Bacteria Useful for Frog Mating?

According to Brazilian scientists, bacteria may be a tool utilized by anurans for mating purposes.

Researchers from São Paulo State University's Rio Claro Bioscience Institute (IBRC-UNESP) conducted a study that focused on the pungent odor produced from the bacteria found on the skin in various species of frogs. For a long time, it has been believed that the odor certain amphibian species emit is used to deter predators, similar to the function of aposematic coloration present in some species. It is widely assumed that the main function of the odor was to repel predators.

 However, Argentinean biologist, Andres Eduardo Brunetti, wanted to challenge these assumptions. The research he conducted shows that there was "... a pronounced difference in the odors emitted by frogs of opposite sexes." The results from this study suggest that the odor is used for the purpose of mutual recognition of females and males of the same species. In this way, when there are multiple potential male-mates surrounding a particular female, she can use these scents to differentiate between males of her species, and males of a different species. In this sense, the odor is used by females to recognize potential mates in a densely aggregated area, such as a marsh or lake that is shared by numerous species of frogs.

Furthermore, the results of the study suggest that the odor is used as a type of "mating call" for anurans. Similar to the use of vocalization by anurans, odor can be used by males to attract females. Brunetti's research suggested that when a multitude of males are vocalizing at the same time, females can use the scent to recognize males of their species.

In his research, Brunetti studied a variety of Brazilian tree frogs. His team specifically focused on the volatile compounds released from the skin of the frogs and the bacteria found on their skin. This idea was sparked by previous research he had done on the specimens of Boana prasina. While doing this research, Brunetti realized some of the volatile compounds he looked at were traced to the presence of skin bacteria. From this, Brunetti wanted to "...investigate whether the selected tree frogs had skin bacteria that produced the characteristic odor of each species, and if so, which compounds they produced." Using mass spectrometry and gas chromatography, it was found that the same compounds are found in both males and females of the species, but the differing concentrations of terpenes, thioethers, and methoxypyrazines accounted for a huge difference in their odors.


The most interesting thing about this article to me was the finding that both females and males of these species have the same bacteria on their skin that metabolize the same exact volatile compounds. The only difference is that males metabolize the compounds at a much higher rate than females! Additionally, Brunetti's research suggests that frogs may use olfactory communication based on their specific odors.


Adult female (left) and calling male of Boana prasina. 



https://www.sciencedaily.com/releases/2019/03/190314123141.htm

1. Andrés E. Brunetti, Mariana L. Lyra, Weilan G. P. Melo, Laura E. Andrade, Pablo Palacios-Rodríguez, Bárbara M. Prado, Célio F. B. Haddad, Mônica T. Pupo, Norberto P. Lopes. Symbiotic skin bacteria as a source for sex-specific scents in frogs. Proceedings of the National Academy of Sciences, 2019; 116 (6): 2124 DOI: 10.1073/pnas.1806834116