A model for the evolution of dioecy
Several species are complex polyploids with a range of breeding systems, including apomixis and dioecy
, that promote interspecific hybridization and introgression (Muntzing, 1940; Clausen, 1961).
how hermaphrodite and male sexes are determined) are especially important, because 1) androdioecy is an evolutionary transition phase between hermaphroditism and dioecy
(Weeks et al.
in Actinida polygama: a test of the pollinator attraction hypothesis.
The New Zealand geoduck exhibits functional protandric dioecy
with all geoducks first maturing males and a significant proportion of individuals changing sex to females as they age (Gribben & Creese 2003).
While strictly genetic or chromosomal dioecy
is widespread, other types of reproduction such as hermaphroditism, parthenogenesis, and biased sex ratio appear to be the rule in many species.
Additionally, species in the Caryophyllaceae exhibit a range of breeding systems from hermaphroditism to dioecy
(Muller 1883, Gleason and Cronquist 1963, Thrall et al.
As pointed out earlier, dioecy
offers problems for a switch to animal pollinators because a similar attractant must exist in individuals of both genders, as is most striking in Gnetales.
In other superorders of Cirripedia, namely Acrothoracica and Rhizochephala, dioecy
with coexistence of large females and dwarf males is the norm (Klepal, 1987; Hoeg, 1995).
Key words: Hechtia schottii, Bromeliaceae, reproductive biology, dioecy
, pollinators, Mexico, Yucatan.
Leptostemonum have been studied due to their andromonoecy or functional dioecy
(Wakhloo, 1975a, b; Anderson, 1979; Dulberger et al.
As a group, molluscs exhibit highly diverse modes of sexual reproduction, ranging from functional, simultaneous hermaphroditism to sequential hermaphroditism, to strict dioecy
and genic determination (Coe 1943, Guo & Allen 1994b).