Adaptive Gene Substitutions in Tasmanian Eucalypts: I. Genes Controlling the Development of Glaucousness

Abstract

7 of the 24 Tasmanian species of Eucalyptus show clines in the degree of development of waxy glaucousness. Transplant and segregation studies have shown that the degree of glaucousness is genetically controlled. In all 7 species the environmental variable best correlated with the clinical change is frost, the glaucous genotypes having been selected out in those regions of the species range with maximum frost activity. While it is possible that interspecific introgression may have provided some of the genetic variability on which selection has worked, evidence from sterility barriers etc. shows that this parallel clinal variation must have arisen independently several times within the genus. The melting point of the wax shows an interesting correlation with other classical taxonomic characters.