BEN # 179

Adolf Ceska aceska at CUE.BC.CA
Fri Nov 28 03:35:17 EST 1997


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No. 179                              November 28, 1997

aceska at 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 at 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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