Pollen competition and environmental effects on hybridization dynamics between Phlox drummondii and Phlox cuspidata |
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Authors: | Lauren G Ruane Kathleen Donohue |
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Institution: | (1) Department of Organismic and Evolutionary Biology, Harvard University Herbaria, 22 Divinity Avenue, Cambridge, Massachusetts 02138, USA |
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Abstract: | Pollen competition between species strongly influences hybridization dynamics in plants. By performing single- and mixed-donor
pollinations, we show that soil Ca alters the outcome of interspecific pollen competition in the annual Phlox hybrid system of Phlox cuspidata and P. drummondii. In the absence of interspecific pollen competition, heterospecific pollen siring success of both species was influenced
most strongly by the maternal growth environment, such that hybridization was facilitated when heterospecific pollen was deposited
on stigmas of maternal plants growing in high Ca soils. When heterospecific pollen was forced to compete against conspecific
pollen, however, the maternal growth environment did not influence hybridization, but the environmental origin of heterospecific
pollen did, and this effect depended on the maternal species. Pollen of P. drummondii was more effective at outcompeting P. cuspidata pollen and preventing hybridization in P. drummondii dams when P. cuspidata pollen was derived from low Ca. Pollen competition within pistils of P. cuspidata was unaffected by pollen Ca environment. In situations in which P. cuspidata grows in lower soil Ca than P. drummondii, as has been documented in one population, these results suggest that the competitive ability of heterospecific pollen will
be diminished by environmental effects of soil Ca. Thus, the environment in which pollen develops can influence interspecific
pollen competition and hybridization frequency. |
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Keywords: | Hybridization Interspecific pollen competition Population differentiation Post-pollination pollen performance Reproductive isolation Soil calcium environment |
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