Abstract:

With their critical role in plant pollination and mating system, the adaptive significance of herkogamy and floral behavior has well been studied in plant reproductive biology and evolutionary ecology. Here we review recent progress in this field, especially discuss the adaptive significance of movement approach herkogamy in monadelphous tube in Malvaceae, which involves decrease of herkogamy resulting from the curvature of stigma lobe.

Herkogamy, the spatial separation of pollen presentation and pollen receipt within flowers, appears in many animal_pollinated plants. Due to its positive correlation with outcrossing rates in some species with mixed_mating systems, herkogamy has been previously considered as a mechanism to prevent self_pollination. However, increasing evidences suggest that herkogamy may act as a mechanism to reduce interference between the reproductive functions of female and male organs. Functional studies of heterostylous species indicate that sex_organ reciprocity serves to promote cross_pollen transfer between floral morphs and that enantiostyly and stigma_height dimorphism function in a similar manner.

Intra_floral sex interference often contains physical interference and pollen clogging. The former involves stamens obstructing the deposition of outcrossing pollen on stigmas and pistil reducing pollen export (an experimental evidence is given recently). The latter involves pollen discounting and ovule discounting, and its experimental evidence has been largely reported in many plants.

The behaviors of different floral parts (style, stamen, pollen, corolla, etc.) may have adaptive significance, including reducing intrafloral male_female interference, avoiding self_pollination, promoting delayed autonomous selfing, and responding to the harsh environment. Movement approach of herkogamy in monadelphous tube in Malvaceae, making the herkogamy decrease by the curvature of stigma lobe, is unusual and intriguing, and its adaptive significance may involves promoting outcrossing, facilitating delayed selfing if outcrossing fails, and interferences between two sexual organs.

We believe that the trends studying on the their functions are transiting from the research stage mainly depending on the description to comprehensive research phase combining modern experimental technology (e.g. the molecular markers of SSR, SNP, AFLP) and advanced apparatus multi_seasons with traditional method, and with the development of the capacity of field experiments and control conditions,transiting from traditional and classical observations to combining floral manipulation in the field experiments.

Key words: Herkogamy, Floral behavior, Stigma movement in monadelphous tube, Adaptive significance