NSF Postdoctoral Fellowship in Biology FY 2017: Mites, microbes, and fungal pathogens: the ecology and evolution of an indirect defense trait

Zemenick Ash T, Davis CA

Investigators

Abstract

This is an NSF Postdoctoral Research Fellowship in Biology, under the program Broadening Participation of Groups Under-represented in Biology. The fellow, Ash Zemenick, is conducting research and receiving training that is increasing the participation of groups underrepresented in biology. The fellow is being mentored by Marjorie Weber at the Michigan State University. This research explores how mites influence the pathogens of plants. Many plants have small tufts of hairs on the leaf ("domatia") that house mites. Mites can benefit plants by reducing the success of pathogens (bacteria and fungi), but the mechanisms and extent of variation are not well understood. Mites can directly reduce success of pathogens by eating them. Also, by influencing the abundance of microbes that inhibit pathogens, mites may indirectly influence pathogen success. Finally, because not all plants have domatia, the way in which mites and/or microbes influence pathogens may vary across plant species. The fellow is disentangling these effects using an experiment that manipulates the access of mites to plants, and the occurrence of potential pathogens. This research will increase the understanding of these widespread ecological interactions, and contribute to sustainable pathogen management in agroecosystems. This project also includes two explicit broader impacts that address some stereotypes that fuel underrepresentation in biology. First, the fellow has experienced life as a woman and transgender person, and thus serves as a role model in mentoring undergraduates involved in research. Second, the fellow is developing a repository of teaching materials to humanize biology and biologists by highlighting how research applies to societal issues and what it's like to be a biologist. The fellow is using examples provided by biologists that self-identify as members of underrepresented groups in STEM (e.g. in terms of race, ethnicity, gender, income, nationality, immigrant status, cognitive and physical ability, etc.).  The fellow is conducting manipulative experiment to understand how mites influence pathogen success directly (via consumption) and/or indirectly (via an altered microbial community composition that is less invasible). Leaves from 20 species of grapes (Vitis) will be experimentally manipulated with four treatments. Two (T1 and T2) will block mites, and two (T3 and T4) will have mites. After 2 weeks, half of all leaves will be harvested to assess leaf microbial communites. Fungal and bacterial DNA will be amplified using barcoded ITS and 16S primers and the resulting multiplexed amplicons will be subject to Illumina sequencing. A difference between no-mite (T1 and T2) and mite (T3 and T4) leaf microbial communities would empirically demonstrate that domatia-inhabiting mites influence leaf microbe community structure, and could therefore indirectly influence pathogen success in Vitis. The other half of replicates will remain in the field, with mites allowed only on T2 and T4. All leaves will be challenged with powdery mildew. If mite presence lowers pathogen infection of Vitis leaves, then leaves from T2-T4 will have lower infestation of powdery mildew than control (T1) leaves. If this reduction in pathogen infection is through direct consumption rather than indirectly through a modified leaf microbe community, then T2 and T4 leaves will have lower powdery mildew infestation than T2 leaves. To evaluate patterns of microbial community evolution and pathogen resistance across leaves, multi- and unidimensional comparative phylogenetic models will be used to assess whether microbial community composition and structure, as well as pathogen resistance, are evolutionarily correlated with domatia presence and size across Vitis species. If domatia presence and size are correlated with powdery mildew resistance across the phylogeny, there will be evidence for either: A) the selective environment for domatia included pathogen resistance, or B) evolution of domatia selected for the loss of direct pathogen resistance.