DISCOVERING HOW COMMUNITIES ASSEMBLE IN NOVEL ENVIRONMENTS IS CRITICAL TO UNDERSTANDING THE EVOLUTION OF EARLY LIFE AND THE BIOSPHERE. INCREASINGLY OBSERVATIONS EXPERIMENTS AND THEORY SUGGEST THAT EVOLUTION CAN AFFECT THE FORMATION OF COMPLEX COMMUNITIES. WE DEVELOPED THEORY ON ONE SUCH DYNAMIC CALLED THE MONOPOLIZATION EFFECT. A SPECIES MONOPOLIZES A SYSTEM IF IT ARRIVES EARLY ADAPTS TO NOVEL CONDITIONS AND THEREBY ALTERS THE ESTABLISHMENT OF OTHER SPECIES. IMPORTANTLY MONOPOLIZATION THEORY SUGGESTS THAT THE CHARACTERISTICS OF REMOTE ECOSYSTEMS WILL DEPEND STOCHASTICALLY ON THE TRAITS OF THE FIRST LIFE TO EVOLVE OR ARRIVE. THE EXTREMOPHILE MICROBES WE STUDY ARE LIKELY ANALOGUES FOR EXTRA-TERRESTRIAL LIFE. ARCHAEA FROM THE SALT EXTREMOPHILE GENUS HALOFERAX CAN SURVIVE THE EXTREME HIGH TEMPERATURES (>50 C) AND SALTY CONDITIONS LIKELY FOUND IN EXPOSED LOW-PRECIPITATION PLANETARY ENVIRONMENTS. OUR WORK SUGGESTS THAT THESE EXTREMOPHILES CAN ADAPT QUICKLY TO NOVEL CONDITIONS AND NOT JUST BY MUTATION: HALOFERAX CAN TAKE UP DNA DIRECTLY FROM OTHER SPECIES (HORIZONTAL GENE TRANSFER) OR FROM THE ENVIRONMENT WHICH CAN FACILITATE THEIR RAPID ADAPTATION. THUS A LATE-ARRIVING COLONIZER COULD CHEAT MONOPOLIZATION BY TAKING UP DNA FROM RESIDENTS THUS FACILITATING ITS ADAPTATION AND ESTABLISHMENT. KEY OBJECTIVES 1) DOES ADAPTATION OF A RESIDENT SPECIES ALLOW IT TO MONOPOLIZE A NOVEL ENVIRONMENT AND DECREASE THE COLONIZATION SUCCESS OF FUTURE COLONIZERS? 2) DOES DNA UPTAKE ALLOW A LATE-ARRIVING SPECIES TO ADAPT AND ESTABLISH DESPITE MONOPOLIZATION? 3) HOW DOES GENETIC BACKGROUND AND EPISTASIS INFLUENCE THE ROLE OF HORIZONTAL GENE TRANSFER? 4) HOW DO VARYING LEVELS OF COLONIZATION INFLUENCE COMMUNITY DYNAMICS IN MULTI-PATCH LINKED SYSTEMS? METHODS SUMMARY WE WILL ALLOW RESIDENTS (HALOFERAX VOLCANII) TO ADAPT TO NOVEL ENVIRONMENTS CREATED BY COMBINING DIFFERENT TEMPERATURES AND SALT CONCENTRATIONS. FOLLOWING DIFFERENT PERIODS OF ADAPTATION WE WILL INTRODUCE A SECOND SPECIES (HALOFERAX MEDITERRANEI) ADAPTED TO STANDARD CONDITIONS. WE PREDICT THAT LONGER PERIODS OF ADAPTATION WILL ENHANCE MONOPOLIZATION BY H. VOLCANII. LIKE MANY EARLY LIFE FORMS HALOFERAX CAN EXCHANGE GENETIC MATERIAL. THE RESIDENT S ADAPTATIONS COULD BE PASSED ON TO THE INVADER OVERCOMING THE MONOPOLIZATION EFFECT. BY USING GENETIC KNOCKOUTS WE WILL CREATE TREATMENTS WITH AND WITHOUT HORIZONTAL GENE TRANSFER. WE PREDICT THAT HORIZONTAL GENE TRANSFER WILL ALLOW THE LATE COLONIST TO ADAPT EVENTUALLY AND OVERCOME MONOPOLIZATION. HOWEVER EPISTATIC INTERACTIONS BETWEEN THE INVADER S GENES AND HORIZONTALLY TRANSFERRED GENES MIGHT REDUCE THEIR FITNESS ADVANTAGE. THEREFORE WE WILL CONTRAST THE EFFECT OF HORIZONTAL GENE TRANSFER ON THE ESTABLISHMENT OF INVADERS WITH THE SAME VERSUS A DIFFERENT GENETIC BACKGROUND. WE PREDICT THAT EPISTATIC INTERACTIONS FROM THE DIVERGENT SPECIES GENOME WILL REDUCE THE ADVANTAGES OF HORIZONTAL GENE TRANSFER. LASTLY WE WILL CREATE A SYSTEM OF LINKED HETEROGENEOUS PATCHES TO TEST HOW EVOLUTION AND STOCHASTIC COLONIZATION AFFECT THE ENTIRE METACOMMUNITY. WE PREDICT THAT LOWER COLONIZATION RATES WILL ENHANCE MONOPOLIZATION OF HABITATS BY ONE SPECIES WHEREAS HIGHER COLONIZATION WILL LEAD TO PARTITIONING OF ENVIRONMENTS BY SPECIES AND GREATER REGIONAL AND LOCAL DIVERSITY. SIGNIFICANCE THIS RESEARCH WILL DIRECTLY ADDRESS THREE MAJOR GOALS (II. IV. V. VI.) OF THE EXOBIOLOGY EMPHASIS ON EARLY EVOLUTION OF LIFE AND THE BIOSPHERE INCLUDING HORIZONTAL GENE TRANSFER THE COEVOLUTION OF MICROBIAL COMMUNITIES THE PROCESSES BY WHICH NEW SPECIES ARE ADDED TO EXTANT COMMUNITIES THE EVOLUTION OF MICROBIAL SPECIES SUBJECT TO LONG-TERM ENVIRONMENTAL CHANGE AND DEVELOPMENT OF KEY BIOLOGICAL PROCESSES. MORE GENERALLY RESEARCH WILL PROVIDE AN IMPORTANT TEST FOR NOVEL THEORIES ABOUT THE EVOLUTION OF COMMUNITIES AND ECOSYSTEMS IN REMOTE AND EXTREME ENVIRONMENTS.