The Mushroom at the End of the World: On the Possibility of Life in Capitalist Ruins (33 page)

One down for the long-distance travel of spores. But other possibilities have just become more thrilling. How then do kinds travel?

Dr. Chapela, working with his colleague Dr. Garbelotto, has a story to tell about matsutake’s travel.
¹⁰
The Eocene ancestral population, he argues, developed in North America’s Pacific Northwest, where
T. magnivelare
continues to associate with both broadleafs and conifers, in resonance with that broadleaf-loving ancestor. The rest of the matsutake group jumped to conifers and has followed conifer forests ever after around the northern hemisphere. When conifers retreated into refugia, matsutake followed, especially with pine. Wherever the pine forest went, matsutake went too. Migrating across the Bering Straits, matsutake colonized Asia, and then Europe. The Mediterranean Sea blocked gene exchange between southern Europe and North Africa; populations on each side are independent extensions of the vast Eurasian trek. Meanwhile, Chapela and Garbelotto imagine that southeastern North America was colonized by matsutake from the rich pine-oak refugia in Mexico.

Their story was shocking, in part, because at the time they published, most people thought of matsutake as an “Asian” species complex. After all, only Japanese and Koreans loved matsutake—and thought of it as their own. How could it be a North American mushroom that came late to Asia—even if millions of years ago? (Chapela and Garbelotto date the separation of
T. magnivelare
and other matsutake as having occurred 28 million years ago, with the rise of the Rocky Mountains.) Indeed, not everyone agrees with the story they tell; this is an open-ended field. Dr. Yamanaka of the Kyoto Mycological Institute argues for a Himalayan origin for matsutake.
¹¹
Many new species came into being with the rise of the Himalayas, which forcefully threw old kinds into new environments, stimulating difference. At the time of Chapela and Garbelotto’s research, the evidence of host differentiation among matsutake in southwest China was not readily available, at least in California. It turns out that Chinese matsutake associate not just with conifers but with
Quercus
as well as
Castanopsis
and
Lithocarpus
, which find their center of species diversity in the Himalayas. (Dr. Yamanaka reminds me that the major broadleaf host of North America’s
T. magnivelare
is tanoak, the only non-Asian
Lithocarpus
.
¹²
Might this be
a clue?) Dr. Yamanaka found matsutake shiro in China associating with both conifer and broadleaf hosts. He argues for Himalayan origins, based in part on the sheer variety of mycorrhizal arrangements in that area. Diversity is often a sign of time in place.

Yet even newer research has shown that southwest China’s matsutake are not particularly genetically diverse, at least in the ITS region most commonly sequenced by researchers. They are a whole lot less diverse than Japanese matsutake, which everyone agrees to be latecomers on the evolutionary scene. But this does not mean they are a newer population. Jianping Xu of Canada’s McMaster University suggests that Chinese matsutake just fill up more of the available space than in Japan.
¹³
This “saturation,” he points out, can lead to longer-living clones with less genetic competition. The stress of industrial pollution might also lead to genetic competition in Japan. Southwest China is far less industrialized. Diversity is not just about time in place.

Dr. Xu brings back the question of spores. “Many mushroom species are widespread. They are opportunistic; whenever there is food they can survive. Dispersal is not such a significant barrier for most of them.” He brings up the “panspermia” hypothesis, which posits that spores are everywhere, traveling even in outer space. “For most microbial species, you can find them everywhere. Dispersal is not the barrier. It’s whether they are able to survive in those environments.” He jokes, “It’s like Chinese now, they are everywhere. If there are business opportunities, you are probably going to find Chinese; if there’s a small town, you’ll probably find a Chinese restaurant.” We laugh together. He talks of how well spores are dispersed. “For many species, there are limited genetic differences among populations from very different geographic areas.” One example is the bacteria in our mouths: he says that the bacteria in the mouths of middle-class urban Chinese are vastly different from those of their peasant neighbors—but just the same as the bacteria of North Americans on a similar diet. It is the environment, not the location, that matters. For many fungi, too, he confirms, “dispersal is not the problem—especially since humans emerged.”

