Dioecious plants often display biased sex ratios. While there is considerable evolutionary theory describing conditions under which biased sex ratios should occur, there is limited empirical data testing this theory in plants. The studies that do exist are often incomplete and simply infer potential mechanisms to explain the observed bias. We’ve utilized data from 76 studies, on 71 different species of which 30 reported female bias ratios, 35 reported male bias ratios, and 11 reported an even or changing sex ratio. Of the 71 species, 27 exhibited a female bias, 34 a male bias and 10 reported a sex ratio of unity. Our goal was to apply statistical analysis to see what relationships, if any, exist between life history features and bias sex ratios.
Results/Conclusions
Our analysis shows that the biased sex ratios, and the bias itself is not independent of key life history features such as the type of fruit dispersal or the species life form. Species with abiotic seed dispersal, e.g., wind and gravity, had sex ratios that were significantly more often female biased, while species whose seeds were mammal dispersed were male biased. Bird dispersal occurred evenly in both types. We also determined that tree species were twice as likely to be male bias over female bias, while the smaller plants such as herbs and shrubs were heavily female bias. Building upon existing theory, we show that the relative dispersal of pollen versus seeds plays a significant roll in determining whether the ratio will be bias and in what direction.
