Paternal care in stickleback fish

Parental care in animals consists of an incredible diversity of forms, providing powerful opportunities for studying the proximate basis of behavior. Three-spined stickleback fish, a classic model system in ecology, evolution, and behavior, are good subjects for studying the neurobiological basis of paternal care as male sticklebacks are solely responsible for providing care to their developing offspring. Here we review what is known about the neural, neuroendocrine, genetic, and molecular basis of paternal care in sticklebacks, highlighting the ways in which natural phenotypic variation within and among populations has been leveraged to improve our understanding of the proximate basis of behavioral variation. For example, diversity in care among populations, including the complete evolutionary loss of parental care in the so-called "white" sticklebacks, provides insight into the proximate mechanisms by which highly divergent behavior in whites diverged so rapidly and dramatically from the ancestral care-giving form. Moreover, comparisons within populations across stages of care reveal deeply conserved neural, genomic, and neuroendocrine mechanisms regulating paternal and maternal behavior across vertebrates. Moving forward, improved neuroscientific tools and resources for sticklebacks will enable functional manipulations and in vivo studies, opening up novel opportunities to address outstanding questions about the origin of behavioral diversity.