Poison frog dietary preference depends on prey type and alkaloid load

The ability to acquire chemical defenses through the diet has evolved
across several major taxa. Chemically defended organisms may need to
balance chemical defense acquisition and nutritional quality of prey
items. However, these dietary preferences and potential trade-offs are
rarely considered in the framework of diet-derived defenses. Poison frogs
(Family Dendrobatidae) acquire defensive alkaloids from their arthropod
diet of ants and mites, although their dietary preferences have never been
investigated. We conducted prey preference assays with the Dyeing Poison
frog (Dendrobates tinctorius) to test the hypothesis that alkaloid load
and prey traits influence frog dietary preferences. We tested size
preferences (big versus small) within each of four prey groups (ants,
beetles, flies, and fly larvae) and found that frogs preferred interacting
with smaller prey items of the fly and beetle groups. Frog taxonomic prey
preferences were also tested as we experimentally increased their chemical
defense load by feeding frogs decahydroquinoline, an alkaloid compound
similar to those naturally found in their diet. Contrary to our
expectations, overall preferences did not change during alkaloid
consumption, as frogs across groups preferred fly larvae over other prey.
Finally, we assessed the protein and lipid content of prey items and found
that small ants have the highest lipid content while large fly larvae have
the highest protein content. Our results suggest that consideration of
toxicity and prey nutritional value are important factors in understanding
the evolution of acquired chemical defenses and niche partitioning as a
whole.