Evolutionary change is usually too slow for us to detect on the timescales in which we live—hours, days, even months. To illustrate selection in action, Darwin turned to domesticated species, which act as a kind of temporal microscope, magnifying patterns of phenotypic and genetic variation within a population. On the Origin of Species does not begin with a description of the fantastic organisms that Darwin observed on his travels through South America, but rather with a description of the humble domestic pigeon. Darwin pointed out that by applying the same principles of selection that exist in nature, humans have been able to generate incredible variety in domesticated species—fantails, frillbacks, Jacobins—and do so relatively quickly.
For millennia, humans have used artificial selection to create desirable traits: edible plants, useful animals, and aesthetic curiosities. In the edited volume Experimental Evolution: Concepts, Methods, and Applications of Selection Experiments, researchers review the enormous range of ways artificial selection can be used to test hypotheses that are of central interest and importance to evolutionary biologists. The book explores the methods that underlie experimental evolution and the breadth of conceptuai topics that have been explored using this approach, from anatomy to altruism, sex to speciation, physiology to phages, and more.
The authors in this volume take a broad view of experimental evolution, defining it as any study that exposes a genetically variable population to some selective pressure. This selection could be deliberate (such as selection for flies with a particular wing shape) or inadvertent, as happens simply by bringing a wild species into the laboratory (discussed in detail in the chapter by Simões and colleagues). In either case, the response to these selective pressures can then be used to address evolutionary questions.
This book will surely be of interest to researchers looking for new ways to ask evolutionary questions. But the careful reader is advised to read the last chapter of the book first. Although experimental evolution can be a powerful tool with which to test evolutionary hypotheses, the method is not without its challenges, and there are still issues to be resolved. Many of these issues are discussed briefly throughout the book, but in the concluding chapter, Huey and Rosenzweig present an admirable summary of the pitfalls that lie in wait for the experimental evolutionist: The laboratory may be more benign or more stressful than the “real world” in which our study organisms usually live and die; the factors that we alter in the lab might not be the relevant selective forces shaping variation in the wild; and even before we deliberately impose selection in the lab, the very act of bringing an organism in to study can change its genetic and phenotypic architecture in ways that interfere with our experiments. And as others point out (e.g., Rhodes and Kawecki, Estes and Teotónio), once we begin a selection experiment, keeping control lines from evolving, especially in species that cannot be frozen and revived, may not be so simple. We can try to minimize selection (e.g., by keeping lines inbred, or by using Kondrashov's “middle class neighborhood” design), but this can increase the likelihood that novel deleterious mutations accumulate.
Even with these various caveats, this book has something for almost any evolutionary biologist. Reading through its chapters by a first-rate collection of authors, one gets a clear sense that experimental evolution has been used to study an impressive range of organisms (the book covers everything from phage [Forde and Jessup, Turner and colleagues] to fish [e.g., Irschick and Reznick]). Moreover, experimental evolution can be used to study diverse conceptual questions, from the evolution of genomes (e.g., Rosenzweig and Sherlock) to physiology (e.g., Zera and Harshman, Swallow and colleagues, Gibbs and Gefen), morphology (Frankino and colleagues), behavior (Rhodes and Kawecki), speciation (Fry), and more.
Most of the chapters provide excellent overviews of the work that has been done so far. For example, the chapter on the evolution of sex (Turner, McBride, and Zeyl) includes sections on experimental evolution in viruses, bacteria, and yeast with useful summary tables. While for the most part we do not find major new insights in this chapter (and others), it would be hard to find a clearer exposition of the problems and approaches that have been taken. On the whole, the authors of these chapters use the book as an opportunity to review the use of experimental evolution in their specific field. Broader conceptual themes and suggestions for future studies are in most cases left to the reader's imagination.
From a practical standpoint, I found the most useful chapter to be that of Roff and Fairbairn, who present a set of computer-intensive methods for modeling the outcome of selection experiments. These are particularly important for experimental design. Given what we know about a particular system, how long does an experiment need to last, how strong does selection have to be, and how many replicates are necessary to be able to detect the effect of interest? These methods can also be used to test hypotheses about the underlying genetic structure of a system. Given the strength of selection, is the observed response consistent with our understanding of the system? Even though we can't confirm that the system is as we think, we can certainly show that system behavior is inconsistent with our model of the system.
This book has appeared at a particularly exciting time in experimental evolution research. With the advent of high-throughput “omic” approaches, we can now begin to uncover the specific genetic changes that account for responses to selection. Rhodes and Kawecki note that genome sequencing and transcriptomics can help us to identify individual genes associated with traits that vary among selected lines. Rosenzweig and Sherlock's chapter offers a more detailed exploration, showing us that these tools are valuable not only for understanding the evolution of phenotypic traits under selection but also for understanding the evolution of the genome itself.
In some cases, I would have welcomed a more critical perspective on the strengths and weaknesses of previous work. That said, some criticisms are taken too far. In their review on experimental evolution and aging, Rauser and colleagues condemn those who have questioned the validity of assumptions underlying standard theoretical models in aging research. But as is clear from the targets of their criticisms (e.g., Baudisch 2005), to question the simplifying assumptions that underlie a mathematical model of theory is not the same as rejecting the theory. Also dismaying was the selective presentation of data in this chapter. A graph in the chapter claiming to show a plateau in late-age fecundity was missing the late-age increase in fecundity that appeared in the original paper (Rauser et al. 2006).
Overall, this book, almost encyclopedic in its breadth, will provide a valuable entrée for those thinking about carrying out an experimental evolution study. In his well-written chapter on speciation, James Fry suggests in his “general guidelines for experiments on speciation” that one should start by consulting earlier literature, noting that “experiments should be designed in a way that takes advantage of previous methodological advances” (p. 650). For graduate students considering an experimental evolution project for a thesis, or for the more advanced researcher considering the use of experimental evolution for the first time, one would do well to take Fry's advice to heart. For any problem under consideration, this book will lead one quickly and thoroughly into a fascinating literature, and will help one to carry out well-designed experiments.
- A. Baudisch 2005. Hamilton's indicators of the force of selection. Proceedings of the National Academy of Sciences 102: 8263–8268. Google Scholar
- CL Rauser , JJ Tierney , SM Gunion , GM Covarrubias , LD Mueller , MR Rose . 2006. Evolution of late-life fecundity in Drosophila melanogaster. Journal of Evolutionary Biology 19: 289–301. Google Scholar