When alien species invade new regions, they also bring their microbes with them, most notably bacteria found on the skin and in the gut. How extensive this “microbial baggage” is and how it interacts with the environment in an animal’s new home is now shown by a study using the example of Johnstone’s whistling frog, which originally lives in the Caribbean: Even specimens caught in Europe still have microbes from their homeland.
We humans and animals carry trillions of bacteria, viruses, archaea and fungi in our digestive tract and on our skin. This microbiome performs important functions for its host – it fights off pathogens, helps with digestion and performs other important services. On the one hand, the microbial co-inhabitants of an organism are highly individually composed, on the other hand, they also reflect the living environment of their carrier due to their close interaction with the microbial communities in the environment.
Well-travelled whistling frog as a case study
However, what this microbial baggage means for invasive species and their new environments has been poorly understood. “We are interested in how the microbiomes of non-native species affect the native ecosystems and what role they play in the successful settlement of the immigrants,” says senior author Raffael Ernst from the Senckenberg Natural History Collections in Dresden. Ernst, first author Franziska Leonhardt and their colleagues have therefore examined these questions more closely using the example of an invasive frog. “Microbiomes are also found in amphibians, and the skin, which is moist due to their skin breathing, is particularly predestined for this,” explains Ernst.
Johnstone’s pipe frog (Eleutherodactylus johnstonei) served as a case study. This frog, which is only about 17 to 35 millimeters in size, was originally only native to the Lesser Antilles, but has since spread across the entire Caribbean and large parts of Central and South America. This animal immigrant can now also be found in botanical gardens in Europe. “We genetically analyzed the skin and gut microbiome of Eleutherodactylus johnstonei from native populations in St. Lucia and immigrant populations in Guadeloupe, Colombia and from European greenhouses,” explains Leonhardt. For comparison, the researchers also examined soil samples in the respective habitats of the frogs in order to be able to compare the microbial community there.
Microbe transfer and intensive exchange
The analyzes showed that the frogs carried a total of a good 3700 different microbial gene signatures on their skin and a further 4100 in their intestines, and a good 5100 microbial signatures were found in the environmental samples from their environment. The regional comparisons showed that the microbiome of the frogs represented a mixture of species-specific “roommates” and microbes from the environment. The research team also identified some bacterial genera that were typical of Caribbean frogs in the whistling frogs sampled in Europe. Conversely, it was found that the European frogs carried more “new” bacteria from their environment on their skin than their fellow species that stayed in their homeland.
According to the researchers, their results demonstrate that invasive species do not come alone, but also bring numerous non-native microbes with them. “Our results show that amphibian-associated and microbial environmental communities can be viewed as meta-communities that interact with each other,” says Leonhardt. In the new home of the animals, this leads to an exchange of microbes between the carrier and the environment, which can then also colonize other native animals. “The environment could then act as a kind of transmission platform for microbial exchange between species,” say the researchers. The influences and consequences of this have, however, hardly been investigated to date.
The scientists therefore advocate paying more attention to the spread of the microbiota by non-native species, for example to prevent the spread of pathogens, but also non-pathogenic microbes. “Traditional studies have largely failed to account for these nested immigrations, and thus have ignored a potentially important aspect of invasion processes,” says Ernst. “However, in summary, we can say: Alien species do not come alone! Our approach can complement and expand the traditional perspective on biological invasions – also to take better protective measures in the future.”
Source: Senckenberg Research Institute and Natural History Museums; Specialist article: Microbial Ecology, doi: 10.1007/s00248-023-02227-5