Being a botanist, Part II

I recently went to a talk given by two famous botanists, Drs. Doug and Pam Soltis. They have a joint lab at the University of Florida and their work focuses on molecular systematics and evolutionary genetics. I briefly mentioned in my last blog post what this part of my research entails, but their talk was so inspiring that I’d like to talk about how we use DNA molecules and how it all fits into the bigger puzzle of life.

The Soltis’s focused specifically on the portion of their work involving the Tree of Life. The Tree of Life is essentially a diagram outlining the evolution of all living things. The first time life was described like this was by Charles Darwin in his 1859 book, The Origin of Species, where he described evolution “like a branching tree”. The current Tree of Life project has been revolutionized by the advent of DNA sequencing. You may be familiar with DNA—and picture the double helix composed of nucleotides—which carries genetic information. Scientists use the sequence of these four nucleotides (Adenine, Cytosine, Thymine, and Guanine) as the code for distinguishing species. So what does the Tree of Life actually look like? Using fancy algorithms we can take the DNA sequence and create a phylogenetic “tree”, this is a branched diagram that will show us the relationships of species. For the Tree of Life, composed of 2.3 million species, if we printed this out in a 12-point font, it would cover 14 empire state buildings on all 4 sides!!!

Of these 2.3 million species, we only have DNA sequence information for 17%. The rest of the branches of the Tree of Life are based solely on the name of the species. Scientists obtain these names from natural history collections, which worldwide consist of 3–4 billion specimens. The US has approximately 1400 natural history collections containing 1–2 billion specimens. The names of species lacking DNA sequences were compiled in part because of the recent move to digitize natural history collections worldwide. Before digitization, these collections were only known to the visitors of herbaria and museums. Now, thanks to the Internet most are available, usually with images, to the general public.

If we only have DNA sequences for 17 % of species, this leaves almost 2 million species left to sequence. This seems like an overwhelming amount of work to be done! So why is this so important? Using the Tree of Life we can do some pretty amazing things. For example, we can target hotspots—areas on the tree where we can predict certain species will be—like medicinal hotspots, areas for crop improvement and areas in high need for conservation. We can use the Tree of Life to model the distribution of species. Using models of climate change, we can compare where species exist now and where they are predicted to be in the future. Using these predicted future distributions we can work to conserve areas now, in anticipation of a species new range.

We are currently in the Anthropocene, the geological period when human activity has been the dominant influence on climate and the environment. This has caused a biodiversity crisis; extinction rates are currently 1000 times higher than ever before. Ecosystems exist because of biodiversity and when they collapse we lose valuable ecosystem services. These services are the varied benefits that humans freely gain from a properly-functioning ecosystem. For example, pollinators that sustain our food crops, plants that offer flood resistance, clean water, and new foods and medicines. When ecosystems collapse pathogens emerge and invasive species become increasingly harder to combat. Economically, the US spends 120 billion dollars annually to eradicate invasive species.

So although there is urgency to my work, it’s a beautiful thing to zoom in and intricately study the diversity of one small group of plants. It’s work like this that contributes to the vast knowledge that the Tree of Life offers. If you have fifteen minutes, watch this animated Tree Tender video, and put a real visual with the Tree of Life project. 

Image: Based on 3,000 species
David M. Hillis, Derrick Zwickl, and Robin Gutell, University of Texas.

The Tree of Life