Barfod; The palm family Arecaceae: The purpose of this review is to highlight the amazing diversity of sexual expression in palms with a view to proposing scenarios to explain the evolution of this character, drawing on the numerous advances that have been made over the last 20 years in palm systematics, ecology, developmental biology, phylogenetics Sexually ambiguous palm tree genomics. We provide an overview of the variability of sexual expression in palms, with illustrations of the associated morphological diversity and its significance to reproduction.
We discuss the evolution of sexual systems using the most recent phylogenetic framework available for palms. Finally, we review advances made towards unravelling the genetic basis of sexual expression in palms.
Our survey opens new perspectives for understanding how plant sexuality has evolved in angiosperms as a whole. The diversity of reproductive structures Sexually ambiguous palm tree strategies in flowering plants has long fascinated botanists and evolutionary biologists. Reproductive systems in plants may relate to pollination, sexual expression in space and time, and mating or breeding systems, i.
Barrett, ; Charlesworth, Hermaphroditism, in which all flowers bear functional male and female organs, is the most common situation in angiosperms. Monoecy, with male and female flowers borne on the same plant, has received less attention than hermaphroditism and dioecy.
Darwin considered monoecy to be an adaptation to favour outcrossing due to greater spatial separation between pollen and stigmas, whereas dioecy guarantees that selfing will never occur.
In monoecious plants, outcrossing may be further favoured by temporal separation of the sexual phases, a state referred to as dichogamy. Conversely, unisexual flowers allow dimorphism and consequently specialization in the number, shape, size and positioning of male and female flowers, with implications for pollination and fruiting in particular. Dioecy and monoecy are considered to be derived from through pathways that may involve intermediate stages.
The most likely pathway to explain the Sexually ambiguous palm tree from hermaphroditism to monoecy is through andromonoecy male and hermaphrodite flowers produced on the same plant rather than gynomonoecy female and hermaphrodite flowers produced on the same plantas suggested by a sex allocation model de Jong et al. Two main evolutionary pathways have been suggested Barrett, One involves monoecy and hypothesizes a gradual transition in the relative proportions of male and female flowers, eventually leading to sexual separation between Sexually ambiguous palm tree and female plants.
Evidence for this pathway has been found in a few taxa. The other hypothetical pathway leading to dioecy in angiosperms proceeds through gynodioecy, which involves male sterility mutations, invasion of hermaphrodite populations by female individuals and further selection of the male.
A phylogenetic analysis of dioecy in monocots suggested that dioecy probably evolved more often directly from hermaphroditism than from monoecy, meaning that monoecy would have evolved independently Weiblen et al. Among the angiosperms, palms stand out as being particularly diverse in terms of sexual expression patterns in both space and time.
The Sexually ambiguous palm tree comprises c. Although somewhat constrained by their relatively "Sexually ambiguous palm tree" modular body plan, they display an impressive variability in the architectural design of their leaves, stems and floral parts Tomlinson, This variation in sexual systems, combined with the fact that there is a robust comprehensive phylogenetic framework Baker et al.
As a prelude to future research on sexual systems in palms and other angiosperms, we provide here a review of sexual expression across Arecaceae. We synthesize current knowledge of the variability of sexual expression in palms, in terms of morphology, space and time, and its developmental and genetic bases. Building on this information, we discuss putative pathways for the evolution of sexual expression in the family in its phylogenetic framework.
The genera considered in this study follow Palmweb http: The latter is therefore the backbone source of information throughout this review. The number of genera and species follows Palmweb http: More rarely, combinations of bisexual and unisexual flowers are found on the same individual or on separate plants, a phenomenon often referred to as polygamy Dransfield et al.
The spatial separation of male and female functions takes place at various structural levels: Genus- and species-level survey of sexual system in palms, at the family level bottom line and in each of the five subfamilies. Diversity of sexual expression in palms.