| 要旨トップ | 目次 | | 日本生態学会第73回全国大会 (2026年3月、京都) 講演要旨 ESJ73 Abstract

一般講演（口頭発表） J01-14 （Oral presentation）

#### Shifting mycorrhizal partner from Tulasnella to Ceratobasidium is coupled with the gain of crassulacean acid metabolism (CAM) in epiphytic orchids【E】

*Galih Chersy PUJASATRIA, Akira YAMAWO（Kyoto University）

In epiphytic orchids, crassulacean acid metabolism (CAM) is an important adaptation to water-limited arboreal environments, providing protections to drought and maintaining effective carbon fixation from atmosphere. Also, mycorrhizal fungi are vital mutualists that support orchid carbon supply uptake from substrate. Given that 1) CAM is unique to epiphytic orchids and 2) epiphytic orchids associate with mycorrhizal Tulasnella and Ceratobasidium, it remains unclear whether these traits evolved independently or coordinatively as an adaptation mechanism. In this study, we applied phylogenetic frameworks to test for correlated evolution and speciation between these traits, investigating whether their synergy provides the flexibility necessary to drive the high species diversity in epiphytic orchids. We recorded 1100 epiphytic orchid species with their CAM status and the most compatible mycorrhizal fungus. It was found that C3 orchid species are more likely to associate with Tulasnella while CAM orchids evolved to associate with Ceratobasidium. Surprisingly, diversification dynamics are most likely to be driven by other unobserved states rather than CAM evolution and mycorrhizal compatibility. For example, overall diversification is strongly driven by Paleogene global cooling but not atmospheric CO2 decline. The effects of these paleoclimatic changes also vary among major orchid lineages, e.g. depending on their respective traits. These findings suggest that physiological innovations may not necessarily provide a more effective template for diversification in epiphytic orchids.

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