Enter the text here that is the new abstract information for your application. This section must be no longer than 30 lines of text. The Abstract is unchanged. Parental care is critical to the health of both parents and offspring, yet little is known about how molecular substrates act within brain areas and neuronal circuits to alter parental behavior, and this gap is especially wide for paternal care, i.e. the care-giving behavior of fathers. The proposed research capitalizes on natural variation in paternal care within a single species (threespined stickleback fish) to uncover the biological basis of paternal care in vertebrates. The current models for paternal care have biparental care, which makes it difficult to disentangle the behavior of mothers and fathers. Three-spined stickleback fish are a promising new model for paternal care because fathers are solely responsible for providing care. Moreover, the molecular mechanisms related to care are deeply conserved in vertebrates, the stickleback genome is small and compact and there are a growing number of functional tools available to study them. The goals of this proposal are to define the molecular elements responsible for differences in paternal care within a single species and to characterize the neurobiological pathways involved in such variation in behavior. There are two objectives: 1) Identify genes that contribute to differences in paternal care and test their function; 2) Define the ways in which neuropeptide signaling regulates paternal care. The project combines brain gene expression profiling at the bulk and single cell level, viral mediated transgenesis experiments to establish mechanism and pharmacological manipulations of oxytocin and arginine vasopressin signaling. The proposed work offers an innovative solution to the challenge of dissecting the biological basis of paternal care by using a powerful new model for fathering, and by capitalizing on natural variation in paternal care within a single species.