Experimental Evolution
What
is experimental evolution? Garland and Rose (2009) [here's the entire book as a PDF file] 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:
Experimental Evolution in Wikipedia
Last updated 20 Sept. 2016 by T.G.