Land use impacts poison frog chemical defenses through changes in leaf litter ant communities

Abstract

<jats:title>Abstract</jats:title><jats:p>Much of the world’s biodiversity is held within tropical rainforests, which are increasingly fragmented by agricultural practices. In these threatened landscapes, there are many organisms that acquire chemical defenses from their diet and are therefore intimately connected with their local food webs. Poison frogs (Family Dendrobatidae) are one such example, as they acquire alkaloid-based chemical defenses from their diet of leaf litter ants and mites. It is currently unknown how habitat fragmentation impacts chemical defense across trophic levels, from arthropods to frogs. We examined the chemical defenses and diets of the Diablito poison frog (<jats:italic>Oophaga sylvatica</jats:italic>), and the diversity of their leaf litter ant communities in secondary forest and reclaimed cattle pasture. Notably, this research was performed in collaboration with two high school science classrooms. We found that the leaf litter of forest and pasture frog habitats differed significantly in ant community structure. We also found that forest and pasture frogs differed significantly in diet and alkaloid profiles, where forest frogs contained more of specific alkaloids and ate more ants in both number and volume. Finally, ant species composition of frog diets resembled the surrounding leaf litter, but diets were less variable. This suggests that frogs tend to consume particular ant species within each habitat. To better understand how ants contribute to the alkaloid chemical profiles of frogs, we chemically profiled several ant species and found some alkaloids to be common across many ant species while others are restricted to a few species. At least one alkaloid (<jats:bold>223H</jats:bold>) found in ants from disturbed sites was also found in skins from pasture. Our experiments are the first to link anthropogenic land use changes to dendrobatid poison frog chemical defenses through variation in leaf litter communities, which has implications for conservation management of these threatened amphibians.</jats:p>

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

“…Our results pose two hypotheses: First, the distribution of only a few prey species may explain most of the geographic variation in poison frog alkaloids; second, different codistributed prey species may be redundant alkaloid sources. The second hypothesis is supported by a recent analysis of the ants eaten by a different Oophaga species, O. sylvatica (Moskowitz et al, ).…”

“…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 .…”

“…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).…”

Mechanisms of Convergent Egg Provisioning in Poison Frogs

“…Alkaloids were tentatively identified by comparing this LC-MS/MS dataset to a dataset obtained by gas chromatography / mass spectrometry (GC/MS) from the same samples and used in a previous study exploring environmental variation and chemical defenses in the same frogs [45,46]. The alkaloids detected by GC/MS in the previous study were identified using mass spectral data provided in Daly et al [47].…”

Chemical defenses shift with the seasonal vertical migration of a Panamanian poison frog

“…Shifts in frog alkaloid composition can occur rapidly over relatively small spatial and temporal scales (Saporito et al 2006, 2007a, Andriamaharavo et al 2015, McGugan et al 2016, Prates et al 2019, Moskowitz et al 2020). For example, independent studies of Oophaga pumilio and Oophaga sylvatica populations only separated by a few hundred meters across a landscape have shown significantly different alkaloid profiles, which appear largely attributed to small‐scale spatial differences in prey availability across habitats (Saporito et al 2006, 2007a, Moskowitz et al 2020).…”