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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 agriflolia (Fagaceae) dominated forests in the San Francisco Bay Area. We determined whether changes in microbial diversity and composition in both soil and Batrachoseps attenuatus skin were associated with dominant vegetation type. To evaluate animal health across vegetation types, we compared Batrachoseps attenuatus body condition and the presence/absence of the amphibian skin pathogen Batrachochytrium dendrobatidis . We found that Eucalyptus invasion had no measurable effect on soil microbial community diversity and a relatively small effect (compared to the effect of site identity) on community structure in the microhabitats sampled. In contrast, our results show that Batrachoseps attenuatus skin microbiota diversity was greater in Quercus dominated habitats. One amplicon sequence variant identified in the family Chlamydiaceae was observed in higher relative abundance among salamanders sampled in Eucalyptus dominated habitats. We also observed that Batrachoseps attenuatus body condition was higher in Quercus dominated habitats. Incidence of Batrachochytrium dendrobatidis across all individuals was very low (only one Batrachochytrium dendrobatidis positive individual). 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., Competing Interests: The authors declare that they have no competing interests., (© 2020 Hernández-Gómez et al.)

Background: Understanding of the physiological effects of chytridiomycosis is crucial to worldwide amphibian conservation. Therefore, we analyzed the cardiac function of two anuran species ( Xenopus laevis and Physalaemus albonotatus ) with different susceptibilities to infection by the causative agent of chytridiomycosis, Batrachochytrium dendrobatidis (hereafter Bd )., Methods: We analyzed the in situ heart rate ( f H - bpm), relative ventricular mass (RVM -%), and Ca 2+ handling in heart of Bd infected animals compared to uninfected controls of both study species., Results: Bd infection resulted in a 78% decrease in contraction force values in P. albonotatus when compared to the less susceptible X. laevis . This negative effect was even more evident (82%) for the cardiac pumping capacity. The time to reach peak tension was 125% longer in P. albonotatus than in X. laevis , and cardiac relaxation was 57% longer., Discussion: These results indicate a delay in the cardiac cycle of P. albonotatus on a beat-to-beat basis, which was corroborated by the bradycardia observed in situ . In summary, Bd -sensitive species present impaired cardiac function, which could be a factor in mortality risk. The more pronounced effects of Bd in P. albonotatus may not only result from electrolyte imbalance, as previously reported, but also could be an effect of toxins produced by Bd . For X. laevis , the ability to promote cardiac adjustments seems to be an important homeostatic feature that allows greater tolerance to chytridiomycosis. This study provides new physiological mechanisms underlying the tolerance or susceptibility of amphibian species to chytridiomycosis, which determine their adaptability to survive in the affected environments., Competing Interests: The authors declare there are no competing interests.