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Experimental Evolution

Experimental Evolution

 

Experimental Evolution

     What is experimental evolution? Garland and Rose (2009) have defined it as research in which populations are studied across multiple generations under defined and reproducible conditions, whether in the laboratory or in nature (for two recent short overviews, click here and here). This intentionally general definition subsumes various types of experiments that involve evolutionary (cross-generational, genetically based) changes. At one end of the continuum, the study of evolutionary responses to naturally occurring events (e.g., droughts, fires, invasions, epidemics) may constitute a kind of adventitious experimental evolution, especially if these events occur repeatedly and predictably enough that the study can be replicated, either simultaneously or in subsequent years. Next we have intentional "field introductions," in which a population is placed in a new habitat in the wild, or a population's habitat is altered by adding a predator, a pesticide, a food source, fertilizer, etc. The experimental population is then monitored across generations and compared with an unmanipulated control population.
    "Laboratory natural selection" denotes experiments in which the environment of a laboratory-maintained population is altered (e.g., change of temperature, culture medium, food) as compared with an unaltered control population. "Laboratory culling" involves exposing an experimental population to a stress that is lethal (or sublethal) and then allowing the survivors (or hardiest) to become the parents of the next generation. In all of the foregoing types of experiments, the investigator does not specifically measure and select individuals based on a particular phenotypic trait or combination of traits. Rather, selection is imposed in a general way, and the population has relatively great freedom to respond across multiple levels of biological organization (e.g., via behavior, morphology, physiology). "Multiple solutions" are possible and even probable, depending on the kind of organism and experimental design.
     In classical "artificial selection" or "selective breeding" experiments, individuals within a population are scored for one or more specific traits, then breeders are chosen based on their score (e.g., highest or lowest). Depending on the level of biological organization at which selection is imposed -- and the precision with which the phenotype is defined in practice -- multiple solutions may again be common.
     Domestication is an interesting (and ancient) type of experimental evolution that generally involves some amount of intentional selective breeding. In some cases, the process has been replicated enough times that general principles might be discerned (e.g., several species of rodents have been domesticated). Of course, whenever organisms are brought from the wild to the laboratory or agricultural setting some amount of adaptation to the new conditions will occur, and this may be studied. Once domesticated, organisms may be the subject of additional selective breeding programs, with varying degrees of control and replication, leading to multiple breeds or lines.
     More recently, the unintentional effects of various actions by human beings have been studied from the perspective that they constitute selective factors whose consequences may be predictable. Examples include changes in commercial fisheries and in various ungulates that are hunted.
     In any case, to qualify as experimental evolution, we require most if not all of the following fundamental design elements: maintenance of control populations, simultaneous replication, real-time observation over multiple generations, and the prospect of detailed genetic analysis. In short, experimental evolution is evolutionary biology in its most empirical guise.

     Recognizing its importance, the University of California has recently established NERE, the Network for Experimental Research on Evolution, as a Multicampus Research Project (click here for a list of all such UC units).

Table of Contents for:
Garland, T., Jr., and M. R. Rose, eds. 2009. Experimental evolution: concepts, methods, and applications
    of selection experiments. University of California Press, Berkeley, California.

Links to Some Experimental Evolution Labs:

Please contact me (tgarland@ucr.edu) if you would like to see a link added (or removed!).

Some Related Links:

Evolutionary Physiology

Experimental Evolution in Wikipedia

 

Last updated 13 Feb. 2013 by T.G.