The role of geitonogamy in the reproduction success of a nectarless dactylorhiza maculata (orchidaceae)

Abstract

Dactylorhiza maculata is a common terrestrial orchid in Finland. It is nectarless and the seed production is relatively high for a deceptive species. The pollinators of D. maculata do not have frequent visits to the flowers, but the species is capable of over 50 % seed capsule production. Geitonogamy is the transfer of self pollen between flowers on the same individual. It is typical that the pollinators of deceptive inflorescences visit only few flowers and have short stays in them, and therefore it is commonly thought that geitonogamy is infrequent among deceptive species. I examined the role of geitonogamy in the seed production of D. maculata. I prevented geitonogamy in male-sterilization experiment by removing the pollinaria in the experiment group, and in hand-pollination experiment I conducted cross-fertilization and self-fertilization (in the form of both geitonogamy and autogamy). When the seeds had matured I calculated the relative seed capsule production in male-sterilization experiment, and estimated the proportions of embryonic seeds in both experiments. From this data I analyzed the differences in fertilization success and seed quality. The seed quality in both experiments was verified with in vitro germination of the seeds. I found that geitonogamy is not a significant reproduction strategy for D. maculata, because self-pollination is a disadvantage that reduces the seed set and the seed quality. One mechanism to prevent geitonogamy is pollinaria bending, a time delay before the freshly withdrawn pollinaria are able to conduct fertilization. In D. maculata this delay is approximately 50 s which is rather long for a deceptive species. The explanation for the high natural seed capsule production of D. maculata might be a fact that probably the species is not deceptive in all means. Longhorn beetles (Cerambycidae) were found to act as beetle pollinators in the study population. The beetles were found to bear large pollinaria loads of up to approximately 30 pollinaria.