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BEN # 179
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No. 179 November 28, 1997
aceska@freenet.victoria.bc.ca Victoria, B.C.
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Dr. A. Ceska, P.O.Box 8546, Victoria, B.C. Canada V8W 3S2
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EVOLUTION IN ACTION: FROM MUSHROOMS TO TRUFFLES? PART 3
From: Dr. Bryce Kendrick <mycolog@pacificcoast.net>
[Kendrick, B. 1994. Evolution in action: from mushrooms to
truffles. II McIlvainea 11 (2): 39-47.]
I have not mentioned all the sequestrate genera connected with
the families listed in Part 2: many of them are rare, or are
known only from the southern hemisphere. But I have given you
enough information to realize that the evolution of sequestrate
forms is a widespread phenomenon. And from what I have said
about the Russulaceae and the Boletaceae, it will be obvious
that more than one evolutionary pathway may evolve within a
single family, and perhaps even within a single genus.
One or two interesting questions arise from my survey. Why have
sequestrate forms evolved? The generally accepted explanation is
that during dry periods of the Earth's recent history some
mushrooms mutated in such a way as to remain closed, and lose
their spore-shooting mechanism. This gave these lines a selec-
tive advantage over those which exposed their gills to the hot,
dry air. It is easier to maintain an appropriate level of
humidity for spore development inside a closed fruit body. The
next step, of remaining underground, is another way of escaping
drought. Of course, once the spores are retained inside the
fruit body, or kept underground, the problem of dispersal
arises. In many cases, this has been solved by involving small
mammals as vectors. That means evolving mechanisms for attract-
ing these mammals and getting them to dig up or eat the fruit
bodies. So one kind of adaptive change is complicated by the
need for other adaptations. But that is what evolution is all
about, and any organism that survives and propagates itself has
obviously hit on a successful, or at least a functional, com-
bination.
It is less easy to explain the geographic distribution of these
sequestrate and hypogeous forms, since they appear to be con-
centrated in such areas as western North America, parts of South
America, New Zealand and Australia, and to be relatively few in
number in other areas such as eastern North America and northern
Europe.
No sequestrate fungi have yet been connected with two agaric
families, the Hygrophoraceae and the Pluteaceae. Do such fungi
exist, and have we simply not seen or recognized them? And
although the Tricholomataceae is a very large and diverse family
of agarics, a sequestrate derivative (Hydnangium) is known only
for Laccaria. Why have none of the other more than 30 widely
recognized and often very common genera in this family produced
sequestrate offshoots? Or have we simply not yet found them, or
recognized them for what they are?
In most cases, the sequestrate forms are much less common than
their spore-shooting ancestors (though this is not true of
Rhizopogon). Is this scarcity more apparent than real because
they are more difficult to find, since many of them grow below-
ground? Does it indicate that most of these fungi are no more
than rather unsuccessful evolutionary experiments, on their way
to extinction? Or have they arisen so recently that they have
not yet had time to spread very far?
How long ago did the oldest, and the youngest, of these fungi
arise? This question, at least, we may attempt to solve by means
of our newly acquired molecular techniques, which can measure
the amount, and the rate, of change in the genetic material.
Could sequestrate forms be appearing regularly, even now? Are
the changes taking place gradually, as the necessary mutations
slowly accumulate in mushrooms. Or do they appear suddenly and
sporadically as a result of what is called "punctuated" evolu-
tion, involving larger jumps during periods of great environmen-
tal stress?
Why has all this happened? Is it the new trend among mushrooms?
Will all mushrooms eventually become sequestrate? Will our
descendants have to dig if they want to see the fall flush of
fleshy fungi, or fill their cooking pots with boletes and other
fine edibles? Only, I suspect, if the greenhouse effect goes all
the way and our climate becomes much drier and hotter than it is
now. But we'll have to wait and see.
We are not yet in a position to answer all of those questions,
but at least we know know that there is a wide range of such
fungi out there. There is a message here for the amateur: Don't
just throw away those aberrant closed or distorted or partly
hypogeous agarics. Cut them open to see if their gills are
normal vertical plates, and check them to see whether they can
be persuaded to yield a spore print. If the answer to both of
the above is no, then you may very well have a sequestrate
fungus on your hands. One of the professional agaricologists in
your area should be able to check this. If it is indeed one of
these most recently evolved taxa, you may congratulate yourself
on your sharp eyes, and science may thank you for one more piece
of the evidence we need to unravel this great jigsaw puzzle.
Acknowledgments: I would like to acknowledge stimulating discus-
sions with Drs. Jim Trappe, Michael Castellano, Neale Bougher
and Harry Thiers.
Readers who wish to explore the "sequestrate" agarics further
should consult the publications listed below.
Beaton, G., D.N. Pegler & T.W.K. Young. 1985. Gastroid
Basidiomycota of Victoria State, Australia 5-7 Kew Bull. 40:
573-598.
Bruns, T.D., R. Fogel, T.J. White and J.D. Palmer. 1989. Ac-
celerated evolution of a false-truffle from a mushroom ances-
tor. Nature 339: 140-142.
Dring, D.M. and D.N. Pegler. 1977. New and noteworthy gasteroid
relatives of the Agaricales from tropical Africa. Kew Bull.
32: 563-569.
Horak, E. 1973. Fungi Agaricini Novazelandiae I-V. Beihefte zur
Nova Hedwigia, Heft 43. Cramer, Lehre.
Kendrick, B. 1992. The Fifth Kingdom. 2nd Edition. Mycologue
Publications, 8727 Lochside Dr., Sidney, BC V8L 1M8, Canada.
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