Adaptation in Pantothenate‐requiring Neurospora Ii. Nuclear Competition During Adaptation

D avis , R. H. (U. Michigan, Ann Arbor.) Adaptation in pantothenate‐requiring Neurospora . II. Nuclear competition during adaptation. Amer. Jour. Bot. 47(8) : 648–654. Illus. 1960.—The process of adaptation in pantothenate‐requiring Neurospora was studied by the use of heterocaryons constituted of the pan‐1 strain and a modified strain, pan‐1 m , derived from it. Although pan‐1‐m homocaryons grow well on a pantothenate concentration on which pan‐1 grows little or not at all, pan‐1 nuclei often have a selective advantage in pan‐1 + pan‐1‐m heterocaryons grown on the same medium. This results in non‐adaptive changes in nuclear ratios and labile growth rates of the heterocaryons. Nuclear competition does not occur when pantothenate is not limiting to the growth of either homocaryon. The results are discussed, and related to past work on adaptation and nuclear ratio changes in Neurospora hetercaryons.