The wild array of anatomical variety in fungi – from the thread‑like tangles of some mould species to colourful mushrooms with dazzling caps – has its roots in two distinct bursts of evolution hundreds of millions of years ago. These big jumps in variation seem to be linked to evolutionary boosts in the number of traits that make up each species, known as an organism’s complexity.
Detailed analyses of anatomical complexity are limited, says , who is now at the University of Oxford. “They’ve pretty much exclusively been done on the animal kingdom,” he says. Smith and at the University of Bristol, UK, analysed patterns of anatomical variation – known as disparity – in fungi, the closest kingdom-sized branch to animals on the tree of life.
The pair created a data set based on more than 300 physical traits at cellular and multicellular scales from 44 species across the fungi kingdom. They then compared the evolutionary relationships between the species with how their physical features were related to each other, and used computer simulations to recreate how disparity in fungi changed over millions of years.
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They found four major fungi groups that have similar cellular features. These include the flagellated group, which have sperm-like cells, and the zygomycetous fungi, which produce spores from the fusion of two sex cells. Then there are sac‑bearing and club-bearing fungi, to which the grand diversity of fruiting bodies – such as mushrooms – belong.
This variation didn’t develop all at once, or continuously over the past billion or so years of fungus evolution, but seems to have occurred in two distinct bursts associated with jumps in multicellular complexity.
The first occurred roughly 800 million years ago, when the first multicellular body plans in fungi evolved from flagellated ancestors. Then, between about 500 million and 300 million years ago, a series of spikes in new variation arose when the strange shapes of fruiting bodies came into their own.
“The evolution of multicellularity seems to be opening the door to greater morphological variety for fungi,” says Smith.
Surprisingly, says Smith, there doesn’t seem to be a link between expansions of the fungal genome – the set of genetic instructions – and shifts in anatomical variation. “You’d expect more molecular diversity to beget morphological diversity,” he says.
The researchers also found key similarities between the evolutionary paths of fungi and animals.
“Like we’ve seen with the animal kingdom, the distribution of fungal disparities is quite clumpy,” says Smith.
Plotting a “morphospace” for fungi, which shows species as dots that are closer together the more similar they are in physical anatomy, the researchers found that the major groups of fungi cluster as four distinct islands without overlapping.
Between the clusters is empty morphospace that might once have been filled by now-extinct species. “Maybe the picture was once more complete,” says Smith. “Maybe it was more of a splat [shape] rather than a couple of drops in an ocean of morphological possibility.”
One potential next step, says Smith, is applying these analyses to plants to see if any patterns are shared.
(Nature Ecology &Â Evolution
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