| Summary: | The evolution and maintenance of gender dimorphism was investigated in the New
Zealand genus Hebe (Scrophulariaceae). Hebe originated within New Zealand and gender
dimorphism is postulated to have evolved separately four times within the genus. Gender was
found to be controlled at least partially by nuclear genes for one species of Hebe. Most species
are self-compatible, and H. subalpina was shown to exhibit inbreeding depression. The
frequency of females was found to be negatively correlated with the amount of fruit set on the
polleniferous (or male) morpho Dimorphism is correlated with altitude, and it is hypothesized,
based on the pollinators present at different altitudes and degree to which they self-fertilize
flowers, that separate sexes evolved in response to the increased level of self pollination that
occurs at the higher altitudes.
Female frequency varied greatly among the populations of H. strictissima, and was
found to be negatively correlated with the relative seed fitness of the males. Fruit set on the
males varied greatly in response to plant vigour within plants, among plants within populations,
and among populations. Fruit set on females was not correlated with plant vigour, and varied
less between populations. Female plants were more prevalent in relatively poor sites where
male seed fitness was low.
Gender estimates for H. subalpina, based on fruit set, sex ratio, seed production,
inbreeding depression, and the rate of self-fertilization, showed that males received less than
four per cent of their fitness through ovules. H. subalpina is, therefore, near the dioecy end of
gynodioecy. Fruit set on males varies much more than that on females, and is dependent on
both the status of individual shoots and the genotype of the plant. Resource allocation patterns
differ according to sex, and reflect the way in which the sexes receive their fitness.
|
|---|
