Genetic architecture of pollination syndrome transition between hummingbird-specialist and generalist species in the genusRhytidophyllum(Gesneriaceae)

Abstract

Adaptation to pollinators is a key factor of diversification in angiosperms. The Caribbean sister genera Rhytidophyllum and Gesneria present an important diversification of floral characters. Most of their species can be divided in two major pollination syndromes. Large-open flowers with pale colours and great amount of nectar represent the generalist syndrome, while the hummingbird-specialist syndrome corresponds to red tubular flowers with a less important nectar volume. Repeated convergent evolution toward the generalist syndrome in this group suggests that such transitions rely on few genes of moderate to large effect. To test this hypothesis, we built a linkage map and performed a QTL detection for divergent pollination syndrome traits by crossing one specimen of the generalist species Rhytidophyllum auriculatum with one specimen of the hummingbird pollinated R. rupincola. Using geometric morphometrics and univariate traits measurements, we found that floral shape among the second-generation hybrids is correlated with morphological variation observed between generalist and hummingbird-specialist species at the genus level. The QTL analysis showed that colour and nectar volume variation between syndromes involve each one major QTL while floral shape has a more complex genetic basis and rely on few genes of moderate effect. Finally, we did not detect any genetic linkage between the QTLs underlying those traits. This genetic independence of traits could have facilitated evolution toward optimal syndromes.

Association between Petal Form Variation and CYC2-like Genotype in a Hybrid Line of Sinningia speciosa

“…Brock et al (2012) used the natural populations of the model plant Arabidopsis thaliana to examine the association between petal form and genotypic variations. In addition, some studies in non-model plants, such as Rhytidophyllum (Alexandre et al, 2015), Mimulus (Fishman et al, 2015), and Penstemon (Wessinger et al, 2014), the quantitative trait loci (QTL) analysis was performed to determine the gene alleles that affect petal forms. In addition to the petal form variation in nature, the changes in petal form during floricultural domestication exhibited a strong link with a single gene (Chapman et al, 2012).…”

Comparative transcriptome analyses of flower development in four species of Achimenes (Gesneriaceae)

“…This study is among the first to employ RNA sequencing for comparative studies both between species and between developmental stages in flowering plants [ 16 , 18 ]. This study is also among the first to characterize and annotate floral transcriptomes in Neotropical Gesneriaceae, a lineage well known for diverse and colorful flowers [ 50 ]. Achimenes offers a unique opportunity to study the genomics of flower diversification in a comparative context because very closely related species display an extraordinary range of morphological diversity likely tied to pollinator preferences and shifting patterns of gene expression.…”

Co-expression clustering across flower development identifies modules for diverse floral forms inAchimenes(Gesneriaceae)

“…investigated the genetic basis of floral development in the Gesneriaceae family (Alexandre et al, 2015;Roberts & Roalson, 2017). Given that bee, butterfly, and hummingbird pollination syndromes evolved in parallel across Achimenes, we hypothesized that:…”

“…Very few studies have so far investigated the molecular mechanisms involved in the development of flower shape in the Gesneriaceae (Gao et al, 2008;Zhou et al, 2008;Alexandre et al, 2015). However, extensive work has been done in model organisms, such as Arabidopsis thaliana and Antirrhinum majus, which can provide insight into the potential roles that many transcription factors might play in determining floral organ identity and shape in Achimenes.…”

“…Other approaches, such as quantitative trait locus (QTL) analyses may provide more promise in identifying distinct genes that are involved in the divergence of floral traits. QTL studies have already shown promise in identifying genetic loci that underlie pollination syndrome divergence in Mimulus (Yuan et al, 2013), Penstemon (Wessinger, Hileman & Rausher, 2014) and Rhytidophyllum (Alexandre et al, 2015).…”