Adaptive Genetic Variation in the Wild

I opened this book with high anticipation. Its title appeared very timely and, moreover, the reputation of the three co-editors only heightened expectation. As John Endler had argued persuasively in an earlier book, there are many demonstrations of natural selection but the really fascinating issues involve understanding the biological reasons why dierences in reproductive success occur among phenotypes and genotypes. This background, combined with the burgeoning ability to explore genetic variation for ecologically important traits, seemed to ensure a wide and substantial impact for this volume. I certainly enjoyed and learnt a lot from all the chapters in this book, albeit to a lesser or greater degree. I am con®dent this would apply to all readers. I think the book also illustrates how far the ®eld has come in ful®lling the scope for understanding dierences in ®tness among phenotypes. However, I would like to have seen it at least touch on the exciting potential for tracing the whole evolutionary process from genetic variation through development to evolutionary relevant phenotypic variation, through to dierences in ®tness in the wild. Perhaps this was not in the mind of the editors, although any fully satisfying and robust understanding of adaptive evolution will involve not only descriptions of genetic variation and associated dierences in reproductive success among phenotypes, but also the developmental origins of the phenotypic variation. Such studies are scarce at present. However, in this connection, I would like to have seen some revisiting of case studies in earlier books on ecological genetics. I am thinking especially of insecticide resistance in insects and heavy metal tolerance in plants where both ®eldand laboratory-based studies have provided advances in knowledge at every level of biological organisation. Perhaps these examples are not wild enough. To biologists not directly engaged in research on natural selection, the case studies in this book would appear to have a highly biased coverage of dierent organisms. Firstly, the lack of many studies on plants is striking. Plants, or rather ̄owers, only take the central role in one chapter, by Susan Mazer and Daniel Meade. They play a more peripheral role in several chapters, particularly the fascinating account of Susan Mopper, Keli Landau and Peter Van Zandt on insect±plant interactions using intensive studies of leafminer populations on individual oak trees. Microbes and asexual organisms are not represented at all in this book. This may more genuinely re ̄ect the situation that although there are many eorts currently underway, there are few more rounded accounts (but antibiotic resistance and myxomatosis spring to mind). The jacket illustration to this book accurately re ̄ects its coverage of several groups of vertebrates together with a few insects and ̄owering plants. This is perhaps more a commentary of the ®eld rather than of the book. Many chapters cover both patterns of genetic variation and issues of how natural selection in ̄uences phenotypic variation. However, they do tend to concentrate on one or other topics. The genetic direction is represented by excellent reviews of what is known about the inheritance of variation in many ecologically important traits in both Galapagos and African ®nches (Peter and Rosemary Grant; Thomas Smith and Derek Girman), and in crickets (Timothy Mousseau). An additional chapter by Ary Homann provides a useful synthesis of traits, or classes of traits, in Drosophila, where comparisons can be made between estimates of heritabilities derived in the ®eld and in the laboratory. For me, one of the most exciting chapters that takes a genetic perspective shows how novel ways of estimating genetic variances in natural populations are opening up through the use of molecular markers to infer patterns of relatedness among individuals. Although Kermit Ritland has only a limited number of empirical studies to draw on, in many cases led by his own eorts, he certainly demonstrates the potential power of this approach. The complexity of interacting in ̄uences of natural selection is a recurring theme in the chapters with a more phenotypic perspective. Ruedi Nager, Lukas Keller and Arie van Noordwijk show how in great tits the timing of breeding, phenotypic plasticity and environmental variability in food availability are linked together in a complex manner. The study of great tits continues to utilize manipulative experiments in a thoughtful and rewarding way. However, the power of this exciting approach to understanding why dierences in reproductive success arise is perhaps best exempli®ed in the chapter by Barry Sinervo on side-blotched lizards. Development of techniques to manipulate egg size and yolk reserves in these lizards, as illustrated in a beautiful and striking cover photograph in Science (Sinervo et al., 1992), has clearly paid great dividends in opening up the complexity of selective interactions among the associated life-history traits. Phenotypic plasticity in the form of so-called trophic polymorphisms is central to Beren Robinson and Dolph Schluter's description of the patterns of spectacular divergence which have evolved in ®shes inhabiting the northern post-glacial rivers and lakes. The book is rounded o by an attempt at both synthesis and a shopping list from John Endler. I read this twice, partly because there were so many ideas to digest. I don't think anyone could quarrel with Endler's emphasis on understanding how selection on dierent traits interacts and on how genetic correlations arise and are maintained. I would reiterate that the potential is opening up to ®t a mechanistic understanding of the developmental processes that underlie the genetic correlations into this picture, to fully link the genetic Heredity 86 (2001) 638±640