The many faces of Cora lichens. Credit: Lucking et al, 2014. PNAS.
The many faces of Cora lichens. Credit: Lucking et al, 2014. PNAS.

One Lichen Species Is Actually 126, And Probably More

One of the best ways of finding new species is to sequence the genes of existing ones. Often, scientists discover genetically distinct populations that count as species in their own right, hiding in plain sight. So, the African elephant turns out to be two genetically distinct groups of African elephants. A skipper butterfly  is actually ten skipper butterflies. There are two Nile crocodiles, and possibly four killer whales. Time and again, scientists have peered at a creature’s DNA and discovered that one species is actually two, or three, or a dozen.

Or perhaps hundreds.

Until ten years ago, scientists talked about the lichen Dictyonema glabratum as if it were a single species. Its large, conspicuous, and elegant fronds are found throughout the Americas, and many teams have studied its chemistry and ecology. But until Robert Lücking from the Field Museum started looking at its genes, no one realised the most startling truth about D.glabratum: it’s actually 126 different species of lichen, and possibly hundreds more.

It’s “the most spectacular case of unrecognized species richness” in any group of large organisms, says Lücking.

Lichens are fungi that form alliances with either an alga or a bacterium. The fungus captures water and minerals, while its partner makes food by harvesting the sun’s energy. This partnership is clearly a successful one: the beautiful bushes, fronds and pixie cups of lichens are found on every continent, including Antarctica, and there are some 18,000 known species.

D.glabratum was apparently one of them. The late Estonian fungus specialist Erast Parmasto described it in 1978 but Lücking’s team have been slowly chipping away at this single identity since 2004. When they discovered a second distinct lichen in Costa Rica, one species became two. When they compared the genes of a small number of specimens in 2013, two species became 16.

Now, the team, including graduate student Manuela Dal-Forno, has finished analysing 356 samples collected throughout Central and South America—more than ten times the number from their earlier study. And with that, 16 species became 126, which the team are classifying under two new groups: Cora and Corella.

The weird thing is that many of these species aren’t hidden ones. Unlike the African elephants or Nile crocodiles, where genetically distinct populations look very similar, these lichens have striking differences. Some are a soothing turquoise blue, others a ghostly white. Some grow on rocks, others on trees and shrubs. Some have distinctive features, like fine hairs or crinkled margins. They’re so different that it really shouldn’t have taken a genetic analysis to tell them apart.

The problem is that you can only see this glorious diversity by studying the lichens in the wild—and most scientists had worked with specimens that were dried and stored in herbariums. Take them out of their natural setting, and important ecological cues vanish. Dry them out, and their stunning palette collapses into a few boring hues. Lücking’s team escaped this trap by snapping a high-resolution photo of every lichen that they took a sample from. “We were absolutely stunned by the result,” he says.

Lücking also suspects that many lichenologists were also hamstrung by a weird circular logic. Lichens can look very different depending on where and how they grow, so a single species can take on many guises. That made it easier to believe that very different specimens were actually the same lichen, or that very big specimens were simply older versions of smaller ones. Only DNA could shatter that unity, and it’s not finished yet.

The team divided North and South America into a grid, and showed that 101 of their 126 species were found in just one square. This suggests that D.glabratum isn’t a continent-spanning lichen, but hundreds of incredibly localised ones. And all of these came from just 20 of the 209 squares, implying that there are probably many more Cora and Corella lichens left to discover in other parts of the Americas.

How many more? The team tried to predict a number by accounting for how many species they know about in different habitats, how widespread each species is, and how thoroughly they sampled each part of the Americas. They ended up with an estimate of 452 of these lichens in total—“an unthinkably dramatic increase from a single species”.

“This work beautifully illustrates how little we know about the numbers of fungi on Earth,” says Anne Pringle from Harvard University, who studies lichens. “I’m struck by the beauty of the lichens illustrated in the paper, and wonder if local peoples knew these species already, even though they aren’t described within the formal scientific literature.”

“We have already identified other groups of macrolichens that likely will show similar patterns of unrecognized species—at least double the number of species, if not more,” says Lücking. “For taxonomy it means there is a huge amount of work left and nothing can be taken for granted.”

Most of these species live in paramos—small habitats in the Andes Mountains, above the forests but below the snow. In these cool worlds, the lichens control the amount of water and nutrients in the soil, setting stable foundations for food webs that include Andean condors, spectacled bears, and a unique range of fast-evolving plants.

“These ecosystems are highly threatened and have disappeared to a large extent,” says Lücking. “Each paramo that disappears takes unique species down with it. Previously, it was believed that all paramos were similar, so their genetic diversity could be conserved by conserving just a few fragments. But now we know that this is not the case.”

“Lichens are ecosystems, housing myriad other organisms within a thallus (or body), including other fungi and bacteria.” adds Pringle.  “If we lose one of these lichens, I wonder what else we might lose?”

Reference: Lücking, Dal-Forno, Sikaroodi, Gillevet, Bungartz, Moncada, Yanez-Ayabaca, Chaves, Coca, Lawrey. 2014. A single macrolichen constitutes hundreds of unrecognized species. PNAS