Aspectos da ecologia química em anuros: interações entre anuros e invertebrados e variação geográfica no perfil de metabólitos secundários em extratos da pele

Abstract

Anurans present a wide variety of defense strategies, whether visual, chemical, or behavioral, such as non-exclusive breeding in aquatic environments. Unusually, some species have used a defense mechanism considered rare, which is the habit of living with invertebrates. In general, the ecological aspects involved in these interactions are still not understood. Lithodytes lineatus is a frog that has a known distribution for South American countries and has been considered by many researchers to be of low detectability. This characteristic may be associated with the unusual habit that this species has of living next to leafy ants (Atta spp.). It is suggested that the association with Atta ants is mediated by chemical substances in the frog's skin, however, aspects of the chemical ecology of L. lineatus remain unknown. Until now, no study has attempted to investigate patterns of substance composition in the integument, let alone isolate and elucidate the substances in the frog's skin, which are important for understanding the bases of the ant-frog association. Thus, the general objective of this thesis was to investigate the chemical profile of secondary metabolites in the L. lineatus integument. In the first chapter, we investigate the state of the art about biology of interaction between frogs and invertebrates. We found that, to date, there are records of associations of anuran-scorpion, anuran-ant, and anuran-spider and that in all these associations suggest the use of a chemical signal between the frog and the partner organism, however from all the studies evaluated, only one presented the description of the substance that allows coexistence. We also observed that, for the vast majority of records, the ecological relationship between the organisms has not been assessed or defined. In the second chapter, we evaluated the use of benzocaine-based anesthetics as a safe death protocol in frogs for use in chemical composition analyzes or bioassays. We bring robust evidence, using spectroscopic, spectrometric, and chemometric techniques, that there is no conversion of the benzocaine present in the anesthetic to the L. lineatus integument after application directly in the mouth, suggesting that its use is safe and does not cause a negative impact in studies using extracts from the skin of animals killed under this protocol. In the third chapter, we evaluated differences between the chemical profile of secondary metabolites in the skins of individuals of L. lineatus according to the areas of occurrence. We used chromatographic, spectroscopic, and chemometric techniques and showed that there is a geographic variation in the profile of secondary metabolites in the skin extracts of the individuals evaluated. We also found that in addition to the geographic variation there is variation in the chemical profile depending on the type of environment, the most diverse being the chemical profile in individuals collected in primary forest areas. In the fourth chapter, we use chromatographic and spectroscopic techniques to isolate and elucidate a substance present in methanolic extracts made from the skins of the frog L. lineatus. Our analyzes suggest that it is a steroid, cholesterol. We suggest that this steroid be used as a precursor to substances that mediate the association with Atta ants.