Pollination biology and transcriptomics of Cleomaceae species exhibiting different pollination systems

• Author / Creator

  Higuera, Monica P

• Pollinator mediated-selection is responsible for much of the phenotypic diversity exhibited by flowers. Flowering plants or angiosperms that attract a diverse range of pollinators represent a generalist pollination system in which selection is exerted by many different pollinators. However, generalist pollination systems are difficult to study. They are frequently overlooked, because directional selection may be limited and diffuse selection exerted by pollinators in floral traits is hard to test. Thus, specialist angiosperms attract specific pollinator guilds, which mediates directional or stabilizing selection on floral traits. Selection by a guild of pollinators, such as bees, birds or bats, has led to the convergence of floral phenotypes, known as pollination syndromes. Angiosperms associated to pollination syndromes belong to a specialist pollination system. While, angiosperms that attract a diverse range of pollinators represent a generalist pollination system in which selection is exerted by many different pollinators. However, generalist pollination systems are difficult to study. They are frequently overlooked, because directional selection may be limited and diffuse selection exerted by pollinators in floral traits is hard to asses. One way to understand the evolution of floral traits and pollination systems involves exploring the genes encoding floral traits subject to pollinator-mediated selection. One good family for exploration of these topics is the Cleomaceae, which exhibits variation in floral traits, has species displaying generalist and specialist pollination systems and is an emerging model system for studying floral evolution. In this thesis, I used natural history of Cleomaceae species and molecular methods to compare the pollination biology and genes encoding floral traits from plants exhibiting generalized or specialized floral traits. I observed plants with floral traits that could be subject to pollinator-mediated selection such as color, and nectar glands, and then I used transcriptomics to identify candidate genes that may be responsible for differences in these floral traits.
  My thesis proposed a framework that incorporates ecological and genetic pollination studies, which I have defined as integrative pollination studies. I reviewed genetic techniques used to explore genes underlying floral traits and discuss the use of next generation sequencing to study pollination. Second, I studied the pollination biology of two Cleomaceae species present in Alberta: Cleomella serrulata (Pursh) E.H. Roalson and J.C. Hall and Polanisia dodecandra (L.) DC to determine their pollination systems. I determined that both species have a generalist pollination system, but there were differences in the richness and composition of pollinators between them, due to main differences in floral traits and population locations. To examine differences in the floral evolution of species exhibiting generalized and specialized floral traits, I identified putative candidate genes responsible for pollinator attraction, then I studied the floral transcriptome of these generalist species, along with the specialist Melidiscus giganteus (L.) Raf. Despite phylogenetic distance, the generalist species C. serrulata and P. dodecandra shared more transcripts when compare with M. giganteus. I then examined putative candidate genes for floral traits and found differences in genes encoding color and nectary traits between generalist and specialist species that could be subjected to selection by pollinators. However, the genes encoding floral traits in specialist and generalist species were similar overall. Finally, I aimed to down-regulate candidate genes important for pollinator attraction to obtain plants with modified phenotypes that could be used in pollinators preference tests. I tested the feasibility of the virus-inducing gene silencing (VIGS) technique in P. dodecandra. Unfortunately, this species was not amenable to VIGS, but it was feasible in Cleome violacea L., which may be a good candidate species for further pollination studies.
  Overall, my results indicate that species exhibiting generalized and specialized floral traits were similar in terms of gene repertoires despite being pollinated by different pollinators and despite phylogenetic distance. The generalist species were pollinated by different pollinator assemblages, although the populations were located nearby. The transcriptomes of the generalist species were more similar to each other than to that of the specialist, generalists and specialist were alike in terms of gene repertoires. This thesis advances our understanding of the pollination biology and genetics of floral traits in Cleomaceae. I recommend that Cleomaceae be used as a comprehensive model to study the transitions between generalist and specialist pollination systems, and to study the evolution of floral traits important for pollinator attraction.

• Subjects / Keywords

  • Cleomaceae
  • Pollination
  • VIGS
  • Transcriptomics

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R39K4685H

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.