Patterns and consequences of self‐pollen deposition on stigmas in heterostylous Persicaria japonica (Polygonaceae)

Abstract

In order to test the "anti-interference" hypothesis for adaptive significance of reciprocal herkogamy, patterns of illegitimate pollination and effects of self-pollen on the legitimate pollination and fertility were investigated in a naturally pollinated experimental population of distylous Persicaria japonica. Pollen deposition was compared among the emasculation treatments, i.e., emasculation of a single flower from individual inflorescences, emasculation of all the flowers of individual inflorescences, and no emasculation control. In both morphs, considerable illegitimate pollination was found to occur in all the treatments, and there was no significant difference in incompatible pollen load among the treatments. Therefore, it is suggested that herkogamy of P. japonica can sufficiently reduce both intraflower and intra-inflorescence self-pollinations, but not interinflorescence geitonogamous and-or interclonal illegitimate pollination. Measurements of pollen load after the repetitive pollen addition showed that space on the stigma surface may not limit the legitimate pollination under natural pollination conditions. Seed sets after legitimate pollination following prior self-pollination did not differ from the controls without self-pollination. Therefore, there is little possibility that incompatible pollen load interferes with either pollination or fertilization by compatible pollen, suggesting that "anti-interference" is unimportant for adaptive significance of reciprocal herkogamy at least in P. japonica.

Selective flower visitation behavior by pollinators in a radish F1 seed production field

“…Several investigators suggest that phenotypes in floral traits, such as morphology, color, and scent, have changed as a result of the visitation behavior of pollinators acting as a selective force on the plant species, especially in specialist plants that depend on specific animals as pollinators (Richards 1997, Schemske andBradshaw 1999). On the other hand, generalist plants, which have pollen grains that are mediated by various pollinator species, also exhibit variations in their floral traits (Conner and Sterling 1995, Lee and Snow 1998, Nishihiro and Washitani 1998. The evolutionary process of the generalist flower has been debated for years from the studies of the relationship between floral trait variations and pollinator visitation behavior (Young and Stanton 1990, Conner and Rush 1996, Thompson 2001, Larsson 2005, Sahli and Conner 2007.…”

Effect of population spatial structure on pollination and seed set of a clonal distylous plant,Persicaria japonica (Polygonaceae)

“…The species has distylous one-day flowers with strict self-and intra morph incompatibility (Nishihiro and Washitani 1998). The white dish-shaped corolla of the species is around 5 mm in diameter.…”

“…Generally, seed set is higher in plants that receive pollen from genetically diverse pollen donors (Niesenbaum andCasper 1994, Quesada et al 1996) and combination of pollen and ovule parents can affect seed set considerably due to post-pollination rejection of apparently compatible pollen (Marshall andEIIstrand 1986, Marshall 1991). Number of potential pollen donors may be much limited in the single clones because of short distance pollen flow from relatively short flight distances of the predominant pollinators for the species (Nishihiro and Washitani 1998).…”

“…japonica (Nishihiro and Washitani 1998). The importance of unbiased fertility to maintaining the heterostylous incompatibility system was suggested by prediction from ESS models (Casper andCharnov 1982, Charlesworth 1989).…”

“…H. Gross, a distylous plant species with a clonal growth habit, has several floral and reproductive traits advantageous for studying pollination success separately from post pollination processes (Nishihiro and Washitani 1998): (1) Compatibility of a given deposited pollen grain can be relatively precisely judged from the size, which markedly differs between the floral morphs, since selfand intra-morph incompatibility is almost complete in this species. (2) Prior or simultaneous self-pollination will interfere with neither pollination nor fertilization of compatible pollen.…”