Pollen-Tube Competition, Siring Success, and Consistent Asymmetric Hybridization in Louisiana Irises

Emms, Simon K.; Hodges, Scott A.; Arnold, Michael L.

doi:10.2307/2410691

Cited by 41 publications

(56 citation statements)

References 47 publications

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“…In particular, pre-pollination mechanisms, including di¡erences in £owering time and £oral morphology that result in di¡erential pollinator speci¢-city, have often been thought to be among the most important barriers to gene exchange between plants (Levin 1978;Grant 1981;Schemske & Bradshaw 1999) and these were not included in this study. In addition, the pollinations from which these data came were conducted without pollen competition, although in natural conditions pollen competition may be important in determining the probability of hybrid formation (Emms et al 1996;Arnold 1997). Finally, these data did not include the ¢tness of F 1 hybrids grown in natural environments.…”

Section: Discussionmentioning

confidence: 99%

Asymmetrical crossing barriers in angiosperms

Tiffin

Olson

Moyle

2001

Proc. R. Soc. Lond. B

295

374

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Patterns of reproductive isolation between species may provide insight into the mechanisms and evolution of barriers to interspeci¢c gene exchange. We used data from published interspeci¢c hybridization experiments from 14 genera of angiosperms in order to test for the presence of asymmetrical barriers to gene exchange. Reproductive isolation was examined at three life-history stages: the ability of interspeci¢c crosses to produce seeds, the viability of F 1 hybrids, and the fertility of F 1 hybrids. Statistically signi¢cant asymmetries in the strength of reproductive isolation between species were detected in all genera and at each of the three life-history stages. Asymmetries in seed production may be caused by a variety of mechanisms including di¡erences in stigma/style lengths, self compatibility and di¡erential fruit abortion. Asymmetries in post-zygotic isolation are probably caused by nuclear^cytoplasmic interactions. Asymmetrical reproductive isolation between plant taxa may have important implications for the dynamics of hybrid zones, the direction of genetic introgression and the probability of reinforcement.

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Section: Discussionmentioning

confidence: 99%

Asymmetrical crossing barriers in angiosperms

Tiffin

Olson

Moyle

2001

Proc. R. Soc. Lond. B

295

374

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“…Actual patterns of introgression in hybrid zone populations of Louisiana Iris species are affected by a complex cascade of factors. These include ecological setting, timing of flowering, floral traits, pollinator behavior, gamete competition, and hybrid viability and fertility Carney et al 1994;Emms et al 1996;Burke et al 1998;Emms and Arnold 2000;Wesselingh and Arnold 2000;Johnston et al 2001aJohnston et al , 2003. Since all these factors interact, genetic covariance between numerous traits might be important in preventing or facilitating gene flow between I. fulva and I. brevicaulis in natural settings.…”

Section: Discussionmentioning

confidence: 99%

Genetic Mapping of Species Boundaries in Louisiana Irises UsingIRRERetrotransposon Display Markers

et al. 2005

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Genetic mapping studies provide insight into the pattern and extent of genetic incompatibilities affecting hybridization between closely related species. Genetic maps of two species of Louisiana Irises, Iris fulva and I. brevicaulis, were constructed from transposon-based molecular markers segregating in reciprocal backcross (BC 1 ) interspecific hybrids and used to investigate genomic patterns of species barriers inhibiting introgression. Linkage mapping analyses indicated very little genetic incompatibility between I. fulva and I. brevicaulis in the form of map regions exhibiting transmission ratio distortion, and this was confirmed using a Bayesian multipoint mapping analysis. These results demonstrate the utility of transposonbased marker systems for genetic mapping studies of wild plant species and indicate that the genomes of I. fulva and I. brevicaulis are highly permeable to gene flow and introgression from one another via backcrossing.

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“…However, the barriers to hybridization are fundamentally different in these two systems. In Iris, interspecific pollen-tube competition and differential pollen tube growth appear to provide a strong barrier to F 1 hybrid formation and determine the direction asymmetry in hybridization (Carney et al 1996;Emms et al 1996). In Asclepias, F 1 formation appears to be limited by pollinators specializing on each milkweed species, whereas postpollination pollentube competition appears less important (Broyles et al 1996).…”

Section: Discussionmentioning

confidence: 99%

Hybrid Bridges to Gene Flow: A Case Study in Milkweeds (Asclepias)

Broyles¹

2002

Evolution

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Abstract. Natural hybridization occurs throughout areas of sympatry for the North American milkweeds Asclepias exaltata and A. syriaca (Asclepiadaceae), even though the formation of F 1 hybrid seed is a rare event. For introgressive hybridization to proceed, F 1 and advanced hybrids must be released from reproductive barriers and successfully mate with one or both parental species. I investigated the mating system of natural hybrids between A. exaltata and A. syriaca in three populations in Shenandoah National Park, Virginia. Allozyme data and a maximum-likelihood procedure were used to estimate the frequency of six genotypic classes (parentals, F 1 , F 2 , and backcrosses) of the hybridizing populations, the pollinia received by hybrid plants, and the paternal parents of seeds produced by hybrids. F 1 hybrids, backcross A. syriaca, and parental A. syriaca individuals were common in three hybrid populations. Even though self-pollinations and interhybrid pollinations were common, F 2 seed production and the occurrence of F 2 individuals were rare in hybrid populations. Hybrid plants received more pollen from A. syriaca than A. exaltata, which resulted in the production of more backcross-A. syriaca seed than backcross-A. exaltata seed. Asclepias exaltata was rare in the hybrid populations, but A. exaltata pollinia were received by hybrids and this species sired between 15% and 36% of the seeds produced on hybrids. The potential for introgression with A. exaltata populations is lower because this species is unsuccessful as the maternal parent in interspecific and backcross hand-pollinations. The asymetry of hybridization with A. syriaca as the maternal parent is further supported by the incorporation of maternally inherited chloroplast DNA markers in hybrids. Hybrid milkweeds frequently backcross with both parental species and may be released from the reproductive barriers that limit the formation of F 1 hybrids in natural populations. The direction of interspecific gene flow and introgression in milkweeds is influenced by the reproductive biology of hybrids, the constituency of the surrounding population, and failure of some crosses to produce seeds. Finally, introgressive hybridization remains an important evolutionary force even when the initial formation of F 1 hybrids in natural populations is rare.

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Pollen-Tube Competition, Siring Success, and Consistent Asymmetric Hybridization in Louisiana Irises

Cited by 41 publications

References 47 publications

Asymmetrical crossing barriers in angiosperms

Asymmetrical crossing barriers in angiosperms

Genetic Mapping of Species Boundaries in Louisiana Irises UsingIRRERetrotransposon Display Markers

Hybrid Bridges to Gene Flow: A Case Study in Milkweeds (Asclepias)

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