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BOOKREVIEW

Anurag, Agrawal. 2017. Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and Their Remarkable Story of Coevolution. Princeton University Press. Princeton, New Jersey. x + 284 pp., hardcover. ISBN 978-0691- 16635-3. $29.95.

During myfinalyear ofgraduatestudyatNorthernMichiganUniversity,several of my naturalist friends and I decided to take a long weekend, despite our need to continue writing our master’s theses. we loaded up all of our plant presses, field guides, nets, collecting jars, binoculars, and spotting scopes and headed down to Peninsula Point in Delta County, Michigan. It was a beautiful fall day and we arrived early in the morning in order to get a glimpse of any birds making their way from Canada to their overwintering spots in the neotropics. However, the real stars of the show turned out to be the thousands of monarch butterflies that had gathered for their own continental migration. This naturalspectaclesparkedinmemyloveofLepidopteraandeventuallysetmeon a course of studying plant-herbivore interactions when I started a PhD about a year later.

Dr. AnuragAgrawal’s new book has in no doubt been influenced by the hundredsofnaturalistslikemyselfwhoareentrancedbythewondersofmonarchbiology. Dr. Agrawal, with years of studies under his belt, is one of the top plant- herbivore biologists in the world. Carefully tracing the life history of the monarch along its spring migration from Mexico to southern Canada and back again in the autumn, Dr. Agrawal weaves in classic studies, including past monarch research by the Urquharts and Lincoln Brower as well as insights from his own years of studying monarch caterpillars and milkweeds.

Dr. Agrawal’s personal insight is what makes this book unique. Sandwiched between accounts of spring and fall monarch migration (which make up the first and last chapters of the book), are chapters in which Dr. Agrawal draws deeply from his expertise on plant-insect interactions. The discussion of the biology of milkweeds, and particularly their defense traits, is not only interesting in itself, but also provides a great general discussion on how chemistry and biology conspire to create the wonderful co-evolutionary study of monarchs and milkweeds. Dr. Agrawal makes it clear that this story isn’t just about monarchs, but also about the diverse genus that contains milkweed. Here he discusses several speciesofthemilkweedgenus(Asclepias) andthevariouswaysmilkweedshave evolved to defend themselves from herbivore attack through chemical defenses and physical defenses. Dr. Agrawal shows that these defense traits vary among the roughly 140 species of milkweeds; for example, some relying heavily on chemicalstodefendthemselves,whereasothersdon’tbothertoproduceasmany chemicals and instead stick to trichomes for defense. The discussion of milk- weeddiversity,however,isprimarilyframedasbeingaproblemformonarchsto solve. The rich research history on the common milkweed (Asclepias syriaca) is

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used in great effect to demonstrate that these plants are not passive organisms in the evolution of monarchs and milkweeds. These middle chapters are accessible to non-biologists, but are also broad and sufficiently well-written that even serious chemical ecologists will find them interesting. while explaining the basics of milkweed traits that deter attacks by monarch caterpillars, Dr. Agrawal manages to incorporate numerous theories and examples of the biology behind plant defenses against herbivores. This gives a wonderful context behind the specifics of the back and forth co-evolution of monarchs and milkweeds. The description of these theories also makes this book an excellent introduction to many important concepts that have driven research in the field of plant-insect interactions.

Underlying the tale of monarchs strung throughout this book is a very basic introduction to co-evolution, ecology, and population biology. It is this story about population biology that most readers may be interested in, as it addresses the current research on monarch decline. Here Dr. Agrawal wades into the controversyoverthehypothesisthatmonarchdeclineisconnectedtoasupposeddeclineofmilkweedpopulationsintheUnitedStates. Inaverydetailedretellingof personalresearchthatDr.Agrawalandseveralcollaboratorshaveundertaken,he carefully examines what we know about monarch populations and draws upon years of citizen science data. His conclusion that the decline in monarch populationshasnotbeencausedbyadeclinein milkweedsiscarefully cushioned byan engaging section about spurious correlations and which concludes that halting monarch decline will not be solved simply by planting more milkweeds.

This book will be a real pleasure to read for both professional scientists and those that have a love of nature. For non-technical readers, the layout is easy to read and there are no in-text citations. For those that do want to explore the primary literature, the author has provided plenty of citations that can be found in detailed notes organized by chapter at the end of the book. The colorful photos, illustrations, and graphs peppered throughout the book serve to enhance the reader’s understanding of the more complex and technical aspects of this story that are described in the rich discussions. After finishing this book, it was all I could do to keep from from planning my next fall trip to Peninsula Point to witness the magic of a warm fall day and the thousands of monarchs engaging in a long story of evolutionary ecology.

——Michael C. Rotter Department of Biological Sciences NorthernArizona University Flagstaff,AZ 86011-5640 mcr268@nau.edu