Parental behavior in amphibians is exceptionally diverse, but it is relatively understudied and poorly understood. Using Oophaga pumilio, a Neotropical dendrobatid frog that feeds its offspring with unfertilized eggs, this doctoral dissertation research project will test the following hypotheses about the mechanisms behind parental behavior in an amphibian: 1. mothers discriminate between offspring and unrelated young during parental care; 2. the sensory mode of mother-offspring communication is suited to the habitat of the species; 3. mothers use honest begging signals from offspring to allocate their provisioning resources; and 4. mothers provision offspring with an effective defense against predators. This research is conducted at La Selva Biological Station in Costa Rica in collaboration with Dr. Ralph Saporito from John Carroll University and Dr. Mahmood Sasa from the University of Costa Rica. The project has an extensive field setup of 1000 artificial tadpole-rearing sites, using twelve motion-activated IR video cameras placed above cups containing tadpoles to provide unique and efficient observation of mother-offspring interactions in the field.
This study will broaden the comparative understanding of amphibian parental care by elucidating the behavioral mechanisms behind a complex amphibian parental care system. Features of this system allow for fresh ways to explore hypotheses that are of interest to a wide-ranging audience about offspring discrimination, multi-modal sensory integration, honest signaling, and chemical antipredator defenses. The experiments and observations should help answer many important questions relating to parent-offspring behavior more generally. This project also involves outreach, mentoring and environmental education activities with U.S. students participating in undergraduate research programs at La Selva as well as with Costa Rican students and public visitors. Involving U.S. students in first-rate research experiences with international collaborators in a foreign setting helps train a globally engaged work force and is an important goal of NSF's Office of International Science and Engineering.
This study expanded PhD research on the parental care of the strawberry poison frog, which lives in the rainforests of Costa Rica. This frog carries its tadpoles to water pools in the trees and then feeds them with unfertilized eggs for 6 weeks as the tadpoles' only source of food. In previous studies, we explored the ability that mothers have to recognize their own offspring. We also conducted experiments in the field to find out how mothers and their tadpoles communicate with each other and how their communication allows mother frogs to decide how much to feed their tadpoles. Similar questions have thus far only been studied in birds and to a degree in mammals and insects, but have not been explored in an experimental way in amphibians. Finding that tadpoles are able to indicate to mothers that they are hungry while avoiding predators, and that mothers can remember where they left their tadpole (so that they do not need to remember who their tadpole is) are novel findings for behavioral ecology and herpetology. The dissertation enhancement project funded by this grant in the final year of the PhD aimed to expand on the research of how mother frogs feed their offspring on to how mother frogs might protect their offspring from predators. First, we used chemical analysis to show that mother frogs are provisioning their tadpoles via nutritive eggs with the same alkaloid defenses that they have in their skin to protect themselves from predators. Then, we used field experiments to determine whether the chemicals that mothers provide to their offspring are indeed an effective defense against their natural predators. We found that the chemicals are effective in defending tadpoles against invertebrate predators (spiders), but perhaps not against vertebrate predators (snakes). The work was presented at the World Congress of Herpetology in a poster and a symposium talk, and is currently in the submission process to Biology Letters and other journals. This project has been successful in sharing its interesting questions and results with young students and with the public. During this entire project, over 3 dozen visiting groups from US high schools and universities, Costa Rican universities, and other field stations aided with maintanence of the field setup at the La Selva Biological Station in Costa Rica, which allowed them to experience field work on an ongoing project. Also, the project coincided with mentorship of 9 undergraduates (many from backgrounds that are underrepresented in STEM fields) as research assistants and on independent projects. The Co-PI was involved as a mentor, coordinator, and now administrator of the NSF REU program at La Selva, which allows 10-15 undergraduates each summer to participate in independent research with a research mentor at La Selva. Also, the research has been presented over 40 times to university and public interest groups, including during the research station's annual open house days in which over 1000 visitors from the local public attend to view the ongoing research at the site. Lastly, the work was featured in a full page article in the leading newspaper in Costa Rica, La Nación (www.nacion.com/2011-10-24/AldeaGlobal/las-ranitas--lsquo-blue-jeans-rsquo--son-madres-muy-dedicadas-.aspx).