PhD: Angiosperm evolution and the Arctic floral revolution

Angiosperms (flowering plants) are an extremely diverse group of terrestrial plants composed of an estimated 260,000 species. They are characterised by high morphological diversity, with an array of life forms that includes herbs, epiphytes, bulbs, aquatic plants, shrubs and trees. Angiosperms also have unique anatomical features that enable them to be powerful agents of climatic change, and their evolution represents a fundamental event in the evolution of the Earth and the climate system.

Despite the evolutionary and climatic importance of angiosperms, our understanding of their long-term patterns of early evolution remains patchy. Existing data from North America indicate that angiosperms radiated during the Cretaceous period (~150–65 million years ago), but that their taxonomic and morphological evolution was decoupled (Lupia 1999). In particular, the earliest phases of angiosperm evolution were characterised by the rapid and explosive addition of novel and highly disparate morphologies as angiosperms spread over the Earth.

However, this macroevolutionary pattern has only been reported in North America at the stage level using published literature. Consequently, it is currently unclear whether the early and rapid evolution of novel and highly disparate morphologies is characteristic of angiosperm evolution in general, or a regional phenomenon. Additionally, the coarse time-scales of existing macroevolutionary analyses (Lupia 1999) mean that we do not know whether these plants speciated gradually, or their evolution was characterised by a punctuated pattern with periods of rapid speciation followed by long-term stasis (Benton and Pearson 2001).

This PhD project will address these fundamental evolutionary issues by using fossil pollen from existing rock samples taken from the Albian–Maastrichtian Alaskan Arctic Slope (Herman et al. 2016), and the early Cenomanian (~98–95 Ma) Warder Formation, New Zealand. This project has aims to: (1) Make a quantitative assessment of the taxonomic diversity and morphological disparity of angiosperm pollen from the Albian–Maastrichtian of the Alaskan Arctic Slope. (2) Reconstruct the mode of angiosperm evolution in this region. (3) Generate a palaeobiogeographic comparison of the Alaskan Arctic Slope and the Warder Formation, New Zealand.

METHODOLOGY AND TRAINING
Existing rock samples (150 from Alaska and 40 from New Zealand) will be macerated in the laboratory using standard palynological processing techniques to release fossil angiosperm pollen grains. The diversity and disparity of these pollen grains will be assessed by scoring individual specimens for discrete morphological characters and measuring the nature of morphospace occupation through time using the methods of Mander (2016). The mode of angiosperm evolution will be assessed by making morphometric measurements of key taxa. These measurements will be plotted against time to test for gradual versus punctuated modes of evolution. Biogeographic comparison between the Cenomanian of Alaska and New Zealand will involve reconstructing the diversity and composition of the vegetation in these two regions using fossil pollen.

This project will provide specific training in: (1) Palynological techniques to extract fossil pollen from rock samples. (2) The description of plant morphology using morphometric techniques. (3) The use of high-resolution optical and electron microscopy. (4) Macroevolutionary analytical techniques to examine the morphological and taxonomic diversification of major clades.

REFERENCES
Benton, M. J. and Pearson, P. N. (2001) 'Speciation in the fossil record', Trends in Ecology & Evolution, 16, 405-411.
Herman, A. B., Spicer, R. A. & Spicer, T. E. V. (2016) 'Environmental constraints on terrestrial vertebrate behaviour and reproduction in the high Arctic of the Late Cretaceous', PPP, 295, 423-442.
Lupia, R. (1999) 'Discordant morphological disparity and taxonomic diversity during the Cretaceous angiosperm radiation: North American pollen record', Paleobiology, 25, 1-28.
Mander, L. (2016) 'A combinatorial approach to angiosperm pollen morphology', Proceedings of the Royal Society B, 283, 20162033.