Table 3.

Ecological factors that affect the second step in the evolution of dioecy. Predicted effect on sexual system, mechanisms of action, and example citations are given for each

Ecological factor	Expected consequence for sexual system*	Mechanism†	Example citation
Pollen limitation	Selects for SD	Reproductive assurance maintains H	Maurice and Fleming (1995), Ehlers and Bataillon (2007)
Selfing by hermaphrodites	Selects for SD	In combination with pollen limitation favours H	Ehlers and Bataillon (2007), Del Castillo and Argueta (2009)
	Retards D	Geitonogamous selfing and pollen discounting disfavours M	de Jong et al. (1999)
	Selects for D	Prior selfing with negligible pollen discounting in combination with high inbreeding depression favours M	de Jong et al. (1999)
Inbreeding depression	Selects for D	Reduces advantage of selfing by H	Charlesworth and Charlesworth (1978), Maurice and Fleming (1995)
Sex allocation plasticity	Selects for SD	Plasticity of H favoured in heterogeneous environments	Delph and Wolf (2005), Ashman (2006), Ehlers and Bataillon (2007)
Antagonists	Retards D	Male-biased damage reduces pollen fitness gain; male-biased damage increases pollen limitation of F	Ashman (2002)
	Selects for D	Damage to H seed reduces their fitness relative to M	Ashman (2002)

* SD, subdioecy; D, dioecy.

^† H, hermaphrodites; F, female; M, male.