Mating system and the hybridization between self-compatible Phlox cuspidata and self-incompatible Phlox drummondii
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Mating system can impact the frequency of hybridization and therefore the maintenance of species diversity. I evaluate the effects of weak self-incompatibility (SI) in Phlox cuspidata and SI in Phlox drummondii on mating success within species and on hybridization dynamics between species under controlled conditions. The effects of SI on hybridization frequency were assessed by manipulating the relatedness of conspecific pollen and the relative timing of pollen deposition in mixed-donor interspecific pollinations. Selfing as opposed to outcrossing increased hybridization by 16% in P. cuspidata maternal plants and by 48% in P. drummondii maternal plants because self pollen did not compete as well against heterospecific pollen. The relative timing of conspecific versus heterospecific pollen deposition also impacted hybridization. In self-compatible P. cuspidata, the deposition of self pollen 5 h earlier than heterospecific pollen decreased hybridization by 28%. In self-incompatible P. drummondii, a 5 h delay in the deposition of compatible conspecific pollen increased hybridization by 32%. In this hybrid system, early self-pollination can decrease hybridization (but increase inbreeding) by P. cuspidata maternal plants, and SI may increase hybridization by P. drummondii maternal plants.
KeywordsPhlox hybrid system Hybridization Interspecific pollen competition Mixed-donor pollinations Self-fertilization Self-incompatibility (SI)
This work benefited from the help of Kathleen Donohue, Carolyn Griffen, David Haig, Kristina Jones, Donald Levin, Naomi Pierce, Janet Sherwood, and Rich Stomberg. I am also grateful to the following friends in Bastrop: John and Barbara Allbright, Jack and Phyllis Burns, and Ronnie and Graceanna Holder. Funding was provided by an NSF Graduate Student Fellowship and the Department of Organismic and Evolutionary Biology at Harvard University.
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