Venomous Frogs Use Heads as Weapons

Abstract

Venomous animals have toxins associated with delivery mechanisms that can introduce the toxins into another animal. Although most amphibian species produce or sequester noxious or toxic secretions in the granular glands of the skin to use as antipredator mechanisms, amphibians have been considered poisonous rather than venomous because delivery mechanisms are absent. The skin secretions of two Brazilian hylid frogs (Corythomantis greening and Aparasphenodon brunoi) are more toxic than the venoms of deadly venomous Brazilian pitvipers, genus Bothrops; C. greeningi secretion is 2-fold and A. brunoi secretion is 25-fold as lethal as Bothrops venom. Like the venoms of other animals, the skin secretions of these frogs show proteolytic and fibrinolytic activity and have hyaluronidase, which is nontoxic and nonproteolytic but promotes diffusion of toxins. These frogs have well-developed delivery mechanisms, utilizing bony spines on the skull that pierce the skin in areas with concentrations of skin glands. C. greeningi has greater development of head spines and enlarged skin glands producing a greater volume of secretion, while A. brunoi has more lethal venom. C. greeningi and A. brunoi have highly toxic skin secretions and an associated delivery mechanism; they are therefore venomous. Because even tiny amounts of these secretions introduced into a wound caused by the head spines could be dangerous, these frogs are capable of using their skin toxins as venoms against would-be predators.

Multiple anti‐predator mechanisms in the red‐spotted Argentina Frog (Amphibia: Hylidae)

“…Such structures may be inferred from plates published by Jared et al . (, ), who studied the dermal histology of the skulls of Corythomanthis greeningi and Aparasphenodon brunoi . Comparing the three species, A. siemersi and C. greeningi share sculptural ridges with sinuate edges and spiny projections on roofing bones.…”

“…Histology reveals that spines, ridges, protuberances, pits and pores of A. siemersi principally comply with Trueb's definition of exostosis, rather than co‐ossification, as was proposed by Jared et al . (, ). Such structures may be inferred from plates published by Jared et al .…”

“…However, the LD50 values of these two taxa may not be exactly comparable because that of Aparasphenodon brunoi is based on a concentrated chemical compound (protein), whereas that of Argenteohyla siemersi is based on full skin secretions. Among the other factors that may be involved, a fewer number of spiny projections could be offset by a high toxicity of the secretions, as were argued for Aparasphenodon brunoi and Corythomantis greeningi (Jared et al ., ), and which is consistent for A. siemersi . The link between aposematic colouration and diurnal activity is associated with predators such birds, mammals, and fishes that locate their prey visually (Toledo & Haddad, ).…”

Poison frogs, defensive alkaloids, and sleepless mice: critique of a toxicity bioassay

“…One concern pertains to predator proxies being injected with skin extracts; although some amphibians, including anurans, possess skeletal elements that protrude through their integument and subcutaneously deliver skin toxins to offenders (Jared et al 2015), dendrobatids do not. Hence, the method of injecting mice with skin extracts does not correspond to the frogs' natural defense mechanisms.…”

Jedovatí obojživelníci

“…Příčinou bylo poranění kůže nepatrnými kostěnými výrůstky na čel-ní straně hlavy spojenými s jedovými žlázami. Jed z jednoho exempláře zmíněné rosničky Brunovy by údajně dokázal usmrtit až 80 lidí (Jared et al 2015).…”