Abstract
Microbial fitness is easy to measure in the laboratory, but difficult to measure in the field. Laboratory fitness assays make use of controlled conditions and genetically modified organisms, neither of which are available in the field. Among other applications, fitness assays can help researchers detect adaptation to different habitats or locations. We designed a competitive fitness assay to detect adaptation of Saccharomyces paradoxus isolates to the habitat they were isolated from (oak or larch leaf litter). The assay accurately measures relative fitness by tracking genotype frequency changes in the field using digital droplet PCR (DDPCR). We expected locally adapted S.paradoxus strains to increase in frequency over time when growing on the leaf litter type from which they were isolated. The DDPCR assay successfully detected fitness differences among S.paradoxus strains, but did not find a tendency for strains to be adapted to the habitat they were isolated from. Instead, we found that the natural alleles of the hexose transport gene we used to distinguish S.paradoxus strains had significant effects on fitness. The origin of a strain also affected its fitness: strains isolated from oak litter were generally fitter than strains from larch litter. Our results suggest that dispersal limitation and genetic drift shape S.paradoxus populations in the forest more than local selection does, although further research is needed to confirm this. Tracking genotype frequency changes using DDPCR is a practical and accurate microbial fitness assay for natural environments.
Highlights
Evolutionary biologists use microbial fitness assays to describe evolutionary trajectories and make general predictions about evolution (Elena & Lenski 2003; Orr 2009; Kawecki et al 2012)
Our results suggest that dispersal limitation and genetic drift shape S. paradoxus populations in the forest more than local selection does, further research is needed to confirm this
Tracking genotype frequency changes using digital droplet PCR (DDPCR) is a practical and accurate microbial fitness assay for natural environments
Summary
Evolutionary biologists use microbial fitness assays to describe evolutionary trajectories and make general predictions about evolution (Elena & Lenski 2003; Orr 2009; Kawecki et al 2012). Microbes reproduce quickly, and relative fitness can be measured directly by comparing two microbes’ growth rates (Lenski et al 1991). Existing protocols are illsuited for field experiments, making it difficult to study natural selection pressures. Fitness assay protocols require controlled conditions and sterile media, and cannot be carried out on nonsterile substrates. Fitness assays are often performed on genetically modified microorganisms, which can be impractical, unethical or illegal to introduce to natural environments (Francescon 2001). Evolutionary biologists need methods that directly measure fitness differences in situ between nongenetically modified organisms
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
