A Draft Genome of the Ginger Species Alpinia nigra and New Insights into the Genetic Basis of Flexistyly

Angiosperms possess various strategies to ensure reproductive success, such as stylar polymorphisms that encourage outcrossing. Here, we investigate the genetic basis of one such dimorphism that combines both temporal and spatial separation of sexual function, termed flexistyly. It is a floral strategy characterised by the presence of two morphs that differ in the timing of stylar movement. We performed a de novo assembly of the genome of Alpinia nigra using high-depth genomic sequencing. We then used Pool-seq to identify candidate regions for flexistyly based on allele frequency or coverage differences between pools of anaflexistylous and cataflexistylous morphs. The final genome assembly size was 2 Gb, and showed no evidence of recent polyploidy. The Pool-seq did not reveal large regions with high FST values, suggesting large structural chromosomal polymorphisms are unlikely to underlie differences between morphs. Similarly, no region had a 1:2 mapping depth ratio which would be indicative of hemizygosity. We propose that flexistyly is governed by a small genomic region that might be difficult to detect with Pool-seq, or a complex genomic region that proved difficult to assemble. Our genome will be a valuable resource for future studies of gingers, and provides the first steps towards characterising this complex floral phenotype.

Phenotypic plasticity triggers rapid morphological convergence

Phenotypic convergence, the independent evolution of similar traits, is ubiquitous in nature, happening at all levels of biological organizations and in most kinds of living beings. Uncovering its mechanisms remains a fundamental goal in biology. Evolutionary theory considers that convergence emerges through independent genetic changes selected over long periods of time. We show in this study that convergence can also arise through phenotypic plasticity. We illustrate this idea by investigating how plasticity drives Moricandia arvensis, a mustard species displaying within-individual polyphenism in flowers, across the morphological space of the entire Brassicaceae family. By compiling the multidimensional floral phenotype, the phylogenetic relationships, and the pollination niche of over 3000 Brassicaceae species, we demonstrated that Moricandia arvensis exhibits a plastic-mediated within-individual floral disparity greater than that found not only between species but also between higher taxonomical levels such as genera and tribes. As a consequence of this divergence, M. arvensis moves outside the morphospace region occupied by its ancestors and close relatives, crosses into a new region where it encounters a different pollination niche and converges phenotypically with distant Brassicaceae lineages. Our study suggests that, by inducing phenotypes that explore simultaneously different regions of the morphological space, plasticity triggers rapid phenotypic convergence.

The Floral Microbiome: Plant, Pollinator, and Microbial Perspectives

Flowers at times host abundant and specialized communities of bacteria and fungi that influence floral phenotypes and interactions with pollinators. Ecological processes drive variation in microbial abundance and composition at multiple scales, including among plant species, among flower tissues, and among flowers on the same plant. Variation in microbial effects on floral phenotype suggests that microbial metabolites could cue the presence or quality of rewards for pollinators, but most plants are unlikely to rely on microbes for pollinator attraction or reproduction. From a microbial perspective, flowers offer opportunities to disperse between habitats, but microbial species differ in requirements for and benefits received from such dispersal. The extent to which floral microbes shape the evolution of floral traits, influence fitness of floral visitors, and respond to anthropogenic change is unclear. A deeper understanding of these phenomena could illuminate the ecological and evolutionary importance of floral microbiomes and their role in the conservation of plant–pollinator interactions.

Frequency of visits and efficiency of pollination by diurnal and nocturnal lepidopterans for the dioecious tree Randia itatiaiae (Rubiaceae)

In plants pollinated by different groups of animals, the most frequent visitors may not be the most effective for fitness because of their differential efficiency in pollen transfer. We addressed this question by studying a rare dioecious species of Rubiaceae in Brazil. The flowers of Randia itatiaiae are gender-heteromorphic and hypocrateriform with greenish corolla tubes ~2 cm long, and exhale a strong sweet scent during the entire period of anthesis, which starts at sunset for female flowers. Sucrose was the dominant or co-dominant nectar sugar for both genders. In spite of these typical sphingophilous-phalaenophilous traits, the flowers last for 6 days, and nectar was available in both diurnal and nocturnal assessments. Moreover, the flowering of R. itatiaiae did not overlap the phenodynamics of the Sphingidae community. Accordingly, two functional groups of Lepidoptera – Hesperiidae during the day and Sphingidae and Noctuidae at night – visited the flowers. Visits by either group resulted in equivalent fruit set and seed number per fruit, although the frequency of visits to flowers was higher during the day than at night. Diurnal and nocturnal lepidopterans may exert similar pressures on floral morphology, in addition to divergent pressures on other characters, such as the temporal dynamics of anthesis and nectar production. The pollination system of R. itatiaiae is specialised at the coarse scale, because its floral morphology precludes pollination by animals other than lepidopterans; however, its floral phenotype also represents a generalist compromise between the conflicting pressures exerted by diurnal and nocturnal groups of lepidopterans.