Viruses and viroids are the simpler forms of replicating structures inhabiting our biosphere. They are known as the most important intracellular parasites, using genetic information from their hosts in order to replicate themselves. They can only reproduce by invading and controlling other cells as they lack the cellular machinery for self-reproduction. The term virus usually refers to those particles that infect eukaryotes, whilst the term bacteriophage or phage is used to describe those infecting prokaryotes.

We study different aspects of virus complexity, including theoretical models of evolution and coevolution, computer viruses and general models of parasite evolution. In collaboration with Santiago Elena's Lab in Valencia, we are using well-defined experimental systems (mainly viroids infecting plants) together mathematical and computer models looking for understanding of how viruses explore their worlds. Among other questions, we want to know what is the structure of their fitness landscapes, how they cope with their complexity and how they might have originated and perhaps, canalized the evolution of biological complexity. 



 Our interest in viruses is also motivated by a lack of understanding of the nature and definition of life. Viruses place themselves on the boundaries of living systems,  and can be understood as programs. However, the discovery of giant viruses carrying large genomes and defining a complex life cycle casts some doubts about the correctness of the previous statement. New models need to be developed in order to address the coevolution of viruses and their hosts and in particular the role played by genome size, instability, coevolutionary responses and the genotype-phenotype mapping.