The Gongora gibba genome assembly provides new insights into the evolution of floral scent in male euglossine bee-pollinated orchids.

Orchidaceae is one of the most prominent flowering plant families, with many species exhibiting highly specialized reproductive and ecological adaptations. An estimated 10% of orchid species in the American tropics are pollinated by scent-collecting male euglossine bees; however, to date, there are no published genomes of species within this pollination syndrome. Here we present the first draft genome of an epiphytic orchid from the genus Gongora, a representative of the male euglossine bee-pollinated subtribe Stanhopeinae. The 1.83 Gb de novo genome with a scaffold N50 of 1.7Mb was assembled using short- and long-read sequencing and chromosome capture (Hi-C) information. Over 17,000 genes were annotated, and 82.95% of the genome was identified as repetitive content. Furthermore, we identified and manually annotated 26 terpene synthase (TPS) genes linked to floral scent biosynthesis and performed a phylogenetic analysis with other published orchid TPS genes. The Gongora gibba genome assembly will serve as the foundation for future research to understand the genetic basis of floral scent biosynthesis and diversification in orchids. Las orquídeas (Orchidaceae) son una de las familias de plantas con mayor riqueza de especies y exhiben adaptaciones reproductivas altamente especializadas. Se estima que el 10% de las especies de orquídeas en los trópicos americanos son polinizadas por abejas euglosinas; sin embargo, hasta la fecha no existen genomas publicados de especies con este síndrome de polinización. Aquí presentamos el primer genoma de una orquídea epífita del género Gongora, un representante de la subtribu Stanhopeinae, que es polinizada exclusivamente por abejas euglosinas macho. El genoma de 1,83 Gb se ensambló de novo utilizando secuenciación e información de captura de cromosomas (Hi-C), logrando un N50 de 1,7 Mb. Se anotaron más de 17.000 genes y se identificó que el 82,95% del genoma presenta elementos repetitivos. Además, identificamos y anotamos manualmente 26 genes de la familia de genes terpeno sintasa (TPS) y realizamos un análisis filogenético con otros genes TPS de orquídeas publicados. El ensamblaje del genoma de Gongora gibba servirá como base para futuras investigaciones para comprender la base genética de la biosíntesis y la diversificación de los aromas florales en las orquídeas.

Macroevolution of floral scent chemistry across radiations of male euglossine bee-pollinated plantsMacroevolución de olores florales a través de radiaciones de plantas polinizadas por abejas euglosinas machosMacroevolução dos voláteis florais em radiações de plantas polinizadas por machos de abelhas Euglossini.

Floral volatiles play key roles as signaling agents that mediate interactions between plants and animals. Despite their importance, few studies have investigated broad patterns of volatile variation across groups of plants that share pollinators, particularly in a phylogenetic context. The "perfume flowers," Neotropical plant species exhibiting exclusive pollination by male euglossine bees in search of chemical rewards, present an intriguing system to investigate these patterns due to the unique function of their chemical phenotypes as both signaling agents and rewards. We leverage recently developed phylogenies and knowledge of biosynthesis, along with decades of chemical ecology research, to characterize axes of variation in the chemistry of perfume flowers, as well as understand their evolution at finer taxonomic scales. We detect pervasive chemical convergence, with many species across families exhibiting similar volatile phenotypes. Scent profiles of most species are dominated by compounds of either the phenylpropanoid or terpenoid biosynthesis pathways, while terpenoid compounds drive more subtle axes of variation. We find recapitulation of these patterns within two independent radiations of perfume flower orchids, in which we further detect evidence for the rapid evolution of divergent floral chemistries, consistent with the putative importance of scent in the process of adaptation and speciation.

Climate Predicts UV Floral Pattern Size, Anthocyanin Concentration, and Pollen Performance in Clarkia unguiculata.

