Seasonal changes in diet and chemical defense in the Climbing Mantella frog (Mantella laevigata)

Abstract

Poison frogs acquire chemical defenses from the environment for protection against potential predators. These defensive chemicals are lipophilic alkaloids that are sequestered by poison frogs from dietary arthropods and stored in skin glands. Despite decades of research focusing on identifying poison frog alkaloids, we know relatively little about how environmental variation and subsequent arthropod availability impacts alkaloid loads in poison frogs. We investigated how seasonal environmental variation influences poison frog chemical profiles through changes in the diet of the Climbing Mantella (Mantella laevigata). We collected M. laevigata females on the Nosy Mangabe island reserve in Madagascar during the wet and dry seasons and tested the hypothesis that seasonal differences in rainfall is associated with changes in diet composition and skin alkaloid profiles of M. laevigata. The arthropod diet of each frog was characterized into five groups (i.e. ants, termites, mites, insect larvae, or ‘other’) using visual identification and cytochrome oxidase 1 DNA barcoding. We found that frog diet differed between the wet and dry seasons, where frogs had a more diverse diet in the wet season and consumed a higher percentage of ants in the dry season. To determine if seasonality was associated with variation in frog defensive chemical composition, we used gas chromatography / mass spectrometry to quantify alkaloids from individual skin samples. Although the assortment of identified alkaloids was similar across seasons, we detected significant differences in the abundance of certain alkaloids, which we hypothesize reflects seasonal variation in the diet of M. laevigata. We suggest that these variations could originate from seasonal changes in either arthropod leaf litter composition or changes in frog behavioral patterns. Although additional studies are needed to understand the consequences of long-term environmental shifts, this work suggests that alkaloid profiles are relatively robust against short-term environmental perturbations.

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

“…Most ants consumed by O. sylvatica in our study were small and light in coloration (Solenopsis and small Pheidole). While it is generally unknown if other poison frogs have dietary preferences for particular ant traits, a cafeteria test in mantellid poison frogs suggests they have a size-dependent preference for relatively small prey items [46], a pattern later confirmed by examining stomach contents [47]. These results are troubling, as the smallest ant species (along with the largest ones) are the first to disappear due to habitat modification [20].…”

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 .…”

“…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).…”

Bringing immersive science to undergraduate laboratory courses using CRISPR gene knockouts in frogs and butterflies

“…With some editing of language and data visualizations, some articles may be suitable for publication with students as co-authors either as a stand-alone article or as a part of a larger project from the instructor's laboratory (e.g. Moskowitz et al, 2018).…”