There’s a new thought. Humans?

Dr. Xu is not the only one who thinks that human trade and travel have dispersed fungal spores. Dr. Moncalvo finds that very significant, although he disagrees with the idea that spore clouds are everywhere.
(“Mushroom populations are restricted and well defined. The same morphology on two different continents is usually separated by genetic distance.”) There is exchange through spores, he argues, but it is occasional, not constant. But “exchange may be much more common now because there is more trade and more travel.” For example,
Amanita muscaria
was transferred to New Zealand in the 1950s and is now spreading. It is not even out of the question that matsutake spread across the Atlantic with human contact. “There are a lot of Scots pines here. [Scots pine is a major north Eurasian matsutake host, but it is not native to the New World.] Canadians, they still have the Queen on the coin, right? So they think the pine seedlings that are coming from Her Majesty’s garden must be better quality than native pine.” He shakes his head in mock horror, but it is a serious point. Perhaps matsutake traveled to eastern Canada on the roots of pine seedlings. Dr. Moncalvo does not dismiss the possibility of spread without humans, but he does think the spread must be recent, because eastern North American matsutake are so very similar to Eurasian ones. And, he adds, shocking me: who knows which way the spread went? “Especially if we find the two species [western America’s
T. magnivelare
and cosmopolitan
T. matsutake
] coexisting in Central America and possibly in the southern Appalachians, that might be the origin. One [
T. magnivelare
] has been stuck on the west coast, the other [
T. matsutake
] has moved. That is something a phylogenetic study should be able to tell.”

“How might both species have come to Mexico?” I ask. “It was a southern refugia during the glaciation,” he explains. “It’s a well-known phenomenon. The southern limit of oaks and pine are the mountains in Central America. You don’t find them in South America. And you find them with altitude: When it gets cold, everything moves south. When it gets warm again, they move up to a higher altitude. Three thousand meters in Mexico is like sea level here. This can also explain some shuffling. Populations will grow back from local refugia, but they are not salmon, swimming back to the stream in which they were born. There is no reason that one goes one way or the other way. It’s the ecosystem that moves; it’s not the fungus that moves.”

It’s the ecosystem that moves: No wonder humans move so many other species without meaning to; we create new ecosystems all the time. And it’s not just humans that change things
.

“I rather think it can sometimes be events,” Dr. Moncalvo explains to my repeated questions about how kinds spread. “That’s something that many people cannot grasp. The time frame is huge. The tectonic separation between the southern and the northern hemisphere is 100 million years. So we find different species in the southern hemisphere and the northern hemisphere. Australia is a great example. So people say, ‘Oh, they separated 100 million years ago.’ But it’s not true. Now that we have molecular data, we see it’s incorrect in most cases. They are isolated, but there is sometimes transfer. But the transfer is not all the time, so we don’t have something homogeneous. There could be one transfer per million years, or per ten million years. That transfer could be anything; it could be a tsunami wave, starting from the Philippines and crossing the equator—they don’t usually cross the equator, but in 100 million years—and carried on the top of the wave, some soil and some wood with some animals hanging. It could also be wind. It could be anything.” Once mycologists thought that southern and northern hemisphere mushrooms had been isolated for 100 million years, but DNA sequences now show that this could not possibly be true. For
Amanita
, for example, there are many groups with north-south ties, rather than just a single hemispheric dichotomy. Assumptions about slow and constant mutations in place are being displaced by attention to unusual events, indeterminate encounters.

How do kinds emerge, then, in local populations?

Dr. Xu explains it: Scale matters. One cannot use the same tools to study cross-continental and local diversity. The ITS region of fungal DNA is fine for studying big blocks of regional difference, but it is useless to study local populations. There, a completely different clump of DNA is needed to judge the variations that separate one group from another. Dr. Xu has found that single nucleotide polymorphisms (SNP) are good for population-level differentiations.
¹⁴
With this tool, he studied matsutake populations in China, finding little genetic difference between oak- and pine-loving matsutake but a significant geographic separation across sampled regions. Most important, perhaps, this separation added evidence that sexual reproduction is important in matsutake populations.
Spores rise again
.

