Diversity and evolution of the parotoid macrogland in true toads (Anura: Bufonidae)

Abstract

Skin glands in amphibians are either distributed throughout the skin or aggregated in multiglandular structures such as the parotoids typical of most species of Bufonidae. Although many early divergent and derived bufonids lack a discrete parotoid in the postorbital–supratympanic (PoSt) region, they have a great macroscopic diversity in the skin morphology of this region. To understand the origin and evolution of this diversity, in particular of the parotoids, we describe the histomorphology of the skin of the PoSt and dorsal regions in 17 species of bufonids, with or without external evident parotoid, and compare it with previously published descriptions. The survey results in 27 characters that were optimized on a phylogenetic hypothesis of Bufonidae. Our results reveal that the PoSt region has a noteworthy morphological diversity of types of glands, spatial organization and differences in the secretion products. Some morphological characters represent putative synapomorphies of internal clades of Bufonidae and are related to the progressive differentiation towards defined structures (macroglands, parotoids). These morphological results, along with published information on the toxicity of the skin secretions and defensive behaviours in some representative species, allow us to infer possible relationships between these features.

Naturally occurring variability in larval period length is associated with intraspecific differences in late tadpoles of a South American true toad

“…The skin of 6 specimens at late climax was studied for each larval period length. The diameter of syncytial glands (also known as granular or serous glands; see revision of anuran skin glands nomenclature in O'Donohoe et al., 2019, 2022; Regueira et al., 2016) was calculated by following 10–15 individual glands through serially adjacent skin sections. The total number of sections each gland occupied was multiplied by the section thickness of 7 μm.…”

Incilius alvarius cell-based synthesis of 5-MeO-DMT

“…Incilius alvarius parotoid anatomy and morphology were established according to O ‘donohoe et al (O’ donohoe et al, 2019). A partial parotoid gland biopsy was undertaken under aseptic conditions in two anesthetized Incilius Alvarius toads in conformity with the current best practice for the handling of laboratory animals.…”

Variation in size and shape of toxin glands among cane toads from native-range and invasive populations

“…Many bufonids (“true toads”) possess paired postorbital macroglands known as parotoids 18 , 52 that produce cardiotonic steroids such as bufogenins and bufotoxins 50 , 53 – 55 . These toxins have cardio-acceleratory and vasopressor effects on vertebrates 52 , 56 , such that ingestion can be lethal for predators 57 – 59 .…”

“…Like many amphibians, toads synthesise potent chemical defences in the form of steroidal bufotoxins 12 – 14 that are energetically expensive to produce 15 , 16 . Quantifying investment into those chemicals is facilitated by the fact that most toad toxins are produced and stored in parotoid (shoulder) macroglands, whose dimensions can be easily and accurately measured on live animals 17 , 18 (Fig. 1 ).…”