Invasive vegetation affects amphibian skin microbiota and body condition

Invasive plants are major drivers of habitat modification, and the scale of their impact is increasing globally as anthropogenic activities facilitate their spread. In California, an invasive plant genus of great concern is Eucalyptus. Eucalyptus leaves can alter soil chemistry and negatively affect underground macro- and microbial communities. Amphibians serve as excellent models to evaluate the effect of Eucalyptus invasion on ground-dwelling species as they predate on soil arthropods and incorporate soil microbes into their microbiotas. The skin microbiota is particularly important to amphibian health, suggesting that invasive plant species could ultimately affect amphibian populations. To investigate the potential for invasive vegetation to induce changes in microbial communities, we sampled microbial communities in the soil and on the skin of local amphibians. Specifically, we compared Batrachoseps attenuatus skin microbiomes in both Eucalyptus globulus (Myrtaceae) and native Quercus agrifolia (Fagaceae) dominated forests in the San Francisco Bay Area. We determined whether changes in microbial diversity and composition in both soil and B. attenuatus skin were associated with dominant vegetation type. To evaluate animal health across vegetation types, we compared B. attenuatus body condition and the presence/absence of the amphibian skin pathogen Batrachochytrium dendrobatidis (Bd). We found that Eucalyptus invasion had no measurable effect on soil microbial community diversity or structure in the microhabitats sampled. In contrast, our results show that B. attenuatus skin microbiota diversity was greater in Quercus dominated habitats. We also observed that B. attenuatus body condition was higher in Quercus dominated habitats. The effect on body condition demonstrates that although Eucalyptus may not always decrease amphibian abundance or diversity, it can potentially have cryptic negative effects. Our findings prompt further work to determine the mechanisms that lead to changes in the health and microbiome of native species post-plant invasion.