Morphological and biochemical characterization of the cutaneous poison glands in toads (Rhinella marina group) from different environments

Abstract

BackgroundAmphibian defence against predators and microorganisms is directly related to cutaneous glands that produce a huge number of different toxins. These glands are distributed throughout the body but can form accumulations in specific regions. When grouped in low numbers, poison glands form structures similar to warts, quite common in the dorsal skin of bufonids (toads). When accumulated in large numbers, the glands constitute protuberant structures known as macroglands, among which the parotoids are the most common ones. This work aimed at the morphological and biochemical characterization of the poison glands composing different glandular accumulations in four species of toads belonging to group Rhinella marina (R. icterica, R. marina, R. schneideri and R. jimi). These species constitute a good model since they possess other glandular accumulations together with the dorsal warts and the parotoids and inhabit environments with different degrees of water availability.ResultsWe have observed that the toads skin has three types of poison glands that can be differentiated from each other through the morphology and the chemical content of their secretion product. The distribution of these different glands throughout the body is peculiar to each toad species, except for the parotoids and the other macroglands, which are composed of an exclusive gland type that is usually different from that composing the dorsal warts. Each type of poison gland presents histochemical and biochemical peculiarities, mainly regarding protein components.ConclusionsThe distribution, morphology and chemical composition of the different types of poison glands, indicate that they may have different defensive functions in each toad species.

Morphological Evidence for an Oral Venom System in Caecilian Amphibians

“…It is worth mentioning that amphibians are known by their variety of extremely toxic non-protein molecules in the skin ( Duellman and Trueb, 1994 , Jeckel et al., 2015 , Toledo and Jared, 1995 ). Therefore, one cannot rule out the possibility of caecilian dental glands containing molecules from other classes, such as lipids, widely found in toads ( Mailho-Fontana et al., 2018 ) and already identified by histochemistry in S. annulatus tooth-glands.…”

The cost of chemical defence: the impact of toxin depletion on growth and behaviour of cane toads ( Rhinella marina )

“…soluble proteins) stored by the liver. Based on patterns of vascularization and density of organelles involved in biosynthesis, the parotoids themselves appear to be the main site of toxin production [20,43]. Concordantly, experimental removal of toxin generated growth deficits in toads, even over a relatively short duration (5-20 days).…”

“…The cutaneous glands of amphibians secrete toxic substances onto their skin, protecting against predators, parasites and microorganisms [1,[17][18][19]. The cutaneous glands of amphibians are typically dispersed across all skin surfaces but sometimes are concentrated, as in the warts and parotoid glands of bufonids [17,20,21].…”

Chemical and Pharmacological Screening of Rhinella icterica (Spix 1824) Toad Parotoid Secretion in Avian Preparations

“…In a previous report, we showed that RIPS was toxic to the peripheral and central nervous systems of avian, mammalian, and insect species through a digitalis-like action [27,39]. Although preliminary studies of RIPS have identified some chemical components, such as dehydrobufotenine, hellebrigenin, telocinobufagin, marinobufagin, bufotalin, bufalin, and 19-oxo-cinobufagin [13,36,39], no previous study has sought to examine the chemical constitution of this secretion in detail and to assess its specific interaction with the avian nervous system. In this work, we investigated the chemical composition of RIPS to identify the main groups of compounds responsible for the acute neurotoxicity caused by this secretion at avian skeletal neuromuscular junctions.…”

“…For therapeutic applications, the most important amphibian secretions are obtained from toads of the family Bufonidae [6,21] and have been widely used in America, Asia, and Europe as antiviral agents (to treat human immunodeficiency virus (HIV)), as well as for their anti-proliferative [22][23][24], antibacterial [25], antiparasitic [26], insecticidal [27,28], antidiabetic [29], anti-cancer [30,31], anti-inflammatory, and analgesic [7,[32][33][34] activities. Many compounds that occur in toad secretions, e.g., bufalin, telocinobufagin, hellebrin, marinobufagin, and cinobufagin, can vary markedly among individuals, geographic regions, and species in response to environmental conditions, e.g., temperature, and dietary composition, and may involve morphological adaptations [14,35,36].…”