The albino Rattus norvegicus used in laboratories (photo above by Sarah Fleming) goes back to the Wistar Institute in Philadelphia. Physiologist Henry H. Donaldson took four pairs of albino rat with him when he joined the Institute in 1906, and work there by Donaldson, Helen Dean King, and others resulted in the development of a standardised “Wistar rat.”
In his 480-page tome The Rat: Data and reference tables for the albino rat (Mus norvegius albinus) and the Norway rat (Mus norvegius) of 1915 (revised in 1924), Donaldson notes: “In enumerating the qualifications of the rat as a laboratory animal, and in pointing out some of its similarities to man, it is not intended to convey the notion that the rat is a bewitched prince or that man is an overgrown rat, but merely to emphasize the accepted view that the similarities between mammals having the same food habits tend to be close, and that in some instances at least, by the use of equivalent ages, the results obtained with one form can be very precisely transferred to the other.”
What Donaldson means by the latter point is: “If the life span of three years in the rat is taken as equivalent to 90 years in man, it is found that the growth changes in the nervous system occur within the same fraction of the life span (i.e., at the equivalent ages) in the two forms.”
Since Rattus norvegicus has adapted to live with people (e.g. in tunnels under our cities), it makes for a perfect laboratory animal. Running rats through mazes of varying kinds has become an established way of studying learning, as in this video from the San Diego News Network:
Drosophila melanogaster, the vinegar fly or “fruit fly” (photo above by André Karwath), has been enormously important as a model organism in genetics and neuroscience, partly because it is so easy to raise in the laboratory (photo below by “Masur”).
Drosophila genes such as fruitless, rutabaga, and white have been enormously important within biology, and flybase.org provides a modern repository of information on such genes. The Hox genes, first found in Drosophila (see below), form part of the complex machinery of embryonic development, which allows protein synthesis to be controlled in both time and space.
Jonathan Weiner’s 1999 book Time, Love, Memory is one of a number of books which explain how valuable this little insect has been.
Arabidopsis thaliana, the thale cress (photo above by Peggy Greb, picture below by Johann Georg Sturm and Jacob Sturm, 1796) is a small flowering plant in the family Brassicaceae – the mustard/cabbage family.
During much of the 20th century, A. thaliana was the target of extensive research, facilitated by the small size of the plant (and of its genome), its short life cycle, and its suitability for light microscopy. Sequencing of the genome was completed in the year 2000, and the genome is available at arabidopsis.org. The open-access peer-reviewed The Arabidopsis Book also collates information on the plant, which is in many ways the botanical equivalent of Caenorhabditis elegans. It has taught the world a great deal.
The Google Ngram below shows the explosion in Arabidopsis-related literature since about 1990, outstripping even work on C. elegans:
Caenorhabditis elegans (photo above by Bob Goldstein, diagram below by “KDS444”) is a transparent nematode worm, about 1 mm in length. It lives naturally in the soil, where it eats bacteria, but it is also quite happy to make its home in a Petri dish. A 1963 suggestion by Sydney Brenner led to C. elegans becoming the focal point of a vast collaborative effort to understand the worm in detail. Brenner shared the 2002 Nobel Prize in Physiology or Medicine for this work.
The cellular development of C. elegans has been mapped in detail, and its genome had been largely mapped by 1998. The diagram below shows the neural network of the worm, drawn using R, based on data from here (from this paper via this one). In this diagram, colour shows the centrality of neurons in the network. Other information on C. elegans is available at wormbase.org.
Because of the effort that has gone into understanding this humble worm as whole, rather than as just parts, a great deal has been learned about biology in general. Brenner was on to a good thing!