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• Preface

Preface

Contemporary studies of Volvox, the rolling green spheroid that first fascinated Antoni van Leeuwenhoek 300 years ago, illustrate this sort of convergence. When my wife Marilyn and I began to study Volvox more than 20 years ago, our objective was to capitalize on its simplicity to address a central problem of development that we had found it extremely difficult to address with any clarity by studying vertebrate embryos: How do cells with very different phenotypes arise from the progeny of a single cell? But the longer we have worked with Volvox, and implored it to reveal its secrets to us, the more difficult we have found it to think about its development in other than an evolutionary framework. This is because it has become increasingly evident that the genes that Volvox now employs to establish a germ-soma division of labor during development exert their effects by modifying particular aspects of a genetic program and a set of cytological specializations that were inherited from ancestors (resembling modern Chlamydomonas and various colonial flagellates) that had only a single cell type. Therefore, the central premise of this book is that Volvox and its relatives provide us a unique window through which to examine the important roles that a few regulatory genes can play in both development and evolution, and gain fresh insights into a problem that has fascinated both developmental and evolutionary biologists for many generations: How do multicellular organisms with differentiated cell types arise from unicellular antecedents?

An effort has been made to write this book at a level that will be accessible to prospective biologists at the advanced undergraduate level and yet will be capable of holding the interest of more mature practicing biologists with a diversity of research interests. I would be less than forthcoming, however, if I did not admit to being motivated by an evangelistic spirit as I wrote, hoping to capture for an organism that I have come to love the vocational interests of young (or perhaps not so young) biologists who may be looking for a new window through which to view the living world.

In a very real sense, this book had its roots in a piece of advice given to me by my first mentor and scientific father figure, Jerome Gross (a piece of advice that other biologists caught up in the frenetic competitiveness of our current age might do well to consider). On the day that I was saying my farewells, about to leave for graduate school after spending a major portion of my undergraduate years in his laboratory, Jerry said, "If you want a happy and productive career in science, find yourself a quiet backwater where there are lots of big fish to be caught, but not many people fishing, and go after them." It took many years to find such a niche and begin to follow Jerry's sage advice.

It was Richard Starr who eventually led us to this niche, by introducing Marilyn and me to Volvox. For that, and for the friendship, help and encouragement that he has offered over all the intervening years - from the days he first hosted us in his laboratory and shared his cultures with us, up to and including his recent willingness to scrutinize a draft of this manuscript, point out various factual errors, and make many useful suggestions for improvement - I wish to express profound and lasting gratitude.

I also wish to thank two "life-history biologists" who introduced me to a completely new and different way of looking at Volvox and its relatives several years ago: Graham Bell and his then-student, Vassiliki Koufopanou. I was initially astonished at how we could look at the same set of simple organisms, see such different things, use such different lexicons to discuss them, and ask such different questions about their evolutionary origins. While I was consumed with a desire to understand the proximate (i.e., genetic and cytological) causes of the Volvox germ-soma dichotomy, they were consumed with a desire to understand its ultimate (i.e., ecological and adaptive) causes. Over the years the gap has been narrowed (and the minds broadened, I trust) by centripetal movement on both sides. Chapters 3 and 4 of this book constitute my attempt to incorporate into this narrative many ideas gained from interactions with Graham and Vasso, from their papers, and from the additional literature to which they directed me. Some of the original shortcomings of these chapters have been mitigated by suggestions they (particularly Vasso) made after reading a draft version. Thus, to the extent that I have succeeded in my effort to integrate into this book a consideration of the ultimate causes underlying the Volvox germ-soma dichotomy, credit goes to Vasso and Graham. But to the extent that I have failed, the fault is mine alone.

At the other end of the spectrum, the molecular end, an enormous debt of gratitude is owed to our good friend and close collaborator Rüdiger Schmitt and his colleagues. When Rudy and I met at a conference about 10 years ago and realized the extent to which we were attacking related aspects of Volvox biology from different perspectives, we drew up detailed plans for collaborative studies that have dominated the research agendas of both laboratories ever since. Little did we appreciate at the outset what a long-term program that would turn out to be, or how many obstacles would have to be overcome along the way. But as a result of this collaboration, we now have molecular-genetic methods for the study of Volvox that clearly would not yet exist if our two research groups had not worked together so closely over the past decade. Each major step along the way has been the product of a synergistic research relationship and has been enlivened and made much more enjoyable by frequent exchange visits between St. Louis and Regensburg by students, postdoctoral fellows, and technical assistants, as well as by Rudy and myself.

Above all, however, my gratitude extends to my wife and closest collaborator, Marilyn, without whom it is doubtful that Volvox research would still be alive and well in St. Louis, or in the larger community for that matter. For more than two decades she played the critical role of keeping our laboratory running efficiently during all the dreary hours when I was tied up with interminable committee meetings and other academic responsibilities. More importantly, she overcame the innate distaste of a classic biochemist for molecular biology - where one seldom can see a product, let alone weigh it - and was responsible for most of the critical breakthroughs required to bring Volvox research into the modern era. From the weekend on which (while cruising the northern Mississippi on an ancient stern-wheeler) we decided to visit Richard Starr and "go Volvox," to the present day (when she ignores her recent retirement and finds her way back to the bench whenever there is an important experiment that could benefit from her attention) it has been a productive relationship. I only hope that it has been half as rewarding and enjoyable for her as it has been for me. Her painstaking and critical reading of every word of this text, in each of several versions, has engendered both my sympathy and gratitude and has deepened my affection.

Finally, I wish to thank the National Institutes of Health, which supported our Volvox research over many years, the National Science Foundation, which has done so in recent years, and NATO, which provided travel grants to Rudy Schmitt and myself to facilitate our transatlantic collaboration.