Theseus' paradox lichen: how the surprising union between a fungus and an alga raises questions about the nature of identity

Very well-written and informative article on the nature of lichens (including a parasitic lichen!) in Bay Nature on the nature of lichens and the questions they raise on the nature of an 'organism' beyond ordinary lichens, article quoted below.

"And because it’s lichen we’re talking about, there’s one more complicating factor. Some mycobionts—that’s the fungus part of the lichen—are just badly behaved. Take Diploschistes muscorum, for instance: It’s a parasitic lichen, and it starts its development on a Cladonia lichen, gradually replacing Cladonia filaments by growing over them and sucking energy from their algal partner, Trebouxia irregularis. At some point, though, the takeover is complete and Trebouxia irregularis is replaced by our Diploschistes’s preferred algal partner, Trebouxia showmannii. At that point, Diploschistes leaves off with the parasitism and behaves like any other lichen...this is the lichen world’s version of Theseus’s paradox: Is an object that has had every part removed and replaced—as happened with the rotting boards of Theseus’s ship, per Plutarch—the same object?"

Article link: https://baynature.org/article/identifying-with-lichen/

Parasitic lichen and preferred algal partner
Diploschistes muscorum--https://www.inaturalist.org/taxa/124441-Diploschistes-muscorum
Trebouxia showmannii (no species page)--https://www.inaturalist.org/taxa/55163-Trebouxia

Host lichen and algal partner
Cladonia--https://www.inaturalist.org/taxa/49490-Cladonia
Trebouxia irregularis--https://www.inaturalist.org/taxa/996197-Trebouxia-irregularis

Posted on December 16, 2020 03:16 AM by yerbasanta