23 February, 2024
By Alexander Trifunovic
Hooded Pitohui. Photo by Benjamin Freeman.
When thinking about toxicity in animals, amphibians or insects likely come to mind, but several species of birds in Papua New Guinea have also evolved to be poisonous. The Hooded Pitohui (Pitohui dichrous) is the most toxic of the bunch, and its skin and feathers contain homobatrachotoxin, the same compound found in poison dart frogs (Dendrobatidae) of the Neotropics. Batrachotoxins are some of the most potent neurotoxins found in nature, and they work by binding to sodium channels which causes irritation and, in higher concentrations, paralysis and death. The Hooded Pitohui’s burnt-orange and black aposematic coloration broadcasts its toxicity to potential predators, including humans. Pitohuis often take the lead in mixed species flocks by being the most flashy and conspicuous as they search for fruits, seeds, and insects, including the Choresine beetles from which they sequester homobatrachotoxin. Toxicity evolved at least five times in Papuan birds in the superfamily Corvoidea, which includes shrikes (Laniidae), corvids (Corvidae), vireos (Vireonidae), and over two dozen other bird families. This ancient radiation of birds has incredible diversity, nearly eight hundred species, and New Guinea may have served as a stronghold for this group over the last thirty million years. Of the birds using batrachotoxins, Hooded Pitohui and its closest relatives are placed in Oriolidae (Old World orioles). Other poisonous birds formerly lumped as pitohuis form several branches within Pachycephalidae (whistlers) and one species in Oreoicidae (Australo-Papuan bellbirds). The Blue-capped Ifrita, a close relative of birds-of-paradise (Paradisaeidae), is also highly toxic and it has not shared a common ancestor with the pitohuis and whistlers since the earliest radiation of Corvoidea roughly twenty-five million years ago. This serves as a very interesting example of convergent evolution within related species and is a tiny peek at the mind-boggling adaptations within this group of birds.
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