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Gynodioecy is when a population features individuals that produce both male and female gametes and individuals that produce just female gametes. Androdioecy is when a population features individuals that produce both male and female gametes and individuals that produce just male gametes. The former is "not uncommon" and the latter is "virtually unknown."

Charlesworth 1991 states that this is common because cosexual populations would normally evolve a male sterile mutation first, causing gynodioecy, and then female sterility mutation(s) will build up leading to dioecy.

Why should it be so much more common for male sterility mutations to evolve first?

(I think the answer lies within articles cited in the above paper, Charlesworth & Charlesworth 1979 Proc R Soc B, and 1987 Evolution which I'll try to read this weekend, if it is I'll post a self-answer but in the mean time...).

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  • $\begingroup$ I think the short answer is along the lines of: Because ovules represent the limiting factor while there are plenty of pollen grains. Males have a hard time surviving in a androdoiceous population while female might be able to survive in a gynodioceous if it spares enough energy (by not producing any pollen grains) to create ovules. One advantage for a female of not being hermaphrodite compare to other individuals in the population is that it won't lose ovules to produce inbred offspring by selfing. $\endgroup$ – Remi.b Oct 17 '14 at 23:48
  • $\begingroup$ That's what I had interpreted it as $\endgroup$ – rg255 Oct 18 '14 at 7:39

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