Flowering, pollination and pollinators of mangroves in Okinawa

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The duration of this research was 3 years, 2002 to 2004. The main research sites were mangrove forests at the mouth of Okukubi River, Kin, Okinawa, Japan. Regular observations and sample collections were made when possible at weekly intervals. At times especially during 2004, typhoon events made sampling difficult. Bruguiera gymnorrhiza flowing phenology occurred throughout the year, while that of Kandelia candel was once a year. Although B.gymnorrhiza flowered throughout the year, successful fruiting was restricted to the period June to December. Anthers of flowers formed from January to May did not always open and pollen germination abilities of these flowers were very low.When flowers of B.gymnorrhiza were covered with pollen bags to prevent visits by pollinators, rates of petal opening were less than 8 %. In contrast, rates of petal opening under natural conditions were approximately 94 %. Visits to flowers by larger pollinators, such as Sphex argentatus and Zosteropus japonica loo … More chooensis, helped to induce full petal opening and enhance pollen dispersal from anthers. However, flower visiting by very small insects (including moths) such as Macroglossum mediovitta, failed to help petal opening. This suggested that their roles as pollinators were not so important compared to those of lager pollinators. Under the artificial pollen bag treatment of B.gymnorrhiza flowers (prevent cross-pollination) petal-opening rates of such flowers to disperse pollen were approximately 8 %. Within these limited petal-openings some expansions of ovules caused by the self-pollination could be recognized. This indicates that some self-pollination might be possible under natural conditions. Nevertheless, in general, it seems that self-pollination rates of woody plants are small. However, results of microsatellite analyses also suggested that relatively higher self-pollination rates can occur in B.gymnorrhiza and K.candel.Thus these results suggest that mangrove tree species having some self-pollination abilities, such as B.gymnorrhiza and K.candel, had some advantages of easier migration and, once in a new ecohabitat, are able to maintain their communities more efficiently than other mangrove species that lack these self-pollination abilities. Less