Liaisons of Life by Tom Wakeford, Wiley, 拢17.95, ISBN 0471399728
IN Liaisons of Life Tom Wakeford sets out to put right the injustices rained
down upon microbes. For most of us, mention of bacteria, fungi and the
single-celled organisms called protists conjures up bad experiences with airline
food and nasty infections.
Wakeford blames Louis Pasteur for this: it was Pasteur who discovered the
role of microbes in infection and disease, and it was he who renamed bacteria
鈥済erms鈥�. What chance have microbes had of retrieving their good name in face of
such dreadful publicity?
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Wakeford pegs the rehabilitation of the bacteria, fungi and protists to their
role as prodigious evolutionary innovators. Indeed, the theme of Liaisons is
that microbes make possible many of the most important associations in
nature鈥攕ymbiosis, for example. These associations have far-reaching
ecological, economic and evolutionary effects. Anyone interested in how such
small players could have had such large effects will find a ready set of
explanations in this book.
Take orchids, for example. They have 鈥減athetically small鈥� root systems,
incapable of nourishing the plant on their own. Thankfully, orchids survive
through a symbiotic relationship with a root fungus, whose large foraging web
gathers nutrients that the plant can use. In turn, the fungus gleans nutrients
from the orchid. Networks like these may operate in more than 90 per cent of
plant species, so enhancing plants鈥� abilities to glean nutrients from poor soils
that they can change entire ecosystems鈥攁nd not always for the better.
Fescue is a daunting example of the sort of evolutionary innovation that
Wakeford sees as highly influential to the course of evolution. A vigorous
grass, fescue has spread across 35 million hectares of the US and now dominates
much of its prairie land. Cattle find it unpalatable, but when farmers try to
grow other grasses, fescue quickly returns. Huge swathes of prairie are now
unfit for grazing.
It鈥檚 all down to the Acremonium fungus, which grows in the spaces between the
cells of fescue leaves, and it鈥檚 the fungus that confers resistance to drought
and enhanced vigour. Acremonium happily uses fescue (with few complaints from
the grass) as a vehicle for its own reproduction. Plants infected with the
fungus produce a larger than usual number of seeds. Acremonium also produces a
toxic alkaloid that repels cattle and plant-eating insects.
Microbial associations extend far beyond the plants. Many bacteria are
bioluminescent, and deep-sea fish have domesticated these organisms to build
light-emitting organs. Even mitochondria, the energy factories on which
multicellular plants and animals depend, are thought to be ancient bacterial
symbionts that took up residence in our cells.
With so many intriguing stories, Wakeford can be forgiven for occasionally
slipping into a sort of reverie. Passages like 鈥渟taying alive is as much about
bonding with your neighbours as it is about growing and reproducing鈥�, or
鈥渂eneath every garden lawn lies a fungal energy network, one more powerful than
a nationwide energy grid鈥� may lose sight of microbes as selfish players, like
any others, in the game of evolution.
But what deeper evolutionary insights emerge from this analysis? Are microbes
indispensable players in evolution or just convenient contributors? Microbes鈥�
rapid reproductive rates and large populations provide a steady supply of forms
for other species to exploit and to be exploited by. The key question for
Wakeford鈥檚 analysis is whether life on Earth would be substantially different
without the microbes.
At one level, yes. But at another, natural selection鈥檚 own innovativeness
should not be underplayed. Take those delicate orchids as a case in point.
Without microbes to help them out, it is at least plausible that they would have
developed larger and more capable root systems, as other plants have. We would
indeed be poorer without orchids, but I think we would have them even without
microbes to help out.