Given that flower size and pigmentation can mediate plant-pollinator interactions, many studies have focused on pollinator-driven selection on these floral traits. However, abiotic factors such as precipitation, temperature, and solar radiation also contribute to geographic variation in floral color, pattern, and size within multiple species. Several studies have described an ecogeographic pattern within species in which high temperature, high ultraviolet (UV) radiation, low precipitation and/or low latitudes are associated with increased floral anthocyanin production, smaller flowers, and/or larger UV-absorbing floral patterns (nectar guides or bullseyes). However, latitude or elevation is often used as a proxy variable to study variation in floral traits associated with a wide range of climatic variables, making the proximate abiotic drivers of variation difficult to identify. In this study, we tested and corroborated several predictions for how the abiotic environment may directly or indirectly shape geographic patterns of floral color, pattern, and size in Clarkia unguiculata (Onagraceae). This study provides the first report of geographic variation in multispectral floral color and pattern in C. unguiculata, while also providing an experimental test of the putative protective role of UV absorption for pollen performance. We quantified geographic variation among greenhouse-raised populations in UV floral pattern size, mean UV petal reflectance, anthocyanin concentration, and petal area in C. unguiculata across its natural range in California and, using 30 year climate normals for each population, we identified climatic and topographic attributes that are correlated with our focal floral traits. In addition, we examined pollen performance under high and low UV light conditions to detect the protective function (if any) of UV floral patterns in this species. Contrary to our expectations, the nectar guide and the proportion of the petal occupied by the UV nectar guide were largest in low solar UV populations. Estimated floral anthocyanin concentration was highest in populations with high solar UV, which does support our predictions. The size of the UV nectar guide did not affect pollen performance in either of the light treatments used in this study. We conclude that, under the conditions examined here, UV-absorbing floral patterns do not serve a direct "pollen protection" function in C. unguiculata. Our results only partially align with expected ecogeographic patterns in these floral traits, highlighting the need for research in a wider range of taxa in order to detect and interpret broad scale patterns of floral color variation.

Sex-specific floral attraction traits in a sequentially hermaphroditic species.

●Many angiosperms are hermaphroditic and produce bisexual flowers in which male (pollen export) and female (stigma receptivity) functions are separated temporally. This sequential hermaphroditism may be associated with variation in flower size, color, or pattern, all of which may influence pollinator attraction. In this study, we describe variation in these traits across discrete functional sex stages within and between 225 greenhouse-grown individuals of Clarkia unguiculata (Onagraceae). In addition, to identify the effects of floral phenotype on pollinator attraction in this species, we examine the effects of these floral traits on pollen receipt in ~180 individuals in an experimental field array.●Petal area, ultraviolet (UV)-absorbing nectar guide area, and blue and green mean petal reflectance differ significantly across the functional sex stages of C. unguiculata. Male- and female-phase flowers display significantly different pollinator attraction traits. Petal and UV nectar guide area increase as flowers progress from male phase to female phase, while blue reflectance and green reflectance peak during anther maturation.●In field arrays of C. unguiculata, female-phase flowers with large UV nectar guides receive more pollen than those with small nectar guides, and female-phase flowers with high mean blue reflectance values are more likely to receive pollen than those with low blue reflectance. Female-phase flowers with green mean reflectance values that differ most from background foliage also receive more pollen than those that are more similar to foliage. These findings indicate that components of flower color and pattern influence pollen receipt, independent of other plant attributes that may covary with floral traits. We discuss these results in the context of hypotheses that have been proposed to explain sex-specific floral attraction traits, and we suggest future research that could improve our understanding of sexual dimorphism in sequentially hermaphroditic species and the evolution of features that promote outcrossing.

Divergence in pollen performance between Clarkia sister species with contrasting mating systems supports predictions of sexual selection.

Animal taxa that differ in the intensity of sperm competition often differ in sperm production or swimming speed, arguably due to sexual selection on postcopulatory male traits affecting siring success. In plants, closely related self- and cross-pollinated taxa similarly differ in the opportunity for sexual selection among male gametophytes after pollination, so traits such as the proportion of pollen on the stigma that rapidly enters the style and mean pollen tube growth rate (PTGR) are predicted to diverge between them. To date, no studies have tested this prediction in multiple plant populations under uniform conditions. We tested for differences in pollen performance in greenhouse-raised populations of two Clarkia sister species: the predominantly outcrossing C. unguiculata and the facultatively self-pollinating C. exilis. Within populations of each taxon, groups of individuals were reciprocally pollinated (n = 1153 pollinations) and their styles examined four hours later. We tested for the effects of species, population, pollen type (self vs. outcross), the number of competing pollen grains, and temperature on pollen performance. Clarkia unguiculata exhibited higher mean PTGR than C. exilis; pollen type had no effect on performance in either taxon. The difference between these species in PTGR is consistent with predictions of sexual selection theory.