Evolution of microbial dependencies and host-microbe dependencies
Why and how do some species lose functions that leave them dependent on other species? We showed that whether full autonomy, one-way dependency or mutual dependency arises depends on the interplay between costs, essentiality and privatization level of the function (Estrela et al. 2015).
In some cases, such dependencies can be so strong that 'individuals' (or organisms) eventually lose their own 'individuality' and merge together, forming a symbiotic organism. I am interested in why and how this happens. That is, why do different species come together to form a single, fully integrated organism (defined as a major egalitarian transition)? What are the evolutionary paths to symbiotic organismality? We have proposed that classifying host-symbiont associations into two interconnected continuum axes: a symbiont’s dependency for dispersal into new hosts (symbiont mode of transmission) and interdependency for reproduction, growth and survival (dependency for nutrients/services) can help us better understand and predict the evolutionary path to symbiotic organismality (Estrela et al. 2016).