Genetic & Ecological Consequences of Polyploidy

Occurrences of spontaneous polyploidy within a species (autopolyploidy), or as a result of hybridization between species (allopolyploidy), generate opportunities to investigate how the duplication of genes and chromosomes impact the ecology and evolutionary trajectory of populations, species and communities. My postdoctoral work has led to a greater understanding of the predictability of the effects of autopolyploidy on morphological and ecological phenotypes.

I generated more than 100 independent newly-synthesized, or neopolyploid, individuals from over 50 wild Arabidopsis thaliana plants collected throughout its naturally occurring range. I then grew diploid and neopolyploid individuals of each of these ecotypes in a common environment to assess phenotypic variation between and among the ploidy levels of each ecotype at several stages of growth and development. This generated the largest and most complete dataset of phenotypic comparisons between neopolyploids and their diploid progenitors ever produced.

I found that ancestral diploid genotypes differed with respect to nine of 10 vegetative and reproductive traits, and were correlated with longitude and latitude of sampling location. Genome duplication had a significant overall effect on the same nine traits but the direction of effect was not always consistent with the expectation that polyploids are larger. The magnitude of the ploidy effect differed significantly among genotypes and was correlated to different degrees with the phenotype of the ancestral diploid.

This work shows that polyploidy can have highly variable effects on phenotype that are partially dependent on diploid genotype and phenotype. Strong genic-by-genomic interactions may accelerate early evolutionary change by generating phenotypic variance and suggest that success of polyploids is not driven by a singular fitness effect but, rather, is contingent upon the ancestral genotype. This study is the first of its kind at this scale and its results form a substantial part of the base of the research program I will bring to my next position. This work will have a broad impact across the fields of ecology, evolutionary biology, and crop science.

Below is a time-lapse video of part of the major grow-out described above, and a few pictures detailing this project in general.

Creating neopolyploid Arabidopsis

Prior to the large-scale common garden experiment, I created neopolyploid lines of each Arabidopsis ecotype. This was carried out through several steps, the first of which is shown here: growing diploid seeds on a sterile growth matrix. Later, these plants will be exposed to a chemical that induces genome duplication and then extensively assayed for total chromosome count.

Growth chamber

Here, the experimental Arabidopsis ecotypes (both diploids and neopolyploids) begin to germinate. The time-lapse camera that generated the above video can be seen on the far wall. About half of all the plants in this experiment can be seen here.

Arabidopsis seedlings

Five genetically identical seeds were sown into each pot. After a few days, all but one seedling was removed.

Arabidopsis rosettes

By 10 days post-planting, Arabidopsis has begun to form immature rosettes.

Arabidopsis rosettes

About one week post-planting, morphological differences can already be seen among the different ecotypes and ploidy levels of this experimental Arabidopsis plants.

Arabidopsis bolt

As the plants begin to pass though developmental milestones, they are measured and plant tags are marked. In this case, a blue star means the plant has been recorded as bolting.

Flowing Arabidopsis

As each plant becomes mature and begins to flower, additional morphometric measurements are made and developmental time-points are recorded. Here, a gold star has been added to the plant tag, indicating that the flowering date of this plant has been recorded.

Common garden experiment

Emily and I discuss the progress of diploid and polyploid Arabidopsis in my large-scale common garden experiment.

Arabidopsis arrestors

After reaching a certain size, each plant is contained in a custom-built cage (Arabidopsis arrestor). This helps to maintain separation between plants and makes it easier to harvest each individual, collect seed and measure plant traits at the conclusion of the growth phase of the experiment.

Post-harvest drying

After completion of the growth phase of the major common garden experiment, each plant was harvested and allowed to dry, before seed was collected and several morphometric measurements were made. Here, approximately 1/2 of all the plants in this experiement can be seen.