Scott Lyell Gardner - Parasites: The Inside Story

PARASITES THE INSIDE STORY

PARASITES THE INSIDE STORY

SCOTT L. GARDNER
JUDY DIAMOND
GABOR RACZ

ILLUSTRATED BY BRENDA LEE

Princeton University Press

Princeton and Oxford

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ISBN 978-0-691-20687-5

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For Hadasa, Zsombor, Teal, Hudson, Grant, and Clark

1. ix
2. xiii
3. xvii

These color plates follow page 110.

Human beings evolved as part of the global ecosystemas one of the millions of species that it comprisesand we depend on it completely for our continued existence. Over the past five centuries, however, our numbers have grown from an estimated 500 million to nearly 8 billion. This unprecedented growth has turned our activities into an overpoweringly destructive force for the rest of life and the ecosystems themselves. Thus, we are already consuming some 70% more of the worlds potential sustainable productivity than the total available (www.footprintnetwork.org). In the face of this relationship, we will be adding about 2 billion to our numbers over the next 30 yearsby mid-century.

The global biosphere is incredibly complex, with probably tens of millions of evolutionary lines of bacteria interacting with perhaps 10 million or more species of complex cellular organismsplants, animals, and fungi. We have given names to no more than a fifth of these, and even about the great majority of the ones we have named, we know next to nothing. Few people familiar with the situation believe that Earth can continuously support a human population as large as the one that exists now. In fact, we have already launched a great wave of extinction comparable to those that have occurred several times in the past. As much as a fifth of the plants, animals, and fungi that exist now may become extinct over the next several decades, and perhaps as many as twice that number, most of which have never been evaluated scientifically, by the end of this century.

We are not going to be able to learn everything about the world we are destroying as it goes, but we live in a time of unique opportunity to learn something about the variety of life here while it still exists. In this outstanding book, Scott Gardner, Judy Diamond, and Gabor Racz have given us a lovely picture of the importance and indeed fun in studying the members of one particular life formparasites. Ultimately, it is the great satisfaction in learning about biodiversity that will inspire scientists to learn as much as we can while life is still relatively intact.

Parasites are unique and truly fascinating, as the pages of this book make so clear. They form close relationships with their hosts, the balance depending on both internal and external factors. Under one particular set of circumstances, the relationship will persist; under another, it may change, the parasites found in a particular host coming and going accordingly. To the extent that we can understand them, we are able to understand much about the stability and functioning of the hosts in which they occur.

Most extinction of species up to this point in time has been driven by human appropriation of natural lands for agriculture, including grazing, urban sprawl, and other uses. We have altered some 40% of global lands to produce food for humans, allowing villages, towns, and cities to grow and the elements of our civilization to be developed steadily in these centers. Now and in the years to come, however, global climate change is certain to become an even more important factor in driving extinction. We have already driven the average global climate to about 2 F warmer than it was before we entered the industrial era some 150 years ago. Worse, national agreements to contain the rising temperatures have so far been seriously off the mark, and the average temperature increase may reach 2.7 F (1.5 C), said to be the point of no return, by the end of this decade, and move on toward as much as a 5 F increase within a few more decades. Everyone is familiar with the disasters associated with warming temperatureshurricanes, fires, rising sea levelsbut the effects on extinction and the dismembering of ecosystems are even more profound. Much of our current agricultural land will become useless for the crops grown on it at present, with the numbers of starving people rising and climate-driven displacement of people widely evident.

We will be able to do the best possible job of creating a sustainable world if we base our decisions on as much information as possible. As the stories in this book tell so well, it can be a great deal of fun, as well as deeply important, to learn about the organisms that share this world with us. Parasites provide an especially sensitive and interesting key to the vitality of the systems in which they occur. They can also transfer to human beings, so that learning about them, as Scott Gardner, Judy Diamond, and Gabor Racz present so well in these pages, has a deep importancethey are endlessly interesting. I am sure you will enjoy and learn from these pages as much as I have, and I commend them highly to you.

Peter H. Raven

President Emeritus

Missouri Botanical Garden, St. Louis

Parasites are rarely described in positive terms. They are seen as blood suckers, freeloaders, scroungers, flunkies, deadbeats, and the worst kind of groupies. In Bong Joon-hos 2019 award-winning film, the main characters first help the members of a wealthy family by tutoring the kids, cooking, housekeeping, and driving. Eventually the host family becomes dependent on the help, and only then does the relationship turn toxic, hence the films name, Parasite.

In all natural and human impacted ecosystems on Earth, parasites are wildly abundant and represent a most successful lifestyle. They may live at the expense of their hosts, but both host and parasite are fundamentally changed as a result of the partnership. To understand how communities of organisms live together, one must know the parasites, since they play a central role in the dynamics of ecological associations. They are unseen influencers, affecting nearly every other species and contributing massively to the networks of interactions that stabilize ecosystems.

Dependent relationships between different species are the norm among living organisms, and these have evolved in every imaginable form. When the relationship between two different species benefits both, ecologists describe it as mutualism. Mutualism takes cooperation to a high degree of dependence as, for example, between tree roots and their mycorrhizal fungi, termites and their protistan ciliates harboring even smaller bacteria that digest wood, or lichens formed from a union of fungi and algae. When one partner benefits and the other is neither harmed nor helped, this relationship is referred to as commensalism. Examples of commensals are anemone fish that live sheltered among the stinging tentacles of sea anemones, tolerating their venom while being protected from predators, the tiny crabs that snuggle into the shells of oysters, or shrimp that live in glass sponges.