CAREER: On the Brink of Aposematism -- Intermediate States on the Evolution of Alkaloid Sequestration and Color Production Mechanisms in Dendrobatid Frogs

About This Grant

This project will study the origins of aposematism as a defensive strategy linking toxic chemicals and warning signals. This complex trait is thought to have started in cryptic ancestors and evolved through intermediate stages toward an optimal defense strategy. Aposematic poison frogs (Dendrobatidae) are well-studied, and these amphibians display an array of colors (reds, blues, and yellows) that advertise their skin alkaloids obtained from their diet. In contrast, their ancestors are less well-understood but similar to present-day dendrobatids that are non-aposematic, which include two-thirds of the known species in this family of amphibians. These frogs are assumed to be toxin-free, brown or black in color, and to follow a camouflage-based defense. We plan to study these organisms to explain how aposematism evolved in the first place. To investigate this, we will compare the skin profiles of aposematic and non-aposematic species and identify evolutionary signatures in dendrobatid lineages considered non-aposematic as intermediate stages toward aposematism. This integrated approach combines biochemistry, genetics, and evolutionary analyses. Our project also emphasizes the education of teachers with several outreach initiatives that engage participants at all levels and that are open to all Americans from high school to college students and beyond. Hands-on workshops will cover phylogenetics, genomics, chemical analysis, and bioinformatics, supported by online courses and open-access data resources. By linking cutting-edge research with immersive training, our project aims to advance the broad understanding of aposematism during its early stages. Aposematism is predicted to evolve via intermediate phenotypes from non-aposematic ancestors that lack defenses and warning signals. Characterizing these intermediate forms is key to understanding how complex phenotypes emerge and then how they are maintained, reinforced, and have become specialized. However, intermediate forms, by their nature of being transient, are less studied than are those already at selective optima and these intermediate forms are often ignored when mechanisms defining aposematism are being studied. Dendrobatid frogs provide a focal group where intermediate forms are common before aposematism, and many taxa serve as living examples preceding an aposematic optimum. In this project, we will perform comparative biochemical profiling of skin alkaloids and pigments alongside histological analyses across aposematic, non-aposematic, and outgroup species; integrate comparative transcriptomics and genomics to identify candidate genes and cis-regulatory elements underlying the aposematic phenotype; and map signatures of positive selection and adaptive shifts in these loci on a robust dendrobatid phylogeny to infer stepwise genetic changes leading to the full-aposematic phenotype. This multipronged framework will resolve the sequence of molecular and phenotypic innovations that culminated in aposematism as an optimal antipredator strategy. During this project, we anticipate the development of broadly applicable tools for investigating the origins of aposematism in other taxa with non-aposematic close relatives such as butterflies, snakes, and other groups. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.