Pollinarium size as a hybridisation barrier between sympatric inter-compatible orchids
B. C. Vieira A , L. M. Pansarin B , M. E. P. Martucci C , L. Gobbo-Neto C and E. R. Pansarin A DA Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras, Universidade de São Paulo, 14040-901, Ribeirão Preto, SP, Brazil.
B Departamento de Ecologia, Instituto de Biociências, Universidade de São Paulo, Rua do Matão, 321, trav. 14, 05508-900, São Paulo, SP, Brazil.
C Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Av. Do Café s/n°, 14040-903, Ribeirão Preto, SP, Brazil.
D Corresponding author. Email: epansarin@ffclrp.usp.br
Australian Journal of Botany 65(7) 497-506 https://doi.org/10.1071/BT17081
Submitted: 10 May 2017 Accepted: 18 August 2017 Published: 19 September 2017
Abstract
Hybridisation has been recorded for many different organisms, including plants, and is crucial in the diversification of Epidendrum, a neotropical orchid genus with ~1500 species. Based on the evidence of frequent natural hybridisation in Epidendrum and the absence of pre-mating barriers among the species, our main hypothesis was that pollen transfer is occurring between two sympatric species, Epidendrum secundum Jacq. and Epidendrum denticulatum Barb. Rodr. The reproduction of the species was investigated based on morpho-anatomical and histochemical analyses and intra- and interspecific crosses. Also, the relationship between co-occurring species was verified by floral morphometry, principal component analysis and sequence divergence analyses. Results showed that E. secundum and E. denticulatum are rewardless, self- and inter-compatible, and need a biotic vector for pollen transfer. Although there is inter-compatibility among the species, and E. secundum and E. denticulatum share the pollinators, our data showed no intermediary forms in either morphology or molecular data. All data collected suggest that, at least nowadays, no gene flow is occurring, and that hybridisation has been avoided due to the incompatible pollinarium size between the sympatric E. secundum and E. denticulatum, which acts as a pre-mating barrier in the studied population. This new discovery increases the knowledge about the isolation mechanisms and pre-pollination barriers in plants.
Additional keywords: Epidendroideae, floral biology, natural hybridisation, Orchidaceae, pre-mating barriers, reproductive biology.
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