The evolutionary trajectory of life here on Earth has, for the most part, followed a clear trend. From simple, single celled organisms, to more complex multicellular morphologies, it seems like given enough time, biological forms become more and more complex. A great example of this increasing complexity starts to take form when we look at the three basal groups of the animal kingdom. The Phyla that represent the base of the animal tree of relatedness are the Porifera, (sponges) Cnidaria, (jellyfish, corals, anemones, and hydra) and the Ctenophora, (comb jellies). For decades, the sponges have been thought to represent the most ancestral condition. They have multicellularity, but no true tissues. There’s little evidence to show that cells within a poriferan body communicate and work together. Instead, these uncoordinated cells respond to stimuli. In the next step up in complexity, the Cnidaria and Ctenophora have true tissues connected by a nerve net. These cells are coordinated and function as a unit instead of simply responding to stimuli.
Sometimes, this trajectory of increased complexity is not by followed Earth’s organisms. This is not a cardinal rule species must follow. Evolving more complex body structures and physiology has enhanced species fitness since the dawn of time, but other times, simplifying biological structures has offered a fitness reward. This is where our fungus featured in today’s Fungi Friday comes in. Everybody, I’d like you to meet Henningsomyces candidus. Henningsomyces candidus, everybody.
Henningsomyces candidus is a type of cyphelloid fungus; a superficial name given to species that have this similar, simplified body plan. They are small saprotrophs they fly well under the radar. Most of them fruit beneath decaying logs, so unless if you are a log flipper, I doubt you will ever find these awesome inconspicuous fungi. These cyphelloid fungi are tube or cup shaped and are usually under 10 millimeters across. Henningsomyces candidus along with other cyphelloid fungi look like they should belong to the Ascomycota, but genomic analysis has shown that this group of fungi belong in the Basidiomycota.
More recent molecular research carried out by Bodensteiner et al. in 2004 analyzed the phylogenetic relationships of cyphelloid fungi using over 70 samples of these small fungi from around the world. This research confirmed yet again that all of these cyphelloid fungi do indeed have basidiomycete ancestry. These simple and small saprophytes evolved from larger more complex gilled mushrooms, boletes, polypores, and puffballs. Additionally, this same paper has revealed that over millions of years of fungal evolution, this evolutionary reduction has occurred independently 10-12 separate times.
There are actually a handful of species to go through an evolutionary reduction, to then become more complex again. It has been proposed that the beefsteak fungus, (Fistulina hepatica) has done exactly that. If you look closely at the spore producing tubes in a cross section of a Fistulina hepatica fruit body, those tubes look remarkable similar to individual cyphelloid body structures. Over evolutionary time scales, these independent cyphelloid fruit bodies fused together resulting in the genesis of the rather common beefsteak fungus. I call it evolutionary re-complexity, and is most likely the case for the splitgill (Schizophyllum commune) as well as certain Marasmius species.
The independent evolution of anatomically simple organisms from larger, more complex ancestors shows us that complexity is not a measurement of success. Just think back to the sponges in the first paragraph; although they show up in the fossil record nearly 3.5 billion years ago, they are still thriving in today’s oceans. The Porifera have never evolved a nerve network that coordinates largescale physiological functions. Instead individual cells respond to stimuli. In some cases, more complex forms and functions do arise only for certain decedents to revert back to more simplified forms. This evolutionary reduction has shown to be a fruitful adaptation for these cyphelloid fungi. Henningsomyces candidus is quite capable of carrying out its life cycle with this almost primitive looking morphology. And its fitness is remarkable. If you look at the species distribution, it’s found in nearly every corner of the world. It certainly must be doing something right.