Evolutionary Adaptation Of Long Styles In Pedicularis Flowers

Among sympatric species, evolution of flower structure can be affected by pollination competition or interference. And the pollen selection in post-pollination process can drive a race evolution between female and male functions. Therefore, we studied the adaptation of long corolla tube (long style) in post-pollination process using sympatric and simultaneously flowering Pedicularis as materials.In this study, we observed flowering phenology of sympatric Pedicularis species at population and individual levels. We examined the presentation of female and male functions. The results showed that species with long corolla tube (style) have longer period of female function presentation than short corolla tube species, allowing long styled Pedicularis have a longer time to receive the pollen.In the experiment of hand pollination with controlled pollen source and pollen load, we found that all six Pedicularis showed inbreeding depression to some extent. However, inbreeding depression was diminished when pollen load was high. The seed set was significant reduced when we reduced the pollen number applied on stigmas. And the reduction in long styled Pedicularis was much more than than that in short styled ones. Higher germination rates of seeds under low pollen competition indicated that the Pedicularis with longer style could reduce inbreeding depression.The interference of the pollen from related species seriously affected the seed set in Pedicularis. We found that pollen of long styled species had stronger interference ability than pollen of short styled species, and long styled species are better in resisting the interference of relative pollen than short styled species, especially the interference of pollen of short styled species. Longer style is a buffer for pollen interference. Long styled species is advantageous in seed production in the environment where related species are concentrating.No hybrids were found in our study. Eight species of Pedicularis were used to study the reproductive isolation between species. The reproductive isolation in post-pollination process is important because sharing the same pollinators may cause interspecific pollen delivery. We investigated whether style plays a role in reproductive isolation between Pedicularis species. We found that only the interspecific pollen of long styled species can reach the ovary of long styled species, while interspecific pollen of both long and short style species can reach the ovary of short style species, confirming our prediction. We also found that pistil-pollen interaction was significant. Although all interspecific pollen tube can run into the stylar issue, the length of pollen tube was significantly influenced by pistil-pollen interaction. These results indicated that the long styles contributed to the isolation among different species in Pedicularis.This study on the adaptation of long styles to reproduction in post-pollination process provides an alternate explanation for the evolution of long corolla tubes (long styles) in Pedicularis.