Gut bacteria of amphibians are flexible Published in the journal "Nature Communications"

The bacterial community of the Amphibian gut responds in a highly flexible manner to changing conditions, allowing rapid adaptations in response to habitat alterations. This is the conclusion reached by a team of researchers from the Technische Universität Braunschweig and the Thünen Institute for Biodiversity, published in the scientific journal ‘Nature Communications’. In this study, the team investigated two ecotypes of salamander larvae, one living in streams and the other in standing water, in order to compare how their intestinal flora changes when one ecotype is transferred to the other’s habitat.

Amphibians such as frogs, salamanders, and newts live in a variety of habitats, and are strongly influenced by environmental factors including temperature, water quality, or food supply. They are therefore highly sensitive to changes in their habitat. A research team of biologists from the Zoological Institute of the TU Braunschweig and the Thünen Institute for Biodiversity recently investigated the effect of changing environmental conditions on salamander larvae, in order to establish how rapidly and to what extent the composition of the intestinal flora adjusts. Their results have been published in the journal “Nature Communications”. Although the composition of the intestinal bacteria varies, the outcome is similar in terms of function for the animal.

The researchers utilized the common Fire Salamander in Germany as a study system. Salamander larvae live in both streams and standing waters, in which they grow and develop into terrestrial animals. “The salamander larvae eat rather different prey in both habitats, and experience other important environmental differences such as water temperature and oxygen content” explained Sebastian Steinfartz, the Evolutionary Biologist who has studied the ecology and adaptations of salamanders for many years, and has previously demonstrated genetic differences between the two ecotypes.

Using a so-called ‘reciprocal transfer experiment’, in which salamander larvae from streams were placed in standing waters and vice-versa, his research team was able to analyze the composition of intestinal flora before and after the transfer. For this purpose, the larvae were transferred separately and placed in small prey-permeable boxes, necessitating that they cope with the environmental conditions of the new habitat. “We were very surprised to see how differently the ecoytpes were in terms of composition of the bacteria after they were transferred into the new habitat,” explains Molly Bletz, PhD student at the Zoological Institute of the TU Braunschweig.

The research team had expected the transfer to greatly alter the composition of intestinal bacteria, with the flora of transferred animals adjusting to resemble the flora of larvae originating in that habitat. However, only larvae that had been transferred from streams to standing waters fully acquired the intestinal flora composition typical of larvae from their new habitat. Larvae transferred from standing waters to streams maintained some species of their original flora, and acquired only a few species from the new habitat. “In the one case, the expected complete shift of intestinal flora took place, in the other case it did not,” summarizes Sebastian Steinfartz. Nevertheless, the predicted metabolic functions of the intestinal flora in larvae transferred from the standing waters differed only slightly from the typical functions of the larvae naturally occurring in the streams. “Intestinal bacteria can thus react very differently to changes in their habitat, whilst still converging on the same functions,” explains Molly Bletz.

The reason why the intestinal flora of the larvae from standing waters is more resistant to change can only be speculated at present. “In contrast to the streams, larvae from standing waters are exposed to more extreme conditions and often go hungry,” says Steinfartz. It could be therefore, that some gut flora are more resilient and cannot simply be displaced by other species, muses the evolutionary biologist. The study shows, that communities of gut bacteria in amphibians differ already significantly between populations of one species, and not only between different species. “Their flexibility to adapt to new habitats is certainly an important basis for allowing amphibian populations to survive in a constantly changing world,” concludes Steinfartz.