Morphological re-evaluation of the parotoid glands of Bufo ictericus (Amphibia, Anura, Bufonidae)

Abstract

Multicellular glands in the amphibian integument represent a significant evolutionary advance over those of fishes. Bufonids have parotoid glands, symmetrically disposed in a post-orbital position. Their secretion may contribute to protection against predators and parasites. This study provides a re-evaluation of the morphology of the Bufo ictericus parotoid glands. The parotoid gland integument of the medial surface shows rounded depressions with small pores that connect with the duct openings of the larger granular glands. Under light microscopic evaluation the integument is constituted by typical epidermis, supported by dermis subdivided into a spongious dermis, a reticular dermis, and a compact dermis. The Eberth-Katschenko layer is identified as a basophilic material scattered throughout the superficial spongious dermis. The parotoid gland is an integument region, in which three exocrine glandular types occur: mixed glands, smaller granular glands and larger granular glands. The mixed gland is formed by mucous and serous cells while the small granular glands contain a homogene acidophilic intake. The larger granular glands produce a basophilic and alcianophilic material, and are responsible for the macroscopic protuberances designed as parotoid glands. Thus, the end product released by the parotoid glands is a mix of secretions produced by the three glands.

Passive and active defense in toads: The parotoid macroglands inRhinella marinaandRhaebo guttatus

“…On the other hand, the examination of the parotoids of R. marina and R. guttatus revealed many structural similarities, which are also shared by other bufonids that were already studied (Hostetler and Cannon, ; Toledo et al, ; Almeida et al, ; Felsemburgh et al, ; Jared et al, ). In all toads these macroglands are composed of juxtaposed secretory alveoli with a characteristic honeycomb‐like structure.…”

“…In bufonids, the calcified layer is well developed and creates a type of armor that hinders water loss in terrestrial environments and in the open areas where these animals commonly inhabit (Elkan, ; Toledo and Jared, ; Navas et al, ; Jared et al, ). Differently from the rest of the skin, in the parotoids of toads, including R. marina , the calcified layer seems to be exceptionally well developed and allocated above the glandular alveoli, very close to the epidermis (Toledo et al, ; Almeida et al, ; Felsemburgh et al, ; Jared et al, ). According to Baldwin and Bentley () the calcified layer must act as a mechanical barrier on the skin, exerting a protective function and therefore hardening the skin and making it less malleable.…”

“…In some species the poison glands are grouped into large and very conspicuous protuberances, such as the parotoid macroglands of toads (Toledo and Jared, ; Duellman and Trueb, ; Clarke, ; Jared et al, ). These macroglands are located in the post‐orbital region and, on the skin surface, can be identified by the presence of large pores from which the poison is ejected (Hostetler and Cannon, ; Toledo et al, ; Toledo and Jared, ; Almeida et al, ; Jared et al, ). The parotoids are constituted by many alveoli formed by a resistant collagenous connective tissue.…”

Localization of hematopoietic cells in the bullfrog (Lithobates catesbeianus)

“…Several studies have identified anuran molecules by using mammalian/human antibodies (Cianciarullo et al 1999;Ong et al 1993;Raucci et al 2006;Almeida et al 2007;Azevedo et al 2007;Raucci and Di Fiore 2007), indicating that some conservation of antigenic protein has occurred through phylogenetic development. Some studies also corroborate the protein conservation between anurans and mammals.…”

Structure of the sexually dimorphic gland of Cycloramphus fuliginosus (Amphibia, Anura, Cycloramphidae)

“…In B. ictericus, mucous and granular glands of the body integument are surrounded by myoepithelial cells as well as the smaller and larger glandular alveoli of the parotoid gland (Almeida et al, 2007). Mills and Prum (1984) and Delfino et al (1998) related that myoepithelial cells are important in the structural organization of the glandular secretory portion.…”