Phys.Org (Reino Unido)

Bacteria may help frogs attract mates

Publicado em 15 março 2019

Brazilian scientists have found that the sturdy odor launched by some amphibian species is produced by micro organism and that attracting a mate is certainly one of its functions. The micro organism in query are a noteworthy instance of symbiosis as they help within the animal's mating course of. A paper recounting the invention of this function of microorganisms remoted from the pores and skin of frogs has been printed within the journal Proceedings of the National Academy of Sciences (PNAS).

"Frogs emit a pungent odor. Sometimes a selected species could be acknowledged by its scent, however till now, the perform of this odor was unknown. It was usually assumed to be an aposematic odor, that means a chemical warning signal that served to repel predators, as within the case of skunks [Mephitis mephitis] amongst mammals, for instance," mentioned Célio Haddad, a professor at São Paulo State University's Rio Claro Bioscience Institute (IBRC-UNESP) in Brazil and a coauthor of the article.

According to Haddad, who can also be affiliated with the college's Aquaculture Center (CAUNESP) in Jaboticabal, this speculation was thought of believable as a result of many amphibian species, particularly when toxic, are brightly coloured, and this serves as a visible alert to frighten predators. "We thought odor may play an identical function amongst anurans [frogs and toads]," he mentioned.

The new examine resulted from the postdoctoral analysis of Argentinean biologist Andrés Eduardo Brunetti, supervised by Professor Norberto Peporine Lopes. Conducted on the University of São Paulo's Ribeirão Preto School of Pharmaceutical Sciences (FCFRP-USP), the analysis was supported by FAPESP.

"The importance and originality of Brunetti's research is that for the first time it shows a pronounced difference in the odors emitted by frogs of opposite sexes," Haddad mentioned. "No other studies of anurans have ever described this type of behavior. The results suggest that the odor serves to permit mutual recognition between males and females of the same species for mating purposes."

The analysis was additionally supported by the FAPESP Research Program on Biodiversity Characterization, Conservation, Restoration and Sustainable Use (BIOTA-FAPESP) and by the University of São Paulo (USP), the National Council for Scientific and Technological Development (CNPq) and Brazil's Coordination for the Improvement of Higher Education Personnel (CAPES).

"In anurans, you often see different species sharing a lake or marsh. In such places, there are 30 male frogs for every female of the same species on average. The question is how the females recognize males of their own species among a multitude of males belonging to several species while they're all vocalizing at the same time," Brunetti mentioned.

"It's well-known that the function of the call of anuran males is to attract females and that every species has a characteristic song. Our findings suggest that odor appears to play a similar role, serving as an olfactory signal that enables females to recognize males of their own species."

Biologists had been additionally unaware of a distinction within the scents of female and male frogs. Brunetti found this distinction throughout his analysis, whose major aim was to know the chemical composition of the unstable elements emitted by the pores and skin of varied frog species.

His working speculation prompt that odor was a chemical warning signal that served to repel predators. To confirm the speculation, Brunetti carried out area surveys at a number of websites in São Paulo state and Rio de Janeiro state, accumulating specimens of the tree frog Boana prasina.

"It's very hard to collect females in the wild. Initially, we managed to collect only males. When we noticed what appeared to be a sexual difference in their odors, I went into the field again with the specific aim of capturing females for comparison," he mentioned.

"During my doctoral research at the Argentinian Natural Science Museum in Buenos Aires, while investigating the volatile compounds in two other frog species, I discovered that the secretions were made up of a blend of 35 to 42 compounds in nine different chemical classes. We then realized that some of the compounds had the specific signature of compounds produced by bacteria."

Brunetti got here to Brazil to analyze whether or not the chosen tree frogs had pores and skin micro organism that produced the attribute odor of every species, and in that case, which compounds they produced. His laboratory analysis proceeded on two fronts: evaluation of the unstable compounds launched by the pores and skin of those frogs and identification of the micro organism on their pores and skin.

Brunetti and colleagues used gasoline chromatography and mass spectrometry to investigate the variety of the unstable elements secreted by the pores and skin of B. prasina. They discovered that grownup men and women secrete a mix of 60-80 compounds, together with alcohols, aldehydes, alkenes, ethers, ketones, methoxypyrazines, terpenes and thioethers.

The compounds had been precisely the identical in each men and women, however the researchers had been stunned to discover a pronounced sexual distinction within the ranges of methoxypyrazines, terpenes, and thioethers.

"These three components were responsible for the difference between males and females. Thioethers and methoxypyrazines are typically produced by microorganisms," Brunetti mentioned.

They determined to find out whether or not microorganisms had been the supply of those compounds in B. prasina. To achieve this, they remoted, cultivated and recognized micro organism related to the pores and skin of those frogs and analyzed their unstable elements.

No fewer than 128 totally different elements had been detected. Analysis of every element revealed that 4 methoxypyrazines current in men and women had been produced by a single bacterium of the genus Pseudomonas.

In B. prasina, Brunetti found, methoxypyrazines had been rather more ample in females than in males. Two of the 4 varieties of methoxypyrazines had been measured at increased ranges in females, whereas two had been discovered at increased ranges in males.

Symbiotic relationship

"The attention-grabbing factor about Pseudomonas sp. is that these micro organism stay on the pores and skin of men and women, the place they metabolize the identical unstable compounds however at totally different ranges of focus in accordance with the intercourse of the host," Brunetti mentioned.

The ranges of methoxypyrazine measured in these frogs, he added, counsel the existence of a posh mechanism of metabolic interactions that creates a unique surroundings on the pores and skin of men and women, favoring the synthesis of attribute methoxypyrazines in every intercourse.

"These frogs and bacteria have a symbiotic relationship. In exchange for the service provided by the bacteria, entailing sexual differentiation by scent, the frogs provide an environment -- their own skin -- on which the bacteria can proliferate," he defined.

The perform of this sexual distinction in methoxypyrazine ranges is unknown. "However, we assume that the difference in scent helps male frogs of this species recognize females of the same species in places inhabited by other frog species," Brunetti mentioned.

"We know that many anurans use visible communication [shiny pores and skin colours] to repel predators in addition to acoustic communication [vocalization] to attract feminine mates. Perhaps B. prasina makes use of a type of olfactory communication for a similar goal."

Brunetti will try to substantiate this speculation in future analysis. If appropriate, it can have main repercussions. "Only one anuran, in Madagascar, is currently known to communicate by odor. Among amphibians, salamanders, which are distant relatives of anurans, are known to use this form of communication," Haddad mentioned.

"If B. prasina makes use of scent as a type of communication, it may properly be the case that different species additionally use olfactory communication, given that every species has a attribute odor. Brunetti's discovery, if confirmed, opens up a brand new area of investigation in herpetology, which can now deal with olfactory communication amongst anurans, relatively than simply visible and acoustic communication."

More information: Andrés E. Brunetti et al, Symbiotic skin bacteria as a source for sex-specific scents in frogs, Proceedings of the National Academy of Sciences (2019). DOI: 10.1073/pnas.1806834116

Journal reference: Proceedings of the National Academy of Sciences

Provided by: FAPESP

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