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

Abstract

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 diet of the Diablito poison frog (Oophaga sylvatica), 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 (223H) found in ants from disturbed sites was also found in skins from pasture frogs. 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.

A Review of Forest Management Effects on Terrestrial Leaf Litter Inhabiting Arthropods

“…Due to their phylogenetic and functional diversity, leaf litter arthropods can have significant impacts on other trophic levels as well [19]. For example, leaf litter composition has been shown to alter the alkaloid profiles of litter-dwelling ants which then impacts the chemical defenses of poison frogs which feed on these ants [20]. Leaf litter-dwelling arthropods have also been developed as bioindicators of ecosystem and soil health [5,[21][22][23][24].…”

Alkaloid-based chemical defenses and diet in six species of Australian poison frogs in the genus Pseudophryne

“…Collectively, these ndings suggest that the abundance of biosynthesized pseudophrynamines are dependent on the availability of dietary alkaloids. Variation in dietary alkaloids is common among poison frogs and is thought largely to result from spatial and temporal differences in arthropods (Saporito et al 2007a;McGugan et al 2016;Moskowitz et al 2020;Basham et al 2021). It is therefore plausible that changes in availability of dietary alkaloids could lead to differences in the production of pseudophrynamines, something that would be expected to change over the course of a lifetime.…”

What's going to be on the menu with global environmental changes?

“…For streams in Brazil, canopy cover and deforestation affected the consumption of macroinvertebrates by algivorous–insectivorous fish (da Silva Reis et al, 2022). Diablito poison frogs ( Oophaga sylvatica ), which acquire and sequester alkaloid‐based toxins from their ant diet, were shown to have less diverse chemical defenses in reclaimed pasture habitats compared to secondary forests in Ecuador, potentially putting them at higher risk of predation (Moskowitz et al, 2020). Ultimately, changes in favorable conditions will contract species ranges, whether drivers are due to anthropogenic pressures or climatic variables, and fundamentally alter the structure of food webs, rewiring trophic interactions and energy flows (Bartley et al, 2019).…”