Pollination mode significantly influences stigmatic pollen load: A test within two species of Thalictrum (Ranunculaceae)
Despite recognition of pollen-grain aperture numbers variation within some angiosperm genera, the selective pressures that influence pollen-aperture evolution are still largely under investigation.
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Hypothesis: stigmatic pollen loads are consistently and significantly greater in insect-pollinated species than in wind-pollinated species.
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We compared stigmatic pollen loads between two species: the insect-pollinated Thalictrum thalictroides and the wind-pollinated T. dasycarpum. While these species differ in sexual system (hermaphroditic and dioecious, respectively), many characteristics, such as uni-ovulate pistils, are shared within the genus.
Our findings support the hypothesis, and a significant difference persists after statistically accounting for the effect of per-flower stamen number on pollen load in the hermaphroditic species.
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These results are relevant to studies of pollen competition and pollen-grain evolution, especially in genera, like Thalictrum, with aperture-number and pollination-mode variation.
