Effects of selection and migration on geotactic and phototactic behaviour ofDrosophila. III

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Abstract
Three kinds of experiments on the behaviour ofDrosophila pseudoobscurawith respect to light (phototaxis) and gravity (geotaxis) are described. First, populations were subjected to arti­ficial selection, and responded by becoming positively, or negatively, phototactic or geotactic. When the selection was discontinued, the populations showed the effects of genetic homeo­stasis - they gradually converged and became similar in behaviour. Secondly, positive and negative populations were made to exchange unselected migrants. They converged towards identical behaviours, but the points of convergence were influenced by genetic homeostasis. Thirdly, populations being selected towards positively, or towards negativity, received in every generation phenotypically positive or negative immigrants from a population which was not itself being selected. These migrants caused a sharp reduction of the selection effectiveness in the receiving populations. Mathematical analysis of the experimental results was made to estimate the homeostatic points (i. e. the values towards which the populations are homeostatically driven), and homeostatic strengths (homeostatic heritabilities). The strengths turned out to be between 0.05 and 0.07, close to the values of realized heritabilities derived from the present and previously reported experiments.