Differences and Similarities among Parotoid Macrogland Secretions in South American Toads: A Preliminary Biochemical Delineation

Abstract

Amphibians are known by cutaneous glands, spread over the skin, containing toxins (proteins, peptides, biogenic amines, steroidal bufadienolides, and alkaloids) used as chemical defense against predators and microbial infection. Toads are characterized by the presence of parotoid macroglands. The common toads have lately been divided into two genera: Bufo (Europe, Asia, and Africa) and Rhinella (South America). Basal Rhaebo genus is exclusively of Central America and Amazon region. Although Rhinella and Rhaebo are related, species may share differences due to the diversity of environments that they live in. In this work, we have performed a biochemical characterization of the components of the poison of eight Rhinella species and one Rhaebo by means of RP-HPLC with either UV or MS detection and by SDS-PAGE, in order to verify whether phylogenetic and biological differences, such as habitat, diet, and defensive strategies, between them may also be reflected in poison composition. Although some components were common among the secretions, we were able to identify exclusive molecules to some species. The fact that closely related animals living in different habitats secrete different molecules into the skin is an indication that biological features, and not only evolution, seem to directly influence the skin secretion composition.

Biochemical Profile, Biological Activities, and Toxic Effects of Proteins in the Rhinella schneideri Parotoid Gland Secretion

“…However, skin secretions of other amphibian genera such as Phyllomedusa (Conceição et al., ) and Leptodactylus (Limaverde et al., ) contain lower protein contents. On comparing the electrophoretic protein profile of the parotoid glands obtained from R. schneideri with those obtained from different species of the genus Rhinella (Mailho‐Fontana et al., ; Sciani et al., ), we found a similar pattern, especially for the high molecular weight proteins (>55 kDa). However, unique bands were observed for each secretion (30–55 kDa).…”

“…Herein, the R. schneideri parotoid secretion was found to comprise up to 30% (w/w) of soluble proteins, and these proteins of the genus Rhinella are known to be one of the major constituents of the parotoid glands (Mailho‐Fontana et al., ; Sciani et al., ). However, skin secretions of other amphibian genera such as Phyllomedusa (Conceição et al., ) and Leptodactylus (Limaverde et al., ) contain lower protein contents.…”

“…Few studies have described the isolation and biological and toxic effects of molecules from the parotoid secretion of R. schneideri (Cunha‐Filho et al., ; Anjolette et al., ). In the literature, only one study has described the peptide profile of this secretion (Sciani et al., ). Another important aspect that necessitates the investigation of peptides and proteins from frog skin is their structural similarity to vertebrate proteins, explaining their potential for use in pharmacology and medicine (Lee et al., ; Garg et al., ).…”

Toxin depletion has no effect on antipredator responses in common toad (Bufo bufo) tadpoles

“…The relative weakness of the responses may originate from individuals' reliance on chemical defences, although experimental evidence supporting this hypothesis is still lacking. Most bufonid species are known to contain bufadienolides (cardiotoxic steroids), including adults, tadpoles, and eggs (Mebs et al ., ; Hayes et al ., ; Sciani et al ., ) and common toad tadpoles produce several bufadienolide compounds from an early tadpole stage on (Bókony et al ., ; B. Üveges, G. Fera, Á. Móricz, D. Krüzselyi, A. Hettyey, unpubl. data).…”

Toad Poison and Drug Discovery

“…2), including proteins and peptides, biogenic amines, steroids, and alkaloids, depending on species and the environment in which they live (Sciani et al 2013a). …”