POLYPLOIDY: physiology, ecology, evolution
Polyploidy is thought to be an important driver of plant evolution by facilitating diversification and speciation. This is particularly true in plants, and numerous studies have now provided evidence for polyploidization having played a key role in the evolution of many major vascular plant groups. Despite evidence to support polyploidy as an important evolutionary mechanism for species diversification, population ecology theory describes a challenging landscape for newly formed polyploids and suggests that the survival and persistence of newly formed polyploids may occur relatively rarely. Yet, when we look across the landscape, we see myriad polyploid species that apparently indicate that some polyploids are highly successful. This sets up a conflict between the strong evidence of polyploidy for a key evolutionary mechanisms, population ecology theory predictions that polyploids should rarely be ecological successful, and the empirical observations of numerous polyploids that appear ecologically successful. Especially limited is our understanding of how/when polyploidization drives the evolution of novel physiological traits, and how those traits determine species' distributions. My research in polyploid biology focuses on the mechanisms that underlie the ecological success of wild polyploids and the holistic analysis of polyploid niches, traits, and genetics to determine the extent to which mixed empirical ecological patterns may be reconciled with theoretical expectations. I work in a variety of systems but with a strong focus on ferns.
Polyploidy is thought to be an important driver of plant evolution by facilitating diversification and speciation. This is particularly true in plants, and numerous studies have now provided evidence for polyploidization having played a key role in the evolution of many major vascular plant groups. Despite evidence to support polyploidy as an important evolutionary mechanism for species diversification, population ecology theory describes a challenging landscape for newly formed polyploids and suggests that the survival and persistence of newly formed polyploids may occur relatively rarely. Yet, when we look across the landscape, we see myriad polyploid species that apparently indicate that some polyploids are highly successful. This sets up a conflict between the strong evidence of polyploidy for a key evolutionary mechanisms, population ecology theory predictions that polyploids should rarely be ecological successful, and the empirical observations of numerous polyploids that appear ecologically successful. Especially limited is our understanding of how/when polyploidization drives the evolution of novel physiological traits, and how those traits determine species' distributions. My research in polyploid biology focuses on the mechanisms that underlie the ecological success of wild polyploids and the holistic analysis of polyploid niches, traits, and genetics to determine the extent to which mixed empirical ecological patterns may be reconciled with theoretical expectations. I work in a variety of systems but with a strong focus on ferns.
Why ferns? Ferns are an ideal group in which to study polyploidy because over 31% of speciation events in ferns involve changes in ploidal level, compared to only 15% in angiosperms. One of the largest and ecologically diverse polyploid fern complexes in North America is in the genus Polystichum. In particular, the allopolyploid P. scopulinum is an allotetraploid that exhibits significantly expanded ecological range and habitat novelty compared to its progenitors, P. lemmonii and P. imbricans. In addition, P. scopulinum can be found co-occurring either both parent, but not both, because P. lemmonii is endemic to serpentine soils. I use this polyploid complex as a unique opportunity to investigate the evolutionary and physiological mechanisms that drive polyploid ecology in areas of niche overlap and novelty, relative to parental taxa that also represent ecological extremes (specialist vs generalist) - all in the lineage where polyploidy is most prevalent but least understood i.e., ferns.
- Which traits have evolved in the allopolyploid that explain the range expansion and niche novelty?
- Is there evidence for biotic (competitive) interactions between the allopolyploid and parental species in locations where they co-occur? And are biotic interactions different when the polyploid co-occurs with the serpentine specialist vs the ecological generalist?
- Which eco-evolutionary processes generated the ecophysiological diversity in the allopolyploid?
To answering these questions, I flew west and sampled over 30 sites at key locations within the ranges of the two diploids and allopolyploid species in an effort to capture representatives of their niche breadth. I collected data on over a dozen functional and physiological traits including photosynthetic parameters (e.g., maximum rates of carboxylation, Vcmax; electron transport, Jmax; stomatal conductance, gs; mesophyll conductance, gm; net photosynthesis, Amax, etc.), stable isotope chemistry (e.g., carbon isotopes, d13C), specific leaf area (SLA), stomatal traits (size and density), vein density (VLA), and leaf hydraulic conductance (Kleaf), etc. I also collected soil samples for pH, P, K, N, Mg, Ca, Ni, Zn, and Pb, and leaves for the exact same elements to understand soil resource utilization. I collected spores to grow gametophytes for stress tolerance experiments. Finally, I am conducting population genetic analyses, in collaboration with Dr. Emily Sessa and Jessie Pelosi, and Dr. Pamela Soltis.
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