247C Poster - 02. Immunity and the microbiome
Saturday April 09, 1:30 PM - 3:30 PM

Authors:
Jessamyn Perlmutter ¹; Joanne Chapman ²; Robert Unckless ¹

Affiliations:
1) Department of Molecular Biosciences, University of Kansas, Lawrence, KS; 2) Enteric, Environmental and Food Virology Laboratory, Institute of Environmental and Scientific Research, New Zealand

Keywords:
e. anti-microbial peptides; k. host/pathogen interactions

Antimicrobial peptides (AMPs) are at the interface of interactions between hosts and microbes and are therefore expected to be fast evolving to keep pace with pathogens. However, production of these peptides is also costly to animals and the host must balance its own energetic and antimicrobial interests. Previous work identified distinct peptide alleles that are repeatedly maintained not only within populations of Drosophila melanogaster, but also across at least three other fly species. The maintenance of these polymorphisms across both geography and more than 10 million years of divergence, coupled with evidence showing balancing selection on AMPs in flies, suggest there is a distinct functional importance to each allele. Is each allele more effective against specific pathogens (specificity hypothesis), or is one allele more effective generally, but also more costly to produce (autoimmune hypothesis)? One AMP, Metchikowin (Mtk), has a single residue that segregates as either proline (P) or arginine (R) in populations of four Drosophila species. To assess the functional difference between the alleles, we created D. melanogaster lines with the P allele, the R allele, or a Mtk null mutation using CRISPR/Cas9 genome editing. Here, we report results from experiments assessing the specificity versus autoimmune hypotheses using these lines. Testing of the flies against a repertoire of bacteria and fungi demonstrated differences in survival rates across allele or null mutation lines with some pathogens. In addition, measurements of various life history traits in these lines reveal differences in longevity in adulthood, suggesting differential fitness costs to producing the alleles. In summary, there are various measurable functional differences between Mtk alleles in Drosophila melanogaster, providing several lines of support for adaptive maintenance of Mtk polymorphisms in contrast with expectations of rapid AMP evolution.