DIFFERENTIAL GENE EXPRESSION IN THE BRAINS OF BEGGING POISON FROG TADPOLES
Parents often rely on offspring signals to adequately allocate resources to dependent offspring. The mimic poison frog, Ranitomeya imitator, has evolved elaborate parental care behaviors to raise their young. Their tadpoles develop in nutrient-poor pools where they beg to solicit trophic eggs from the mother. Previous research has shown a strong correlation between gene expression in the brain and social behaviors in a variety of taxa. This research focused solely on patterns of gene expression in the adult brain, providing a unique opportunity to investigate the genes that drive tadpole behaviors associated with parent-offspring interactions. In this experiment tadpoles of Ranitomeya imitator were induced to beg and differential gene expression was compared with that of non-begging, conspecific tadpoles as well as to tadpoles of another non-begging congener, Ranitomeya variabilis. RNAseq on the Illumina platform was used to construct transcriptomes and identify patterns of differential gene expression associated with different behaviors and with the highly divergent parental and offspring behaviors that have evolved in these two species with different modes of parental care. Six genes (fdps, h2ax, mfsd9, gabrg3, scoc, and tc3a) were found to be differentially expressed exclusively in R. imitator. Some of these genes are associated with social behavior, motor function behavior, and feeding responses. For example, previous research on mfsd9 shows that expression of this gene increased with food deprivation. Many tadpoles experience predation and thus may experience fear when larger individuals enter the breeding pool. Gabrg3 is a gamma-aminobutyric acid receptor (GABA) known to have a calming effect in humans and was found to be expressed at a higher level in begging treatments. A preliminary cross-species analysis, filtering by a candidate list of genes associated with parental care, indicated that a higher number of social and feeding behavior genes were expressed in R. imitator than in R. variabilis tadpole brains. The results of these analyses provide evidence that R. imitator has evolved patterns of gene expression specifically associated with social behavior and parent-offspring communication in the context of trophic egg-feeding and begging behavior as a result of the evolution of more complex parental care strategies.
East Carolina University