Inter-morph pollen flow and reproductive success in a self-compatible species with stigma-height dimorphism: the influence of herkogamy and reciprocity.

Abstract

Inter-morph pollen transfer and its dependence on herkogamy and reciprocity are not completely understood in species with stigma-height dimorphism. We asked whether total stigmatic pollen loads, inter-morph fraction of pollen load and reproductive success differed between morphs in Jasminum malabaricum, a species exhibiting stigma-height dimorphism. We tested whether higher herkogamy and reciprocity resulted in higher inter-morph pollen deposition and reproductive success. We quantified individual-level estimates of herkogamy, reciprocity, total stigmatic pollen load, inter-morph stigmatic pollen fraction and fruit set for both morphs in naturally occurring populations of J. malabaricum. Total pollen load was higher in the long-styled morph, inter-morph pollen fraction was higher in the short-styled morph, but fruit set did not differ between morphs. Higher herkogamy resulted in a higher inter-morph fraction of pollen load and fruit set in the long-styled morph of one population. In the other population, only reciprocity was found to be related to inter-morph pollen deposition. This study is the first to quantify and report natural inter-morph stigmatic pollen load in a species with stigma-height dimorphism. Morph-specific differences in pollen load were similar to patterns commonly observed in heterostylous species. The results highlight the importance of both herkogamy and reciprocity in facilitating inter-morph pollen transfer. Population-specific patterns indicate that local environmental factors determine the relative functional importance of herkogamy and reciprocity.