Abstract
Florivores and rainfall generally have negative impacts on plant fecundity. However, in some cases, they can mediate fruit set. Some plants face severe pollen-limited fecundity and any additional fruit set, even if from self-pollination, can be advantageous. This is the case in some tropical deceptive orchids, such as the threatened Cyrtopodium hatschbachii. Here we test the hypothesis that florivory of the anther cap would facilitate rain-assisted autogamy in this species. In the field, we followed flowers in which the anther cap was removed by the orthopteran Stenopola sp. and found cases where pollinia self-deposited after rainfall and in one case this resulted in swelling of the column typical of fruit development. This event comprised 33% of all fruit set in the population in 2019. We then experimentally varied anther cap removal and rainfall in a factorial design and found increased fruit set in the group with cap removal (simulated florivory) followed by rain. The water absorption by pollinia makes them heavier, causing the stipe to bend. The droplet of water on the stigma then shrinks and pulls the pollinia back onto the stigma, causing self-pollination. Seeds from self-pollination have considerable viability and may allow population persistence, given that bee-mediated cross-pollination is uncertain and even absent in some years. Our study provides a unique example of how two unrelated factors (i.e., florivory and rain) that are detrimental alone may together promote fruit set.
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Acknowledgements
We are grateful to Hamilton Kikuti for allowing us to use the greenhouse, to Kátia Matiotti for the identification of the florivore, to Ana Silvia F. P. Moreira for lending us the microbalance, to Uiara C. Rezende for assistance in the greenhouse and Bruno Mamede and Vitor Mamede for assistance in the field.
Funding
J.C.F.C. was supported by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) with a PhD grant; S.D.J. by the South African Research Chairs Programme (NRF grant 46372) and P.E.O. by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).
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Cardoso, J.C.F., Johnson, S.D., Maciel, A.A. et al. Florivory can facilitate rain-assisted autogamy in a deceptive tropical orchid. Sci Nat 108, 39 (2021). https://doi.org/10.1007/s00114-021-01752-y
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DOI: https://doi.org/10.1007/s00114-021-01752-y