Abstract
Investigations into the genetic basis of reproductive barriers among recognized and putative varieties in Phacelia dubia have provided evidence that even among closely related taxa, multiple pathways can lead to reproductive isolation. A nuclear-based reproductive barrier, expressed as partial hybrid sterility of both pollen and ovules, isolated each pair of recognized varieties. There was no evidence of pre- or post-fertilization barriers; all reproductive barriers were manifested as hybrid gametic sterility. Reproductive relationships of two putative varieties were studied to examine the early stages of reproductive isolation in this group. Both putative varieties exhibited partial reproductive isolation from the recognized varieties in spite of their lack of morphological differentiation from recognized varieties. The barrier isolating one putative variety was similar to the barrier among recognized varieties. The second putative variety and a recognized variety were partially isolated by a unidirectional, nuclear-cytoplasmic barrier that reduced only pollen fertility. The nuclear-cytoplasmic barrier suggested a new application of Haldane's rule.
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Acknowledgements
Acknowledgements The insightful comments contributed by M. Uyeno-yama are greatly appreciated. Both J. Antonovics and M. Uyenoyama were instrumental in the design and formulation of these experiments. J. Antonovics, N. Gillham, T. Meagher, D. Stone, and E. Walker provided helpful comments on earlier drafts of the manuscript. D. Burdick helped with the statistical analyses and M. Rausher kindly provided a computer program for the analysis of reciprocal crosses. D. Stone provided assistance and laboratory space for the pollen tube analyses. This research was supported in part by funds from NIH grant # 5 T32 GM07754-09 and NSF grant #BSR-8613803.
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Levy, F. A genetic analysis of reproductive barriers in Phacelia dubia. Heredity 67, 331–345 (1991). https://doi.org/10.1038/hdy.1991.97
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DOI: https://doi.org/10.1038/hdy.1991.97
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