title: Coevolution drives the emergence of complex traits and promotes evolvability.
abstract: The evolution of complex organismal traits is obvious as a historical fact, but the underlying causes--including the role of natural selection--are contested. Gould argued that a random walk from a necessarily simple beginning would produce the appearance of increasing complexity over time. Others contend that selection, including coevolutionary arms races, can systematically push organisms toward more complex traits. Methodological challenges have largely precluded experimental tests of these hypotheses. Using the Avida platform for digital evolution, we show that coevolution of hosts and parasites greatly increases organismal complexity relative to that otherwise achieved. As parasites evolve to counter the rise of resistant hosts, parasite populations retain a genetic record of past coevolutionary states. As a consequence, hosts differentially escape by performing progressively more complex functions. We show that coevolution's unique feedback between host and parasite frequencies is a key process in the evolution of complexity. Strikingly, the hosts evolve genomes that are also more phenotypically evolvable, similar to the phenomenon of contingency loci observed in bacterial pathogens. Because coevolution is ubiquitous in nature, our results support a general model whereby antagonistic interactions and natural selection together favor both increased complexity and evolvability.
authors.affiliation: BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan, United States of America; Department of Computer Science and Engineering, Michigan State University, East Lansing, Michigan, United States of America.
authors.forename: Luis
authors.initials: L
authors.lastname: Zaman
authors.affiliation: Department of Systems Biology, Harvard Medical School, Boston, Massachusetts, United States of America.
authors.forename: Justin R
authors.initials: JR
authors.lastname: Meyer
authors.affiliation: School of Medicine, Wayne State University, Detroit, Michigan, United States of America.
authors.forename: Suhas
authors.initials: S
authors.lastname: Devangam
authors.affiliation: BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan, United States of America.
authors.forename: David M
authors.initials: DM
authors.lastname: Bryson
authors.affiliation: BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan, United States of America; Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan, United States of America.
authors.forename: Richard E
authors.initials: RE
authors.lastname: Lenski
authors.affiliation: BEACON Center for the Study of Evolution in Action, Michigan State University, East Lansing, Michigan, United States of America; Department of Computer Science and Engineering, Michigan State University, East Lansing, Michigan, United States of America.
authors.forename: Charles
authors.initials: C
authors.lastname: Ofria
mesh_terms: D000818:Animals; D005075:Biological Evolution; D016678:Genome; D005838:Genotype; D006790:Host-Parasite Interactions; D010271:Parasites / Q000235:genetics / Q000502:physiology; D010802:Phylogeny; D017354:Point Mutation / Q000235:genetics; D019655:Quantitative Trait, Heritable; D013997:Time Factors