NSF project: Rules of life: Evolution of multicellular individuality
Overview
We will study evolutionary transitions in individuality (ETIs) in multicellular forms in the volvocine green algae lineage. We will determine how a new genotype-phenotype map for fitness arises at the group level during the evolution of multicellularity, when initially the map is present only at the cell level. Our previous work has shown that stress responses can be a major impetus for the reorganization of fitness during an ETI. We will determine how two aspects of individuality, group inseparability and somatic cell division of labor, respond to stress in two species of intermediate complexity and individuality. We infer these two species are like transitional forms between unicellular and complex multicellular species. We will determine the genetic basis for the stress responses along with the underlying gene co-option pathway. We will determine whether greater degrees of individuality evolve in experimental populations under conditions predicted by our models. We will test phylogenetically whether the evolution of cell specialization in this group fits a gene-led or phenotype-led view of evolution. We will measure variability in fitness at the cell and group levels in a sample of species of varying degrees of individuality to see (i) whether greater individuality leads to greater canalization of fitness and (ii) if heritable variation in fitness increases at the group level relative to the cell level during an ETI.
Intellectual merit
How do groups of individuals become new kinds of individuals? Answering this question is at the basis of some of biology's greatest challenges: the origin of life in terms of a cooperative group of genes or genome in a protocell, the transition from simple bacterial cells to the eukaryotic cell, the origin of complex multicellular organisms. These ETIs gave rise to life's hierarchical structure as we know it today. Life began simple, so it is not surprising that it became complex, what is surprising is the way in which life became complex, with major gaps and discontinuities between levels in the hierarchy of life. How did evolution bridge those gaps so as to create life's hierarchical organization? We approach this question by studying the evolution of multicellularity in the lineage the volvocine green algae. As developed by the PI, ETIs correspond to a natural kind, a collection of events with common problems and common solutions. Consequently, studying ETIs in a specific algal lineage can inform our understanding of ETIs generally, just as the study of speciation in a lineage informs speciation generally.
Broader Impacts
This project is part of a larger initiative to develop the volvocine green algae as a model system to study biological complexity, much as model organisms such as Drosophila and Caenorhabditis serve the studies of genetics and development. Complexity arises as a distinct issue in evolutionary biology during the major transitions in individuality, for example the transition from unicellular to multicellular life. There is a crisis in our schools concerning the teaching of evolution and biological complexity. The diversity of life is usually taught with no discussion of complexity per se. We believe that, by not addressing the issue of complexity directly, biology curricula have opened the door to claims like those of "intelligent design" advocates who argue that so-called "irreducible" complexity cannot be explained by Darwinian principles. We wish to offer an alternative framework based on evolutionary transitions in individuality and the concepts of cooperation and conflict. These concepts will provide a familiar and intuitive framework for students, as they are social individuals and familiar with cooperation and conflict in their lives. They have experienced how groups may gain new functions through cooperation, but only if within group conflict is regulated. This provides teachers with a familiar framework to explain the remarkable transitions in complexity during the history of life. Accordingly, (i) we will develop study plans and instructional materials for middle school levels for the study of biological complexity by Darwinian principles using volvocine algae as a model, and (ii) we will continue to develop the Volvocales Research and Education Center. By casting molecular and physiological projects in the context of evolution, we seek to provide students with training in theoretical as well as diverse laboratory approaches (physiological, evolutionary, and molecular)-all integrated in a Darwinian framework and tied to the teaching of evolution and complexity in local schools with diverse representation of society.