botanyoneAmborella trichopoda, the sister species of all other extant angiosperms, is typically dioecious, producing male and female flowers on separate individuals. Anger et al. map sex phenotypes onto a phylogeny of basally diverging angiosperms using maximum parsimony. Sex-ratios and phenotypes were studied in parallel over two consecutive flowering seasons for an ex situ population of A. trichopoda. The sex-ratio of an in situ population was also assessed.
The results show that the primary male-female ratio in A. trichopoda is 1:1, suggesting a genetic mechanism of sex determination, however, male-biased sex ratios were evident in natural populations. Rare sex-change events were observed in A. trichopoda, with bisexual flowers manifesting on otherwise male plants. The authors propose a method to date the origin of dioecy in A. trichopoda and deduce that sexual instability in A. trichopoda suggests the evolution of dioecy via a gynodioecious intermediate.
This paper is available with FREE access as an Editor’s Choice from the March issue of Annals of Botany.
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