"How would you go about finding out, when Mars lost it's Warm, wet environment, with a substantial atmosphere?"
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Leaping to land -- physiology and phylogenetics of microscopic desert green algae (2)
PI: Zoe Cardon
A key step in the evolution and diversification of advanced life on Earth was the establishment of life on land. Green plants such as familiar mosses, ferns, conifers, and flowering plants (“embryophytes”) are the largest group of advanced, photosynthetic organisms whose ancestor (a small, freshwater green alga) made that transition. Embryophytes have structural and functional adaptations for living on land, which have been extensively studied. From an evolutionary perspective, however, the diversification of all embryophytes from one common ancestor that moved from water to land presents an analytical problem. A trait common to all terrestrial green plants might be common because it is essential for life on land, or it might be common because embryophytes are all descended from a common algal ancestor that happened to harbor that trait. In order to recognize characteristics among the larger group of green photosynthetic organisms (including green algae) that may be key for survival on land, multiple, independent examples of green organisms that made the leap from water to land are needed for analysis and comparison. Remarkably, microscopic, unicellular, green algae are found free-living in desert microbiotic crusts world-wide. Using molecular phylogenetics, we have discovered that the green algae thriving in microbial crust communities in arid and semi-arid regions of western North America form at least 14 diverse lineages, each independently evolved from aquatic (freshwater) ancestors. Our objective is to use these independently evolved lineages of desert algae to separate habitat-specific traits that correlate with desert survival from those traits resulting from ancestry. We will combine (1) state-of-the-art molecular phylogenetic (sequence) data from multiple isolates of desert and sister aquatic green algae with (2) several types of photophysiological data describing protective pigments produced and photosynthetic activity maintained in the face of the stressful desiccation and high light common in deserts. Using modern, phylogenetic comparative statistical methods, we will test for the presence of physiological traits that correlate clearly with the transition from water to terrestrial life in deserts in this broad sampling of independent, terrestrial green plant lineages. This multi-faceted exploration of the diversity and physiology of desert green algae will directly advance NASA’s Exobiology objective emphasizing enhanced understanding of the evolution of diverse, advanced, eukaryotic life on land and the potential for advanced life to adapt to diverse, and stressful, environments.
