title: Experimental evolution alters the rate and temporal pattern of population growth in Batrachochytrium dendrobatidis, a lethal fungal pathogen of amphibians.
abstract: Virulence of infectious pathogens can be unstable and evolve rapidly depending on the evolutionary dynamics of the organism. Experimental evolution can be used to characterize pathogen evolution, often with the underlying objective of understanding evolution of virulence. We used experimental evolution techniques (serial transfer experiments) to investigate differential growth and virulence of Batrachochytrium dendrobatidis (Bd), a fungal pathogen that causes amphibian chytridiomycosis. We tested two lineages of Bd that were derived from a single cryo-archived isolate; one lineage (P10) was passaged 10 times, whereas the second lineage (P50) was passaged 50 times. We quantified time to zoospore release, maximum zoospore densities, and timing of zoospore activity and then modeled population growth rates. We also conducted exposure experiments with a susceptible amphibian species, the common green tree frog (Litoria caerulea) to test the differential pathogenicity. We found that the P50 lineage had shorter time to zoospore production (T min ), faster rate of sporangia death (d s ), and an overall greater intrinsic population growth rate (λ). These patterns of population growth in vitro corresponded with higher prevalence and intensities of infection in exposed Litoria caerulea, although the differences were not significant. Our results corroborate studies that suggest that Bd may be able to evolve relatively rapidly. Our findings also challenge the general assumption that pathogens will always attenuate in culture because shifts in Bd virulence may depend on laboratory culturing practices. These findings have practical implications for the laboratory maintenance of Bd isolates and underscore the importance of understanding the evolution of virulence in amphibian chytridiomycosis.
authors.affiliation: Department of Biology, New Mexico Tech Socorro, New Mexico, 87801.
authors.forename: Jamie
authors.initials: J
authors.lastname: Voyles
authors.affiliation: Department of Integrative Biology, University of South Florida Tampa, Florida, 33620 ; Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, California, 93106.
authors.forename: Leah R
authors.initials: LR
authors.lastname: Johnson
authors.affiliation: Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, California, 93106.
authors.forename: Cheryl J
authors.initials: CJ
authors.lastname: Briggs
authors.affiliation: School of Public Health, Tropical Medicine and Rehabilitation Sciences, Amphibian Disease Ecology Group, James Cook University Townsville, Queensland, 4811, Australia.
authors.forename: Scott D
authors.initials: SD
authors.lastname: Cashins
authors.affiliation: School of Marine and Tropical Biology, Amphibian Disease Ecology Group, James Cook University Townsville, Queensland, 4811, Australia.
authors.forename: Ross A
authors.initials: RA
authors.lastname: Alford
authors.affiliation: School of Public Health, Tropical Medicine and Rehabilitation Sciences, Amphibian Disease Ecology Group, James Cook University Townsville, Queensland, 4811, Australia.
authors.forename: Lee
authors.initials: L
authors.lastname: Berger
authors.affiliation: School of Public Health, Tropical Medicine and Rehabilitation Sciences, Amphibian Disease Ecology Group, James Cook University Townsville, Queensland, 4811, Australia.
authors.forename: Lee F
authors.initials: LF
authors.lastname: Skerratt
authors.affiliation: School of Public Health, Tropical Medicine and Rehabilitation Sciences, Amphibian Disease Ecology Group, James Cook University Townsville, Queensland, 4811, Australia.
authors.forename: Rick
authors.initials: R
authors.lastname: Speare
authors.affiliation: Department of Environmental Science, Policy and Management, University of California- Berkeley Berkeley, California, 94720-3144.
authors.forename: Erica Bree
authors.initials: EB
authors.lastname: Rosenblum
keywords: Amphibian chytridiomycosis; Batrachochytrium dendrobatidis; amphibian declines; evolution of virulence; experimental evolution; host–pathogen interactions; serial passage experiments