucus are found along wave-swept rocky shores of the Northern Hemisphere, but some species have adapted to brackish and salt marsh habitats. Using five microsatellite loci and mtDNA RFLP, we characterize two populations of morphologically similar, muscoides-like Fucus inhabiting salt marshes in Iceland and Ireland. The Icelandic genotypes were consistent with Fucus vesiculosus × Fucus spiralis F 1 hybrids with asymmetrical hybridization, whereas the Irish ones consisted primarily of polyploid F. vesiculosus .

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Ecological and Genetic Associations in an Iris Hybrid Zone

Cited by 161 publications

References 0 publications

Reproductive Isolation Between Divergent Races of Pea Aphids on Two Hosts. Ii. Selection Against Migrants and Hybrids in the Parental Environments

Reproductive Isolation Between Divergent Races of Pea Aphids on Two Hosts. Ii. Selection Against Migrants and Hybrids in the Parental Environments

Plant hybridization

Convergent adaptation to a marginal habitat by homoploid hybrids and polyploid ecads in the seaweed genusFucus

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