Clinal Variation Between Eucalyptus viminalis Labill. And E. dalrympleana Maiden

Abstract

Populations of Eucalyptus viminalis, E. dalvympleana and intermediates were intensively sampled along two transects in Tasmania. Many characters (especially juvenile leaf characters) were shown to exhibit continuous clinal variation between the two species. Other characters appeared to show ecotypic variation. The characters measured included adult leaf, fruit and bud characters, juvenile leaf characters (from both natural and glasshouse-grown progeny) and physiological characters such as the growth rate, frost sensitivity and the germination rate. The cline in juvenile characters was correlated with several ecological variables. Although some small discontinuities occur along this cline, it is argued that the cline is determined by the action of as yet undetermined selective forces acting on a continuous group of potentially interbreeding populations. The distance over which the cline occurs is shown to vary considerably between areas, possibly reflecting variation in the rate of change of the underlying ecological variables. This situation appears different to that found on mainland Australia where narrow hybrid zones have been reported between these two species. The relationship between these results and those reported for these species on mainland Australia are discussed.