Reproductive Biology of Relict Trillium (Trillium reliquum)

Abstract

Pollination and seed dispersal were studied in six populations of the endangered plant species Trillium reliquum in Bullock and Lee counties in Alabama and in Muscogee County, Georgia. Few populations of this species exist and most are relatively small and isolated. Pollination was studied through field observations of floral visitors, microscopic examination of insects captured on flowers, sticky trap capture of potential floral visitors, fluorescence microscopy of styles for the examination of pollen tubes, and pollen manipulation experiments. In pollen manipulation experiments, plants were covered by insect exclusion bags constructed of no-see-um netting (0.3 mm mesh) and treated as self-pollination (no pollen transfer), hand-pollination single application, hand-pollination

multiple application, and open to pollination naturally. Carrion insects including fly and beetle families dominated floral visitors. A carrion fly pollination syndrome was indicated. In the pollen manipulation study, no visible bag effects were detected. No self-pollinated plants formed fruits, indicating self-incompatibility in spite of pollen tube formation in self-pollinated plants. Seed numbers were significantly higher (though inconsistently) in open pollination treatments than in hand-pollination treatments in the larger populations, indicating a high level of pollinator attraction. Seed numbers in open pollination treatments were consistently lower than or not significantly different from hand-pollination treatments in smaller populations, suggesting that small populations fail to attract pollinators sufficiently. Reproductive rates, as judged by %-developed seeds, were low in all populations. Seed dispersal was studied through field observations of fruit visitors, and through collection of potential seed dispersers on sticky trap platforms supplied with fruit and/or seeds with and without elaiosomes. Ants of several species dominated collections and the larger forms were judged to be effective seed dispersers. Seed dispersal by Vespula wasps was also observed. This is the first report of vespicochory in T. reliquum. Suggestions for preservation of this species include protection of a number of populations in order to preserve genetic diversity and maintenance of populations at sufficient size to attract pollinators.