Dose‐dependent alkaloid sequestration and N‐methylation of decahydroquinoline in poison frogs

Abstract

Sequestration of chemical defenses from dietary sources is dependent on the availability of compounds in the environment and the mechanism of sequestration. Previous experiments have shown that sequestration efficiency varies among alkaloids in poison frogs, but little is known about the underlying mechanism. The aim of this study was to quantify the extent to which alkaloid sequestration and modification are dependent on alkaloid availability and/or sequestration mechanism. To do this, we administered different doses of histrionicotoxin (HTX) 235A and decahydroquinoline (DHQ) to captive‐bred Adelphobates galactonotus and measured alkaloid quantity in muscle, kidney, liver, and feces. HTX 235A and DHQ were detected in all organs, whereas only DHQ was present in trace amounts in feces. For both liver and skin, the quantity of alkaloid accumulated increased at higher doses for both alkaloids. Accumulation efficiency in the skin increased at higher doses for HTX 235A but remained constant for DHQ. In contrast, the efficiency of HTX 235A accumulation in the liver was inversely related to dose and a similar, albeit statistically nonsignificant, pattern was observed for DHQ. We identified and quantified the N‐methylation of DHQ in A. galactonotus, which represents a previously unknown example of alkaloid modification in poison frogs. Our study suggests that variation in alkaloid composition among individuals and species can result from differences in sequestration efficiency related to the type and amount of alkaloids available in the environment.

Noninvasive Detection of Chemical Defenses in Poison Frogs Using the MasSpec Pen

“…Note that while alkaloids have been detected in frog skin as soon as 4–5 days after initial administration by LC-MS, , we did not observe an increase in normalized DHQ signal among alkaloid-fed individuals versus vehicle-fed individuals until day 10 during the feeding study. As alkaloid detection depends on the sensitivity of the mode of analysis and total quantities of accumulated DHQ in skin have been shown to increase with higher doses of the alkaloid, we expect that administration of a higher dose of DHQ would result in earlier detection of the alkaloid in vivo using the MasSpec Pen. It should also be noted that the efficiency of alkaloid accumulation differs among alkaloids; , thus, additional experiments are needed to determine the in vivo detection limit of the MasSpec Pen for various alkaloid compounds.…”

“…As alkaloid detection depends on the sensitivity of the mode of analysis and total quantities of accumulated DHQ in skin have been shown to increase with higher doses of the alkaloid, we expect that administration of a higher dose of DHQ would result in earlier detection of the alkaloid in vivo using the MasSpec Pen. It should also be noted that the efficiency of alkaloid accumulation differs among alkaloids; , thus, additional experiments are needed to determine the in vivo detection limit of the MasSpec Pen for various alkaloid compounds.…”

Mother chemical defenses predict offspring defenses in a dendrobatid poison frog

“…Following collection in the field, we weighed all mother frogs to the nearest 0.1 mg using a Pesola PPS200 digital pocket scale and measured for snout-to-vent length (adults; SVL 19-22 mm) (Donnelly 1989b) to the nearest 0.1 mm using a Traceable® Digital Calipers. We euthanized mother frogs via freezing (Jeckel et al 2019(Jeckel et al , 2022, following which their skins were removed and stored in separate 4mL glass vials with Teflon-lined caps containing 2mL of 100% methanol. We weighed tadpoles to the nearest 0.1 mg using a Pesola PPS200 digital pocket scale, euthanized via freezing, and stored wholly in separate 4mL glass vials with Teflon-lined caps containing 2mL of 100% methanol.…”

“…Most organisms are able to biosynthesize defensive chemicals, whereas some must obtain them secondarily through a specialized diet of chemically defended prey items (Nishida 2002;Saporito et al 2012). The uptake, accumulation, and storage of secondarily derived defenses from diet is generally referred to as sequestration (Mebs 2001;Savitzky et al 2012;Jeckel et al 2022), and is a well-studied phenomenon among phytophagous arthropods (reviewed in Opitz and Muller 2009); however, sequestration has also evolved independently in several lineages of vertebrates (reviewed in Savitzky et al 2012) including snakes (Hutchinson et al 2007), amphibians (Daly et al 1994;Saporito et al 2009), and likely birds (Dumbacher et al 2004;Dumbacher et al 2009).…”

Eco-Metabolomics Applied to the Chemical Ecology of Poison Frogs (Dendrobatoidea)

“…In the case of alkaloids derived from biogenic amines in Phyllobates vitattus (Protti-Sánchez et al 2019 ), they probably come from the biosynthesis of tryptophan as in bufonids (Scott Chilton et al 1979 ). In contrast, for most of the lipophilic alkaloids, a dietary intake of precursors that may or may not undergo metabolic transformations has been proven (Daly et al 2003 , 2009 ; Santos et al 2016 ; Jeckel et al 2022 ). Inter-individual variation among species, populations, and specimens probably depends on genetic/transcriptomic differences that delimit resistance to dietary toxins (Santos et al 2016 ; Tarvin et al 2016 ), different metabolic capabilities (Abderemane-Ali et al 2021 ; Márquez 2021 ), and the heterogeneous occurrence of dietary items on the forest in space and time (Saporito et al 2012 ).…”