Oribatid mites as a major dietary source for alkaloids in poison frogs

Abstract

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.

Diversity of ants and mites in the diet of the Brazilian frog Chiasmocleis leucosticta (Anura: Microhylidae)

“…Saporito et al (2007) isolated more than 80 alkaloids from oribatid mites, and half of them are also present in the dendrobatid Oophaga pumilio. Oribatid mites are the main source of alkaloids to Dendrobatidae and Eleutherodactylidae (Raspotnig et al 2011).…”

Discovery of skin alkaloids in a miniaturized eleutherodactylid frog from Cuba

“…Oribatid mites, known as alkaloid sources for frogs in Central America [14], were well represented in the diet of these two species (table 2). Numerically, mites made up 66 per cent of the 35 prey items of E. orientalis, and 71 per cent of the 62 prey items of E. iberia.…”

“…However, more recently, evidence has accumulated for the major importance of oribatid mites [13] which are a common prey, especially for miniaturized frogs [20], including the dwarf Eleutherodactylus studied here (table 2). Two alkaloids of E. iberia have previously been detected in arthropods, 307A in mites and ants, and 323A in ants, suggesting a dietary source for these compounds [13,14].…”

“…Data for mites (Acari) are given separately for orders/suborders, and for families within the Oribatida. Asterisks denote families of oribatids that were present in alkaloid-containing samples of a previous study in Costa Rica and Panama [14]. Frog specimens were labelled with field numbers of A.R.…”

“…Stomach contents of a subset of the specimens collected were analysed using a stereomicroscope. Special attention was given to identifying oribatid mites to the family level, because of their known importance as an alkaloid source for poison frogs [14].…”