What are the consequences of water stress on the development of late postzygotic reproductive isolation in an orchid hybrid zone?
ID: 613 / 331
Proposed Symposium Title: What are the consequences of water stress on the development of late postzygotic reproductive isolation in an orchid hybrid zone?
Karolyne Wanessa de Jesus1, Bárbara Simões Santos Leal1,2, Rafael Silva Oliveira1, Matheus Pena Passos1, Juliana Lischka Sampaio Mayer1, Fabio Pinheiro1
Affiliations: 1 Universidade Estadual de Campinas, Instituto de Biologia, Departamento de Biologia Vegetal, Campinas – SP, Brazil 2 Instituto Tecnológico Vale, Belém – PA, Brazil
Studies on reproductive isolation (RI) in angiosperms often focus on early postzygotic barriers, whereas research on established generations of hybrids and their ecological interactions is still limited. Several hybrid zones have been studied in the orchid genus Epidendrum, which is often found in extreme environments such as rock outcrops and sand dunes. This study aimed to compare the morphophysiological performance of E. × purpureum with its parental species, E. orchidiflorum and E. denticulatum, under water deficit conditions. The experiment consisted of one control (plants watered three times a week) and two water treatments per species (moderate stress: plants watered approximately every 25 days; severe stress: plants that did not receive water during the entire experimental period). To investigate the effects of water deficit on the parental species and hybrids, the following measurements were taken along the experiment: growth, water potential, succulence, titratable acidity, membrane resistance, and survival. Both growth, water potential, and succulence were not significantly changed across treatments. On the other hand, significant changes were observed in the titratable acidity, indicating changes in the CAM metabolism. Additionally, a significantly lower survival rate of hybrid plants was observed, with all hybrids dying at the end of the experiment. Membrane resistance was also lower in the hybrids, increasing the electrolytes leakage and decreasing the potential for water storage. The significant vulnerability of hybrids to water stress conditions can be interpreted as strong late postzygotic barriers, which limit the distribution and survival of hybrid plants. Such barriers may increase in scenarios of climate change predicting aridification of some regions, decreasing the potential for heterospecific gene exchange between co-occurring species. As heterospecific gene exchange is considered an important source of genetic variation, the vulnerability of hybrid plants may have a long-term effect also on parental species.