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dc.contributor.advisor Delph, Lynda F en Brothers, Amanda en 2010-12-13T21:03:11Z en 2027-08-13T20:03:11Z en 2012-05-04T18:04:56Z 2010-12-13T21:03:11Z en 2010 en
dc.identifier.uri en
dc.description Thesis (Ph.D.) - Indiana University, Biology, 2010 en
dc.description.abstract How boundaries are maintained between closely related species is one of the central questions in evolutionary biology. I addressed three questions regarding how species boundaries are maintained in closely related species of <italic>Silene</italic>. First I tested whether pollinator-mediated selection for particular floral traits shapes the phenotypes of <italic>S. latifolia</italic> and <italic>S. diclinis</italic>, thus contributing to pre-zygotic isolating barriers. These two species occur sympatrically and cross successfully in the greenhouse, although hybrids between the two have not been observed in the wild. I tested for both differential visitation and seed set using F2 hybrids to understand which traits may be important for pollinator-mediated selection. Floral visitors preferred short flowers during the day and tall flowers at night. Larger flowers were more likely to be predated at night. These results suggest that differential visitation by pollinators has shaped floral traits and that selection by pollinators may contribute to reproductive isolation between these two species in nature. Second, I investigated whether Haldane's Rule applies to plants. Haldane's rule states that in the F1 hybrid generation between two species, the heterogametic sex (e.g. XY) is more likely to be rare, absent, or sterile, thus providing a post-zygotic isolating mechanism. Haldane's rule has been observed in over 250 species of animals, but has not been documented in plants. <italic>Silene latifolia</italic>, <italic>S. diclinis</italic>, and <italic>S. dioica</italic>, are unique in that all three are dioecious with heteromorphic sex chromosomes. Males are heterogametic, although the sex chromosomes are relatively young. Male F1 hybrids exhibited rarity and sterility, extending Haldane's rule to plants. Finally, to further investigate what might cause chromosomal incompatibilities between <italic>S. latifolia</italic> and <italic>S. diclinis</italic> I used solid staining techniques to look at the sex chromosomes. Unlike <italic>S. latifolia</italic> or <italic>S. dioica</italic>, <italic>S. diclinis</italic> has neo-sex chromosomes. This is likely the result of a reciprocal translocation between the Y-chromosome and an autosome. Because <italic>S. latifolia</italic> and <italic>S. diclinis</italic> successfully produce viable F1 hybrids, the neo-sex chromosomes of <italic>S. diclinis</italic> must be able to pair with species that do not have neo-sex chromosomes. Using solid staining techniques, we observed the arrangement of the X, Y, and neo-sex chromosomes in both pure species and hybrids. We found that the neo-sex chromosomes found in <italic>S. diclinis</italic> can be inherited across species and are not an absolute barrier to hybridization between <italic>S. latifolia</italic> and <italic>S. diclinis</italic> at the F1 generation. The results of these studies suggest that multiple pre- and post-zygotic barriers are important for maintaining species boundaries in dioecious <italic>Silene</italic>. en
dc.language.iso en en
dc.publisher [Bloomington, Ind.] : Indiana University en
dc.rights This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported (CC BY-NC-SA 3.0) license. en
dc.rights.uri en
dc.subject reproductive isolation en
dc.subject Haldane's rule en
dc.subject pollinator isolation en
dc.subject neo-sex chromosomes en
dc.subject Silene en
dc.subject Speciation en
dc.subject.classification Biology en
dc.title Pre- and post-zygotic isolating barriers in Silene en
dc.type Doctoral Dissertation en

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