Direction, agency and function in the evolution of symbiotic integration

Symbiosis refers to long-term biological interactions between organisms. A familiar example is the symbiotic relationship between clownfish and anemone: the anemone provides a safe environment while the clownfish provides nutrients and predator defense. In this example, it is easy to distinguish the two symbiotic partners. However, some symbioses are so highly integrated that the partners have entirely merged to form a new, functional whole: the chloroplast, the compartment within plant cells that carries out photosynthesis, was once a free-living cyanobacterium that entered into symbiosis with a non-photosynthetic cell to give rise to algae and plants. 

These examples demonstrate two ends of a spectrum of symbiotic associations, from cooperation between largely independent organisms through to complete endosymbiotic merger. Our project seeks to understand how these symbiotic interactions develop over time, which is recorded in the loss and transfer of genes between the genomes of symbiotic partners. We will test whether there is a common underlying process that drives increasing interdependence and organismal integration between partners, or alternatively whether each symbiotic relationship is a singularity that can only be understood on its own terms. 

Answering these questions is important for two main reasons. First, symbioses have shaped the history of life and underlie the function of the modern biosphere, from the plants that make the oxygen we breathe through to the origin of our own cells, which appear to have arisen through ancient symbiosis. We seek to understand symbiotic integration in order to understand the formation of the biosphere and our own origins. Second, our analyses will address fundamental, unanswered questions about long-term trends, directionality and agency in the history of life. Does symbiotic integration imbue life’s history with directionality, does it facilitate the evolution of complexity, and what are the implications for organismal agency as two lifeforms merge into one?