Transfer of individuals as a means of investigating natural selection in operation

摘要

Populations of Philaenus spumarius (Homoptera) displaying colour polymorphism at stable equilibrium were subjected to the introduction of alien phenotypes. In an exchange experiment between populations of isolated islands, 2/3 of population A, from Allgrundet, was transferred to Porskobben, and 2/3 of population P from Porskobben to Allgrundet. The immediate result of the transfer was A-type allele frequencies on Porskobben and P-type frequencies on Allgrundet. After four generations, the pre-transfer frequencies were almost completely restored. This change implies strong island-specific selection pressures. The process was remarkably rapid in view of the mixed composition of the gene pools and the fact that population size and mortality fluctuated greatly in the post-transfer generations.In an insertion experiment, an alien phenotype was introduced into population K, on Kummelgrundet. In the four post-insertion generations studied, the new artificial balance was maintained, i. e., the result was the opposite of that of the exhange experiment. K. is much smaller than A or P, and probably less effectively buffered against the stochastic establishment of a new equilibrium. Besides, the ecological requirements of the inserted phenotype are met with by the habitat on Kummelgrundet.