Einflussnahme der Ernährung auf das Verhalten und die Entwicklung von Pfeilgiftfrosch-kaulquappen
Evolutionäre Zell- und Entwicklungsbiologie der Tiere
Kognitive, systemische und Verhaltensneurobiologie
Zusammenfassung der Projektergebnisse
Poison frogs obtained their toxins (alkaloids) from the diet, which is likely energetically costly. Alkaloids affect the nervous system, but how alkaloid consumption affects the brain and behavior of poison frogs has never been addressed. Furthermore, several species of poison frogs show parental care in which mothers feed their tadpoles with alkaloid-containing eggs, thus likely influencing their development. Understanding how the consumption of alkaloids modulates the development, metabolic rate, and behavior of poison frogs is paramount to elucidate the evolution of aposematism in these amphibians. During my postdoctoral research at Stanford University, I fed tadpoles of Ranitomeya imitator with the alkaloid decahydroquinoline (DHQ). In the first try, I used a 1% DHQ supplemented food but observed high mortality at the prometamorphosis. In the second try, I experimented with both freshly hatched tadpoles and juveniles for three weeks using 0.5% DHQ supplemented food. Surprisingly, while for tadpoles the mortality was higher in the DHQ treatment, in juveniles it was lower. I speculate it is because juveniles can breath through both their lungs and skin to cope with the side effects of alkaloids. Using the ratio of the breaths and movements given in the 30 min trial as a proxy to metabolic rate in tadpoles, I observed a strong shift to a higher metabolic rate in the DHQ treatment. In general, the data from both treatments at the three weeks is comparable as no differences in developmental stages and morphometry were strongly evident. In my experiments, all individuals would go through 30 min open field assay followed by 30 min feeding assay once a week. By now, most the open field videos and about 30% of the feeding videos have been analyzed. Preliminary data shows that most behavioral traits measured are very variable, and at this point, no differences between treatments were observed. However, DHQ tadpoles took less time to start eating, approaching the food always with a purpose, as I was expecting when started this project. After the three weeks of treatment, I sampled the brains of tadpoles and extracted the RNA from 4 brain regions (dorsal pallium, ventral pallium, hypothalamus, and cerebellum). Before the pandemic-lockdown at Stanford University, I was about to measure the expression of genes related to feeding. Establishing the RNA extraction and qPCR for these samples was very challenging because they only had a tiny quantity of RNA as tadpole brains were too small. Preliminary data from the dorsal pallium shows a slight difference in the expression of NPY but not CART; however, this needs to be properly measured and analyzed. I further sampled tadpole and juvenile brains for immunohistochemistry. These samples are ready for staining through the iDISCO protocol but await the gene expression results to make an informed decision on which antibodies to use. This is the first study on which the behavioral and developmental effects of alkaloids are measured on poison frogs, and thus will have a high impact on the field of chemical ecology. Learning the techniques used during this postdoc was paramount for developing my research line in Germany.
