Pannell lab overview
Current projects in the group are addressing a number of questions concerning evolutionary transitions between sexual systems and their implications for mating and resource allocation. Some of these are summarised under the project descriptions below. For further details, follow the links to the corresponding webpages of the postdocs or students concerned.
Transitions between combined and separate sexes in Mercurialis annua
Several projects aim to explain and understand transitions between combined and separate sexes in the European annual plant Mercurialis annua, which displays dioecy (fully separate sexes), monoecy (self-fertile functional hermaphroditism) and androdioecy (the coexistence of males and hermaphrodites) and occasional male sterility.
Male (A), female (B) and monoecious (C) individuals of Mercurialis annua. Photos: J. Baker.
Using whole genome sequencing and transcriptomics analysis postdoc Katie Ridout (in collaboration with Dr. Dmitry Filatov at the University of Oxford) is assembling and annotating the sex chromosomes of Mercurialis annua in order to investigate the evolution of sex chromosomes and dioecy in Mercurialis. Using a combination of these tools, analysis of interspecific crosses, and natural selection experiments, PhD student Guillaume Cossard is attempting to further unravel the ecological and genetic factors responsible for sexual-system variation in the group. Postdoc Dr. Camille Roux is using Approximate Bayesian Computation to understand the order of key events that have been involved in the diversification of the group, notably sexual-system and ploidy transitions.
Diagrams depicting four of the many possible scenarios underlying genome duplication via autotetraploidy and subsequent diploidisation of the genome (the cessation of gene flow between homoleogous genomes). Tube width reflects population size. Approximate Bayesian Computation is being used to discriminate among these and other scenarios.
Evolutionary ecology of flower and inflorescence strategies under wind pollination
We are also using phenotypic variation in Mercurialis annua to test hypothesis concerning the evolution of inflorescence architecture and how it affects the population mating system. One study, conducted by postdoc Dr. Anne-Marie Labouche, considers the effects of pollen limitation and pollen competition on offspring number and quality as a function of plant density. Another, conducted by postdoc Dr. Luis Santos del Blanco, attempts to tease apart the effects of density and plant size on plant mating (selfing and outcrossing rates) under wind pollination. Luis is also using field and manipulative array experiments to understand the costs and benefits of different inflorescence architecture found across the species’ range.
Experimental arrays of wind-pollinated Mercurialis annua, in which distance from a pollen source regulates the intensity of pollen competition. Photo: A-M. Labouche
Transitions between nocturnal and diurnal pollination
Postdoc Dr. Anne-Marie Labouche is studying the characters that have diverged between the nocturnally pollinated Silene latifolia and diurnally pollinated Silene dioica. Nocturnal pollination would appear to be costly for S. latifolia, because the pollinator (Hadena bicruris) lays eggs in the flowers that hatch seed-eating caterpillars. By assessing the fitness costs and benefits in experimental hybrid populations, Marie is attempting to understand why an apparently maladaptive pollination syndrome is maintained.
Female flower of Silene latifolia being visited by Hadena bicruris. Photo : A-M. Labouche
Breakdown of self-incompatibility in Linaria cavanillesii
Self-incompatibility has been lost on numerous occasions in flowering plants. To contribute to our understanding of how and why this transition occurs, PhD student Marie Voillemot is using self-compatible and self-incompatible (SI) populations of the Spanish toadflax Linaria cavanillesii as a model. Commonly, when SI breaks down, plants evolved smaller, less rewarding flowers. Interestingly, this ‘selfing syndrome’ does not appear to have evolved in L. cavanillesii. The project aims to determine what might have caused this loss of SI, to ascertain its effect on the mating system and pollination biology, and to characterize the population genetic consequences at the locus causing SI and other loci across the genome.
Habitat of Linaria cavanillesii in southeastern Spain. Photo: J.R. Pannell
Maintenance of males with hermaphrodites in Fraxinus ornus
Over the last decade or so, my lab has contributed much that is known about how males can be maintained with hermaphrodites (the androdioecious sexual system), with substantial effort invested into understanding androdioecy in Mercurialis annua. We are currently also working on this sexual system in the Mediterranean tree Fraxinus ornus. In collaboration with Miguel Verdu at CSIC in Valencia, Spain, and PhD student Marie Voillemot, postdoc Dr. Alok Gupta is testing the hypothesis that differences in the fitness of male-sired and hermaphrodite-sired progeny in the Mediterranean tree Fraxinus ornus can be attributed to differences in paternally transmitted patterns of gene expression. Alok is also studying the evolution of sexual dimorphism in this species using gas chromatography-mass spectrometry (GC-MS) to analyze the scent volatiles from males and hermaphrodites in natural populations of F. ornus, followed by the use of next-generation sequencing to identify scent-related floral transcripts.
The lab group at a recent research and fondue away day on the top of Moléson.