Role of Soil Phosphorus in Trait Evolution and Diversification of Hakea (Proteaceae) in the Southwest Australian Floristic Region

The southwest Australian floristic region (SWAFR) is considered one of the world's biodiversity hotspots (Myers et al. 2000). Almost half of its 7380 native plant species are endemic to the region, and more than a quarter of the total number are threatened (Hopper and Gioia 2004). The SWAFR is an old and infertile landscape, similar climatically and in soil age to only two other regions on Earth: South Africa's Cape and Venezuela's Pantepui Highlands (Hopper 2009). The great diversity of this region is of interest in part due to the strikingly different characteristics of the landscape in comparison to the more familiar flora and terrain of the Northern Hemisphere (Hopper 2009). While plant growth on most of the world's soils is nitrogen limited, plant growth on Australia's soils is limited by phosphorus (Lambers et al. 2008), as this nutrient has washed away to the ocean during the hundreds of millions of years that this landscape has been exposed and there has been no tectonic activity to rejuvenate these ancient, weathered soils (Pillans 2007). At 859 species (~1,100 total spp. in Australia), the Proteaceae is the second largest plant family in the SWAFR (Hopper and Gioia 2004), with approximately 690 species endemic to this region (Sauquet et al. 2009). Taken together, these two factors make this family an ideal focus for exploring patterns of diversity. Hakea (Proteaceae) is a woody genus of 150 species of shrubs and trees, with its center of diversity in the SWAFR; the majority (~70%) of its species are endemic to the region (Groom and Lamont 1996). I have combined phylogeny with distributional, physiological, and ecological data in order to explore trait evolution and correlations with soil phosphorus in a small focal clade (22 spp.) of Hakea endemic to the SWAFR. This project contains three parts: (1) phylogenetic reconstruction and biogeographic inference, (2) soil phosphorus sampling of populations of the focal species, and (3) ancestral state reconstruction and tests of evolutionary correlation in the distribution along the soil phosphorus gradient and other plant features (e.g., leaf mass per area). I resolved the relationships of a 22-species focal clade of Hakea, and discovered an initial split about 15 Ma ago between an ancestor distributed in the northern sandplains and one distributed across the southern sandplains in the SWAFR. Further, I found that the arrival in Australia of Oenochrominae moths with green, horned larvae pre-dates the diversification of horned fruits in Hakea. I did not find significant evolutionary correlations among soil phosphrous levels and the three the traits that I tested: phosphorus sensitivity, leaf mass area, and fire survival strategy.