In the world of fungi this is not at all self-evident. Fungi propagate through many mechanisms, and sexual reproduction through the mat
ing of germinated spores is just one. A good deal of fungal propagation is clonal; some clones—including those of the famous Armillaria root rot—are large and very, very old. Fungi also propagate through asexual spores, which are produced in times of stress; with their thick walls, they withstand hard times to germinate when better conditions return. For some species, sexual reproduction is absent or rare. For matsutake, however, the evidence suggests that sexual spores are important. This is investigated by examining the genetic composition of clonal patches: Are they mutating independently or exchanging genetic materials? For example, do you find more genetic diversity in older forests rather than in younger ones, where you would expect a “founder effect” rather than free spore dispersal? For matsutake, the answer to this last question is yes; spores appear to be exchanged among patches of mycelial growth.
¹⁵
However, landscape features can block the exchange of spores; researchers found that ridges, for example, block genetic exchange among matsutake populations.
¹⁶

This seems familiar enough—but don’t relax. Matsutake does something strange and wonderful that can turn your idea of sexual reproduction upside down.
It was another meal—tea this time, in Tsukuba City, with Hitoshi Murata of the Forestry and Forest Products Research Institute and Matsutake Worlds team member Lieba Faier.
¹⁷
I was so excited when I understood that I spilled tea all over my tray
. Dr. Murata had been studying the genetics of matsutake populations. It was a painstaking process, since matsutake is not an easy research subject. Figuring out how to get spores to germinate was itself a problem; they germinated, he found, in the presence of other matsutake parts, for example, mushroom gills. This suggested that spores might germinate best on living shiros, that is, mycelial mats, including that of the parental body that gave rise to the mushroom.
¹⁸
And what happened then, when they germinated? This is where his research revealed something wondrous. Matsutake spores are haploid, that is, bearing only one series of chromosomes, rather than paired sets. We might expect them to mate with other haploid spores, thus making full pairs; they do. Human eggs and sperm join that way. But matsutake spores are capable of something else. They can join with body cells that already have chromosomal pairs. This is called “di-mon” mating, from the prefixes for “two”—the number of chromosome copies in fungal body cells—and “one”—the number in the germinating spore.
¹⁹
It’s as if I decided to mate with (not clone) my own arm: how queer
.

The spore brings new genetic material into the shiro, even if it is the shiro’s offspring, because the shiro itself is a mosaic, a combination of multiple genomes. Even emerging from the same shiro, different mushrooms might have different genomes. Even emerging on the same mushroom, different spores might have different genomes. The genetic apparatus of the fungus is open-ended, able to add new material. This adds to its ability to adapt to environmental shifts and to mend internal damage. Evolution in one body: the fungus can discard less competitive genomes to pick up others. Diversity emerges right there inside the patch.
²⁰

Dr. Murata explains that he was able to ask these questions because of his unusual background for a mycologist: He was originally trained in bacteriology. Most mycologists come from botany, where they see one organism at a time, or ecology, where they see interactions across organisms. But bacteria are too small to care about one at a time; we know them in patterns and masses. As a bacteriologist, he knew about “quorum sensing,” the ability of each bacterium to chemically sense the presence of others and to behave differently en masse. From his very first studies of fungi he found quorum sensing there: in fungal mosaics, each cell line can sense the others, forming mushrooms in unison. By examining fungi differently, a new object came into sight: the genetically diverse fungal body, the mosaic.

Mushrooms with genetically diverse spores! Mosaic bodies! Chemical sensing that creates communal effects! How strange and wonderful the world
.

I struggle: Isn’t it time to come back to patches, incompatible scales, and the importance of history? Shouldn’t I return to multiple rhythms, the tempos through which patches emerge in both landscape and science? But how happy it feels to fly with spores and to experience cosmopolitan excess. For the moment, the reader must make do with hasty conclusions: