Competition is a fundamental component of ecological processes and is widely considered to occur when organisms are closely related. In microbes, antibiotic production is a wide-spread tactic adopted by microbial organisms to harm microbial competitors. However, as most organisms contain internal microbial communities (i.e., microbiomes) the effects of antibiotic compounds may not be limited to microbes, but may represent a competitive tactic that crosses domains of life. We hypothesize that saprotrophic invertebrates are competitors for microbial taxa due to their shared habitat and food resources, making them potential targets for antibiotic compounds. Here we test whether naturally- and synthetically-derived antibiotic compounds impact the survival and fitness of soil invertebrates, and whether these compounds disrupt and simplify host microbiomes. We also examine how the anthropogenic introduction of these potent compounds via livestock waste may be affecting soil invertebrates by disrupting their microbiomes and potentially creating invertebrate vectors for antibiotic resistance.
Results/Conclusions
The effect of antibiotics on growth and survival for our three focal taxa--isopods, millipedes, and termites—varied but was generally negative. Isopods avoided all areas of antibiotic activity, while termites only avoid antifungal environments. Millipedes by contrast did not avoid antibiotic compounds. Contrary to predictions, isopod, millipede and termite microbiome composition was not altered when antibiotic treatments were added to soil mesocosms. However, when invertebrates were raised on manure from antibiotically-treated cattle, their microbiomes shifted and became more dissimilar over time. Combined, our results suggest that, antibiotic production may be one of the underlying chemical mechanisms microbe use to deter animal competitors and the anthropogenic introduction of these compounds may be disrupting nature invertebrate communities.