Herein we review what is known about the chemical ecology of poison frogs with a focus on dendrobatid poison frogs. While five anuran families are known to have an alkaloid-derived chemical defense, the dendrobatids have been studied in greatest detail and provides chemical ecologists with a complex model system for understanding how chemical defenses operate in real time and may have evolved through evolutionary time. We describe the diversity of alkaloid defenses known from frogs, alkaloid sequestration, biosynthesis and modification, and we review what is known concerning arthropod sources for alkaloids. There is variation in nearly every attribute of the system and we try to describe some of the challenges associated with unraveling the complexities of this model system.

Alkaloids in the skin glands of poison frogs serve as a chemical defense against predation, and almost all of these alkaloids appear to be sequestered from dietary arthropods. Certain alkaloid-containing ants have been considered the primary dietary source, but dietary sources for the majority of alkaloids remain unknown. Herein we report the presence of ≈80 alkaloids from extracts of oribatid mites collected throughout Costa Rica and Panama, which represent 11 of the ≈24 structural classes of alkaloids known in poison frogs. Forty-one of these alkaloids also occur in the dendrobatid poison frog, Oophaga pumilio , which co-occurs with the collected mites. These shared alkaloids include twenty-five 5,8-disubstituted or 5,6,8-trisubstituted indolizidines; one 1,4-disubstituted quinolizidine; three pumiliotoxins; and one homopumiliotoxin. All but the last of these alkaloid classes occur widely in poison frogs. In addition, nearly 40 alkaloids of unknown structure were detected in mites; none of these alkaloids have been identified in frog extracts. Two of these alkaloids are homopumiliotoxins, five appear to be izidines, four appear to be tricyclics, and six are related in structure to poison frog alkaloids that are currently unclassified as to structure. Mites are common in the diet of O. pumilio , as well as in the diets of other poison frogs. The results of this study indicate that mites are a significant arthropod repository of a variety of alkaloids and represent a major dietary source of alkaloids in poison frogs.

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No abstract

Poison frogs are chemically defended from predators and/or microorganisms by the presence of alkaloids in dermal skin glands. Over the past 40 years, more than 800 alkaloids, which are generally organized into 28 structural classes, have been identified in several lineages of poison frogs worldwide. Originally, the presence of alkaloids in frogs was thought to be the result of biosynthesis, however research led largely by John W. Daly resulted in the discovery that most of these alkaloids are sequestered unchanged from dietary arthropods. In the present paper, we review the most significant findings and studies that led to the proposal of the 'dietary hypothesis'.