Common club moss. Image © adamikarl/Shutterstock
Establishing why certain groups go extinct while others prevail remains a key question in evolutionary biology. Here you will establish why the lycopsids survived while the zosterophylls went extinct.
Project background
The lycophytes are the earliest diverging lineage of vascular plants and have an evolutionary history stretching back over 430 million years. At the end of the Silurian and in the early Devonian lycophytes were the most diverse and complex plants on Earth. However, during this time interval a fundamental divergence was taking place separating the lycophytes into two broad groups, the zosterophylls and the lycopsids. By the end of the Devonian the zosterophylls had all gone extinct whereas the lycopsids thrived and survive through to the present day.
Why the lycopsids prevailed when the zosterophylls went extinct is unclear and in this PhD you will seek to answer this key question. To do this will involve describing new fossils, building phylogenetic trees and characterising trait evolution in both fossil and living lycophytes. Finally, you will interpret the changes recorded in lycophyte fossils in light of global changes at the time to make predictions about the causes of extinction. The description of extinction in the geological past will allow you to search for characteristics that may make lycophyte species more prone to extinction today. The outcome of the project will therefore provide a better framework for understanding how plants cope with global change and establish why certain groups go extinct while others survive.
Research questions
Establish if zosterophylls are a monophyletic or paraphyletic grouping?
What anatomical and developmental traits differ between zosterophylls and lycopsids?
When and where did the extinction of zosterophylls begin?
Was extinction in zosterophylls correlated with global change?
Can we predict which living species of lycophytes are at higher risk of extinction today?
Methodology
Year 1 – Describe new fossils and establish a new phylogeny for lycophytes
In year one you will start off by describing undescribed fossil lycophytes at National Museums Scotland and the London Natural History Museum. These descriptions will provide increased sampling of lycophytes and allow the description of new characteristics to be incorporated in a cladistics matrix. The assembly of the cladistics matrix will then allow you to build a new time calibrated cladistics phylogeny for the group.
Year 2 – Investigate functional and developmental traits in living and fossil lycophytes
Base on your new phylogeny you will have a framework to investigate trait evolution in the lycophytes. You will carry out new detailed anatomical descriptions of traits with new cutting-edge imaging techniques in Edinburgh and London – including confocal laser scanning microscopy, X-Ray Micro Computed Tomography and photogrammetry. You will draw comparisons between both fossils and living plants and interpret development from fossils. This will allow you to establish which key traits, both anatomical and developmental, differ between living and extinct lycopsids and extinct zosterophylls.
Year 3 – Correlate changes in lycophyte diversity and extinction with global change
In the final part of your PhD you will establish if the extinction in lycophytes was influenced by global change in the Devonian. Using published proxies and global biogeochemical models you will look for the signatures of extinction, and evaluate these in light of your new anatomical and developmental data. Finally, you will bring your predictions through to the present day by using published datasets of living lycophytes to help predict living species particularly at risk today due to global change.
Training
A comprehensive training programme will be provided comprising both specialist scientific training and generic transferable and professional skills.
Specific training for the project:
- Phylogenetic methods and cladistics phylogenies.
- Use of museum collections (palaeontology and herbarium) at the Natural History Museum, London
- Anatomical and developmental descriptions of both living and fossil lycophytes.
- Advanced imaging including confocal laser scanning microscopy, X-Ray Micro Computed Tomography and photogrammetry
Requirements
The project is suitable for anyone with a passion for plant evolution with either a Life or Earth Sciences background.
Further reading
Turner HA, Humpage M, Kerp H, Hetherington AJ. 2023. Leaves and sporangia developed in rare non-Fibonacci spirals in early leafy plants. Science. 380: 1188-1192. DOI: https://www.science.org/doi/10.1126/science.adg4014
Hetherington AJ, Bridson SL, Lee Jones A, Hass H, Kerp H, Dolan L. 2021. An evidence-based 3D reconstruction of Asteroxylon mackiei the most complex plant preserved from the Rhynie chert. eLife. 10:e69447. DOI: https://doi.org/10.7554/eLife.69447
Delaux P-M, Hetherington AJ, Coudert Y, Delwiche C, Dunand C, Gould S, Kenrick P, Li F-W, Philippe H, Rensing SA, Rich M, Strullu-Derrien C, de Vries J. 2019. Reconstructing trait evolution: A guideline for plant evo-devo studies (and beyond). Current Biology. 29: R1110-R1118. DOI: https://doi.org/10.1016/j.cub.2019.09.044
Hetherington AJ, Dolan L. 2018. Stepwise and independent origins of roots among land plants. Nature. 561: 235–238. DOI: https://doi.org/10.1038/s41586-018-0445-z
Kenrick P, Crane PR. 1997. The origin and early evolution of plants on land. Nature, 389: 33-39. DOI: https://doi.org/10.1038/37918
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