Ant And Mite Diversity Drives Toxin Variation In The Little Devil Poison Frog

Abstract

20Poison frogs sequester chemical defenses from arthropod prey, although the details of how 21 arthropod diversity contributes to variation in poison frog toxins remains unclear. We 22 characterized skin alkaloid profiles in the Little Devil frog, Oophaga sylvatica (Dendrobatidae), 23 across three populations in northwestern Ecuador. Using gas chromatography mass 24 spectrometry, we identified histrionicotoxins, 3,5-and 5,8-disubstituted indolizidines, 25 decahydroquinolines, and lehmizidines as the primary alkaloid toxins in these O. sylvatica 26 populations. Frog skin alkaloid composition varied along a latitudinal gradient across 27 populations in a principal component analysis. We also characterized diversity in arthropods 28 isolated from frog stomach contents and confirmed O. sylvatica specialize on ants and mites. To 29 test the hypothesis that poison frog toxin diversity reflects species and chemical diversity in 30 arthropod prey, we (1) used liquid chromatography mass spectrometry to chemically profile 31 consumed ants and mites, and (2) used sequencing of cytochrome oxidase 1 to identify 32 individual prey specimens. We show that chemical profiles of consumed ants and mites cluster 33 by frog population, suggesting different frog populations have access to chemically distinct prey. 34We identified 45 ants and 9 mites isolated from frog stomachs, finding several undescribed 35 species. Finally, by comparing chemical profiles of frog skin and isolated prey items, we were 36 able to trace the arthropod source of four poison frog alkaloids, including 3,5-and 5,8-37 disubstituted indolizidines and a lehmizidine alkaloid. Together, our data shows the diversity of 38 alkaloid toxins found in O. sylvatica can be traced to chemical diversity in arthropod prey. 39 40

Links between prey assemblages and poison frog toxins: A landscape ecology approach to assess how biotic interactions affect species phenotypes

“…After eliminating those ants that contributed little to the GDM (<0.1%), only nine out of 68 species were retained in the final model. These nine species belong to five genera, of which four ( Anochetus , Brachymyrmex , Monomorium , and Solenopsis ) are known to be eaten by Oophaga or other alkaloid‐sequestering frogs (Clark et al, ; McGugan et al, ; Moskowitz et al, , ). Therefore, a few prey items (i.e., ant species) may contribute disproportionately to the uniqueness of chemical defenses among populations of O. pumilio .…”

“…This result may reflect challenges to quantifying spatial turnover of prey species that act as alkaloid sources. Due to restricted taxonomic and distribution information, we estimated species distribution models only for a set of well‐sampled ant species and were unable to include other critical sources of dietary alkaloids, particularly mites (McGugan et al, ; Saporito et al, ). Although not being able to incorporate a substantial fraction of the prey assemblages expected to influence poison composition in O. pumilio , the GDM explained about 23% of poison variation in this species.…”

“…Ants are O. pumilio's primary prey type, corresponding to more than half of the ingested volume (Caldwell, ; Darst, Menéndez‐Guerrero, Coloma, & Cannatella, ; Donnelly, ). This frog also eats a large proportion of mites; however, limited occurrence data and taxonomic knowledge for mite species (e.g., McGugan et al, ) precluded their inclusion in our spatial analyses. Following a comprehensive literature search (as per late 2016) of alkaloid occurrence in ant taxa (Adams et al, ; Chen, Rashid, Feng, Zhao, & Oi, ; Clark, Raxworthy, Rakotomalala, Sierwald, & Fisher, ; Daly et al, , , ; Fox et al, ; Jones et al, , , , ; Jones, Blum, Andersen, Fales, & Escoubas, ; Jones, Blum & Fales, ; Jones, Blum, Howard, et al, ; Leclercq, Braekman, Daloze, & Pasteels, ; Ritter, Rotgans, Talman, Verwiel, & Stein, ; Saporito et al, , ; Schröder et al, ; Spande et al, ; Touchard et al, ; Wheeler, Olubajo, Storm, & Duffield, ), we estimated ant composition dissimilarity based on the distribution of ant species from 10 genera, as follows: Acromyrmex , Anochetus , Aphaenogaster , Atta , Brachymyrmex , Megalomyrmex , Monomorium , Nylanderia , Solenopsis , and Tetramorium .…”

“…We focus on these ant genera because species in each of them are known to harbor alkaloids (see Text for decisions on alkaloid presence in ant taxa). Six out of these 10 ant genera were found in the guts of Oophaga species ( Anochetus , Brachymyrmex , Nylanderia , Solenopsis ; McGugan et al, ; Moskowitz et al, ) or other alkaloid‐sequestering frogs ( Anochetus , Monomorium , Solenopsis , Tetramorium ; Clark et al, ; Moskowitz et al, ). The presence of a poison frog alkaloid class in an ant taxon was sufficient for including this taxon in our dataset, regardless of whether the same alkaloid class was also found in another arthropod group (e.g., mites).…”

“…This geographic variation in toxin profiles has been attributed to local differences in prey availability because poison frogs obtain their defensive alkaloids from dietary arthropods (Daly et al, ; Jones et al, ; Saporito, Donnelly, Norton, et al, ; Saporito et al, ; Saporito, Spande, Garraffo, & Donnelly, ). For instance, specific alkaloids in the skin of a frog may match those of the arthropods sampled from its gut (McGugan et al, ). However, individual alkaloids may be locally present in frog skins but absent from the arthropods they consume, and vice‐versa; thus, the extent to which frog chemical traits reflect arthropods assemblages is unclear (Daly et al, , ; Jones et al, ; Saporito, Donnelly, Norton, et al, ).…”