Labile sex expression in angiosperm species with sex chromosomes

Here, we review the literature on sexual lability in dioecious angiosperm species with well-studied sex chromosomes. We distinguish three types of departures from strict dioecy, concerning either a minority of flowers in some individuals (leakiness) or the entire individual, which can constantly be bisexual or change sex. We found that for only four of the 22 species studied, reports of lability are lacking. The occurrence of lability is only weakly related to sex chromosome characteristics (number of sex-linked genes, age of the non-recombining region). These results contradict the naive idea that lability is an indication of the absence or the recent evolution of sex chromosomes, and thereby contribute to a growing consensus that sex chromosomes do not necessarily fix sex determination once and for all. We discuss some implications of these findings for the evolution of sex chromosomes, and suggest that more species with well-characterized lability should be studied with genomic data and tools.This article is part of the theme issue 'Sex determination and sex chromosome evolution in land plants'.

Automated summary

In this article, we review the literature on sexual lability in dioecious angiosperm species and find that the occurrence of lability is weakly related to sex chromosome characteristics. These results contradict the idea that lability indicates the absence or recent evolution of sex chromosomes, suggesting that sex chromosomes do not necessarily fix sex determination permanently.