hermaphroditism to dioecy (Willson, 1979; Casper & Chamov, 1982).
evolution of dioecy meant the optimization of outbreeding met with
The presumed association between dioecy and outbreeding is
evidence is mounting of a putative association between dioecy and
In addition, dioecy is overrepresented on the Juan Fernandez Islands in species with small green flowers, a pattern also reported in Hawaii (Sakai et al.
In two genera, it seems likely that dioecy arose in situ.
Outcrossing is mainly achieved through dioecy and SI, promoted by dichogamy, and facilitated by wind pollination.
We propose that the progenitors of Coprosma, Juania, Fagara, and Pernettya already exhibited at least incipient dioecy; in Robinsonia dioecy seems to have arisen in situ.
Charnov (1982) used an evolutionary stable strategy argument (ESS) to show that hermaphroditism cannot be displaced by dioecy if the rate of increase in male fitness decreases as the resources allocated to male fitness increase, i.
As outcrossing would already exist, dioecy is not necessary to generate outcrossing.
Moreover, we believe that in some cases it is possible to identify taxa that evolved dioecy primarily as a result of one mechanism or the other.
A number of observations in terms of basic plant reproductive biology, and a series of case histories, should help to explain the conclusions we have drawn concerning the evolution of dioecy in relation to pollination, breeding syndrome of close relatives, sexual lability, sexual inconstancy, and sexual niche partitioning.