A Phylogenomic Analysis of the Floral Transcriptomes of Sexually Deceptive and Rewarding European Orchids, Ophrys and Gymnadenia

Abstract

The orchids (Orchidaceae) constitute one of the largest and most diverse families of flowering plants. They have evolved a great variety of adaptations to achieve pollination by a diverse group of pollinators. Many orchids reward their pollinators, typically with nectar, but the family is also well-known for employing deceptive pollination strategies in which there is no reward for the pollinator, in the most extreme case by mimicking sexual signals of pollinators. In the European flora, two examples of these different pollination strategies are the sexually deceptive genus Ophrys and the rewarding genus Gymnadenia, which differ in their level of pollinator specialization; Ophrys is typically pollinated by pseudo-copulation of males of a single insect species, whilst Gymnadenia attracts a broad range of floral visitors. Here, we present and describe the annotated floral transcriptome of Ophrys iricolor, an Andrena-pollinated representative of the genus Ophrys that is widespread throughout the Aegean. Furthermore, we present additional floral transcriptomes of both sexually deceptive and rewarding orchids, specifically the deceptive Ophrys insectifera, Ophrys aymoninii, and an updated floral transcriptome of Ophrys sphegodes, as well as the floral transcriptomes of the rewarding orchids Gymnadenia conopsea, Gymnadenia densiflora, Gymnadenia odoratissima, and Gymnadenia rhellicani (syn. Nigritella rhellicani). Comparisons of these novel floral transcriptomes reveal few annotation differences between deceptive and rewarding orchids. Since together, these transcriptomes provide a representative sample of the genus-wide taxonomic diversity within Ophrys and Gymnadenia (Orchidoideae: Orchidinae), we employ a phylogenomic approach to address open questions of phylogenetic relationships within the genera. Specifically, this includes the controversial placement of O. insectifera within the Ophrys phylogeny and the placement of “Nigritella”-type morphologies within the phylogeny of Gymnadenia. Whereas in Gymnadenia, several conflicting topologies are supported by a similar number of gene trees, a majority of Ophrys gene topologies clearly supports a placement of O. insectifera as sister to a clade containing O. sphegodes.

Why are there so many bee‐orchid species? Adaptive radiation by intra‐specific competition for mnesic pollinators

“…Secondly, the analyses of the composition of pheromone analogues within the Ophrys insectifera clade, which is the most basal clade according to most molecular phylogenetic hypotheses [Fig. 1; but see Bateman, Sramkó, & Paun, 2018 and Piñeiro Fernandes et al ., 2019], using DNA sequence data showed the simultaneous emission of both esters and non‐polar hydrocarbons (Joffard, Buatois, & Schatz, 2016; Gervasi et al ., 2017). Moreover, among the three species in this clade, O. aymoninii , which is the only one to be pollinated by a species of Andrena ( A. combinata ), is also the only one to emit esters (Joffard, Buatois, & Schatz, 2016).…”

“…As in other biological systems, this limitation is now being overcome by the increasing availability of high‐throughput sequencing technologies. The genomic information available for Ophrys is currently limited to the three published plastid genomes [ O. iricolor , O. sphegodes and O. aveyronensis (Roma et al ., 2018; Bertrand et al ., 2019)], and to the floral transcriptomes of O. iricolor , O. sphegodes , O. insectifera and O. aymoninii (see Piñeiro Fernándes et al ., 2019). Below, we speculate on the mechanisms that would allow phenotypic changes, particularly changes in the organic compounds comprising the floral olfactory phenotypes.…”

Identification of (Z)-8-Heptadecene and n-Pentadecane as Electrophysiologically Active Compounds in Ophrys insectifera and Its Argogorytes Pollinator

“…The phylogenetic relationships within Ophrys are currently under debate [33][34][35][36][37], with some phylogenetic analyses indicating that the Argogorytes-pollinated O. insectifera group represents a basal taxon, while the latest studies place the O. fusca complex, including O. iricolor, as ancestral [36,37]. All studies agree that wasp pollination is ancestral to bee pollination in Ophrys.…”

Whole plastid genome-based phylogenomics supports an inner placement of theO. insectiferagroup rather than a basal position in the rapidly diversifyingOphrysgenus (Orchidaceae)

“…However, recent findings based on genomic data: SNPs derived from RAD-seq approaches (Bateman et al . 2018) or transcriptomes (Piñeiro Fernández et al 2019) rather support that the group insectifera (A) is directly related to the ‘recent Euophrys ’ (groups F to H) both of which being sister to the clade comprising the ‘archaic Euophrys ’ + Pseudophrys (groups B to E) ( T inner ).…”

“…Most of the molecular phylogenetic hypotheses have (historically) rather supported a basal position (T basal ) for the O. insectifera (A) group (Devey et al 2008;Breitkopf et al 2015, Zitoun et al in prep). However, recent findings based on genomic data: SNPs derived from RAD-seq approaches (Bateman et al 2018) or transcriptomes (Piñeiro Fernández et al 2019) rather support that the group insectifera (A) is directly related to 'non-basal Ophrys'…”