Gonzalez et al. take us through their study showing that the frog genus Silverstoneia should no longer be assumed as a non-chemically defended genus. Poison frogs within the superfamily Dendrobatoidea (the superfamily of poison frogs) contains numerous species that use bright coloration to visually advertise their toxicity or unpalatability to predators. The presumably most toxic vertebrate on earth, the frog Phyllobates terribilis, with its bright yellow coloration also uses this strategy. However, a recent publication in Frontiers in Zoology demonstrated the presence of toxic alkaloids and possibly repellent smells in a brown little frog from the same superfamily, which was thought by decades to lack chemical defences. This finding shows how little we know about chemical defences in cryptically colored species (e. g. brownish) and increases the chemo diversity of compounds found in poison frogs.
The golden poison frog (Phyllobates terribilis). Photo by Adolfo Amézquita.
Silverstoneia punctiventris carrying two tadpoles. Photo by Pablo Palacios-Rodríguez.
Have you ever wondered what is the smell of a poison frog?
A headspace technique was used (HS-SPME/GC-MS) to characterize the smell of Silverstoneia punctiventris, an endemic poison frog from Colombia. The smell is composed of a mixture of 6 toxic alkaloids and 20 volatile organic compounds (VOC) reported for the very first time in this species and the complete superfamily. This technique allowed a simultaneous analysis of alkaloids and VOCs, in contrast with previous analysis in other species exclusively focused on alkaloid profiles. The alkaloids detected are known to be harmful to predators, thanks to their toxic effects and bitter taste.
Compounds extracted from Silverstoneia punctiventris
In the same way as, bright coloration could be a useful visual signal to advertise toxicity, a bad smell could be a useful olfactory signal to advertise toxicity.
The characterization of the smell of this less colorful frog incorporates a new olfactory dimension of chemical defence in dendrobatids, where frogs’ smells could be airborne transported and perceived by distance (without contact). In the same way, as bright coloration could be a useful visual signal to advertise toxicity, a bad smell (whatever that means to a predator) could be a useful olfactory signal to advertise toxicity. Possible behavioural functions proposed in this article need to be verified in the future. In addition, surveys of the volatilome in other dendrobatids will be essential to examine our hypotheses. Right now, we know that humans (as potential predators) can detect, at least, some poison frogs’ volatiles. Indeed, the motivation of the authors to characterize this cryptic frog volatilome came from observations, or better, smells from field work after manipulating the frogs.
In opposition to what was thought some decades before, not always the most colorful poison frogs are more toxic, and we need to gain more knowledge about the biology and the chemistry about brownish dendrobatid frogs.
Reference:
First characterization of toxic alkaloids and volatile organic compounds (VOCs) in the cryptic dendrobatid Silverstoneia punctiventris
By Shreeya Poojary
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