MORPHOLOGICAL VARIATION IN MULGA. I. VARIATION AND COVARIATION WITHIN AND AMONG ACACIA ANEURA POPULATIONS

Abstract

ABSTRACT Morphological variability is extremely high in the Australian mulga, Acacia aneura, even within local populations. This variation appears to be genetically based, and its maintenance can be related to two sorts of hypotheses: (a) ecotypic selection for morphological divergence related to the segregation of individuals into distinct, autogenic microniches, and (b) apostatic selection to foil foliar herbivores or seed predators. Morphological variation in the growth form, phyllodes, and pods of mulga is analyzed within and among populations at five topographically uniform sites in southwestern Australia along a gradient of annual precipitation. Phenotypic variability among sites is negatively correlated with annual precipitation, while within sites growth form and phyllode variability covary, and phyllode morphology covaries with pod morphology. Although the two sorts of hypotheses, ecotypic versus apostatic selection, are not clearly separable by morphological data alone, the former appears to be ...