Post‐metamorphic development of skin glands in a true toad: Parotoids versus dorsal skin

Abstract

Chemical defenses in amphibians are a common antipredatory and antimicrobial strategy related to the presence of dermal glands that synthesize and store toxic or unpalatable substances. Glands are either distributed throughout the skin or aggregated in multiglandular structures, being the parotoids the most ubiquitous macrogland in toads of Bufonidae. Even though dermal glands begin to develop during late-larval stages, many species, including Rhinella arenarum, have immature glands by the end of metamorphosis, and their post-metamorphic growth is unknown. Herein, we compared the post-metamorphic development of parotoids and dorsal glands by histological and allometric studies in a size series of R. arenarum. Histological and histochemical studies to detect proteins, acidic glycoconjugates, and catecholamines, showed that both, parotoids and dorsal glands, acquire characteristics of adults in individuals larger than 50 mm; that is, a moment in which the cryptic coloration disappears. Parotoid height increased allometrically as a function of body size, whereas the size of small dorsal glands decreased with body size. The number of glands in the dorsum was not linearly related to body size, appearing to be an individual characteristic. Only adult specimens had intraepithelial granular glands in the duct of the largest glands of the parotoids. Since toxic secretions accumulate in the central glands of parotoids, allometric growth of parotoids may translate into greater protection from predators in the largest animals. Conversely, large glands in the dorsum, which produce a proteinaceous secretion of unknown function, grow isometrically to body size. Some characteristics, like intraepithelial glands in the ducts and basophilic glands in the dorsum, are limited to adults.

Toads phenotypically adjust their chemical defences to anthropogenic habitat change

“…Cautionarily, we cannot exclude the possibility that the differences seen in the adults are genetically determined but are only expressed after maturity and/or during the breeding season. However, the juveniles had well developed gonads by the time of sampling and, in other toad species, parotoids acquire the morphological and histochemical characteristics of adults before sexual maturity 28 and little if any seasonal variation has been found in parotoid size and toxin composition 29,50 . Also, we cannot rule out that some similarity in habitat effects between the two age groups might have been masked by the minor differences in the methods applied to adults and juveniles to measure parotoids and sample toxins.…”

“…We transported the captured animals to our laboratory in Budapest, where they were kept until spawning as described in an earlier paper 27 (see Supplementary Methods 1.2). After spawning, we measured each toad’s snout-vent length (SVL) and the length and width of the left parotoid 28,29 to the nearest 0.1 mm with a calliper (Fig. 1).…”

“…As proxy for parotoid size, we estimated the base area of the left parotoid gland from its length and width by assuming the shape of an ellipse 28 (Fig. 1, Fig.…”

Integrating morphology and physiology of the key endocrine organ during tadpole development: The interrenal gland

“…Herein, we present the histological and physiological pattern of development of the interrenal gland in the common toad R. arenarum (Hensel, 1867) (Bufonidae), a large true toad from southern South America with a generalized pond‐type larva (Altig & Johnston, 1989; Vera Candioti, 2006). This species is a model organism for ongoing research on skin development, skeletogenesis, stress response, and ecotoxicological studies (Alcalde, 2017; Cuzziol Boccioni et al, 2020; Distler et al, 2016; Gómez et al, 2017; Regueira et al, 2016, 2017), among others.…”

Form and Function of the skin glands in the Himalayan newt Tylototriton verrucosus

“…Granular glands, the second type of lissamphibian skin glands are found throughout the skin, but some areas show higher concentrations of enlarged granular gland fields [ 2 , 9 , 11 , 13 , 25 , 31 , 41 , 50 , 51 ]. Although granular glands can differ substantially in form and content amongst lissamphibians, they are generally acinar in nature and are built up by giant cells containing granular material that often fuse into syncytia [ 19 , 23 , 24 , 28 , 29 , 33 , 34 , 52 , 62 , 69 ]. Granular glands are capable of synthesizing and secreting mainly bioactive substances such as amines, peptides, and alkaloids [ 26 ] and are considered the site of skin toxin production and storage (e.g.…”