NICKEL TOLERANCE AND COPPER-NICKEL CO-TOLERANCE IN MIMULUS-GUTTATUS FROM COPPER MINE AND SERPENTINE HABITATS

Previous work on M. guttatus suggested that nickel tolerance in copper mine populations may also be given by the genes for copper tolerance. It has been shown that copper tolerance in M. guttatus is controlled by a single major gene, plus a number of minor genes (or modifiers) wh ich elevate copper tolerance. Crosses between nickel tolerant individu als from three families and non - tolerants showed that nickel toleran ce in M. guttatus is heritable. In order to study the effects of the m ajor copper tolerance gene on copper - nickel co - tolerance in M. gut tatus, homozygous copper tolerant and non - tolerant lines were screen ed against nickel. Significant differences occur between these lines f or copper, but were not found when analysed for nickel, indicating tha t copper - nickel tolerance is not governed by the major gene for copp er tolerance. To test whether the minor genes for copper have a pleiot ropic effect on nickel tolerance, five selection lines derived from th ree copper mines (Copperopolis, Penn and Quail) in Calaveras county, C alifornia, which vary in degree of tolerance to copper, by the presenc e or absence of minor copper genes, were also screened against nickel. Two out of three of the lines from Copperopolis showed elevated toler ance to nickel, but two further selection lines derived from Penn and Quail copper mines gave no indication of increased nickel tolerance. T hese results suggest that the minor genes for copper do not give toler ance to nickel. This was confirmed by the screening of modifier lines, in which modifiers for differing degrees of copper tolerance were ins erted into a non - tolerant background. Genotypes possessing fewer cop per modifiers yielded higher nickel tolerance than those genotypes whi ch have a greater number of modifiers. Thus nickel tolerance in this s pecies is heritable and under the control of different genes to those producing copper tolerance.