Invertebrate photographs and taxonomic information from: Nuance in the narrative of a brown poison frog: Environmental alkaloids and specialized foraging in a presumed toxin-free and diet-generalized species

In poison frogs (Dendrobatidae), conspicuous colors have evolved
repeatedly in tandem with high numbers and quantities of skin toxins
(alkaloids). Here, we focus on an inconspicuously-colored
species—Silverstoneia flotator—which has long been deemed toxin-free and
thought to forage opportunistically on mites and ants. Both assumptions
have received some empirical support, but there is also evidence that
predators avoid S. flotator. In a Panamanian S. flotator population, we
sampled invertebrates in frog diets and the surrounding environment (using
Berlese and pitfall traps) and screened for skin, dietary, and
environmental alkaloids using untargeted metabolomics. We found that while
the frogs are opportunistic consumers of mites and ants, they display
preferences at finer taxonomic scales (for symphypleonan springtails and
Pheidole ants). We also annotated 64 skin compounds as alkaloids, 38 of
which were present in the environment. One alkaloid present in the skin
and environment is likely the highly potent epibatidine. While the average
biosynthetic (class and superclass) diversity of alkaloids in a dorsal
skin sample is higher than that of a ventral skin and environmental—but
not dietary—sample, environmental samples diverge more in their alkaloid
biosynthetic diversities than do dietary or skin samples. The frogs
consume a consistent set of alkaloids, forage in a variable chemical
space, and possess diverse dorsal skin alkaloids. They might use
finer-scale diet specialization to modulate the types, quantities, and
numbers of alkaloids they ingest. We encourage further examination of
inconspicuously-colored taxa to better understand the ecological
importance of diet-acquired toxins and specialized diets in cryptic
organisms.