Most people are familiar with South and Central America’s iconic poison dart frogs, especially the golden poison frog (Phyllobates terribilis), that carry the potent neurotoxic alkaloid batrachotoxin. The discovery of two new poisonous bird species in New Guinea — which carry the same toxin in their skin and feathers — demonstrates that batrachotoxin is more widespread than once believed.
The rufous-naped bellbird (Aleadryas rufinucha). Image credit: Knud Jønsson.
Toxicity has evolved independently multiple times across the animal tree of life, with iconic examples from divergent groups such as jellyfish, cephalopods, nudibranchs, insects, spiders and vertebrates.
Toxic compounds are either produced by the animal or symbionts or are acquired through the animal’s diet. Toxicity serves important functions related to hunting, defense and parasite deterrence.
While multiple animal species can feed on toxic diets, only a fraction of these have evolved the ability to sequester the ingested toxins to their own advantage.
Toxic vertebrates carry different types of toxins, some of which can be lethal, even in small amounts.
One such example is the alkaloid batrachotoxin found in New Guinean toxic birds and in Neotropical poison dart frogs in the genus Phyllobates.
“We managed to identify two new species of poisonous birds on our most recent trip,” said Dr. Knud Jønsson, a researcher at the Natural History Museum of Denmark.
“These birds contain a neurotoxin that they can both tolerate and store in their feathers.”
The regent whistler (Pachycephala schlegelii). Image credit: Ian Shriner.
The two new toxic bird species are the regent whistler (Pachycephala schlegelii) and the rufous-naped bellbird (Aleadryas rufinucha).
“We were really surprised to find these birds to be poisonous as no new poisonous bird species has been discovered in over two decades,” Dr. Jønsson said.
“Particularly, because these two bird species are so common in this part of the world.”
Dr. Jønsson and his colleagues also compared six species of toxic birds from New Guinea, including the two species that they discovered to be toxic in their research, to 21 non-toxic bird species belonging to the superfamily Corvoidea.
They focused on genomic adaptations that could facilitate resistance to the diet-acquired batrachotoxin in the toxic birds.
They found that these birds carry multiple mutations in the SCN4A gene that are under positive selection.
“Our discovery of several mutations in the batrachotoxin-binding pore-forming segment of the SCN4A gene that reduce the binding affinity of batrachotoxin in toxic birds and the previous discovery of mutations in the same gene in Phyllobates frogs imply that molecular-level convergently evolved adaptations provide autoresistance to batrachotoxin in two distantly related vertebrate clades,” they said.
“These mutations are found in different positions of the SCN4A gene in birds and frogs, and even in different positions across toxic bird species.”
“Further comprehensive comparative studies of birds and frogs are warranted to improve our understanding of the evolution of batrachotoxin resistance across these charismatic vertebrate clades.”
The discovery is reported in a paper in the journal Molecular Ecology.
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Kasun H. Bodawatta et al. Multiple mutations in the Nav1.4 sodium channel of New Guinean toxic birds provide autoresistance to deadly batrachotoxin. Molecular Ecology, published online February 13, 2023; doi: 10.1111/mec.16878
