For my Ph.D., I studied the behavioral ecology of parental care in a poison frog, Oophaga pumilio. This charismatic frog displays complex parental behavior: males guard egg clutches in the leaf litter for a week or so until mothers come to carry tadpoles on their backs to small arboreal water pools, and then proceed to feed them with unfertilized eggs for 6 weeks until tadpoles metamorphose. I think this is amazing, especially for an animal that is considered a “lower vertebrate”.
Parent-Offspring Communication and Discrimination
With the help of Deniz Ozel (University of Miami), we found that mother frogs, which do not possess complex brain structures like mother mammals or birds, use a very specific memory of tadpole location rather than direct recognition to ensure that their provisioning behavior is only benefitting their own offspring (PDF).
With technical assistance from my engineer brother, Peter Stynoski (University of Illinois), I explored the hot topic of honest begging in this tadpole system, which is well studied in birds and some mammals and insects but unexplored in amphibians. We found that mother frogs utilize the “honest” signals of tadpole hunger via vibration to determine when to feed tadpoles. This study also showed that tadpole begging vibrations (see video below) are significantly costly to tadpole growth, which is likely the reason that tadpoles only beg when they are truly hungry and their signal remains “honest”.
Currently, I am working with Dr. Matt Dugas (Case Western Reserve University) and Dr. Cori Richards-Zawacki (Tulane University) to go deeper into the question of honest begging. This ongoing project will determine the effects of immediate offspring hunger and long-term condition on begging and maternal provisioning and will more specifically explore components of the vibration signal.
Virginia Noble (University of British Columbia) and I found that tadpoles use multimodal sensory information to modulate their behavior in the presence of a mother frog, potential predator, or heterospecific frog (PDF).
Defending Offspring from Predators
Along with chemical ecology expert Dr. Ralph Saporito (John Carroll University), we have found that mother frogs provision their tadpoles with alkaloids in the eggs that they feed to tadpoles (PDF). Based on chemical analysis of the tadpoles, the origin of their alkaloids is most likely the ants and oribatid mites that the mother frogs eat from the leaf litter. When we fed tadpoles with another source of food, those tadpoles did not contain alkaloids.
Now, we are working to explore maternal alkaloid provisioning from a phylogenetic perspective with the help of Lisa Schulte (Universitat Trier) and Bibiana Rojas (University of Jyväskylä), the two other amazing members of our poison frog trifecta, “Team Tadpole”:
With the help of Peter Stynoski (University of Illinois), Dr. Mahmood Sasa (University of Costa Rica), and two Costa Rican high school interns, Ana Brenes and Marco Arguedas, we have identified 4 natural predators of O. pumilio tadpoles in field videos: elaterid beetle larvae, ctenid spiders, and 2 species of snakes!
Georgia Shelton (Harvard University) and I conducted an experiment that showed that the alkaloids that mother frogs provision to tadpoles are an effective defense against some of those predators (spiders), but not all of them (snakes)(PDF).